Assessing the Power-to-Gas potential: GIS-based suitability analysis of biogas plant sites in Lower Saxony, Germany

Assessing the Power-to-Gas potential: GIS-based suitability analysis of biogas plant sites in Lower Saxony, Germany | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Assessing the Power-to-Gas potential: GIS-based suitability analysis of biogas plant sites in Lower Saxony, Germany Mareike Liefer, Yannik Weber, Jochen Hack This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7148209/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Background To decarbonise the energy system, offsetting fluctuations in renewable energy (RE) sources is crucial, for which biogas plants are well-suited. In Lower Saxony, Germany, the impending expiration of the 20-year Renewable Energy Sources Act subsidy for numerous biogas plants creates an opportunity to transition them to biomethane production within a Power-to-Gas (P2G) framework. However, detailed data on the suitability of these sites for conversion is lacking due to diverse site-specific conditions. Therefore, mapping the P2G potential of these sites is essential, paying particular attention to agricultural and environmental compatibility. Methods A multi-parametric Geographic Information System-based spatial analysis was conducted to assess the suitability of individual biogas plant sites in Lower Saxony for implementing methanisation with green hydrogen. Biogas plant sites were evaluated based on five criteria. The regional RE potential for wind turbines and ground-mounted photovoltaic systems and the installed electrical power of biogas plants criteria had to be met for the suitability of a biogas plant site. Additionally, water withdrawal conditions , biogas substrate use , and distance to the gas grid were evaluated as further sustainability criteria, considering the environmental impact. Results The spatial analysis showed that about 60% were suitable as environmentally friendly P2G sites since they met all the criteria. Concentrations of suitable biogas plant sites were found in western Lower Saxony, from the Emsland to the Diepholz district, and the Rotenburg (Wümme) district, as well as in the northern part of the Heidekreis in north-central Lower Saxony and the southern part of the Celle district near Hanover. Approximately 12% of biogas plant sites were considered conditionally suitable because they only met the essential criteria. Conclusions The criteria-based spatial suitability analysis enables comprehensive mapping of the potential for P2G at existing biogas plant sites in Lower Saxony. We identified 1,014 suitable sites for environmentally friendly implementation of methanisation with green hydrogen as an end-of-subsidy strategy. Considering agricultural and nature conservation compatibility can reduce land-use conflicts, promoting broader acceptance of the RE transition. These findings provide an advisory resource for stakeholders, highlighting the urgent need for action as the Renewable Energy Sources Act subsidy period comes to an end. Hydrogen sustainable energy transition biogas plant sites Power-to-Gas spatial analysis Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 1. Background It is paramount to decarbonise the energy system to achieve the climate objectives set out by the European Union (EU) for 2030 and 2050. Yet, 75% of the greenhouse gas (GHG) emissions in the EU are produced in the generation and use of energy. Therefore, the EU aims to develop a power sector based largely on renewable sources [ 1 ]. In 2022, the proportion of energy derived from renewable sources in gross final consumption was 23%, with the goal of attaining at least 42.5% by 2030 [ 2 ] [ 3 ]. Renewable energy (RE) in Germany provided just 22% in 2023. The share of renewables in gross electricity consumption was 51.8%, of which wind energy contributes 52.2%, solar energy 22.5%, biogas 10.5%, and biomethane 1.1% [ 4 ]. To contribute to future decarbonisation and GHG neutrality, further energy concepts must be considered to offset fluctuations or deficiencies in RE sources, such as wind and solar energy. Biogas plants are able to compensate for such fluctuations. In some German federal states, such as Lower Saxony, a large number of biogas plants have been built since 2000 as a result of subsidies under the Renewable Energy Sources Act Erneuerbare-Energien-Gesetz (EEG) [ 5 ] of Germany and favourable agricultural conditions [ 6 ]. By 2022, almost a quarter of the installed capacity of 1,360 MW in Germany, provided by 1,691 biogas plants, was located in Lower Saxony [ 7 ]. However, the 20-year subsidy period under the EEG, which guarantees a fixed feed-in tariff, will expire for many of the biogas plants in Lower Saxony in the near future. The use of biomass for energy production is currently being criticised, inter alia due to its potential negative impact on food production, biodiversity, and the environment [ 8 ]. The result is a gradual reduction in the size of tenders for biogas plants in Germany (EEG § 28c [ 5 ]). This will affect one-third of the biogas plants of Lower Saxony in the next five years and two-thirds in the next ten years [ 9 ]. After the expiry of subsidies, the risk of losing profitability resulting in plant decommissioning rises [ 5 ]. However, the situation brings new opportunities for appropriate decentralised P2G end-of-subsidy strategies for existing biogas plants in Lower Saxony to compensate for the fluctuation from RE and to push forward a sustainable energy transition. Additionally, considering agricultural and nature conservation interests from the outset when identifying suitable biogas plants for end-of-subsidy strategies can prevent land competition among different uses. Erler et al. [ 10 ] describe an end-of-subsidy strategy suitable for many on-site electricity generation plants of Lower Saxony. Using a concept called 'methanisation' (Power-to-Gas, P2G), biogas can be converted to biomethane. In a biogas plant, biogas is produced through anaerobic fermentation. This biological process involves the breakdown of complex organic substances, such as biomass, into simpler components under anaerobic conditions, in the absence of oxygen. The result is the release of biogas, which is essentially composed of biomethane (CH 4 ) and carbon dioxide (CO 2 ) [ 11 ] [ 12 ]. The methanisation concept involves first coupling existing plants to an electrolyser to produce green hydrogen powered by RE. Second, in a methanisation reactor, the previously unused CO 2 from the biogas plant and the green hydrogen are converted into renewable methane. This can be fed into the natural gas grid with the biomethane from the biogas plant [ 10 ]. The feasibility of coupling biogas and P2G plants was already demonstrated in several studies [ 13 ] [ 14 ] [ 15 ] [ 16 ] [ 17 ]. Furthermore, it was shown that coupling can be economically viable under certain conditions [ 18 ] [ 19 ]. The coupling has various advantages, such as the low complexity of a P2G process chain, which increases the probability of implementation [ 18 ], the continuously available, cost-effective and renewable CO 2 , which is required for the methanisation [ 18 ] [ 20 ] and the possibility of dual energy generation, i.e., when hydrogen is not available, the plant can generate electricity, and when it is available, renewable methane can be fed into the gas grid [ 10 ]. Furthermore, the biomethane yields can be increased without the use of additional biomass [ 10 ]. The process of methanisation eliminates the necessity for CO₂ separation, which represents the primary cost factor associated with the upgrading of biogas to natural gas quality. This enables the utilisation of green CO 2 in a manner that is both materially and energetically meaningful [ 10 ]. The oxygen produced during electrolysis can be employed for the coarse desulphurisation of the raw biogas [ 10 ]. Additionally, the storage capacity of the natural gas grid can be used to indirectly store surplus electricity from RE [ 16 ]. The biogas plants of Lower Saxony offer a wide range of synergies for P2G, making them well-suited for the decentralised production of renewable methane. For P2G, the 1,255 on-site electricity generation plant sites [ 21 ] are of potential use. Additionally, Lower Saxony offers a large number of potentially suitable areas for the production of RE from wind and sun [ 22 ], which is required for the production of green hydrogen from electrolysis. Lower Saxony also has sufficient water resources for sustainable water extraction for electrolysis, although these are unevenly distributed across the region [ 23 ]. Large quantities of biowaste (1,216,604.14 tonnes in 2022) [ 24 ] and organic fertiliser (37.25 million tonnes in July 2022 to June 2023) [ 25 ] are also present in the region, which can be used as substrates in the biogas plants [ 26 ]. The change in the substrates used can reduce the competition for land previously caused by the cultivation of energy crops. The natural gas pipeline network also offers a high potential for the purchase and transport of renewable methane, as it is widely branched in many districts, especially in the western half of Lower Saxony [ 27 ]. Despite the general potential suitability of biogas plant sites in Lower Saxony for upgrading to P2G, a lack of knowledge exists regarding the most suitable plant sites of the 1,704 due to their individual site conditions. The sites that can meet the interests of agriculture and nature conservation to avoid land competition between different uses need to be identified. To support the decision on the biogas plant sites suitable for upgrading to P2G as an end-of-subsidy strategy, the potential of the biogas plant sites for P2G needs to be assessed. Our objective is to map the P2G potential of existing biogas plant sites in Lower Saxony, with special consideration of agricultural and nature conservation compatibility. We present a GIS-based spatial suitability analysis of the individual biogas plant sites in Lower Saxony. The high-resulted biogas plant sites 1 previously identified by Plinke et al.[ 28 ] are analysed for their suitability on the basis of five criteria: Regional RE potential, biogas plant installed power, water withdrawal conditions, substrate use, and distance to gas grid. The suitability is then derived from this set of criteria. The analysis is being undertaken as part of the H2-FEE research project: Flexible energy carriers for the energy transition (running from July 2022 to June 2025) funded by the Lower Saxony Investment and Development Bank (Investitions- und Förderbank Niedersachsen, NBank). 2. Methodology 2.1 Study area The study area is located in the northwest of Germany: the federal state of Lower Saxony (Fig. 1 ). With an area of 47,710 km 2 , consisting of 45 administrative districts ( Landkreise and kreisfreie Städte ), Lower Saxony is the second largest of all 16 German federal states [ 29 ]. Despite its size, it has the fifth-lowest population density [ 30 ]. As a dominantly rural state, it is suitable for this study because of its large amount and spatially dispersed biogas plants, which will soon phase out of subsidies by the German government (Fig. 1 ) and will require an end-of-subsidy strategy. By the end of 2025, 184 of the 1,704 biogas plant sites will no longer receive subsidies. Between 2026 and 2035, a further 1,253 sites will phase out, accounting for almost 85% of the total. The remaining sites will be phased out by 2045. It is also a great advantage that the state has a high potential for RE (wind turbines and ground-mounted photovoltaic systems) production [ 22 ]. 2.2 Suitability criteria and assessment The methodological approach for identifying biogas plant sites with environmentally friendly P2G potential in Lower Saxony encompasses criteria-based, spatial GIS analysis using the geoinformation software ArcGIS Pro (Version 3.3.2). For this purpose, the 1,704 biogas plant sites, whose exact locations were spatially determined in Plinke et al. [ 28 ], were examined individually for their suitability to implement the methanisation concept described above. To identify the environmentally friendly P2G potential of these biogas plant sites, the three phases of the P2G life cycle (RE production used for green hydrogen production, P2G process including biogas production and methanisation, and consumers as distance to the gas grid) served as the basis for a five-criterion evaluation of the suitability of the biogas plant sites (Fig. 2). As the regional RE potential for wind turbines and ground-mounted photovoltaic systems, as well as the biogas plant installed electrical capacity, are mandatory for the methanisation process with green hydrogen described by Erler et al. [ 10 ], these were treated as hard criteria that had to be met for a biogas plant site to be suitable. The criteria water withdrawal conditions (for hydrogen production), substrate use (for biogas production), and gas grid connection (for methane distribution to consumers) were considered as soft criteria, which function as further sustainability criteria considering the environmental impact. The suitability of biogas plant sites was assessed for each suitability criterion on the basis of three suitability levels: suitable , conditionally suitable , and unsuitable (Table 1 ). Table 1 Suitability criteria catalogue with suitability levels for environmentally friendly P2G potential of biogas plant sites Suitability criteria Suitability levels Suitable Conditionally suitable Unsuitable Regional RE potential (hard criterion) Required installable capacity from wind turbines and ground-mounted photovoltaic systems within 500 m radius from biogas plant site to achieve the lowest hydrogen cost Required installable capacity from wind turbines and ground-mounted photovoltaic systems within a radius > 500 m and ≤ 5 km from biogas plant site to achieve the lowest hydrogen cost Required installable capacity from wind turbines and ground-mounted photovoltaic systems within a radius > 5 km from biogas plant site to achieve the lowest hydrogen cost Biogas plant installed electrical power (hard criterion) ≥ 250 kW installed electrical capacity/site - < 250 kW installed electrical capacity/site Water withdrawal conditions (soft criterion) ≥ 70% remaining sustainably usable groundwater available ≥ 40% and < 70% remaining sustainably usable groundwater available < 40% remaining sustainably usable groundwater available Substrate use (soft criterion) ≤ 30% proportion of organic fertiliser/biowaste used in biogas plants in relation to existing organic fertiliser/biowaste by district > 30% and ≤ 60% proportion of organic fertiliser/biowaste used in biogas plants in relation to existing organic fertiliser/biowaste by district > 60% and ≤ 100% proportion of organic fertiliser/biowaste used in biogas plants in relation to existing organic fertiliser/biowaste by district Distance to gas grid (soft criterion) ≤ 1 km > 1 km and ≤ 10 km > 10 km The individual suitability criteria are further outlined in the following subsections. The importance of the criteria for identifying suitable P2G sites is explained, as well as the methodological approach for their assessment and data sources used. Regional RE potential We assumed that the targeted regional production of green gases (green hydrogen and biomethane) at the biogas plant site is based on the exclusive use of additional RE sources located in the immediate vicinity (definition below). Instead of diverting RE from other uses, new RE capacities should be added to contribute to the energy transition [ 2 ]. As many areas of Lower Saxony offer great potential for the installation of human- and nature-compatible wind turbines and ground-mounted photovoltaic systems [ 22 ] [ 33 ], these potential installations were considered for the generation of RE in this study. Human- and nature-compatible installation of RE in an area implies that it is not at the expense of the quality of life of people, biodiversity, or food production [ 34 ]. However, the RE potential is geographically unevenly distributed [ 22 ] [ 33 ], which is the reason for individually assessing the suitability of each biogas plant site for the implementation of the methanisation concept. Within the H2-FEE research project, the installed capacity of wind turbines and ground-mounted photovoltaic systems required to achieve the lowest cost of hydrogen per kg at each biogas plant site was calculated. This was done by conducting a detailed energy system analysis on a 0.25-degree grid using the Energy System Transformation Model (ESTRAM) [ 35 ] developed at the Institute of Solid State Physics at Leibniz University Hannover, Germany. The calculation is based on the potential annual production of hydrogen at each biogas plant site 2 from wind turbines and ground-mounted photovoltaic systems. The hydrogen production depends on the amount of CO 2 produced in a biogas plant, as it is supposed to be fully used for methanisation. The by-product CO 2 produced in the biogas plant is assumed to be used for the production of renewable methane and could then be fed into the natural gas grid together with the biomethane produced in the biogas plant [ 18 ]. To produce renewable methane, hydrogen and CO 2 are required in a 4:1 ratio [ 15 ]. The CO 2 concentration in raw biogas varies between 25 and 45 vol% [ 36 ]. Therefore, the calculation is based on the mean value of 35 vol%. We derived the amount of raw biogas orienting on Berndmeyer [ 18 ], who identified it based on Erler et al. [ 10 ]. We used the ratio of 1.52 of the installed electrical capacity at the biogas plant site in MW and the annual volume of raw biogas produced in million m 3 . This installable electrical capacity at the biogas plant sites was derived from the georeferenced vector dataset of biogas plants registered by Plinke et al. [ 28 ]. Next, suitable areas for the installation of wind turbines and human- and nature-compatible ground-mounted photovoltaic systems were identified on the basis of vector data of areas with low and medium spatial vulnerability to wind turbines and ground-mounted photovoltaic systems from the area suitability calculation by Wagenfeld et al. [ 37 ]. The distances to settlements, industry, and commerce as well as to motorways, main roads, electric overhead lines, cable cars, and railway lines were recalculated on the basis of the large reference wind turbines for inland and coastal areas by Lüers [ 38 ]. To better account for land-use conflicts tailored to the study area, the criteria for suitable areas were adjusted based on Peters et al. [ 39 ], § 3a of the Lower Saxony Climate Act ( Niedersächsisches Klimagesetz (NKlimaG)) as well as from the Lower Saxony Association of Districts ( Niedersächsischer Landkreistag , NLT) and Towns and Municipalities ( Niedersächsischer Städte- und Gemeindebund , NSGB) [ 40 ] (refer to Appendices A and B for a detailed list of criteria unsuitable for wind turbines and ground-mounted photovoltaic systems). Existing plant sites were not excluded, as it is possible to generate additional RE capacity through repowering [ 41 ]. Based on this, the installable capacity per ha of the areas suitable for human- and nature-compatible wind turbine installations was calculated. As part of the H2-FEE research project, these areas were planned using the reference wind turbines projected for 2030 by Lüers [ 38 ], maintaining a distance between wind turbines with 2.5 times the rotor diameter. Additionally, within the research project, the power density per ha for ground-mounted photovoltaic systems with a southern area occupancy was assumed to be 1.12 MW per ha. The power density was determined based on the assumptions for the structure of ground-mounted systems according to Badelt et al. [ 42 ], adapted to the current QCELLS Q.PEAK DUO M-G11S+ SERIES 2023 solar module. The power density per ha was allocated to the areas considered to be human- and nature-compatible for the installation of these systems (areas not classified as unsuitable according to the criteria in Appendix B ). RE production in the immediate vicinity of biogas plant sites was favoured, because it avoids additional infrastructure construction (e.g. power lines), saves costs, and reduces the impact on the landscape [ 43 ]. To define the immediate vicinity, we employed a radius of 500 m as a simplified assumption. The installable capacity of wind turbines and ground-mounted photovoltaic systems within a 500 m radius of the biogas plants was summed up and compared with that of the installed capacity required to achieve the lowest hydrogen production cost (as described above). A biogas plant site was considered suitable if the required amount of installable capacity could be generated by wind turbines and ground-mounted photovoltaic systems to achieve the lowest hydrogen cost in the immediate vicinity of 500 m on human- and nature-compatible areas. Biogas plant sites were considered to be conditionally suitable if the required amount of installable capacity could only be generated within a radius of more than 500 m including 5 km from the biogas plant site. A distance of 5 km represents a typical farm-to-field distance (cf. [ 44 ]), where land suitable for RE is likely owned by the biogas plant operators. This distance also corresponds to the spatial relationship between the electricity producer and the consumption point, where the consumption of RE produced is favoured according to § 21b (4) EEG 2023 and § 12b (5) of the German Electricity Duty Act ( Stromsteuergesetz (StromStV)). Biogas plant installed electrical power For biogas plant sites to be suitable as P2G sites, a sufficient biogas plant-installed electrical capacity is also essential. Erler et al. [ 10 ] assumed that conventional on-site electricity generation plants with an installed electrical capacity of 250 kW or more are necessary for the methanisation concept to be suitable. It is also possible to combine plants located close to each other, which in sum achieve at least 250 kW [ 10 ]. This summed installable electrical capacity at each biogas plant site was derived directly from the biogas plant register Plinke et al. [ 28 ]. Only plant sites with on-site electricity generation with an installed electrical capacity of 250 kW were considered suitable for the end-of-subsidy strategy. Water withdrawal conditions For the production of hydrogen, water has to be extracted from water bodies. To prevent a lowering of the groundwater level and potential damage to groundwater-dependent ecosystems, it is important to use only sustainably renewable amounts of water for electrolysis [ 23 ]. The spatial analysis by Badelt & Haaren [ 23 ] and the produced georeferenced vector data served as the basis for the assessment of sustainable groundwater availability. They first identified the annual reserves of the groundwater (sub)bodies (i.e., the portion of groundwater bodies within administrative districts in Lower Saxony) and then compared them with those of forecasted groundwater withdrawals, considering the climate [ 45 ]. To assess the utilisation rate of natural groundwater reserves, Badelt & Haaren [ 23 ] used the Water Sustainability Index (WSI) developed by Schlattmann et al. [ 46 ], which is presented in Eq. 1. Note that WW denotes water withdrawal. $$\:WSI=\frac{Field\:irrigation\:+\:Livestock\:WW\:+\:Industrial\:WW\:+\:Other\:WW\:+\:Electrolysis\:WW}{Groundwater\:recharge\:-\:(Public\:water\:supply+Ecosystem\:requirements)}$$ For groundwater recharge, Badelt & Haaren [ 23 ] calculated the mean value of the annual groundwater reserves for the period from 2021–2050 based on the mGROWA water balance model [ 47 ]. Field irrigation, livestock water withdrawal (WW), industrial water withdrawal, other water withdrawal, and public water supply were taken from the Water supply concept for Lower Saxony ( Wasserversorgungskonzept Niedersachsen ) [ 45 ]. In addition to Badelt & Haaren [ 23 ], we calculated the amount of water withdrawn for electrolysis at each biogas plant site based on the biogas plant register by Plinke et al. [ 28 ]. We assumed that the amount of water to be withdrawn depends on the amount of hydrogen required for methanisation (to calculate the amount of hydrogen required per biogas plant site, see above). According to the German Technical and Scientific Association for Gas and Water (DVGW) [ 48 ], around 12 to 13 l of groundwater are required for the electrolysis of 1 kg of hydrogen; the average value used here is 12.5 l. Biogas plant sites for which the amount of water required for electrolysis cannot be calculated due to a lack of data are included with a requirement of zero litres for electrolysis, as it is assumed that other groundwater uses are usually decisive for groundwater availability. It is also necessary to avoid damaging groundwater-dependent terrestrial ecosystems due to water extraction at the biogas plant site. Therefore, the ecosystem requirements were calculated based on Badelt & Haaren [ 23 ]. The recommended distance of 50 m must be maintained between the electrolyser at the biogas plant site and groundwater-dependent terrestrial ecosystems [ 49 ], which have a resilience of ecosystems to groundwater drawdowns ranging from very low to low to medium, available as vector-data in scale 1:50.000. This distance regulation also applies to drinking water protection areas ( Trinkwasserschutzgebiete , § 51 of the German Federal Water Act Wasserhaushaltsgesetz (WHG)), protection zones I and II (catchment area and inner protection zone). If the distance could not be maintained, the value for ecosystem requirements was considered to be the amount of water from groundwater recharge. Derived from Schlattmann et al. [ 46 ], a biogas plant site was considered suitable if at least 70% of the sustainably usable water in the groundwater sub-body was still available after extraction for electrolysis (0 ≤ WSI > 0.3). Sites were considered conditionally suitable if at least 40% but less than 70% of the water was still available after extraction (0.3 ≤ WSI < 0.6). Substrate use Adjusting the substrates used in biogas plants is an effective way of reducing biogas plants’ environmental impact. Depending on the substrate used, land consumption and competition with other land uses, such as food production and nature conservation, more or less exist [ 50 ] [ 51 ] [ 52 ]. The input substrates used in Lower Saxony in 2021 were made up of 82.4% of energy crops and plant by-products, 13.0% of agricultural residues such as liquid and solid manures and fermentation residues, and 4.7% of biowaste such as fats, flotates and organic waste, based on the proportion of electrical output [ 53 ]. To reduce the environmental impact, it is essential to reduce the share of energy crops and to incorporate a significant share of organic fertiliser and biowaste used in biogas plants. This will ensure an effective utilisation of available substrates and their potential. The criterion appraises the proportion of organic fertiliser/biowaste used in biogas plants in relation to existing organic fertiliser/biowaste by district, though it varies between organic fertiliser and biowaste. It incorporates the current use of organic fertiliser/biowaste in biogas plants and the potential for increasing the proportion. By increasing, the impact on the environment and the pressure on agricultural land use would be reduced. The data was retrieved from the following sources: data on agricultural residues used in biogas plants from the Nutrient Report for Lower Saxony [ 25 ], data on biowaste from the Waste Balance Sheet [ 54 ] and from the data provided by 3N for the Biogas Inventory 2021 [ 55 ]. The nutrient report records the reported movements of organic fertiliser such as pig, cattle and poultry manure, digestate from biogas plants and mineral nitrogen fertilisers at the district level. The report covers the reporting period from 1 July 2022 to 30 June 2023 and is based on the legal requirements of the Fertiliser Ordinance 2020 [ 56 ]. The Waste Balance Sheet documents the waste generated as part of public waste disposal in Lower Saxony by disposal area. This includes organic waste such as the organic waste bin, garden, and park waste [ 54 ]. The Biogas Inventory 2021 [ 53 ] shows the current status of biogas production and use in Lower Saxony for the years 2019–2021. The underlying data is available upon request. Decoding these data at NUTS 3 level reveals an uneven distribution of agricultural residues and biowastes available and used in biogas plants. A distinction is made between the amount of organic fertiliser or biowaste used. Suitability levels for both are assigned as follows: suitable for 0 to 30%, conditionally suitable for over 30 to 60%, and unsuitable for over 60 to 100% proportion of organic fertiliser or biowaste used in biogas plants in relation to existing organic fertiliser or biowaste, respectively. The suitability of the 0 to 30% range assumes that a lot of potential for substrate adaptation in the districts exists. In districts where the proportion of organic fertiliser and biowaste is over 30 to 60%, approximately doubling this figure is assumed to be feasible. Conversely, districts deemed unsuitable are those where an increase of merely one-third of the total in biogas plants used material can be attained. The study focuses on the potential for agricultural and environmental development and therefore favours areas where the current proportional use of organic fertiliser/biowaste does not exceed 30% or 60%. It is not deemed necessary to increase the proportion of both organic fertiliser and biowaste. Consequently, it is sufficient if either the proportion of organic fertiliser or the proportion of biowaste in a district can be raised. Distance to gas grid Connecting the biogas plant sites to the natural gas grid allows the renewable methane produced at the biogas plant sites to be transported and used elsewhere. Furthermore, connecting the plant sites to a gas pipeline as close as possible has economic advantages. For instance, shorter connection pipelines between the plant and the gas supply network result in lower pro rata costs for the connection applicant according to the Law on access to gas supply networks Gas Network Access Ordinance (§ 33 (1) Gasnetzzugangsverordnung (GasNZV) [ 57 ]) and simultaneously minimises the impact on the landscape [ 58 ]. Spatial data on the natural gas grid in Lower Saxony was used to investigate the feasibility of connecting to the natural gas grid. As the gas grid is classified as critical infrastructure [ 59 ], no high-resolution geodata were provided for this study at the request of the gas grid operators. However, the Spatial Planning Register ( Raumordnungskataster (ROK)) and Regional Spatial Planning Programmes ( Regionale Raumordnungsprogram me (RROP)) provide alternative geodata on the natural gas grid at a resolution of 1:25,000, respectively 1:50,000 (Data provided via Nefino GmbH [ 60 ]), which was merged and used for this analysis. Due to the high costs of crossing rivers, railway lines, and motorways [ 61 ], these were considered as barriers when determining the distance between the biogas plant site and the nearest pipeline section. High-resolution vector geodata of rivers, railways, and motorways from the Digital Landscape Model (DLM) [ 62 ] were considered (Table 2 ) barriers. The distance between biogas plant sites and gas pipelines was calculated with the ArcGIS Pro Tool Distance Accumulation. Table 2 Infrastructure and water barriers extracted from the Digital Landscape Model (DLM): Infrastructure, and water barriers extracted from DLM [ 62 ] Type DLM (Data Basis) [ 63 ] Object type Attribute type Definition Rivers AX_Gewaesserachse BRG is 12 Linear feature data of linear water bodies with a width of more than 6 m and up to 12 m AX_Fliessgewaesser / Polygon feature data of running waters with a width of more than 12 m and waters created for shipping Railways AX_Gleis / Linear feature data of laid rail pairs for railway vehicles AX_Bahnstrecke / Linear feature data of rail transport network Motorways AX_Fahrbahnachse WDM is 1301 Linear feature data of the Federal motorways AX_Strassenachse WDM is 1301 We assumed that biogas plant sites are suitable for connection to the gas grid if the distance to the gas grid is up to 1 km without barriers. Sites located more than 1 km and up to 10 km from the gas grid were conditionally suitable , as plant operators within this distance pay lower pro rata costs for connecting the plants to the supply network (§ 33 (1) GasNZV). 2.3 Overall suitability assessment In a final step, the overall suitability of the biogas plant sites for upgrading to P2G was determined based on the suitability according to the five previously described criteria (Fig. 3 ). If the suitability of a biogas plant site could not be assessed for one or more criteria due to a lack of data, the site was considered to be conditionally suitable for the criteria. Therefore, biogas plant sites were not automatically downgraded from the overall suitability assessment due to the incomplete database. A site was considered unsuitable for P2G, if at least one of the two hard criteria (regional RE potential and biogas plant installed electrical power) was rated unsuitable. As the sites were considered unsuitable as P2G sites, the soft criteria had not to be further analysed. A site was identified conditionally suitable if all hard criteria were rated at least conditionally suitable. Additionally, the soft criteria (water withdrawal conditions, substrate use, and distance to gas grid) were considered at these sites to further indicate environmental impacts. If all three soft criteria were assessed as at least conditionally suitable, the biogas plant site was considered suitable as an environmentally friendly P2G site. An assessment of 'conditionally suitable' based on a criterion indicates that there is no fundamental barrier to the site's suitability, but additional measures or conditions may be required. 3. Results The spatial analysis of biogas plant sites for their suitability as environmentally friendly P2G sites showed that 1,223 of the 1,704 biogas plant sites met the hard criteria, and were therefore, at least conditionally suitable. Of these sites, 1,014 were suitable as P2G sites because they also met the soft criteria. 3.1 Suitability of plant sites by criteria Regional RE potential A total of 2% of the biogas plant sites in Lower Saxony proved suitable for the regional supply of RE (Fig. 4 ). Within a 500 m radius of the 34 sites, we found enough areas that could be used in a human- and nature-compatible manner for the installation of wind turbines and ground-mounted photovoltaic systems to generate a mix of RE for the electrolysis at the biogas plant site to achieve the lowest hydrogen cost. These sites were mainly located in eastern Lower Saxony. The majority (72.7%) of the sites proved conditionally suitable for regional RE supply. At these 1,239 sites, the required amount of suitable area for human- and nature-compatible RE installations existed within a radius of more than 500 m and a maximum of 5 km to create a required RE mix of installed capacity of RE to achieve the lowest cost of hydrogen per kg. However, 261 biogas plant sites were not suitable for regional RE supply, as the RE mix could not be sourced within a 5 km radius. These unsuitable sites were mainly located in the northern Lower Saxony, but also along the Ammerland, Oldenburg, and all the way to the Osnabrück district. No assessment could be performed for 170 biogas plant sites due to a lack of data on the performance of the biogas plants. Biogas plant installed electrical power Over 70% of the biogas plant sites in Lower Saxony are conventional on-site electricity generation plants with an installed electrical capacity of 250 kW or more (Fig. 5 ). These 1,232 sites proved suitable for implementing the methanisation concept. Almost 17% of the biogas plant sites are unsuitable for implementing the methanisation concept, with 31 out of these 284 sites lacking on-site electricity generation capacities. Data on installed electrical capacity is not available for 188 biogas sites. Water withdrawal conditions At 83.7%, 1,427 of the 1,704 biogas plant sites proved suitable for the extraction of groundwater for hydrogen production (Fig. 6 ). At least 70% of the remaining sustainably usable groundwater remained available. The sites are spread over Lower Saxony. 18 biogas plant sites are conditionally suitable for groundwater extraction. At least 40% but less than 70% of the remaining usable groundwater was still available for hydrogen production. These biogas plant sites are situated on groundwater bodies in the Osterholz district, the southern Celle district, and the southern Osnabrück city. These sites are distributed throughout Lower Saxony. With 256 biogas plant sites, 15% of the sites are unsuitable for extraction due to a lack of remaining sustainable usable groundwater. Of the 189 biogas plant sites, 168 proved unsuitable for groundwater withdrawal because they are located too close to groundwater-dependent ecosystems that need to be protected. The high concentration of unsuitable biogas plant sites, particularly in the districts of Friesland, Wesermarsch, and Lüchow-Dannenberg, was due to the scarcity of groundwater. Substrate use The biogas plant sites in 39 districts are suitable for increasing the proportion of organic fertiliser or biowaste in the biogas plants (Fig. 7 ). In these districts, a maximum of 30% of the available organic fertiliser or biowaste has been used thus far in biogas plants. Only in the districts of Diepholz, Heidekreis, Uelzen, Lüneburg, and Lüchow-Dannenberg was from 30 to 60% of organic fertiliser and biowaste already being used. The biogas plant sites are considered to be conditionally suitable for a change in substrate use. Only the biogas plant sites in the Gifhorn district are unsuitable for the conversion of the substrate, as over 60% of the organic fertiliser or biowaste was already being used. Comparing the resources of organic fertiliser and biowaste across Lower Saxony, unused reserves of organic fertiliser were found in the north-west of Lower Saxony. Reserves of biowaste were available in the north, west, and the south of the federal state. Distance to gas grid Considering linear infrastructure and water barriers, 683 of the 1,704 biogas plant sites are located within 1 km of the natural gas network (Fig. 8 ). This represents just over 40% of biogas plant sites in Lower Saxony. The majority of these plants are located in the west and south of Lower Saxony. In this region, not only does the density of biogas plants peak, but the natural gas network also has extensive branches. These biogas plant sites are suitable for connection to the gas grid. More than half of the sites (927 sites) are located more than 1 km away, although a maximum of 10 km from the natural gas network. These biogas plant sites are conditionally suitable for connection to the gas grid. With 94 sites, i.e., just around 5%, are more than 10 km away from the natural gas network. 3.2 Environmentally friendly P2G potential of biogas plant sites Almost 60% of the biogas plant sites (1,014 sites) are considered suitable as environmentally friendly P2G sites (Fig. 9 ). Accumulations of suitable biogas plant sites are found from the Emsland district in the west of Lower Saxony, through Cloppenburg, Oldenburg to Diepholt as well as in Rotenburg (Wümmer), the north of Heidekreis, and the south of Celle districts. Additionally, about 12% (209 sites) are considered conditionally suitable, and almost 30% (481 sites) are unsuitable. The density of suitable plants is the lowest in the south-east and far north-west of Lower Saxony. Numerous biogas plant sites that are unsuitable for environmentally friendly P2G are situated along the northern and the south-western borders of Lower Saxony, extending from Grafschaft Bentheim to the Göttingen district. A large number of unsuitable sites are also found in the districts of Ammerland, Oldenburg, and Osnabrück. Of the 481 biogas sites unsuitable for P2G, only 64 are unsuitable based on both hard criteria (Fig. 10 ). The required installed RE capacity neither exists in the immediate vicinity of the plants, nor is the minimum required installed electrical capacity of on-site generation plants present. Each hard criterion resulted in a further 40% of sites being considered unsuitable. This does not consider sites with a lack of data. Of the 209 biogas plant sites conditionally suitable for upgrading to P2G, over 60% of the sites are conditionally suitable due to the lack of remaining sustainably usable groundwater at the biogas site. The majority of 1,014 biogas plant sites are suitable based on all five criteria. 4. Discussion The criteria-based spatial suitability analysis identified 1,014 of the 1,704 biogas plant sites as suitable for an environmentally friendly implementation of the methanisation concept as an end-of-subsidy strategy. The high spatial resolution at the level of individual biogas plant sites throughout Lower Saxony is a unique feature of our suitability analysis. A handful of P2G spatial suitability analyses of biogas plants in Germany exist covering large areas such as the entire country. However, these were mainly conducted at the district level (cf. [ 10 ], [ 65 ], [ 66 ]) which does not qualify these analyses for individual biogas site assessment. Additionally, as we focus on Lower Saxony, we were able to integrate high-resolution base data (e.g. DLM [ 62 ]) tailored to the region, which allowed us to make multi-criteria based location-specific evaluations for individual biogas plant sites. We particularly benefited from the high-resolution biogas plant register for Lower Saxony [ 28 ]. This register was created as part of the H2-FEE research project and enables spatial analyses of biogas plant sites to be conducted. Based on the regional RE potential criterion, only 2% of the biogas plant sites in Lower Saxony are suitable for environmentally friendly P2G. The installable RE capacity can be built within 500 m of the plant on human- and nature-compatible areas for wind turbines and ground-mounted photovoltaic systems. The suitability of the biogas plant site is primarily limited by the lower availability of compatible areas for wind turbines. Efficient green electrolysis in most cases requires RE from both wind and solar [ 67 ]. Although, unlike the 5,349 km 2 of compatible areas for ground-mounted photovoltaic systems in Lower Saxony, only 1,086 km 2 are available for wind turbines. As the human and nature compatible areas for wind turbines are distributed across Lower Saxony, three quarters of the biogas plant sites have the required compatible areas for wind turbines located within a radius of 5 km. This allows them to be rated as conditionally suitable according to the regional RE potential criterion. Contrary to the analysis of potential areas for onshore wind energy in Lower Saxony ( Flächenpotenzialanalyse Windenergie an Land in Niedersachsen , WinNiePot) commissioned by the Lower Saxony Ministry for the Environment, Energy and Climate Protection in 2023 [ 39 ], we assume not 6.2% but only 2.3% of Lower Saxony as potential area. The difference is not least due to the additional detailed, high-resolution database provided by Nefino GmbH. Particularly, we go one step further than that by Peters et al. [ 39 ] in WinNiePot and place great emphasis on human- and nature-compatibility of areas for wind turbines. Less suitable areas, such as those with a high-quality visible landscape, were excluded. Nevertheless, the provision of 2.3% land area of Lower Saxony for wind energy utilisation is sufficient to meet the target of 2.2% laid down in the Wind Energy Area Requirements Act ( Windenergieflächenbedarfsgesetz (WindBG)). Considering the human and nature conservation interests at an early stage in spatial planning also minimises land use conflicts, which promotes acceptance of RE and green gas expansion. The criterion involves the additional installation of RE capacities, as required by the EU [ 2 ]. It should be noted that commissioning new wind turbines for smaller projects, such as implementing the methanisation concept at biogas plant locations as described above, may present economic challenges. When initially assessing capacity requirements, we estimated the approximate required installed RE capacity for the methanisation concept at individual biogas plant sites. When considering individual sites in more detail, this value must be refined using additional, high-resolution, site-specific data. Biogas plant sites located far from areas human- and nature-compatible for the installation of wind turbines may still be suitable for P2G. The identified areas serve as a guide to the suitability of sites in terms of agricultural and environmental compatibility. Therefore, we have decided not to take the legally binding priority areas for wind energy into account. These areas must be designated in their final form by 2026, in accordance with the WindGB. However, when considering individual biogas plant sites, it is advisable to check the actual availability of land for RE, taking into account site-specific parameters. When assessing the water withdrawal conditions at the biogas plant sites, groundwater recharge and water withdrawals were taken into account at the level of groundwater (sub)bodies. Adopting a differentiated approach to electrolysis water withdrawal and ecosystem requirements enabled individual sites to be assessed separately [ 23 ]. The calculated values for the quantities of water required for electrolysis are only approximate. The amount of cooling water required was not considered. This is because, depending on the availability of water, different water-intensive cooling systems can be chosen [ 68 ]. These approximate assumptions are perfectly acceptable, given that the amount of water used for electrolysis was of little value in comparison to the total water consumption of Lower Saxony. Badelt and Haaren [ 64 ] assume that 77 million m 3 of water per year will be required for electrolysis in 2045. This is less than 6% of the total groundwater used annually for field irrigation, livestock water withdrawal, industrial water withdrawal, and public water supply [ 45 ]. To assess the ecosystem requirements, the water requirements necessary to preserve biodiversity were determined based on groundwater-dependent terrestrial ecosystems. It is not yet possible to conduct a high-resolution analysis for the quantitative determination of water requirements in Lower Saxony due to a lack of high-resolution data, such as biotope-specific evapotranspiration and soil science parameters [ 2 ]. Only 256 of the 1,704 biogas plant sites lack sustainable groundwater supply for electrolysis. However, water withdrawal conditions are a limiting criterion for more than 50% (114 sites) of the plants classified as conditionally suitable. When examining individual biogas plants in more detail, it is advantageous to consider the individual circumstances. Alternative water sources, such as river, sea, or wastewater, must be considered for these biogas plant sites and included in further analyses. In the context of the H2-FEE research project, Locker [ 69 ] calculated the maximum possible water withdrawal from rivers for electrolysis while maintaining the minimum water discharge. However, it was difficult to make detailed area-wide statements. This was due to the patchy discharge data available for the gauges. Additionally, cases where cost-intensive water treatment [ 48 ] [ 68 ] is beneficial should be examined. The substrate use criterion shows that in almost all districts (with the exception of the Gifhorn) 60% or more of the existing organic fertiliser or biowaste was not yet used in the biogas plant sites. This offers the opportunity to switch to using organic fertiliser or biowaste instead of growing energy crops. The electrical output, of which 82.4% (2021) came from energy crops and plant by-products [ 53 ], can alternatively be generated from organic fertilisers and biowaste. This would imply that 283,000 ha (10.8%) of agricultural land currently used to grow energy crops would be available not only for food production but also for nature conservation. RE development can also benefit from reduced pressure on agricultural land [ 70 ]. As substrate flows between districts were not yet considered, the possibility of importing substrate surpluses from neighbouring regions should be considered, especially for the Gifhorn district. The individual biogas plant sites in the districts are not assessed. Instead, the assessment at district level is broken down into the individual plants. This is due to the lack of comprehensive, detailed information on the substrate composition in the individual biogas plants. Earlier surveys of biogas plant sites only allow for ascertaining the selection of biogas plant sites (cf. [ 69 ]). This means that sites which already use organic fertiliser and biowaste as substrates cannot be assessed individually. Collecting data on substrate composition at individual biogas plants could allow for a more detailed assessment of the sites. However, this would require considerable resources. The criterion distance to gas grid can serve as an indicator to estimate the distance from the biogas plant site to the natural gas grid. A total of 41 biogas plant sites are not considered suitable for P2G, although they are conditionally suitable due to the distance to the gas grid criterion. A further 20 sites are conditionally suitable for P2G, partly on the basis of this criterion. At these sites, island operation of the plants could be an alternative. This can become possible through a nearby consumer [ 71 ]. A more detailed assessment is possible with spatially high-resolved data on the natural gas grid, gas distribution network and connection points to the gas network. However, this data was not publicly available at the time of the study because the gas network is classified as critical infrastructure [ 59 ]. This high-resolution spatial data is only accessible upon request when analysing individual locations and must be considered in subsequent detailed planning. Nevertheless, the barriers considered in the analysis, including rivers, railways and motorways, are available at a high spatial resolution in the base DLM [ 62 ]. For future analyses, it is optional to consider compatibility with humans and the environment further by including additional barriers, such as nature reserves, in the analysis. However, the distance between the biogas plant and the gas network can only be determined accurately if high-resolution spatial data on the gas network is available alongside information on the barriers. When the criteria were combined, the overall suitability assessment was strongly influenced by the hard criteria. As soon as the regional RE potential or the biogas plant installed electrical power was rated as unsuitable, the site was considered unsuitable for the methanisation concept. This enabled the most relevant implementation criteria to play a more important role. In order to break down the complexity of the individual criteria, individual aspects were brought to the fore. As described above, in the case of the regional RE potential criterion, these include, for example, the additional placement of RE plants and the construction of these plants in areas that are compatible with humans and nature. Nevertheless, it should be noted that the methanisation concept may be feasible at biogas plant sites even if the criteria are deemed unsuitable. For example, aspects such as the compatibility of the selected areas with the designated priority areas for wind energy and the economic challenges of commissioning new RE plants have not yet been considered. Therefore, when individual biogas plants are examined at a later stage, it could be shown that the methanisation concept can indeed be implemented. This once again illustrates that, while the results of the overall suitability assessment provide a useful initial overview, a detailed examination of the individual locations is also necessary if the concept is to be implemented at specific sites. When analysing the suitability of biogas plant sites in Lower Saxony as environmentally friendly P2G sites, the focus was on the agricultural and environmental compatibility of the sites. Further, we focused on criteria that received less attention in P2G potential analyses, including decentralised human- and nature-compatible RE capacity and water availability for electrolysis. These unique features enable a more compatible transition to a GHG-emitting net energy sector. Considering agricultural- and nature-compatibility, the integration of additional criteria can lead to an even more holistic assessment of the suitability of biogas plant sites for environmentally friendly P2G. Criteria from comparable spatial P2G potential analyses of biogas plants in Germany can be used as a first orientation for the selection of further criteria to be considered. Some authors already considered a number of criteria that also were identified here to determine the suitability of biogas plants for P2G in Germany. Mertins et al. [ 66 ] and Erler et al. [ 10 ] considered the gas grid, while Dögnitz et al. [ 65 ] examined the input substrates of the biogas plants. However, some authors already considered criteria that were less focused in our analysis. For example, Mertins et al. [ 66 ] and Erler et al. [ 10 ] also considered biomethane capacity compared with that of the German natural gas demand. Another example, we identified a large number of biogas plant sites in the Emsland district suitable for P2G, whereas Mertins et al. [ 66 ] assessed the Emsland district as a region with a relatively low gas demand that was studied earlier to an above-average extent. The Institute of Energy Economics at the University of Cologne (EWI) [ 72 ] also placed a stronger focus on regional hydrogen demand when strategically positioning small electrolysers. Including current and future heating networks as consumers in the suitability analyses could also be promising. Despite the different criteria used to analyse suitability, some spatial similarities of areas suitable for P2G can already be identified. Similar to that of the current study (Fig. 9 ), Erler et al. [ 10 ] highlighted a higher potential in the Emsland, Cloppenburg, Oldenburg, and Diepholz districts. Additionally, clear spatial synergies exist between the biogas plant sites identified here as suitable for P2G and the system-serving electrolysers < 10 MW identified by EWI [ 72 ] at the district level. EWI additionally identified a high potential in the Emsland district [ 72 ]. To meet the goal of achieving CO 2 neutrality in Lower Saxony by 2040 (§ 3.1.1 NKlimaG), our analysis serves as a basis for deciding the suitability of biogas plant sites for upgrading to the methanisation concept. Deciding on an appropriate end-of-subsidy strategy for biogas plant sites is particularly important as the 20-year subsidy period under the EEG is about to expire. Erler et al. [ 10 ] recommended completing the conceptual planning about two years before the end of the EEG subsidy period. Between 2025 and 2035, the 20-year EEG subsidy period will end for 790 sites considered suitable for the above-described methanisation concept. A need exists for prompt action for all parties involved. 5. Conclusions The criteria-based spatial suitability analysis enables comprehensive mapping of the P2G potential of 1,704 existing biogas plant sites in Lower Saxony. It identified 1,014 sites suitable for environmentally friendly implementation of the methanisation concept, as an end-of-subsidy strategy according to Erler et al. [ 10 ]. While highlighting sites with high P2G potential, the analysis also identified regions where alternative strategies are necessary. By considering agricultural and nature conservation compatibility, this research ensures that diverse interests are integrated from the outset, reducing land-use conflicts and promoting broader acceptance of the transition to RE. We demonstrate the significant spatial potential for implementing the methanisation concept in Lower Saxony. Implementing this concept will offset fluctuations or deficiencies in RE sources and help Lower Saxony achieve its goal of CO₂ neutrality by 2040. The findings also serve as a vital decision support for stakeholders, including biogas plant operator-, small and medium-sized enterprises, local authorities and districts, as well as policy advisers, emphasising the urgent need for action as the EEG subsidy period is nearing its end. The analysis provides adaptable criteria to support tailored decision-making processes. To ensure the results reach the intended stakeholders, they will be made available on a publicly accessible WebGIS platform at the end of 2025 as part of the H2-FEE research project. Once the stakeholders have selected specific sites, it is recommended that they examine their suitability in detail. This is because a clear statement about the sites requires consideration of parameters that are not available across Lower Saxony. To capture an even more holistic picture of the potential of the biogas plant sites for the methanisation concept, the methodology can be further developed in the future. Possible refinements to the criteria may include integrating economic aspects, which would enable the economic sustainability of the concept to be assessed at individual sites. This includes the capital expenditure costs of installing new wind turbines and ground-mounted photovoltaic systems, for example. Another approach is to adjust the weighting of the criteria in order to counteract the premature exclusion of sites that are deemed unsuitable because of the strict criteria. To verify the method, the accuracy of the results can be evaluated by comparing the assumed suitability of biogas plants from the analysis with spatial overlaps with similar existing and planned projects at biogas plant sites. Finally, it should be noted that the above analysis could form the basis for similar location analyses in the future. One example may be the potential of biogas plant sites for power-to-hydrogen production. List of Abbreviations ASR....................................................... Military Airport Surveillance Radar ATKIS....................... Official Topographic Cartographic Information System CO 2 .................................................................................... carbon dioxide DLM..................................................................... Digital Landscape Model DVGW......... German Technical and Scientific Association for Gas and Water EEG............................................................. Renewable Energy Sources Act ESTRAM........................................... Energy System Transformation Model EU.................................................................................... European Union EWI................... Institute of Energy Economics at the University of Cologne GasNZV...................................................... Gas Network Access Ordinance GHG.................................................................................. greenhouse gas H2-FEE................. H2-FEE: Flexible energy carriers for the energy transition LÖWE+ … updated Lower Saxony programme for long-term ecological forest development in the Lower Saxony state forests MVA.............................................................. Minimum Vectoring Altitude NBank............................ Lower Saxony Investment and Development Bank NKlimaG............................................................. Lower Saxony Climate Act NLT................................................... Lower Saxony Association of Districts NSGB....................... Lower Saxony Association of Towns and Municipalities NWE10.................................... programme for natural forest development P2G..................................................................................... Power-to-Gas RE................................................................................. renewable energy ROK..................................................................... Spatial Planning Register RROP.............................................. Regional Spatial Planning Programmes StromStV...................................................................... Electricity Duty Act WHG................................................................. German Federal Water Act WindBG.............................................. Wind Energy Area Requirements Act WinNiePot analysis of potential areas for onshore wind energy in Lower Saxony WSI................................................................... Water Sustainability Index Declarations Ethics approval and consent to participate Not applicable. Consent for publication Not applicable. Availability of data and materials The datasets generated during the current study are available in the Research Data Repository of the Leibniz University Hannover, https://doi.org/10.25835/x2seo1d8 [74]. Competing interests The authors declare no competing interests. Funding The article is a result of the NBank funded research project H2-FEE: Flexible energy carriers for the energy transition (duration from July 2022 to June 2025). Authors' contributions ML and YW developed the method and generated the resulting dataset. ML drafted most of the manuscript, while YW added sections on the background and the method for using the substrate criterion. JH provided advice on the development of the method and was actively involved in further development of the manuscript. Acknowledgements The authors thank Jonas Berndmeyer, Alexander Mahner, and Marie Jeuk for their collaboration in the H2-FEE research project. Jonas Berndmeyer placed the reference wind turbines on suitable areas. Alexander Mahner determined the installable capacity per hectare for ground-mounted photovoltaic systems. Marie Jeuk calculated the installed capacity of RE required to achieve the lowest cost of hydrogen at each biogas plant site. The authors also thank Ole Badelt, Ines Lüdders, and Johannes Wiese for their support during this study. The authors thank Elsevier Language Services, Alina Kupper and Christina Amacher for linguistic corrections. The authors acknowledge using DeepL Write and ChatGPT by OpenAI for text editing assistance and take full responsibility for any remaining errors. References European Union (2019) The European Green Deal. https://eur-lex.europa.eu/resource.html?uri=cellar:b828d165-1c22-11ea-8c1f-01aa75ed71a1.0002.02/DOC_1&format=PDF . Accessed: 13 Jun 2025 European Parliament, Council of the European Union (2023) Directive (EU) 2023/2413 of the European Parliament and of the Council of 18 October 2023 amending Directive (EU) 2018/2001, Regulation (EU) 2018/1999 and Directive 98/70/EC as regards the promotion of energy from renewable sources, and repealing Council Directive (EU) 2015/652. https://eur-lex.europa.eu/legal-content/EN/ALL/?uri=CELEX:32023L2413 . 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Accessed 15 Jun 2025 Nefino GmbH (2024) Luftfahrt und FFH. Auszug aus den Geodaten der Nefino GmbH. Unpublished. Accessed 28 Sep 2023 Plinke M, Weber Y, Hack J (2025) Environmentally friendly Power-to-Gas potential of biogas plant sites in Lower Saxony, Germany. LUIS. https://doi.org/10.25835/x2seo1d8 Footnotes According to Plinke et al. [21], biogas plant sites are neighbouring biogas plants grouped on the basis of the surface areas obtained from the Lower Saxony Digital Landscape Model (DLM) vector data [62], which is part of the Official Topographic Cartographic Information System (Amtliches Topographisch-Kartographisches Informationssystem, ATKIS). In ESTRAM hydrogen in kg is used as input. We assume a hydrogen density of 0.0899 kg/m3 (15 degrees Celsius, 1 bar) according to B. Adler et al. 2021. Additional Declarations No competing interests reported. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7148209","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":627002891,"identity":"8a76518d-2c8b-4a50-a95a-9418a6336e0d","order_by":0,"name":"Mareike 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[28]\u003cem\u003e)\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7148209/v1/7b1a837cb5a1a258223d803d.jpeg"},{"id":107508554,"identity":"b61b0bea-dcbc-4c0d-b3ca-7fda05a1635f","added_by":"auto","created_at":"2026-04-22 07:21:41","extension":"jpeg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":705259,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eSpatial distribution of biogas plant sites in terms of their suitability for P2G in Lower Saxony based on the criterion water withdrawal conditions, assessed by the remaining sustainability usable groundwater at the biogas plant sites (Geodata basis:\u003c/em\u003e [32], [28], [64]\u003cem\u003e)\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage6.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7148209/v1/b5ada36c248952374d290d17.jpeg"},{"id":107705676,"identity":"65ba1922-7b18-4bb1-add9-baf80f3fb3a9","added_by":"auto","created_at":"2026-04-24 09:14:22","extension":"jpeg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":633255,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eSpatial distribution of biogas plant sites in terms of their suitability for P2G in Lower Saxony based on the criterion substrate use, assessed by the proportion of organic fertiliser/biowaste used in biogas plants in relation to existing substrate (Geodata basis:\u003c/em\u003e [32], [28]\u003cem\u003e)\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage7.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7148209/v1/28070cc764a09b237ea2865e.jpeg"},{"id":108006073,"identity":"e051aea7-f75e-4cc1-82d5-fe071e126ff0","added_by":"auto","created_at":"2026-04-28 12:52:51","extension":"jpeg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":775601,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eSpatial distribution of biogas plant sites in terms of their suitability for P2G in Lower Saxony based on the criterion for distance to gas grid, assessed by the distance of biogas plant sites to the gas grid (Geodata basis: \u003c/em\u003e[32], [28], [60]\u003cem\u003e)\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage8.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7148209/v1/97aeb7e5f351392bd7f2f036.jpeg"},{"id":107508556,"identity":"f84fe32b-b2fe-4db2-bbfb-7483f47e2b26","added_by":"auto","created_at":"2026-04-22 07:21:41","extension":"jpeg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":580601,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eSpatial distribution of biogas plant sites in terms of their suitability for P2G in Lower Saxony (Geodata basis: \u003c/em\u003e[32], [28]\u003cem\u003e)\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage9.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7148209/v1/086a0a64dd12b52917f1b052.jpeg"},{"id":107706023,"identity":"f14bbba0-661c-4c6c-a267-78dc8953c694","added_by":"auto","created_at":"2026-04-24 09:17:09","extension":"jpeg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":92608,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eDistribution of biogas plant sites in terms of their suitability as P2G sites based on the five criteria\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage10.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7148209/v1/afb401545a4a1b61234d3062.jpeg"},{"id":108008457,"identity":"d7e69361-fc4b-4283-ae04-c3c57889615f","added_by":"auto","created_at":"2026-04-28 13:06:46","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5449896,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7148209/v1/cd1f06c6-3eef-4a0a-b59d-acd2002eeba1.pdf"},{"id":107508550,"identity":"a2821499-28da-4c26-8f49-eb5abb7fc900","added_by":"auto","created_at":"2026-04-22 07:21:41","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":23997,"visible":true,"origin":"","legend":"","description":"","filename":"AppendixAandB.docx","url":"https://assets-eu.researchsquare.com/files/rs-7148209/v1/3900879b2eb6f9c8c6a21c87.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Assessing the Power-to-Gas potential: GIS-based suitability analysis of biogas plant sites in Lower Saxony, Germany","fulltext":[{"header":"1. Background","content":"\u003cp\u003eIt is paramount to decarbonise the energy system to achieve the climate objectives set out by the European Union (EU) for 2030 and 2050. Yet, 75% of the greenhouse gas (GHG) emissions in the EU are produced in the generation and use of energy. Therefore, the EU aims to develop a power sector based largely on renewable sources [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. In 2022, the proportion of energy derived from renewable sources in gross final consumption was 23%, with the goal of attaining at least 42.5% by 2030 [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e] [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Renewable energy (RE) in Germany provided just 22% in 2023. The share of renewables in gross electricity consumption was 51.8%, of which wind energy contributes 52.2%, solar energy 22.5%, biogas 10.5%, and biomethane 1.1% [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. To contribute to future decarbonisation and GHG neutrality, further energy concepts must be considered to offset fluctuations or deficiencies in RE sources, such as wind and solar energy. Biogas plants are able to compensate for such fluctuations. In some German federal states, such as Lower Saxony, a large number of biogas plants have been built since 2000 as a result of subsidies under the Renewable Energy Sources Act \u003cem\u003eErneuerbare-Energien-Gesetz\u003c/em\u003e (EEG) [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e] of Germany and favourable agricultural conditions [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. By 2022, almost a quarter of the installed capacity of 1,360 MW in Germany, provided by 1,691 biogas plants, was located in Lower Saxony [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. However, the 20-year subsidy period under the EEG, which guarantees a fixed feed-in tariff, will expire for many of the biogas plants in Lower Saxony in the near future. The use of biomass for energy production is currently being criticised, inter alia due to its potential negative impact on food production, biodiversity, and the environment [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. The result is a gradual reduction in the size of tenders for biogas plants in Germany (EEG \u0026sect;\u0026nbsp;28c [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]). This will affect one-third of the biogas plants of Lower Saxony in the next five years and two-thirds in the next ten years [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. After the expiry of subsidies, the risk of losing profitability resulting in plant decommissioning rises [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eHowever, the situation brings new opportunities for appropriate decentralised P2G end-of-subsidy strategies for existing biogas plants in Lower Saxony to compensate for the fluctuation from RE and to push forward a sustainable energy transition. Additionally, considering agricultural and nature conservation interests from the outset when identifying suitable biogas plants for end-of-subsidy strategies can prevent land competition among different uses.\u003c/p\u003e \u003cp\u003eErler et al. [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] describe an end-of-subsidy strategy suitable for many on-site electricity generation plants of Lower Saxony. Using a concept called 'methanisation' (Power-to-Gas, P2G), biogas can be converted to biomethane. In a biogas plant, biogas is produced through anaerobic fermentation. This biological process involves the breakdown of complex organic substances, such as biomass, into simpler components under anaerobic conditions, in the absence of oxygen. The result is the release of biogas, which is essentially composed of biomethane (CH\u003csub\u003e4\u003c/sub\u003e) and carbon dioxide (CO\u003csub\u003e2\u003c/sub\u003e) [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. The methanisation concept involves first coupling existing plants to an electrolyser to produce green hydrogen powered by RE. Second, in a methanisation reactor, the previously unused CO\u003csub\u003e2\u003c/sub\u003e from the biogas plant and the green hydrogen are converted into renewable methane. This can be fed into the natural gas grid with the biomethane from the biogas plant [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. The feasibility of coupling biogas and P2G plants was already demonstrated in several studies [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e] [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e] [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Furthermore, it was shown that coupling can be economically viable under certain conditions [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e] [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. The coupling has various advantages, such as the low complexity of a P2G process chain, which increases the probability of implementation [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e], the continuously available, cost-effective and renewable CO\u003csub\u003e2\u003c/sub\u003e, which is required for the methanisation [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e] [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e] and the possibility of dual energy generation, i.e., when hydrogen is not available, the plant can generate electricity, and when it is available, renewable methane can be fed into the gas grid [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Furthermore, the biomethane yields can be increased without the use of additional biomass [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. The process of methanisation eliminates the necessity for CO₂ separation, which represents the primary cost factor associated with the upgrading of biogas to natural gas quality. This enables the utilisation of green CO\u003csub\u003e2\u003c/sub\u003e in a manner that is both materially and energetically meaningful [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. The oxygen produced during electrolysis can be employed for the coarse desulphurisation of the raw biogas [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Additionally, the storage capacity of the natural gas grid can be used to indirectly store surplus electricity from RE [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe biogas plants of Lower Saxony offer a wide range of synergies for P2G, making them well-suited for the decentralised production of renewable methane. For P2G, the 1,255 on-site electricity generation plant sites [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e] are of potential use. Additionally, Lower Saxony offers a large number of potentially suitable areas for the production of RE from wind and sun [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e], which is required for the production of green hydrogen from electrolysis. Lower Saxony also has sufficient water resources for sustainable water extraction for electrolysis, although these are unevenly distributed across the region [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Large quantities of biowaste (1,216,604.14 tonnes in 2022) [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e] and organic fertiliser (37.25\u0026nbsp;million tonnes in July 2022 to June 2023) [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e] are also present in the region, which can be used as substrates in the biogas plants [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. The change in the substrates used can reduce the competition for land previously caused by the cultivation of energy crops. The natural gas pipeline network also offers a high potential for the purchase and transport of renewable methane, as it is widely branched in many districts, especially in the western half of Lower Saxony [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eDespite the general potential suitability of biogas plant sites in Lower Saxony for upgrading to P2G, a lack of knowledge exists regarding the most suitable plant sites of the 1,704 due to their individual site conditions. The sites that can meet the interests of agriculture and nature conservation to avoid land competition between different uses need to be identified. To support the decision on the biogas plant sites suitable for upgrading to P2G as an end-of-subsidy strategy, the potential of the biogas plant sites for P2G needs to be assessed. Our objective is to map the P2G potential of existing biogas plant sites in Lower Saxony, with special consideration of agricultural and nature conservation compatibility. We present a GIS-based spatial suitability analysis of the individual biogas plant sites in Lower Saxony. The high-resulted biogas plant sites\u003csup\u003e1\u003c/sup\u003e previously identified by Plinke et al.[\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e] are analysed for their suitability on the basis of five criteria: Regional RE potential, biogas plant installed power, water withdrawal conditions, substrate use, and distance to gas grid. The suitability is then derived from this set of criteria. The analysis is being undertaken as part of the H2-FEE research project: Flexible energy carriers for the energy transition (running from July 2022 to June 2025) funded by the Lower Saxony Investment and Development Bank (Investitions- und F\u0026ouml;rderbank Niedersachsen, NBank).\u003c/p\u003e"},{"header":"2. Methodology","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Study area\u003c/h2\u003e \u003cp\u003eThe study area is located in the northwest of Germany: the federal state of Lower Saxony (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). With an area of 47,710 km\u003csup\u003e2\u003c/sup\u003e, consisting of 45 administrative districts (\u003cem\u003eLandkreise\u003c/em\u003e and \u003cem\u003ekreisfreie St\u0026auml;dte\u003c/em\u003e), Lower Saxony is the second largest of all 16 German federal states [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. Despite its size, it has the fifth-lowest population density [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. As a dominantly rural state, it is suitable for this study because of its large amount and spatially dispersed biogas plants, which will soon phase out of subsidies by the German government (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) and will require an end-of-subsidy strategy. By the end of 2025, 184 of the 1,704 biogas plant sites will no longer receive subsidies. Between 2026 and 2035, a further 1,253 sites will phase out, accounting for almost 85% of the total. The remaining sites will be phased out by 2045. It is also a great advantage that the state has a high potential for RE (wind turbines and ground-mounted photovoltaic systems) production [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Suitability criteria and assessment\u003c/h2\u003e \u003cp\u003eThe methodological approach for identifying biogas plant sites with environmentally friendly P2G potential in Lower Saxony encompasses criteria-based, spatial GIS analysis using the geoinformation software ArcGIS Pro (Version 3.3.2).\u003c/p\u003e \u003cp\u003eFor this purpose, the 1,704 biogas plant sites, whose exact locations were spatially determined in Plinke et al. [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e], were examined individually for their suitability to implement the methanisation concept described above. To identify the environmentally friendly P2G potential of these biogas plant sites, the three phases of the P2G life cycle (RE production used for green hydrogen production, P2G process including biogas production and methanisation, and consumers as distance to the gas grid) served as the basis for a five-criterion evaluation of the suitability of the biogas plant sites (Fig.\u0026nbsp;2).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs the regional RE potential for wind turbines and ground-mounted photovoltaic systems, as well as the biogas plant installed electrical capacity, are mandatory for the methanisation process with green hydrogen described by Erler et al. [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], these were treated as hard criteria that had to be met for a biogas plant site to be suitable. The criteria water withdrawal conditions (for hydrogen production), substrate use (for biogas production), and gas grid connection (for methane distribution to consumers) were considered as soft criteria, which function as further sustainability criteria considering the environmental impact. The suitability of biogas plant sites was assessed for each suitability criterion on the basis of three suitability levels: \u003cem\u003esuitable\u003c/em\u003e, \u003cem\u003econditionally suitable\u003c/em\u003e, and \u003cem\u003eunsuitable\u003c/em\u003e (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSuitability criteria catalogue with suitability levels for environmentally friendly P2G potential of biogas plant sites\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSuitability criteria\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e \u003cp\u003eSuitability levels\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSuitable\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eConditionally suitable\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eUnsuitable\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eRegional RE potential\u003c/b\u003e (hard criterion)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRequired installable capacity from wind turbines and ground-mounted photovoltaic systems within 500 m radius from biogas plant site to achieve the lowest hydrogen cost\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRequired installable capacity from wind turbines and ground-mounted photovoltaic systems within a radius\u0026thinsp;\u0026gt;\u0026thinsp;500 m and \u0026le;\u0026thinsp;5 km from biogas plant site to achieve the lowest hydrogen cost\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRequired installable capacity from wind turbines and ground-mounted photovoltaic systems within a radius\u0026thinsp;\u0026gt;\u0026thinsp;5\u0026nbsp;km from biogas plant site to achieve the lowest hydrogen cost\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eBiogas plant installed electrical power\u003c/b\u003e\u003c/p\u003e \u003cp\u003e(hard criterion)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026ge;\u0026thinsp;250 kW installed electrical capacity/site\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;250 kW installed electrical capacity/site\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eWater withdrawal conditions\u003c/b\u003e\u003c/p\u003e \u003cp\u003e(soft criterion)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026ge;\u0026thinsp;70% remaining sustainably usable groundwater available\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026ge;\u0026thinsp;40% and \u0026lt;\u0026thinsp;70% remaining sustainably usable groundwater available\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;40% remaining sustainably usable groundwater available\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eSubstrate use\u003c/b\u003e\u003c/p\u003e \u003cp\u003e(soft criterion)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026le;\u0026thinsp;30% proportion of organic fertiliser/biowaste used in biogas plants in relation to existing organic fertiliser/biowaste by district\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026gt;\u0026thinsp;30% and \u0026le;\u0026thinsp;60% proportion of organic fertiliser/biowaste used in biogas plants in relation to existing organic fertiliser/biowaste by district\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026gt;\u0026thinsp;60% and \u0026le;\u0026thinsp;100% proportion of organic fertiliser/biowaste used in biogas plants in relation to existing organic fertiliser/biowaste by district\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eDistance to gas grid\u003c/b\u003e\u003c/p\u003e \u003cp\u003e(soft criterion)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026le;\u0026thinsp;1 km\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026gt;\u0026thinsp;1 km and \u0026le;\u0026thinsp;10 km\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026gt;\u0026thinsp;10 km\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe individual suitability criteria are further outlined in the following subsections. The importance of the criteria for identifying suitable P2G sites is explained, as well as the methodological approach for their assessment and data sources used.\u003c/p\u003e \u003cp\u003e \u003cb\u003eRegional RE potential\u003c/b\u003e \u003c/p\u003e \u003cp\u003eWe assumed that the targeted regional production of green gases (green hydrogen and biomethane) at the biogas plant site is based on the exclusive use of additional RE sources located in the immediate vicinity (definition below). Instead of diverting RE from other uses, new RE capacities should be added to contribute to the energy transition [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. As many areas of Lower Saxony offer great potential for the installation of human- and nature-compatible wind turbines and ground-mounted photovoltaic systems [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e] [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e], these potential installations were considered for the generation of RE in this study. Human- and nature-compatible installation of RE in an area implies that it is not at the expense of the quality of life of people, biodiversity, or food production [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. However, the RE potential is geographically unevenly distributed [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e] [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e], which is the reason for individually assessing the suitability of each biogas plant site for the implementation of the methanisation concept.\u003c/p\u003e \u003cp\u003eWithin the H2-FEE research project, the installed capacity of wind turbines and ground-mounted photovoltaic systems required to achieve the lowest cost of hydrogen per kg at each biogas plant site was calculated. This was done by conducting a detailed energy system analysis on a 0.25-degree grid using the Energy System Transformation Model (ESTRAM) [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e] developed at the Institute of Solid State Physics at Leibniz University Hannover, Germany. The calculation is based on the potential annual production of hydrogen at each biogas plant site\u003csup\u003e2\u003c/sup\u003e from wind turbines and ground-mounted photovoltaic systems. The hydrogen production depends on the amount of CO\u003csub\u003e2\u003c/sub\u003e produced in a biogas plant, as it is supposed to be fully used for methanisation. The by-product CO\u003csub\u003e2\u003c/sub\u003e produced in the biogas plant is assumed to be used for the production of renewable methane and could then be fed into the natural gas grid together with the biomethane produced in the biogas plant [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. To produce renewable methane, hydrogen and CO\u003csub\u003e2\u003c/sub\u003e are required in a 4:1 ratio [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. The CO\u003csub\u003e2\u003c/sub\u003e concentration in raw biogas varies between 25 and 45 vol% [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. Therefore, the calculation is based on the mean value of 35 vol%. We derived the amount of raw biogas orienting on Berndmeyer [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e], who identified it based on Erler et al. [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. We used the ratio of 1.52 of the installed electrical capacity at the biogas plant site in MW and the annual volume of raw biogas produced in million m\u003csup\u003e3\u003c/sup\u003e. This installable electrical capacity at the biogas plant sites was derived from the georeferenced vector dataset of biogas plants registered by Plinke et al. [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eNext, suitable areas for the installation of wind turbines and human- and nature-compatible ground-mounted photovoltaic systems were identified on the basis of vector data of areas with low and medium spatial vulnerability to wind turbines and ground-mounted photovoltaic systems from the area suitability calculation by Wagenfeld et al. [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. The distances to settlements, industry, and commerce as well as to motorways, main roads, electric overhead lines, cable cars, and railway lines were recalculated on the basis of the large reference wind turbines for inland and coastal areas by L\u0026uuml;ers [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. To better account for land-use conflicts tailored to the study area, the criteria for suitable areas were adjusted based on Peters et al. [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e], \u0026sect;\u0026nbsp;3a of the Lower Saxony Climate Act (\u003cem\u003eNieders\u0026auml;chsisches Klimagesetz\u003c/em\u003e (NKlimaG)) as well as from the Lower Saxony Association of Districts (\u003cem\u003eNieders\u0026auml;chsischer Landkreistag\u003c/em\u003e, NLT) and Towns and Municipalities (\u003cem\u003eNieders\u0026auml;chsischer St\u0026auml;dte- und Gemeindebund\u003c/em\u003e, NSGB) [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e] (refer to Appendices A and B for a detailed list of criteria unsuitable for wind turbines and ground-mounted photovoltaic systems). Existing plant sites were not excluded, as it is possible to generate additional RE capacity through repowering [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. Based on this, the installable capacity per ha of the areas suitable for human- and nature-compatible wind turbine installations was calculated. As part of the H2-FEE research project, these areas were planned using the reference wind turbines projected for 2030 by L\u0026uuml;ers [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e], maintaining a distance between wind turbines with 2.5 times the rotor diameter. Additionally, within the research project, the power density per ha for ground-mounted photovoltaic systems with a southern area occupancy was assumed to be 1.12 MW per ha. The power density was determined based on the assumptions for the structure of ground-mounted systems according to Badelt et al. [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e], adapted to the current QCELLS Q.PEAK DUO M-G11S+ SERIES 2023 solar module. The power density per ha was allocated to the areas considered to be human- and nature-compatible for the installation of these systems (areas not classified as unsuitable according to the criteria in Appendix \u003cspan refid=\"Sec12\" class=\"InternalRef\"\u003eB\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eRE production in the immediate vicinity of biogas plant sites was favoured, because it avoids additional infrastructure construction (e.g. power lines), saves costs, and reduces the impact on the landscape [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]. To define the immediate vicinity, we employed a radius of 500 m as a simplified assumption. The installable capacity of wind turbines and ground-mounted photovoltaic systems within a 500 m radius of the biogas plants was summed up and compared with that of the installed capacity required to achieve the lowest hydrogen production cost (as described above).\u003c/p\u003e \u003cp\u003eA biogas plant site was considered \u003cb\u003esuitable\u003c/b\u003e if the required amount of installable capacity could be generated by wind turbines and ground-mounted photovoltaic systems to achieve the lowest hydrogen cost in the immediate vicinity of 500 m on human- and nature-compatible areas. Biogas plant sites were considered to be \u003cb\u003econditionally suitable\u003c/b\u003e if the required amount of installable capacity could only be generated within a radius of more than 500 m including 5 km from the biogas plant site. A distance of 5 km represents a typical farm-to-field distance (cf. [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]), where land suitable for RE is likely owned by the biogas plant operators. This distance also corresponds to the spatial relationship between the electricity producer and the consumption point, where the consumption of RE produced is favoured according to \u0026sect;\u0026nbsp;21b (4) EEG 2023 and \u0026sect;\u0026nbsp;12b (5) of the German Electricity Duty Act (\u003cem\u003eStromsteuergesetz\u003c/em\u003e (StromStV)).\u003c/p\u003e \u003cp\u003e \u003cb\u003eBiogas plant installed electrical power\u003c/b\u003e \u003c/p\u003e \u003cp\u003eFor biogas plant sites to be suitable as P2G sites, a sufficient biogas plant-installed electrical capacity is also essential. Erler et al. [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] assumed that conventional on-site electricity generation plants with an installed electrical capacity of 250 kW or more are necessary for the methanisation concept to be suitable. It is also possible to combine plants located close to each other, which in sum achieve at least 250 kW [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. This summed installable electrical capacity at each biogas plant site was derived directly from the biogas plant register Plinke et al. [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eOnly plant sites with on-site electricity generation with an installed electrical capacity of 250 kW were considered \u003cb\u003esuitable\u003c/b\u003e for the end-of-subsidy strategy.\u003c/p\u003e \u003cp\u003e \u003cb\u003eWater withdrawal conditions\u003c/b\u003e \u003c/p\u003e \u003cp\u003eFor the production of hydrogen, water has to be extracted from water bodies. To prevent a lowering of the groundwater level and potential damage to groundwater-dependent ecosystems, it is important to use only sustainably renewable amounts of water for electrolysis [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. The spatial analysis by Badelt \u0026amp; Haaren [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e] and the produced georeferenced vector data served as the basis for the assessment of sustainable groundwater availability. They first identified the annual reserves of the groundwater (sub)bodies (i.e., the portion of groundwater bodies within administrative districts in Lower Saxony) and then compared them with those of forecasted groundwater withdrawals, considering the climate [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]. To assess the utilisation rate of natural groundwater reserves, Badelt \u0026amp; Haaren [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e] used the Water Sustainability Index (WSI) developed by Schlattmann et al. [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e], which is presented in Eq.\u0026nbsp;1. Note that WW denotes water withdrawal.\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:WSI=\\frac{Field\\:irrigation\\:+\\:Livestock\\:WW\\:+\\:Industrial\\:WW\\:+\\:Other\\:WW\\:+\\:Electrolysis\\:WW}{Groundwater\\:recharge\\:-\\:(Public\\:water\\:supply+Ecosystem\\:requirements)}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eFor groundwater recharge, Badelt \u0026amp; Haaren [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e] calculated the mean value of the annual groundwater reserves for the period from 2021\u0026ndash;2050 based on the mGROWA water balance model [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e]. Field irrigation, livestock water withdrawal (WW), industrial water withdrawal, other water withdrawal, and public water supply were taken from the Water supply concept for Lower Saxony (\u003cem\u003eWasserversorgungskonzept Niedersachsen\u003c/em\u003e) [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]. In addition to Badelt \u0026amp; Haaren [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e], we calculated the amount of water withdrawn for electrolysis at each biogas plant site based on the biogas plant register by Plinke et al. [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. We assumed that the amount of water to be withdrawn depends on the amount of hydrogen required for methanisation (to calculate the amount of hydrogen required per biogas plant site, see above). According to the German Technical and Scientific Association for Gas and Water (DVGW) [\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e], around 12 to 13 l of groundwater are required for the electrolysis of 1 kg of hydrogen; the average value used here is 12.5 l. Biogas plant sites for which the amount of water required for electrolysis cannot be calculated due to a lack of data are included with a requirement of zero litres for electrolysis, as it is assumed that other groundwater uses are usually decisive for groundwater availability. It is also necessary to avoid damaging groundwater-dependent terrestrial ecosystems due to water extraction at the biogas plant site. Therefore, the ecosystem requirements were calculated based on Badelt \u0026amp; Haaren [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. The recommended distance of 50 m must be maintained between the electrolyser at the biogas plant site and groundwater-dependent terrestrial ecosystems [\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e], which have a resilience of ecosystems to groundwater drawdowns ranging from very low to low to medium, available as vector-data in scale 1:50.000. This distance regulation also applies to drinking water protection areas (\u003cem\u003eTrinkwasserschutzgebiete\u003c/em\u003e, \u0026sect;\u0026nbsp;51 of the German Federal Water Act \u003cem\u003eWasserhaushaltsgesetz\u003c/em\u003e (WHG)), protection zones I and II (catchment area and inner protection zone). If the distance could not be maintained, the value for ecosystem requirements was considered to be the amount of water from groundwater recharge.\u003c/p\u003e \u003cp\u003eDerived from Schlattmann et al. [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e], a biogas plant site was considered suitable if at least 70% of the sustainably usable water in the groundwater sub-body was still available after extraction for electrolysis (0\u0026thinsp;\u0026le;\u0026thinsp;WSI\u0026thinsp;\u0026gt;\u0026thinsp;0.3). Sites were considered conditionally suitable if at least 40% but less than 70% of the water was still available after extraction (0.3\u0026thinsp;\u0026le;\u0026thinsp;WSI\u0026thinsp;\u0026lt;\u0026thinsp;0.6).\u003c/p\u003e \u003cp\u003e \u003cb\u003eSubstrate use\u003c/b\u003e \u003c/p\u003e \u003cp\u003eAdjusting the substrates used in biogas plants is an effective way of reducing biogas plants\u0026rsquo; environmental impact. Depending on the substrate used, land consumption and competition with other land uses, such as food production and nature conservation, more or less exist [\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e] [\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e] [\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e]. The input substrates used in Lower Saxony in 2021 were made up of 82.4% of energy crops and plant by-products, 13.0% of agricultural residues such as liquid and solid manures and fermentation residues, and 4.7% of biowaste such as fats, flotates and organic waste, based on the proportion of electrical output [\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e]. To reduce the environmental impact, it is essential to reduce the share of energy crops and to incorporate a significant share of organic fertiliser and biowaste used in biogas plants. This will ensure an effective utilisation of available substrates and their potential.\u003c/p\u003e \u003cp\u003eThe criterion appraises the proportion of organic fertiliser/biowaste used in biogas plants in relation to existing organic fertiliser/biowaste by district, though it varies between organic fertiliser and biowaste. It incorporates the current use of organic fertiliser/biowaste in biogas plants and the potential for increasing the proportion. By increasing, the impact on the environment and the pressure on agricultural land use would be reduced. The data was retrieved from the following sources: data on agricultural residues used in biogas plants from the Nutrient Report for Lower Saxony [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e], data on biowaste from the Waste Balance Sheet [\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e] and from the data provided by 3N for the Biogas Inventory 2021 [\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e]. The nutrient report records the reported movements of organic fertiliser such as pig, cattle and poultry manure, digestate from biogas plants and mineral nitrogen fertilisers at the district level. The report covers the reporting period from 1 July 2022 to 30 June 2023 and is based on the legal requirements of the Fertiliser Ordinance 2020 [\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e]. The Waste Balance Sheet documents the waste generated as part of public waste disposal in Lower Saxony by disposal area. This includes organic waste such as the organic waste bin, garden, and park waste [\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e]. The Biogas Inventory 2021 [\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e] shows the current status of biogas production and use in Lower Saxony for the years 2019\u0026ndash;2021. The underlying data is available upon request.\u003c/p\u003e \u003cp\u003eDecoding these data at NUTS 3 level reveals an uneven distribution of agricultural residues and biowastes available and used in biogas plants. A distinction is made between the amount of organic fertiliser or biowaste used. Suitability levels for both are assigned as follows: suitable for 0 to 30%, conditionally suitable for over 30 to 60%, and unsuitable for over 60 to 100% proportion of organic fertiliser or biowaste used in biogas plants in relation to existing organic fertiliser or biowaste, respectively. The suitability of the 0 to 30% range assumes that a lot of potential for substrate adaptation in the districts exists. In districts where the proportion of organic fertiliser and biowaste is over 30 to 60%, approximately doubling this figure is assumed to be feasible. Conversely, districts deemed unsuitable are those where an increase of merely one-third of the total in biogas plants used material can be attained. The study focuses on the potential for agricultural and environmental development and therefore favours areas where the current proportional use of organic fertiliser/biowaste does not exceed 30% or 60%. It is not deemed necessary to increase the proportion of both organic fertiliser and biowaste. Consequently, it is sufficient if either the proportion of organic fertiliser or the proportion of biowaste in a district can be raised.\u003c/p\u003e \u003cp\u003e \u003cb\u003eDistance to gas grid\u003c/b\u003e \u003c/p\u003e \u003cp\u003eConnecting the biogas plant sites to the natural gas grid allows the renewable methane produced at the biogas plant sites to be transported and used elsewhere. Furthermore, connecting the plant sites to a gas pipeline as close as possible has economic advantages. For instance, shorter connection pipelines between the plant and the gas supply network result in lower pro rata costs for the connection applicant according to the Law on access to gas supply networks \u003cem\u003eGas Network Access Ordinance\u003c/em\u003e (\u0026sect;\u0026nbsp;33 (1) \u003cem\u003eGasnetzzugangsverordnung\u003c/em\u003e (GasNZV) [\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e]) and simultaneously minimises the impact on the landscape [\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e]. Spatial data on the natural gas grid in Lower Saxony was used to investigate the feasibility of connecting to the natural gas grid. As the gas grid is classified as critical infrastructure [\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e], no high-resolution geodata were provided for this study at the request of the gas grid operators. However, the Spatial Planning Register (\u003cem\u003eRaumordnungskataster\u003c/em\u003e (ROK)) and Regional Spatial Planning Programmes (\u003cem\u003eRegionale Raumordnungsprogram\u003c/em\u003eme (RROP)) provide alternative geodata on the natural gas grid at a resolution of 1:25,000, respectively 1:50,000 (Data provided via Nefino GmbH [\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e]), which was merged and used for this analysis. Due to the high costs of crossing rivers, railway lines, and motorways [\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e], these were considered as barriers when determining the distance between the biogas plant site and the nearest pipeline section. High-resolution vector geodata of rivers, railways, and motorways from the Digital Landscape Model (DLM) [\u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e] were considered (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) barriers. The distance between biogas plant sites and gas pipelines was calculated with the ArcGIS Pro Tool Distance Accumulation.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eInfrastructure and water barriers extracted from the Digital Landscape Model (DLM): Infrastructure, and water barriers extracted from DLM [\u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e]\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eType\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e \u003cp\u003eDLM (Data Basis) [\u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e63\u003c/span\u003e]\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eObject type\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAttribute type\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDefinition\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eRivers\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAX_Gewaesserachse\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eBRG is 12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLinear feature data of linear water bodies with a width of more than 6 m and up to 12 m\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAX_Fliessgewaesser\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePolygon feature data of running waters with a width of more than 12 m and waters created for shipping\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRailways\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAX_Gleis\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLinear feature data of laid rail pairs for railway vehicles\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAX_Bahnstrecke\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLinear feature data of rail transport network\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eMotorways\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAX_Fahrbahnachse\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eWDM is 1301\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eLinear feature data of the Federal motorways\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAX_Strassenachse\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eWDM is 1301\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eWe assumed that biogas plant sites are \u003cb\u003esuitable\u003c/b\u003e for connection to the gas grid if the distance to the gas grid is up to 1 km without barriers. Sites located more than 1 km and up to 10 km from the gas grid were \u003cb\u003econditionally suitable\u003c/b\u003e, as plant operators within this distance pay lower pro rata costs for connecting the plants to the supply network (\u0026sect;\u0026nbsp;33 (1) GasNZV).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Overall suitability assessment\u003c/h2\u003e \u003cp\u003e In a final step, the overall suitability of the biogas plant sites for upgrading to P2G was determined based on the suitability according to the five previously described criteria (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003e). If the suitability of a biogas plant site could not be assessed for one or more criteria due to a lack of data, the site was considered to be conditionally suitable for the criteria. Therefore, biogas plant sites were not automatically downgraded from the overall suitability assessment due to the incomplete database.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eA site was considered unsuitable for P2G, if at least one of the two hard criteria (regional RE potential and biogas plant installed electrical power) was rated unsuitable. As the sites were considered unsuitable as P2G sites, the soft criteria had not to be further analysed.\u003c/p\u003e \u003cp\u003eA site was identified conditionally suitable if all hard criteria were rated at least conditionally suitable. Additionally, the soft criteria (water withdrawal conditions, substrate use, and distance to gas grid) were considered at these sites to further indicate environmental impacts. If all three soft criteria were assessed as at least conditionally suitable, the biogas plant site was considered suitable as an environmentally friendly P2G site. An assessment of 'conditionally suitable' based on a criterion indicates that there is no fundamental barrier to the site's suitability, but additional measures or conditions may be required.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results","content":"\u003cp\u003eThe spatial analysis of biogas plant sites for their suitability as environmentally friendly P2G sites showed that 1,223 of the 1,704 biogas plant sites met the hard criteria, and were therefore, at least conditionally suitable. Of these sites, 1,014 were suitable as P2G sites because they also met the soft criteria.\u003c/p\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Suitability of plant sites by criteria\u003c/h2\u003e \u003cp\u003e \u003cb\u003eRegional RE potential\u003c/b\u003e \u003c/p\u003e \u003cp\u003eA total of 2% of the biogas plant sites in Lower Saxony proved suitable for the regional supply of RE (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Within a 500 m radius of the 34 sites, we found enough areas that could be used in a human- and nature-compatible manner for the installation of wind turbines and ground-mounted photovoltaic systems to generate a mix of RE for the electrolysis at the biogas plant site to achieve the lowest hydrogen cost. These sites were mainly located in eastern Lower Saxony. The majority (72.7%) of the sites proved conditionally suitable for regional RE supply. At these 1,239 sites, the required amount of suitable area for human- and nature-compatible RE installations existed within a radius of more than 500 m and a maximum of 5 km to create a required RE mix of installed capacity of RE to achieve the lowest cost of hydrogen per kg. However, 261 biogas plant sites were not suitable for regional RE supply, as the RE mix could not be sourced within a 5 km radius. These unsuitable sites were mainly located in the northern Lower Saxony, but also along the Ammerland, Oldenburg, and all the way to the Osnabr\u0026uuml;ck district. No assessment could be performed for 170 biogas plant sites due to a lack of data on the performance of the biogas plants.\u003c/p\u003e \u003cp\u003e \u003cb\u003eBiogas plant installed electrical power\u003c/b\u003e \u003c/p\u003e \u003cp\u003eOver 70% of the biogas plant sites in Lower Saxony are conventional on-site electricity generation plants with an installed electrical capacity of 250 kW or more (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e5\u003c/span\u003e). These 1,232 sites proved suitable for implementing the methanisation concept. Almost 17% of the biogas plant sites are unsuitable for implementing the methanisation concept, with 31 out of these 284 sites lacking on-site electricity generation capacities. Data on installed electrical capacity is not available for 188 biogas sites.\u003c/p\u003e \u003cp\u003e \u003cb\u003eWater withdrawal conditions\u003c/b\u003e \u003c/p\u003e \u003cp\u003eAt 83.7%, 1,427 of the 1,704 biogas plant sites proved suitable for the extraction of groundwater for hydrogen production (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e6\u003c/span\u003e). At least 70% of the remaining sustainably usable groundwater remained available. The sites are spread over Lower Saxony. 18 biogas plant sites are conditionally suitable for groundwater extraction. At least 40% but less than 70% of the remaining usable groundwater was still available for hydrogen production. These biogas plant sites are situated on groundwater bodies in the Osterholz district, the southern Celle district, and the southern Osnabr\u0026uuml;ck city. These sites are distributed throughout Lower Saxony. With 256 biogas plant sites, 15% of the sites are unsuitable for extraction due to a lack of remaining sustainable usable groundwater. Of the 189 biogas plant sites, 168 proved unsuitable for groundwater withdrawal because they are located too close to groundwater-dependent ecosystems that need to be protected. The high concentration of unsuitable biogas plant sites, particularly in the districts of Friesland, Wesermarsch, and L\u0026uuml;chow-Dannenberg, was due to the scarcity of groundwater.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eSubstrate use\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThe biogas plant sites in 39 districts are suitable for increasing the proportion of organic fertiliser or biowaste in the biogas plants (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e7\u003c/span\u003e). In these districts, a maximum of 30% of the available organic fertiliser or biowaste has been used thus far in biogas plants. Only in the districts of Diepholz, Heidekreis, Uelzen, L\u0026uuml;neburg, and L\u0026uuml;chow-Dannenberg was from 30 to 60% of organic fertiliser and biowaste already being used. The biogas plant sites are considered to be conditionally suitable for a change in substrate use. Only the biogas plant sites in the Gifhorn district are unsuitable for the conversion of the substrate, as over 60% of the organic fertiliser or biowaste was already being used. Comparing the resources of organic fertiliser and biowaste across Lower Saxony, unused reserves of organic fertiliser were found in the north-west of Lower Saxony. Reserves of biowaste were available in the north, west, and the south of the federal state.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eDistance to gas grid\u003c/b\u003e \u003c/p\u003e \u003cp\u003eConsidering linear infrastructure and water barriers, 683 of the 1,704 biogas plant sites are located within 1 km of the natural gas network (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e8\u003c/span\u003e). This represents just over 40% of biogas plant sites in Lower Saxony. The majority of these plants are located in the west and south of Lower Saxony. In this region, not only does the density of biogas plants peak, but the natural gas network also has extensive branches. These biogas plant sites are suitable for connection to the gas grid. More than half of the sites (927 sites) are located more than 1 km away, although a maximum of 10 km from the natural gas network. These biogas plant sites are conditionally suitable for connection to the gas grid. With 94 sites, i.e., just around 5%, are more than 10 km away from the natural gas network.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Environmentally friendly P2G potential of biogas plant sites\u003c/h2\u003e \u003cp\u003eAlmost 60% of the biogas plant sites (1,014 sites) are considered suitable as environmentally friendly P2G sites (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e9\u003c/span\u003e). Accumulations of suitable biogas plant sites are found from the Emsland district in the west of Lower Saxony, through Cloppenburg, Oldenburg to Diepholt as well as in Rotenburg (W\u0026uuml;mmer), the north of Heidekreis, and the south of Celle districts. Additionally, about 12% (209 sites) are considered conditionally suitable, and almost 30% (481 sites) are unsuitable. The density of suitable plants is the lowest in the south-east and far north-west of Lower Saxony. Numerous biogas plant sites that are unsuitable for environmentally friendly P2G are situated along the northern and the south-western borders of Lower Saxony, extending from Grafschaft Bentheim to the G\u0026ouml;ttingen district. A large number of unsuitable sites are also found in the districts of Ammerland, Oldenburg, and Osnabr\u0026uuml;ck.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eOf the 481 biogas sites unsuitable for P2G, only 64 are unsuitable based on both hard criteria (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e10\u003c/span\u003e). The required installed RE capacity neither exists in the immediate vicinity of the plants, nor is the minimum required installed electrical capacity of on-site generation plants present. Each hard criterion resulted in a further 40% of sites being considered unsuitable. This does not consider sites with a lack of data. Of the 209 biogas plant sites conditionally suitable for upgrading to P2G, over 60% of the sites are conditionally suitable due to the lack of remaining sustainably usable groundwater at the biogas site. The majority of 1,014 biogas plant sites are suitable based on all five criteria.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cp\u003eThe criteria-based spatial suitability analysis identified 1,014 of the 1,704 biogas plant sites as suitable for an environmentally friendly implementation of the methanisation concept as an end-of-subsidy strategy.\u003c/p\u003e \u003cp\u003eThe high spatial resolution at the level of individual biogas plant sites throughout Lower Saxony is a unique feature of our suitability analysis. A handful of P2G spatial suitability analyses of biogas plants in Germany exist covering large areas such as the entire country. However, these were mainly conducted at the district level (cf. [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], [\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e], [\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e]) which does not qualify these analyses for individual biogas site assessment. Additionally, as we focus on Lower Saxony, we were able to integrate high-resolution base data (e.g. DLM [\u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e]) tailored to the region, which allowed us to make multi-criteria based location-specific evaluations for individual biogas plant sites. We particularly benefited from the high-resolution biogas plant register for Lower Saxony [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. This register was created as part of the H2-FEE research project and enables spatial analyses of biogas plant sites to be conducted.\u003c/p\u003e \u003cp\u003eBased on the \u003cb\u003eregional RE potential\u003c/b\u003e criterion, only 2% of the biogas plant sites in Lower Saxony are suitable for environmentally friendly P2G. The installable RE capacity can be built within 500 m of the plant on human- and nature-compatible areas for wind turbines and ground-mounted photovoltaic systems. The suitability of the biogas plant site is primarily limited by the lower availability of compatible areas for wind turbines. Efficient green electrolysis in most cases requires RE from both wind and solar [\u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e67\u003c/span\u003e]. Although, unlike the 5,349 km\u003csup\u003e2\u003c/sup\u003e of compatible areas for ground-mounted photovoltaic systems in Lower Saxony, only 1,086 km\u003csup\u003e2\u003c/sup\u003e are available for wind turbines. As the human and nature compatible areas for wind turbines are distributed across Lower Saxony, three quarters of the biogas plant sites have the required compatible areas for wind turbines located within a radius of 5 km. This allows them to be rated as conditionally suitable according to the regional RE potential criterion. Contrary to the analysis of potential areas for onshore wind energy in Lower Saxony (\u003cem\u003eFl\u0026auml;chenpotenzialanalyse Windenergie an Land in Niedersachsen\u003c/em\u003e, WinNiePot) commissioned by the Lower Saxony Ministry for the Environment, Energy and Climate Protection in 2023 [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e], we assume not 6.2% but only 2.3% of Lower Saxony as potential area. The difference is not least due to the additional detailed, high-resolution database provided by Nefino GmbH. Particularly, we go one step further than that by Peters et al. [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e] in WinNiePot and place great emphasis on human- and nature-compatibility of areas for wind turbines. Less suitable areas, such as those with a high-quality visible landscape, were excluded. Nevertheless, the provision of 2.3% land area of Lower Saxony for wind energy utilisation is sufficient to meet the target of 2.2% laid down in the Wind Energy Area Requirements Act (\u003cem\u003eWindenergiefl\u0026auml;chenbedarfsgesetz\u003c/em\u003e (WindBG)). Considering the human and nature conservation interests at an early stage in spatial planning also minimises land use conflicts, which promotes acceptance of RE and green gas expansion.\u003c/p\u003e \u003cp\u003eThe criterion involves the additional installation of RE capacities, as required by the EU [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. It should be noted that commissioning new wind turbines for smaller projects, such as implementing the methanisation concept at biogas plant locations as described above, may present economic challenges. When initially assessing capacity requirements, we estimated the approximate required installed RE capacity for the methanisation concept at individual biogas plant sites. When considering individual sites in more detail, this value must be refined using additional, high-resolution, site-specific data.\u003c/p\u003e \u003cp\u003eBiogas plant sites located far from areas human- and nature-compatible for the installation of wind turbines may still be suitable for P2G. The identified areas serve as a guide to the suitability of sites in terms of agricultural and environmental compatibility. Therefore, we have decided not to take the legally binding priority areas for wind energy into account. These areas must be designated in their final form by 2026, in accordance with the WindGB. However, when considering individual biogas plant sites, it is advisable to check the actual availability of land for RE, taking into account site-specific parameters.\u003c/p\u003e \u003cp\u003eWhen assessing the \u003cb\u003ewater withdrawal conditions\u003c/b\u003e at the biogas plant sites, groundwater recharge and water withdrawals were taken into account at the level of groundwater (sub)bodies. Adopting a differentiated approach to electrolysis water withdrawal and ecosystem requirements enabled individual sites to be assessed separately [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. The calculated values for the quantities of water required for electrolysis are only approximate. The amount of cooling water required was not considered. This is because, depending on the availability of water, different water-intensive cooling systems can be chosen [\u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e68\u003c/span\u003e]. These approximate assumptions are perfectly acceptable, given that the amount of water used for electrolysis was of little value in comparison to the total water consumption of Lower Saxony. Badelt and Haaren [\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e] assume that 77\u0026nbsp;million m\u003csup\u003e3\u003c/sup\u003e of water per year will be required for electrolysis in 2045. This is less than 6% of the total groundwater used annually for field irrigation, livestock water withdrawal, industrial water withdrawal, and public water supply [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]. To assess the ecosystem requirements, the water requirements necessary to preserve biodiversity were determined based on groundwater-dependent terrestrial ecosystems. It is not yet possible to conduct a high-resolution analysis for the quantitative determination of water requirements in Lower Saxony due to a lack of high-resolution data, such as biotope-specific evapotranspiration and soil science parameters [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eOnly 256 of the 1,704 biogas plant sites lack sustainable groundwater supply for electrolysis. However, water withdrawal conditions are a limiting criterion for more than 50% (114 sites) of the plants classified as conditionally suitable. When examining individual biogas plants in more detail, it is advantageous to consider the individual circumstances. Alternative water sources, such as river, sea, or wastewater, must be considered for these biogas plant sites and included in further analyses. In the context of the H2-FEE research project, Locker [\u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e69\u003c/span\u003e] calculated the maximum possible water withdrawal from rivers for electrolysis while maintaining the minimum water discharge. However, it was difficult to make detailed area-wide statements. This was due to the patchy discharge data available for the gauges. Additionally, cases where cost-intensive water treatment [\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e] [\u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e68\u003c/span\u003e] is beneficial should be examined.\u003c/p\u003e \u003cp\u003eThe \u003cb\u003esubstrate use\u003c/b\u003e criterion shows that in almost all districts (with the exception of the Gifhorn) 60% or more of the existing organic fertiliser or biowaste was not yet used in the biogas plant sites. This offers the opportunity to switch to using organic fertiliser or biowaste instead of growing energy crops. The electrical output, of which 82.4% (2021) came from energy crops and plant by-products [\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e], can alternatively be generated from organic fertilisers and biowaste. This would imply that 283,000 ha (10.8%) of agricultural land currently used to grow energy crops would be available not only for food production but also for nature conservation. RE development can also benefit from reduced pressure on agricultural land [\u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e70\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAs substrate flows between districts were not yet considered, the possibility of importing substrate surpluses from neighbouring regions should be considered, especially for the Gifhorn district. The individual biogas plant sites in the districts are not assessed. Instead, the assessment at district level is broken down into the individual plants. This is due to the lack of comprehensive, detailed information on the substrate composition in the individual biogas plants. Earlier surveys of biogas plant sites only allow for ascertaining the selection of biogas plant sites (cf. [\u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e69\u003c/span\u003e]). This means that sites which already use organic fertiliser and biowaste as substrates cannot be assessed individually. Collecting data on substrate composition at individual biogas plants could allow for a more detailed assessment of the sites. However, this would require considerable resources.\u003c/p\u003e \u003cp\u003eThe criterion \u003cb\u003edistance to gas grid\u003c/b\u003e can serve as an indicator to estimate the distance from the biogas plant site to the natural gas grid. A total of 41 biogas plant sites are not considered suitable for P2G, although they are conditionally suitable due to the distance to the gas grid criterion. A further 20 sites are conditionally suitable for P2G, partly on the basis of this criterion. At these sites, island operation of the plants could be an alternative. This can become possible through a nearby consumer [\u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e71\u003c/span\u003e]. A more detailed assessment is possible with spatially high-resolved data on the natural gas grid, gas distribution network and connection points to the gas network. However, this data was not publicly available at the time of the study because the gas network is classified as critical infrastructure [\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e]. This high-resolution spatial data is only accessible upon request when analysing individual locations and must be considered in subsequent detailed planning. Nevertheless, the barriers considered in the analysis, including rivers, railways and motorways, are available at a high spatial resolution in the base DLM [\u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e]. For future analyses, it is optional to consider compatibility with humans and the environment further by including additional barriers, such as nature reserves, in the analysis. However, the distance between the biogas plant and the gas network can only be determined accurately if high-resolution spatial data on the gas network is available alongside information on the barriers.\u003c/p\u003e \u003cp\u003eWhen the criteria were combined, the overall suitability assessment was strongly influenced by the hard criteria. As soon as the regional RE potential or the biogas plant installed electrical power was rated as unsuitable, the site was considered unsuitable for the methanisation concept. This enabled the most relevant implementation criteria to play a more important role. In order to break down the complexity of the individual criteria, individual aspects were brought to the fore. As described above, in the case of the regional RE potential criterion, these include, for example, the additional placement of RE plants and the construction of these plants in areas that are compatible with humans and nature. Nevertheless, it should be noted that the methanisation concept may be feasible at biogas plant sites even if the criteria are deemed unsuitable. For example, aspects such as the compatibility of the selected areas with the designated priority areas for wind energy and the economic challenges of commissioning new RE plants have not yet been considered. Therefore, when individual biogas plants are examined at a later stage, it could be shown that the methanisation concept can indeed be implemented. This once again illustrates that, while the results of the overall suitability assessment provide a useful initial overview, a detailed examination of the individual locations is also necessary if the concept is to be implemented at specific sites.\u003c/p\u003e \u003cp\u003eWhen analysing the suitability of biogas plant sites in Lower Saxony as environmentally friendly P2G sites, the focus was on the agricultural and environmental compatibility of the sites. Further, we focused on criteria that received less attention in P2G potential analyses, including decentralised human- and nature-compatible RE capacity and water availability for electrolysis. These unique features enable a more compatible transition to a GHG-emitting net energy sector.\u003c/p\u003e \u003cp\u003eConsidering agricultural- and nature-compatibility, the integration of additional criteria can lead to an even more holistic assessment of the suitability of biogas plant sites for environmentally friendly P2G. Criteria from comparable spatial P2G potential analyses of biogas plants in Germany can be used as a first orientation for the selection of further criteria to be considered. Some authors already considered a number of criteria that also were identified here to determine the suitability of biogas plants for P2G in Germany. Mertins et al. [\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e] and Erler et al. [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] considered the gas grid, while D\u0026ouml;gnitz et al. [\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e] examined the input substrates of the biogas plants. However, some authors already considered criteria that were less focused in our analysis. For example, Mertins et al. [\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e] and Erler et al. [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] also considered biomethane capacity compared with that of the German natural gas demand. Another example, we identified a large number of biogas plant sites in the Emsland district suitable for P2G, whereas Mertins et al. [\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e] assessed the Emsland district as a region with a relatively low gas demand that was studied earlier to an above-average extent. The Institute of Energy Economics at the University of Cologne (EWI) [\u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e72\u003c/span\u003e] also placed a stronger focus on regional hydrogen demand when strategically positioning small electrolysers. Including current and future heating networks as consumers in the suitability analyses could also be promising.\u003c/p\u003e \u003cp\u003eDespite the different criteria used to analyse suitability, some spatial similarities of areas suitable for P2G can already be identified. Similar to that of the current study (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e9\u003c/span\u003e), Erler et al. [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] highlighted a higher potential in the Emsland, Cloppenburg, Oldenburg, and Diepholz districts. Additionally, clear spatial synergies exist between the biogas plant sites identified here as suitable for P2G and the system-serving electrolysers\u0026thinsp;\u0026lt;\u0026thinsp;10 MW identified by EWI [\u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e72\u003c/span\u003e] at the district level. EWI additionally identified a high potential in the Emsland district [\u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e72\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTo meet the goal of achieving CO\u003csub\u003e2\u003c/sub\u003e neutrality in Lower Saxony by 2040 (\u0026sect;\u0026nbsp;3.1.1 NKlimaG), our analysis serves as a basis for deciding the suitability of biogas plant sites for upgrading to the methanisation concept. Deciding on an appropriate end-of-subsidy strategy for biogas plant sites is particularly important as the 20-year subsidy period under the EEG is about to expire. Erler et al. [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] recommended completing the conceptual planning about two years before the end of the EEG subsidy period. Between 2025 and 2035, the 20-year EEG subsidy period will end for 790 sites considered suitable for the above-described methanisation concept. A need exists for prompt action for all parties involved.\u003c/p\u003e"},{"header":"5. Conclusions","content":"\u003cp\u003eThe criteria-based spatial suitability analysis enables comprehensive mapping of the P2G potential of 1,704 existing biogas plant sites in Lower Saxony. It identified 1,014 sites suitable for environmentally friendly implementation of the methanisation concept, as an end-of-subsidy strategy according to Erler et al. [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. While highlighting sites with high P2G potential, the analysis also identified regions where alternative strategies are necessary. By considering agricultural and nature conservation compatibility, this research ensures that diverse interests are integrated from the outset, reducing land-use conflicts and promoting broader acceptance of the transition to RE.\u003c/p\u003e \u003cp\u003eWe demonstrate the significant spatial potential for implementing the methanisation concept in Lower Saxony. Implementing this concept will offset fluctuations or deficiencies in RE sources and help Lower Saxony achieve its goal of CO₂ neutrality by 2040. The findings also serve as a vital decision support for stakeholders, including biogas plant operator-, small and medium-sized enterprises, local authorities and districts, as well as policy advisers, emphasising the urgent need for action as the EEG subsidy period is nearing its end. The analysis provides adaptable criteria to support tailored decision-making processes. To ensure the results reach the intended stakeholders, they will be made available on a publicly accessible WebGIS platform at the end of 2025 as part of the H2-FEE research project. Once the stakeholders have selected specific sites, it is recommended that they examine their suitability in detail. This is because a clear statement about the sites requires consideration of parameters that are not available across Lower Saxony.\u003c/p\u003e \u003cp\u003eTo capture an even more holistic picture of the potential of the biogas plant sites for the methanisation concept, the methodology can be further developed in the future. Possible refinements to the criteria may include integrating economic aspects, which would enable the economic sustainability of the concept to be assessed at individual sites. This includes the capital expenditure costs of installing new wind turbines and ground-mounted photovoltaic systems, for example. Another approach is to adjust the weighting of the criteria in order to counteract the premature exclusion of sites that are deemed unsuitable because of the strict criteria. To verify the method, the accuracy of the results can be evaluated by comparing the assumed suitability of biogas plants from the analysis with spatial overlaps with similar existing and planned projects at biogas plant sites. Finally, it should be noted that the above analysis could form the basis for similar location analyses in the future. One example may be the potential of biogas plant sites for power-to-hydrogen production.\u003c/p\u003e"},{"header":"List of Abbreviations","content":"\u003cp\u003eASR....................................................... Military Airport Surveillance Radar\u003c/p\u003e\n\u003cp\u003eATKIS.......................\u0026nbsp;Official Topographic Cartographic Information System\u003c/p\u003e\n\u003cp\u003eCO\u003csub\u003e2\u003c/sub\u003e....................................................................................\u0026nbsp;carbon dioxide\u003c/p\u003e\n\u003cp\u003eDLM.....................................................................\u0026nbsp;Digital Landscape Model\u003c/p\u003e\n\u003cp\u003eDVGW.........\u0026nbsp;German Technical and Scientific Association for Gas and Water\u003c/p\u003e\n\u003cp\u003eEEG.............................................................\u0026nbsp;Renewable Energy Sources Act\u003c/p\u003e\n\u003cp\u003eESTRAM...........................................\u0026nbsp;Energy System Transformation Model\u003c/p\u003e\n\u003cp\u003eEU....................................................................................\u0026nbsp;European Union\u003c/p\u003e\n\u003cp\u003eEWI...................\u0026nbsp;Institute of Energy Economics at the University of Cologne\u003c/p\u003e\n\u003cp\u003eGasNZV......................................................\u0026nbsp;Gas Network Access Ordinance\u003c/p\u003e\n\u003cp\u003eGHG..................................................................................\u0026nbsp;greenhouse gas\u003c/p\u003e\n\u003cp\u003eH2-FEE.................\u0026nbsp;H2-FEE: Flexible energy carriers for the energy transition\u003c/p\u003e\n\u003cp\u003eL\u0026Ouml;WE+\u0026nbsp;\u0026hellip;\u003cem\u003eupdated Lower Saxony\u0026nbsp;\u003c/em\u003eprogramme for long-term ecological forest development in the \u003cem\u003eLower Saxony state forests\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eMVA.............................................................. Minimum Vectoring Altitude\u003c/p\u003e\n\u003cp\u003eNBank............................\u0026nbsp;Lower Saxony Investment and Development Bank\u003c/p\u003e\n\u003cp\u003eNKlimaG.............................................................\u0026nbsp;Lower Saxony Climate Act\u003c/p\u003e\n\u003cp\u003eNLT...................................................\u0026nbsp;Lower Saxony Association of Districts\u003c/p\u003e\n\u003cp\u003eNSGB.......................\u0026nbsp;Lower Saxony Association of Towns and Municipalities\u003c/p\u003e\n\u003cp\u003eNWE10.................................... programme for natural forest development\u003c/p\u003e\n\u003cp\u003eP2G.....................................................................................\u0026nbsp;Power-to-Gas\u003c/p\u003e\n\u003cp\u003eRE.................................................................................\u0026nbsp;renewable energy\u003c/p\u003e\n\u003cp\u003eROK.....................................................................\u0026nbsp;Spatial Planning Register\u003c/p\u003e\n\u003cp\u003eRROP..............................................\u0026nbsp;Regional Spatial Planning Programmes\u003c/p\u003e\n\u003cp\u003eStromStV...................................................................... Electricity Duty Act\u003c/p\u003e\n\u003cp\u003eWHG................................................................. German Federal Water Act\u003c/p\u003e\n\u003cp\u003eWindBG..............................................\u0026nbsp;Wind Energy Area Requirements Act\u003c/p\u003e\n\u003cp\u003eWinNiePot\u0026nbsp;analysis of potential areas for onshore wind energy in Lower Saxony\u003c/p\u003e\n\u003cp\u003eWSI................................................................... Water Sustainability Index\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets generated during the current study are available in the Research Data Repository of the Leibniz University Hannover, https://doi.org/10.25835/x2seo1d8 [74].\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe article is a result of the NBank funded research project H2-FEE: Flexible energy carriers for the energy transition (duration from July 2022 to June 2025).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors' contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eML and YW developed the method and generated the resulting dataset. ML drafted most of the manuscript, while YW added sections on the background and the method for using the substrate criterion. JH provided advice on the development of the method and was actively involved in further development of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors thank Jonas Berndmeyer, Alexander Mahner, and Marie Jeuk for their collaboration in the H2-FEE research project. Jonas Berndmeyer placed the reference wind turbines on suitable areas. Alexander Mahner determined the installable capacity per hectare for ground-mounted photovoltaic systems. Marie Jeuk calculated the installed capacity of RE required to achieve the lowest cost of hydrogen at each biogas plant site. The authors also thank Ole Badelt, Ines Lüdders, and Johannes Wiese for their support during this study. The authors thank Elsevier Language Services, Alina Kupper and Christina Amacher for linguistic corrections. The authors acknowledge using DeepL Write and ChatGPT by OpenAI for text editing assistance and take full responsibility for any remaining errors.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eEuropean Union (2019) The European Green Deal. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://eur-lex.europa.eu/resource.html?uri=cellar:b828d165-1c22-11ea-8c1f-01aa75ed71a1.0002.02/DOC_1\u0026amp;format=PDF\u003c/span\u003e\u003cspan address=\"https://eur-lex.europa.eu/resource.html?uri=cellar:b828d165-1c22-11ea-8c1f-01aa75ed71a1.0002.02/DOC_1\u0026amp;format=PDF\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e. 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Accessed 15 Jun 2025\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNefino GmbH (2024) Luftfahrt und FFH. Auszug aus den Geodaten der Nefino GmbH. Unpublished. Accessed 28 Sep 2023\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePlinke M, Weber Y, Hack J (2025) Environmentally friendly Power-to-Gas potential of biogas plant sites in Lower Saxony, Germany. LUIS. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.25835/x2seo1d8\u003c/span\u003e\u003cspan address=\"10.25835/x2seo1d8\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Footnotes","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003e According to Plinke et al. [21], biogas plant sites are neighbouring biogas plants grouped on the basis of the surface areas obtained from the Lower Saxony Digital Landscape Model (DLM) vector data [62], which is part of the Official Topographic Cartographic Information System (Amtliches Topographisch-Kartographisches Informationssystem, ATKIS).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003e In ESTRAM hydrogen in kg is used as input. We assume a hydrogen density of 0.0899 kg/m3 (15 degrees Celsius, 1 bar) according to B. Adler et al. 2021.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Hydrogen, sustainable energy transition, biogas plant sites, Power-to-Gas, spatial analysis","lastPublishedDoi":"10.21203/rs.3.rs-7148209/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7148209/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003eTo decarbonise the energy system, offsetting fluctuations in renewable energy (RE) sources is crucial, for which biogas plants are well-suited. In Lower Saxony, Germany, the impending expiration of the 20-year \u003cem\u003eRenewable Energy Sources Act\u003c/em\u003e subsidy for numerous biogas plants creates an opportunity to transition them to biomethane production within a Power-to-Gas (P2G) framework. However, detailed data on the suitability of these sites for conversion is lacking due to diverse site-specific conditions. Therefore, mapping the P2G potential of these sites is essential, paying particular attention to agricultural and environmental compatibility.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eA multi-parametric Geographic Information System-based spatial analysis was conducted to assess the suitability of individual biogas plant sites in Lower Saxony for implementing methanisation with green hydrogen. Biogas plant sites were evaluated based on five criteria. The \u003cem\u003eregional RE potential\u003c/em\u003e for wind turbines and ground-mounted photovoltaic systems and the \u003cem\u003einstalled electrical power of biogas plants\u003c/em\u003e criteria had to be met for the suitability of a biogas plant site. Additionally, \u003cem\u003ewater withdrawal conditions\u003c/em\u003e, biogas \u003cem\u003esubstrate use\u003c/em\u003e, and \u003cem\u003edistance to the gas grid\u003c/em\u003e were evaluated as further sustainability criteria, considering the environmental impact.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eThe spatial analysis showed that about 60% were suitable as environmentally friendly P2G sites since they met all the criteria. Concentrations of suitable biogas plant sites were found in western Lower Saxony, from the Emsland to the Diepholz district, and the Rotenburg (W\u0026uuml;mme) district, as well as in the northern part of the Heidekreis in north-central Lower Saxony and the southern part of the Celle district near Hanover. Approximately 12% of biogas plant sites were considered conditionally suitable because they only met the essential criteria.\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e \u003cp\u003eThe criteria-based spatial suitability analysis enables comprehensive mapping of the potential for P2G at existing biogas plant sites in Lower Saxony. We identified 1,014 suitable sites for environmentally friendly implementation of methanisation with green hydrogen as an end-of-subsidy strategy. Considering agricultural and nature conservation compatibility can reduce land-use conflicts, promoting broader acceptance of the RE transition. These findings provide an advisory resource for stakeholders, highlighting the urgent need for action as the \u003cem\u003eRenewable Energy Sources Act\u003c/em\u003e subsidy period comes to an end.\u003c/p\u003e","manuscriptTitle":"Assessing the Power-to-Gas potential: GIS-based suitability analysis of biogas plant sites in Lower Saxony, Germany","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-22 07:21:33","doi":"10.21203/rs.3.rs-7148209/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"f6edbd7f-3b68-4991-b40a-d1c68d652ffb","owner":[],"postedDate":"April 22nd, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-04-22T07:21:33+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-22 07:21:33","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7148209","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7148209","identity":"rs-7148209","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}