Harnessing energy abundance: sustainable expansion of solar parks in Lower Saxony through harmonized spatial planning

Abstract

Background

The shift from fossil fuels to renewable energy sources brings substantial changes in land use. Germany, with limited land availability, needs a spatial framework to allocate renewable energy while safeguarding biodiversity and ecosystem services. This process should include public participation at the local level. Respective models have been developed for decision support on wind turbine allocation but methods are still lacking for solar parks. This paper aims to identify the safe operating space for solar energy supply that is inclusive and compatible with humans and nature. We propose criteria for Germany with different classes of legal legitimization to define the local decision space. The method is applied in the exemplary case of the federal state of Lower Saxony and the two municipalities—Springe and Wedemark.

Results

The results show that this decision space is sufficiently large to involve both the local public and decision-makers in determining the energy mix and siting of renewable plants. In Lower Saxony, 13% of the state's area (611.932 ha) has low spatial resistance to solar parks. With a reference plant's power density of 1.01 MW/ha, this land could generate up to 667 TWh/a, far exceeding the share needed for Lower Saxony’s contribution to Germany’s projected energy demand in 2050. This provides flexibility for regional and local stakeholders to shape their energy landscape within the bounds of downscaled national climate targets and human- and nature-compatible development. In addition, co-benefits with other extensive land-use objects, such as groundwater protection, can be provided on these sites.

Conclusions

Our findings offer valuable guidance for regional planning boards and encourage public participation in the decision-making process by providing transparent information about the spatial options and limits of solar development. The model can improve planning, since different planning levels could access and utilize the scalable data. Equal criteria at all levels increase the intersubjectivity and comprehensibility of approval decisions and thus also the legal certainty of land designations for solar parks.

Background

Solar energy is of crucial importance for the energy transition worldwide and thus for climate protection. It is expected to be the largest source of renewable energy (RE) in terms of installed power capacity by 2027 [1] and has the potential to meet 20% of the estimated global energy supply in 2050 [2]. In a densely populated country like Germany, space is a highly contested resource. Ground-mounted photovoltaic (PV) solar energy parks (solar parks) are seen critically because of higher direct land requirement than wind energy plants, which leads to greater land competition [3]. However, although both forms of energy plants inevitably cause changes to the landscape aesthetic and thus affect residents' living environments, the spatial scale of impacts on the visual landscape and soundscape are very different [4]. In principle, photovoltaic systems—including solar parks—are associated with lower environmental impacts than wind energy (impairment of biodiversity, noise) or the cultivation of energy crops (greenhouse gas emissions, high land demand, pesticides, nitrate ground water pollution) [5–7]. Depending on the previous use of the land, solar parks can even have pollutant-reducing effects [8]. The electricity generation costs for solar power have been falling for years, and forecasts show that this trend will continue in the future [9]. Moreover, PV is more scalable compared to wind and thus citizen-friendly in terms of participation in decisions about size, design and economic involvement [10].

Theoretically, the projected electricity demand in 2050, including storage and transformation losses (for Germany: 1500–3000 TWh/year, [11]) could be met only with wind energy and rooftop PV even without using land that is not compatible with the aim of protecting both humans and nature [12]. However, this would require a regionally unequal distribution of wind turbines and centralized spatial planning without much leeway for local participation as well as overcoming the many impediments for rooftop PV [13, 14]. Solar parks seem to be needed as an important component of the energy mix to implement the energy transition in a more inclusive and environmentally compatible way.

For an energy transition that is compatible with or even promotes democracy, it is necessary to involve citizens at the local level and give them ownership of decisions [15, 16] on where the plants are to be located, which energy mix between wind and solar is to be chosen, and how landscape loss and the associated ecosystem services (ES), i.e., the benefits that humans derive from natural ecosystems, should be compensated [17]. The latter offset obligations of the polluters are prescribed in Germany and are increasingly being incorporated into ‘no net loss’ policies in other countries [18]. However, a prerequisite for such a strategy is that both citizens and local councils are made aware of what they can decide, i.e., what falls under specific local responsibility. This is defined, on the one hand, by the down-scaled responsibility from the national level for the success of the energy transition—most directly expressed by the amount of energy that must be produced locally with RE so that the national energy goal for 2045 (completely avoiding the combustion of fossil fuels) can be collectively met. On the other hand, local freedom of choice is limited by supra-local interests. For example, local communities cannot assume responsibility for the impairment of nationally endangered species or ecosystems that transcend municipal boundaries [19, 20]. It must also be made clear which political contexts at higher levels prevent solutions that appear sensible and responsible at the local level. If these boundaries are not clarified (for example, what conditions fuel the competition for land with agriculture) frustration and a retreat from inclusive, democracy-promoting approaches will result [21]. The scientific questions that arise from this situation are:

• How can local energy goals be accurately calculated by scaling down national RE demand for 2045 while balancing human and environmental compatibility with on-site generation potentials?

• How can the decision-making process for citizen participation in RE siting be made transparent, ensuring clarity on areas that that are off-limits, conditionally acceptable, or fully open to RE installations?

• What political and regulatory factors drive competition for agricultural land use, and how do local or regional strategies address these constraints?

The state of knowledge on these issues varies. Initial approaches to downsizing national energy goals can be found in [11] and [22]. However, solar parks were not considered in this context, and only building-integrated and rooftop PV was included. The latter, however, is hampered by various obstacles to implementation [14]. To date, there is no approach that calculates the local energy goal transparently, considering all local RE potentials. For this, a transparent definition of local PV potentials according to uniform nationally applicable criteria is necessary.

The field of solar park suitability and energy potential mapping has been extensively explored in recent years, with numerous studies investigating various methodologies and approaches. Geographic Information Systems (GIS) are commonly employed in these studies, often integrated with different methods, such as Multi-Criteria Decision Making (MCDM) techniques [23–25]. The scale of these studies varies significantly, ranging from global approaches [26] to national [27, 28] as well as regional and local levels [23, 29,30,31].

A common thematic focus in the literature is the use of participatory approaches to enhance public acceptance. For instance, Spyridonidou et al. [32] discuss spatial energy planning in Israel using sustainability criteria validated through expert, public, and energy planner inputs. Similarly, methods emphasizing citizen engagement and acceptance have been highlighted [33].

In addition, there is a growing trend towards incorporating artificial intelligence in solar suitability studies. Sachit et al. [26] applied AI on a global scale, noting that local allocation often suffers from biased and non-generalizable weightings. Studies that integrate solar energy potential mapping with energy demand are also emerging, albeit less frequently [34, 35]. A comprehensive overview of various site selection procedures for photovoltaic (PV) and concentrated solar power (CSP) technologies is provided in Spyridonidou and Vagiona [36], offering valuable insights into different approaches to site selection.

However, none of these methods consistently classifies the participation space, considering both the human and nature compatibility of the sites and the legally binding effects with which these criteria limit the decision space. Furthermore, the decision contexts that hinder potentially feasible local solutions are not explicitly communicated for participation and local political decision making. This is particularly relevant in Germany given the extensive agricultural land use. To address this knowledge gap, the objective of our research is to demonstrate ways to include solar parks in an inclusive approach for determining the decision space and role of RE in the local energy transition. This includes:

• classifying land based on its suitability for solar park installation by considering criteria that encompass environmental and landscape aesthetic impacts, as well as the legal status of these criteria, which reflect the political level at which natural assets or human demands are protected;

• proposing a way for downscaling the national RE target for 2050 to the local level including the generation potential for solar parks;

• defining the leeway for local communities according to these criteria to choose about the energy mix and localities for RE according to their preferences for 2050 without compromising national targets

Next, we explain our methodological approach including the legal and geodata basis and then elaborate the results of an application of the approach in the German state of Lower Saxony. Finally, we discuss the results in light of applications in local participation processes.

Methods

Land suitability assessment for solar park installation

We utilize a multi-criteria GIS model to categorize land in Lower Saxony based on ecological sensitivity and legal constraints, aiming to identify areas that can support solar parks without compromising natural habitats or human interests. The study was conducted in 2020 using available geodata, academic literature, and documents related to policy and planning. The data used in the model has been updated since and can be found in the supplementary files. In addition to solar parks, we also conducted a suitability assessment for agrivoltaics, taking into account the technical differences of this type of power plant.

In a precautionary approach to RE allocation, areas where solar parks are likely to cause significant environmental damage should be excluded [37]. We developed the criteria on the basis of an analysis of scientific publications as well as international and national legislation. We tested the method as to suitability of metrics and data availability in the federal state of Lower Saxony. To investigate the question of how much potential land is available for the installation of solar parks, we chose a spatial approach using GIS (ArcGIS 10.5). The GIS model can be applied in other regions with freely available geodata. The method is based on the geospatial approach of [37] to calculate wind energy potentials and vulnerabilities of humans and nature.

However, the approach presented here focuses on the ecological impact and degree of environmental protection to be expected from solar parks (Fig. 1), whose technical dimensions and variations, and, therefore, their ecological impacts, are fundamentally different from wind turbines. We operationalize the ecological impact using the criteria of sensitivity and value in the assessment of ‘spatial resistance’ by applying methods used in environmental impact analysis and landscape planning. We define spatial resistance as the degree to which a particular area or landscape resists changes or disturbances, such as land use modifications, infrastructure development, or environmental interventions. This resistance can arise due to ecological, social, legal, or physical factors that make it challenging to alter the space without causing significant disruption to its natural functions, biodiversity, or cultural significance.

Fig. 1

Methodological framework for defining the spatial resistance against solar parks: projected ecological impact of solar parks and degree of environmental protection of landscape assets

The sensitivity of ES and biodiversity against specific pressures was evaluated in terms of projected impacts. The main criteria for biodiversity evaluation are scarcity and rarity [38] and general landscape preference in the case of landscape aesthetic evaluation [39]. It is important to acknowledge that landscape preferences, especially in countries with significant regional differences, often do not fully reflect the wishes and values of local inhabitants, as they are frequently modeled at larger scales and disproportionately influenced by non-resident landscape users. The energy transition, while a national task, must be implemented locally, requiring a balance between the principles of spatial equity and the consideration of region-specific environmental values and sensitivities. To identify nationally significant protected areas, a standardized evaluation system is necessary.

In a next step, we related the projected ecological impact to the degree of legitimacy and specificity of underlying legal norms. Using the legal dimension as an additional criterion in the assessment for identifying the safe operating space, though rarely used, can support the decision-making-process and promote effective implementation in land use planning by increasing acceptability of results [40,41,42]. The safe operating space refers to the environmental boundaries within which human activities can occur without causing significant harm to Earth's systems. By incorporating legal norms alongside ecological considerations, this approach helps ensure that land use decisions are both environmentally sustainable and aligned with societal expectations and regulations, contributing to long-term environmental stability and public trust in the planning process.

The criterion of legitimacy helps ensure that decisions reflect at least a minimum level of democratically legitimized public welfare [46]. This provides guidance to decision-makers in planning the energy transition, particularly when it comes to legally justified exclusions of certain areas from solar energy development, which are, in principle, democratically legitimized. Therefore, it provides public authorities with a justification basis for defining the safe operating space and at the same time is defining the space and subjects open to public participation. ‘Specificity’ describes the degree to which a norm (here, the protection of an environmental good) is specified in law. The more precisely thresholds, targets or the measures for protection are defined in law, the more enforceable their implementation.

We classify the land according to these criteria and built the model in six related steps:

• 1. Description of the pressure induced by solar parks.

• 2. Classification of spatial units according to their pressure specific sensitivity (potential change) and effects on their biodiversity and/or ES;

• 3. Classification of the value of biodiversity and ES.

• 4. Classification of different degrees of legitimacy.

• 5. Classification of different degrees of specificity.

• 6. Application of the criteria in GIS analysis: identifying areas with different degrees of suitability and eligibility to be sustainably used for solar parks

For modelling the safe operating space, we use either already existing biodiversity and ES assessments (biotope mapping, landscape planning) or indicators that comply with the state of knowledge in ES mapping and are applicable in a spatially explicit assessment.

The underlying data for the model includes geodata about land cover, soil type, hydrology, elevation, landscape features and ecological value. These allow for the deduction of site-specific vulnerabilities to the use of solar parks on the one hand, and related normative restrictions on the other [43]. The spatial units are assessed according to sensitivity, value, legitimacy and specificity and assigned to a spatial resistance class, which results in a differentiated suitability for solar parks from an environmental perspective (Table 1). Because geodata from different classes can overlap, intersecting areas are associated to the highest class. In general, a high class corresponds to a high assessment of sensitivity and value, whereas high or low legitimacy and specificity determines the distinction between a very high or high class and a medium or low class.

Table 1 Rules of aggregating the four spatial resistance classes according to the classification of sensitivity, value, legitimacy and specificity

Pressure induced by solar parks

As a first step, we investigated the influence solar parks can have on the environment. This influence may also be described as pressures originating from solar parks as used in the DPSIR concept [44]. The DPSIR concept is a framework used to analyze environmental issues by categorizing them into five components: Drivers, Pressures, State, Impacts, and Responses. It helps to understand the cause–effect relationships between human activities and the environment, guiding decision-makers in addressing environmental challenges through targeted responses [44]. Of fundamental importance to how much specific pressures affect the environment is the state and sensitivity of different ecosystems and their services. Within the causal relationship of the DPSIR concept, sensitivities against pressures can be defined as the likelihood of a change in state of an ecosystem in response to specific pressures [45]. With regard to solar parks, there are many criteria that affect the degree of pressures. Especially, since there is not just one type of solar park and their design can vary greatly depending on, among others factors, exposition, location, degree of sealing, and inclination of panels [46, 47]. Although we mainly focused on negative impacts on the ecosystem’s state, some pressures can also have a positive impact [6, 48,49,50]; be it from management and design of the park itself [51] or the change of land use, such as formerly intensively managed farmland [52].

These positive impacts, or co-benefits, for ES and natural capital are often linked to changes in land use intensity and site-specific management [8]. We advocate providing these co-benefits at ‘no regret’ locations [37, 53] with a low spatial resistance, where there is both high potential for enhancement and minimal harm to be expected [54].

With co-benefits in mind, our assessment allows for comparison with other spatially relevant aspects, particularly related to land use, land-use change, and forestry (LULUCF). For example, solar park development can be linked to areas sensitive to nitrate and phosphate emissions. Based on the EU Nitrates Directive (91/676/EEC), the state government has designated areas with specific restrictions on the fertilization of agricultural land to protect water bodies from nitrate or phosphate contamination. In areas where low spatial resistance overlaps with sensitivity to nitrate and phosphate emissions, solar parks can have positive impacts on soil and water balance. One potential conclusion could be to replace intensively used cropland in these areas with solar parks, which would not only prevent emissions from fertilization but also provide an alternative source of income for farmers. We analyzed these areas and show the results in terms of overlapping area and potential energy yield in the results. With a focus on negative impacts, above all, the size of the solar park itself and the design of the module technology determine the extent of the pressures (i.e., the height of the modules, their size, the distance between the module rows, their distance from the ground, and their inclination [55]). Because of that variability in appearance, and since the environmental impact depends to a large extent on the design of the solar park, we have defined—as a variable—a reference system to determine possible impacts as accurately as possible (Table 2). The input variables were derived from the Institute for Solar Energy Research in Hamelin (ISFH) and do not represent the current state of the art with regard to power density and energy yield. They are, however, based on averaged irradiation and weather data, which allows for a conservative but reliable calculation of the potential energy yield. For the agrivolatic system, we used the configurations mentioned in [56] with a south-facing monofacial fixed-tilt PV system.

Table 2 Input variables of the reference system of a solar park and an agrivolatic system for calculating the potential energy yield in Lower Saxony

As a second step we conducted a literature search on the general effects and relationships between solar parks and ecosystems with particular focus on biodiversity, soil, water and visual landscape (Table 3). We limited the number of publications found by only including articles published between the years 2014 to 2021.

Table 3 Main search terms and subterms used in the literature scan (ISI Web of Science)

The findings of the literature review revealed a number of environmental pressures originating from solar parks and agrivoltaic systems which we related to attributes of sensitivity (Table 4). This in turn allows the translation into concrete spatial units or geodata.

Table 4 Relationship between pressures originating from solar parks and spatial attributes, where those pressures can lead to change in state

Pressure-specific assessment and classification of sensitivity

The findings were evaluated and used to classify the model region according to its sensitivity to pressures from solar parks. To translate the findings into a spatial model, geodata containing site-specific information (e.g., land cover, species abundance, soil fertility) was gathered to assess the sensitivity of a site. The conflict risk describes the probability that constructing a solar park would impair biodiversity or ES. In this model, sensitivity is defined as a function of both the probability of such an effect occurring and the severity of the expected impact on the ecosystem. Sensitivity is classified into four levels (Table 5).

Table 5 Classes of sensitivity to solar parks, based on probability and expected impact

Sensitivity represents a combination of the likelihood that an adverse effect will occur (probability) and the severity of its impact (effect) [57]. For example, a site with high probability of long-term ecological change would be classified as having 'very high sensitivity,' while a site with low probability of short-term change would be classified as having 'low sensitivity.'

Classification of biodiversity and ES value

Similar to the classification of sensitivity, the value of an area is also determined via spatial data and the associated value of biodiversity and ES. To determine overall vulnerability, the value criterion is crucial, as it reflects the relevance of the natural resources or functions represented by the spatial unit. The value, however, may be perceived differently by various stakeholders [58]. Experts might prioritize scientific and ecological aspects, local stakeholders may value ES that directly affect their livelihoods (e.g., agricultural productivity or water resources), while policymakers and politicians might focus on the economic and societal implications of conserving natural resources.

In addition, societal valuation of an area is often formalized through institutional or governmental decisions, such as land designations or restrictions in the public interest (e.g., protected areas). In these cases, the protection status of a landscape can serve as a proxy for high societal appreciation, indicating a broad valuation through society, including decision-makers, experts, and the general public [59, 60]. However, the conclusions drawn from the model's results are strongly dependent on the data input. This includes who influenced or provided the data, what assumptions were made, and which stakeholders' interests were represented. For instance, if data predominantly reflects institutional or expert perspectives, it may underrepresent local stakeholders' concerns. These factors greatly shape the outcomes and must be considered when interpreting the model’s outputs and their implications for policy or decision-making. The valuation of habitats and species is based on the criteria of scarcity or rareness and endangerment—expressed in red lists, expert classifications, as well as classifications of protected species and habitats in legislation. Evaluation criteria for cultural ES are based on general societal preferences, for which we use a national evaluation of aesthetic value supported by a representative survey for all of Germany that was later modelled [39]. The evaluation of the provisioning service of soil (in particular the natural production capacity) is based on an evaluation of soil fertility classified on a scale from 1 to 7 for Germany [61]. The evaluation of water provisioning service is based on data of a European-wide monitoring of a good qualitative and quantitative status of all waterbodies implemented through the European Union Water Framework Directive (WFD).

Therefore, a very high value from an environmental perspective arises from a) an essential importance for the performing and functioning of biodiversity and ES or b) additionally through availability in the form of scarcity and rarity (Table 6).

Table 6 Classes of value of biodiversity and ES with their definition

Classification of different degrees of legitimacy to exclude land use categories from solar park installation

In accordance with ([40]:557), “legitimacy is understood as based on legal norms, which have been developed in legitimized ways. Such legal norms have to be accepted, in principle, by everybody as a societal consent even if individual interests stand against them.” Legitimacy defines the space and issues open to public participation and provides public authorities with a justification for the decisions derived from it.

Political decisions in environmental and energy policy can substantially affect economic and social interests, often making them conflictual [62]. To justify the decisions that ultimately resort in the ‘state’s monopoly of legitimate coercion’, arguments are needed ‘to establish a moral duty to obey’ [63]. Legality is usually the precondition for legitimacy [64]. Having said this, it is often not sufficient to justify decisions on the basis of their legality to achieve acceptance.

However, the model and its underlying methods are not intended to replace democratically legitimized planning processes, but to support them. Where and where not to build solar parks should, therefore, be based on transparent criteria in the decision-making process, and the concerns of all stakeholders. The criterion of legitimacy represents the degree of normative binding of relevant land categories to reveal the space for decision-making.

A very high degree of normative binding means that legal documents (e.g., laws, regulations or ordinances) prohibit the installation solar parks in these areas (Table 7). Their exclusion is mandatory and legally binding. In contrast, a high legitimacy does not lead to a general exclusion of solar parks a priori (since reasons for exclusion may be legitimate but not explicitly defined by law). The medium legitimacy class includes spatial units, where legal approval is possible under certain conditions (e.g., if a protected good is not impaired). These areas are conditionally suitable but require further verification with region-specific and local information. For areas with a low degree of normative binding, solar parks are not generally excluded as there are no direct legal criteria prohibiting them. However, this does not imply automatic approval, as other legitimate but model-external factors (e.g., local planning laws, region-specific ecological concerns) may still lead to exclusion. It is important to note that this framework does not account for all potential legal or contextual exclusions. The results provided by the model indicate areas, where solar park installations might be legally feasible based on the general legal frameworks included, but additional, specific local regulations or policies not integrated into the model may still prevent the installation. This represents a limitation of the model, as certain legal frameworks or legitimate reasons (such as regionally applicable zoning laws or unforeseen environmental concerns) may not be fully captured. Further consultation with local authorities and detailed legal reviews would be necessary to fully confirm the legal viability of solar park installations in any specific location. The underlying legal norms for the classification (as of 2024) of each spatial unit can be found in Table 9.

Table 7 Classes of legitimacy according to their degree of normative binding

Classification of different degrees of specificity

The specificity of a legal norm plays a decisive role for estimating its legal feasibility: the more clearly a restriction of for solar parks can be derived from the legal norm, the higher is the implementation effect [40]. Their specification (Table 8) ranges from very high specificity, which allows for a quantitative measurement or numerical thresholds (e.g., the sustainable use of available water), to general statements about norms and principles without specification [40]. The first is particularly important for landscape planning, where the evaluation and deduction of objectives are essential for decision makers [65, 66].

Table 8 Classes of specificity of legal norms

The more precisely the measures for protection are laid out in the norm, e.g., through quantitative specifications of threshold values,

• the more likely it is to be implemented,

• the less room for interpretation there is, and

• the more transparent are the decisions derived from it (i.e., allocation of a solar park).

The degree of specificity, therefore, provides guidance for decision-makers as to how well a norm is suited to implement an objective or how much leeway there is for decision-making (Table 1).

Calculating the local RE target for 2050

The first step of this study is to calculate local energy targets, scaled down from national targets while accounting for both national RE demand by 2050 and the human and nature-compatible generation potentials on-site. Calculating local energy targets also supports participatory planning. Tools like ‘Vision:En 2040’ [17] have shown that involving citizens in interactive simulations of RE siting can enhance understanding, reduce biases, and foster local responsibility for the energy transition. By linking energy targets with participatory tools, citizens can make informed decisions and actively contribute to achieving the set goals. Our approach builds on the multilevel energy allocation and planning framework proposed by Thiele et al. [11]. This framework addresses the operationalization gap between national RE goals and local implementation, especially the “problem of fit”, where local regions lack clarity on their role and contribution to the energy transition [67, 68]. The "problem of fit" refers to the misalignment between national climate goals and local-level understanding of their contributions to the energy transition. To bridge this gap, Thiele et al. [69] proposed a multilevel approach with two key components:

• 1. National-level allocation of RE generation goals, ensuring each region's energy potential is factored into their responsibility for achieving national targets.

• 2. Local decision-making regarding the energy mix and siting of RE installations, within the broader national framework.

In this approach the German electricity demand was estimated at 1500 TWh/a, 91.3% (1376 TWh/a) of which can be covered by rooftop PV, onshore and offshore wind energy, geothermal energy and hydropower. However, as the solar park potential was not yet calculated, it was assumed that the remaining electricity demand of 8.27% (124 TWh/a) would be covered by solar parks. Our model now closes this gap. The local energy targets can be calculated using the existing solar park potential for Lower Saxony and an assumed electricity demand of 234 TWh/a from [69]. The calculation is based on the key components mentioned above: each municipality must produce a share of the national electricity demand based on its RE potential areas. We define this share as the local energy target, which results from the share of the local potential in the total energy potential. For the total energy potential and the total energy demand, we take the values for Lower Saxony, since, as described above, the Germany-wide solar park potential is not available. This formula is expressed as follows:

$${Energy Goal}_{local}= \frac{{Energy Potential}_{local}}{{Energy Potential}_{total}}\times {Energy Demand}_{total}$$

(1)

By taking all RE into account, the actual local leeway in the choice of energy mix becomes clear. We will demonstrate the approach for Lower Saxony as well as the municipalities of Springe and Wedemark.

GIS analysis and calculation of the sustainable electricity yield potential

In the last step we aggregated the four vulnerability classes in a spatial GIS model. We used the GIS-software ArcGIS 10.7.1 with the extensions “Geostatistical Analyst” and “Spatial Analyst”. For each spatial unit, geodata was compiled and then merged into respective layers of vulnerability classes resulting in four layers of vulnerability classes. The four layers were intersected with priority from very high vulnerability to low vulnerability, i.e., the higher vulnerability on one location is always given preference. Areas that are not suitable due to technical–economic reasons were added to the highest class. These include slopes with an inclination > 45°, north-facing slopes with an inclination > 30°, and 50 m and 20 m buffers around forest and wooded areas (see supplementary material).

For areas with low spatial resistance, the potential energy yield for the reference plant and the agrivoltaic system was calculated according to their annual energy yield (1.09 GWh/ha and 0.255 GWh/ha). We define the potential electricity yield as the electricity yield that can theoretically be generated depending on the available area and specification of the plant. The calculation was made using the following formula:

$$Available \, Area \, \left( {ha} \right) \, \times \, Energy \, Yield \, \left( {GWh/ha} \right) \, = \, Electricity \, Yield \, Potential \, \left( {GWh} \right)$$

(2)

Model region

We test the model in the federal state of Lower Saxony in north-western Germany as well as the two municipalities, Springe and Wedemark (Fig. 2).

Fig. 2

Model region of Lower Saxony (light red) located in Germany. The municipalities Springe and Wedemark can be seen in dark red

The area of the whole model region amounts to 47.710 km² [70]–13.34% of the total area of Germany. Although Lower Saxony is the second largest federal state in Germany, its share of PV and ground mounted systems is rather low in comparison [71]. The Springe and Wedemark case study areas are located in the centre of Lower Saxony and have an area of 160 and 174 km².

Results

The analysis identified areas in Lower Saxony, where solar park development aligns with ecological and human well-being while helping meet future energy demands. The classification of geodata in terms of ecological impact and degree of environmental protection can be seen in Table 9. A detailed description of the area categories can be seen in the supplementary material.

Table 9 Classification of spatial resistance to solar parks

Potential in terms of area and energy

We classified Lower Saxony's land into four levels of spatial resistance (Fig. 3), revealing that approximately 13% (611,932 ha) is suitable for solar parks (Fig. 4).

Fig. 3

Spatial resistance classes for the reference plant (RP) and agrivoltaic systems (AV) in the territory of Lower Saxony (1), Springe (2) and Wedemark (3). The last column shows nitrate sensitive areas within the low spatial resistance class of the reference plant (RP_N) to highlight potential co-benefits with ES

Fig. 4

Relative distribution of spatial resistance classes in Lower Saxony (percent) for the reference plant. Within the low resistance class 6% of the area are also nitrate sensitive areas suitable for realizing co-benefits with ES

Particularly in the southwest, large areas are suitable for producing renewable solar energy. The overlap of areas of low spatial resistance with areas sensitive to nitrate emissions comprises an area of 6% (276,642 ha) in Lower Saxony, 11 ha in Springe and 1592 ha in Wedemark. In these overlapping areas, the production of solar energy can produce synergetic outcomes regarding water and soil protection with minimal reduction of other ES. This is especially true for intensively used grassland and crop land with low soil fertility and high fertilizer input. Taking these areas out of agricultural use (or combining them with AV) could have positive effects on nitrate levels in groundwater, soil structure and biodiversity (Fig. 5).

Fig. 5

Relative distribution of spatial resistance classes in Lower Saxony (percent) for agrivoltaic systems

Areas with medium spatial resistance, covering 18% (859,268 ha) of the land, can potentially accommodate solar parks under specific conditions, with adaptations, such as height and spacing adjustments. For example, landscape protection areas may be suitable if they align with conservation goals. Decision-making for these areas involves careful case-by-case assessment.

Areas of high spatial resistance (48%, 2,276,314 ha) tend to experience severe ecological impacts, thus limiting their suitability for solar development. These regions often boast high visual quality or ecological value, such as contiguous landscapes or habitats for sensitive bird species. Similarly, fertile agricultural lands and flood zones are prioritized for traditional farming. Crop land within the biotope network is excluded here and assigned a medium spatial resistance, because the conversion of intensively used crops to solar parks can lead to an enhancement of the connectivity function within the biotope network [72].

Since avifauna in particular react sensitively to solar parks, we added input data of sensitive bird species outside protected areas. Studies indicate a potential loss of habitat for the curlew (Numenius arquata), the black-tailed godwit (Limosa limosa), the redshank (Tringa totanus) and the ruff (Philomachus pugnax) (for a detailed list, see [55]). Ecologically valuable grasslands should also be protected from solar parks, even though there is no specific legal context for this. The same applies to areas of high soil fertility, which must be kept free for food production, as well as flood areas.

Finally, very high resistance areas, accounting for 21% (1,015,444 ha), are excluded from solar installations due to significant ecological and legal restrictions. These include protected sites such as military areas and regions with critical environmental importance, such as the Elbe and Weser river corridors.

Based on the specifications in Table 10, the reference plant can generate 1.09 GWh/ha/a. For all areas with low spatial resistance this results in an electricity potential of 667.01 TWh/a for Lower Saxony, 0.79 TWh/a for Springe and 1.74 TWh/a for Wedemark. For the agrivoltaic system an additional area of 222,308 ha is classified as low spatial resistance leading to an additional energy yield of 56.69 TWh/a for all of Lower Saxony, 1.34 TWh/a for Springe and 0.41 TWh/a for Wedemark. The overlap of areas of low spatial resistance with areas sensitive to nitrate emissions comprises an area of 276,642 ha in Lower Saxony, 11 ha in Springe and 1592 ha in Wedemark.

Table 10 Area (ha) and energy yield (TWh/a) within the class of low spatial resistance for the reference plant (RP) and agrivolatic systems (AV)

To account for the differences of the agrivoltaic system, the spatial resistance class was adapted to its characteristics. The added value of agrivoltaics lies in the dual use of energy production and agriculture, which is why AV is particularly effective on fertile soils or at least does not take land away from food production. Crop land with high soil fertility was, therefore, assigned to the low spatial resistance class.

Local RE target

The energy potential in the low spatial resistance category is 667.01 TWh/a for all of Lower Saxony, 0.79 TWh/a for Springe, and 1.74 TWh/a for Wedemark (Table 11). When combined with the potential from other RE sources, Lower Saxony's total energy potential amounts to 846.46 TWh/a. Using the RE target from Thiele et al. [69], which is 234 TWh/a, we can calculate the local energy targets for Springe and Wedemark according to Formula 1. The local energy target for Springe is 0.49 TWh/a, and for Wedemark, it is 0.63 TWh/a.

Table 11 Overview of solar park potential and RE targets in Lower Saxony, Springe and Wedemark

Discussion

The findings underscore the importance of region-specific energy planning frameworks that incorporate participatory elements and adjust to spatial resistance and potential co-benefits, such as enhanced biodiversity on converted agricultural lands. By enabling local engagement in energy decisions, our approach aligns with democratic ideals and provides a template for reconciling national energy policies with local ecological and social priorities. The German situation may be specific, but basic considerations of competition about land use are also to be found in other countries [73, 74]. The results of the spatial application of the concept show that there is a high potential for solar parks in Lower Saxony. Within the areas of low spatial resistance, 667.01 TWh/a can potentially be produced in Lower Saxony, which represents 13% of the total area. As a comparison, [11] estimate that the total energy demand for Germany in 2050 will be 1789 TWh/a, including 1500 TWh/a which will come from RE. With the federal state serving as a study area to test the model for its applicability, calculating the potential for Lower Saxony can give a first rough impression of the potential of solar parks in Germany.

The substantial energy potential in Lower Saxony highlights the importance of public participation in the strategic allocation of solar parks. This, combined with effective spatial planning, can facilitate a successful energy transition. If one compares the results of the modelling with the nationwide energy targets, it quickly becomes clear that these can be achieved if solar parks are integrated sensibly. According to the “German Renewable Energy Sources Act” (EEG [75, 76]), Germany's solar expansion target until 2030 is 600 TWh/a and the scientifically calculated target for 2045 is about 1700TWh/a. The scope for municipal involvement in the designation of wind and solar energy plants is, therefore, very large overall in Lower Saxony. However, not only the wind but also the solar energy potential is very unevenly distributed. Furthermore, the aim should not be to exploit the full potential and cover 13% of Lower Saxony with solar parks. Initially, only enough RE should be produced to meet the state-specific share of the nation’s projected demand for 2050. As solar parks were not considered when adjusting the local RE targets, the solar park potential was the backup or the "optional leg" for achieving the target if wind energy and rooftop PV were not to be exhausted in the participation process. This jeopardized the intended distribution of responsibility, considering the principle that each municipality makes a fair contribution to the combined national/state target according to its own capacity. By adding the solar park potential to this capacity, we could calculate a RE generation target that corrects the structural disadvantage of regions or municipalities with only low solar park potential. If the solar park potential, i.e., the "free leg" of the energy transition, is very small—such as in municipalities with very fertile soils or a high proportion of areas with high landscape aesthetic quality—the scope for citizens to make decisions is also much more limited. In contrast, municipalities with similar wind potential but a much higher proportion of PV-capable areas offer greater decision-making opportunities.

An additional advantage of coordinated RE allocation is that the better the site selection, the less additional compensation area would be required for impact regulation and species protection through continuous ecological functionality-measures (CEF-measures) [77]. A differentiated potential area analysis is, therefore, an important planning basis for reducing the area required for solar parks.

Furthermore, the literature scan showed that the impacts of solar parks on biodiversity, soil, water and cultural ES can be both negative and positive, and that the intensity of the impacts (also negative and positive) strongly depends on the location and previous land use, as well as the design and management of the solar park. The model can help to prevent or mitigate potential negative impacts by identifying the areas that are most sensitive to pressures. This makes the approach comparable to the routines in environmental impact assessments (EIA) and strategic environmental assessments (SEA) for plans and programs "which are likely to have significant effects on the environment" (SEA Directive 2001/42/EC). SEA is performed at an early stage of the planning process, where it prevents damage to biodiversity and ES from occurring in the first place (precautionary principle). At the same time, the model enables the identification of co-benefits with ES: there are growing examples in which the installation of solar parks can be seen as a win–win situation for RE expansion and nature conservation or even agriculture [8, 78]. With appropriate management, solar parks can be specifically linked to biodiversity conservation [79] and promote biodiversity and ES.

Intersecting the geodata on solar park potential with nitrate sensitive areas, where a reduction in agricultural pressure on arable land and ecosystems would be beneficial, shows an opportunity for regional planning to overcome the land use conflicts caused by agriculture. In our case, highly concentrated livestock farming leads to both land consumption due to feed production and competition for land for manure spreading. Solar parks could become an alternative source of income if land use planning were to link approval for the construction of PV to the obligation to reduce livestock numbers. This is just one example of the possibilities to use the modelling for informing regional and local decision making about creative solutions for persistent unsolved problems caused by locally unchangeable frame conditions. Furthermore, the GIS model used in the study is adaptable and can integrate changes in environmental pressures resulting from the introduction of innovative PV technologies or shifts in environmental and energy policies.

Conclusion

This study underscores the importance of strategic, socially inclusive spatial planning for the development of solar parks in Lower Saxony. By integrating ecological, legal, and aesthetic criteria into our GIS-based model, we have identified areas with low spatial resistance that can accommodate solar energy without substantially compromising biodiversity, ES, or human interests.

We have proposed standardized criteria for the allocation of solar parks in Germany. We classified the land area into four classes according to their spatial resistance in terms of ecological impact (sensitivity and value) and the degree of environmental protection (legitimacy and specificity). By applying these criteria in the case of the state of Lower Saxony, the paper has found 13% of the state's area suitable for solar park installation.

Our findings reveal that Lower Saxony possesses a substantial energy potential of 667,01 TWh/a, far exceeding the contribution needed for a successful energy transition within the state (243 TWh/a). This abundance creates a unique opportunity for public participation in energy planning, allowing for locally tailored solutions that align with national climate protection goals. Encouraging local engagement in determining the energy mix facilitates democratic participation and mitigates potential conflicts related to land use.

Moreover, our assessment shows that thoughtful integration of solar parks and agrivoltaic systems can yield co-benefits, such as improved soil and water quality, particularly when aligned with existing agricultural and environmental policies like those addressing nitrate pollution. The study also highlights the potential of agrivoltaics as a dual-use strategy that supports both energy generation and agricultural productivity, offering additional flexibility for regions with high soil fertility or specific conservation needs. As policymakers and regional planners strive for an inclusive energy transition, our model presents a valuable tool for making informed decisions that consider both ecological and social dimensions.