Mega solar park in Hilden – This is how a city wants to become climate-neutral: A 40,000 square meter project is intended to achieve this – Creative image: Xpert.Digital
Hilden's path to the solar park: A groundbreaking decision for the energy future
City council approves future-oriented energy supply
After months of intensive discussions and careful consideration of various interests, the Hilden city council has made a groundbreaking decision. By a clear majority of 44 to 17 votes, the way was cleared for a solar park in the Karnap-West area. This decision marks an important milestone on Hilden's path to climate neutrality by 2035 and demonstrates how municipalities can practically address the challenges of the energy transition.
The vote was held by secret ballot, underscoring the sensitivity of the issue. Even the CDU parliamentary group lifted party discipline to allow each council member to vote according to their own conscience. This democratic approach reflects the complexity that municipalities face when implementing sustainable energy projects.
Project specifications and technical details
The planned solar park will be built on a 40,000-square-meter municipal plot of land on An den Gölden street. The plant is expected to reach a peak output of 5.2 megawatts and will be supplemented by a battery storage system with a capacity of 4 megawatt-hours. With this configuration, the solar park is expected to generate approximately 5,000 kilowatt-hours per year, which corresponds to about seven percent of the electricity sales potential of the Hilden municipal utility.
The project will be implemented in an east-west orientation, which allows for optimal land use and more consistent electricity production throughout the day. This orientation has proven particularly advantageous for modern solar parks, as it better covers the morning and evening hours, thus contributing to a more stable grid feed-in.
The facility must meet various requirements, including a minimum distance of five meters from the farm track and hiking trail "An den Gölden". This buffer zone will be created as a sown wildflower and protective strip, which not only offers ecological benefits but also improves the integration into the landscape.
Legal framework and approval procedures
The construction of ground-mounted photovoltaic systems in Germany is subject to a clearly structured approval process. Generally, a building permit is required for such systems, which is issued according to the respective state building codes. In most federal states, a permit is mandatory for ground-mounted systems exceeding three meters in height and nine meters in length.
Building planning law generally requires the preparation of a development plan, as open-space photovoltaic systems do not fall under the privileged provisions of the Federal Building Code. This means that the municipality must carry out a corresponding urban planning process that includes both public participation and the involvement of relevant specialist authorities.
With the Solar Package I, which came into force in May 2024, the framework for ground-mounted photovoltaics was significantly improved. So-called disadvantaged areas are now generally open to EEG subsidies nationwide. This represents a reversal of the previous opt-in system, under which the federal states had to explicitly approve these areas by decree.
In addition, minimum environmental protection criteria were introduced to ensure the sustainable development of solar parks. These include the requirement that the maximum area occupied by the modules may not exceed 60 percent of the total project area.
Energy policy context and climate targets
The decision to build the solar park in Hilden is in line with Germany's ambitious climate targets. The goal is to achieve a photovoltaic capacity of 215 gigawatts by 2030, with half coming from rooftop installations and half from ground-mounted systems. This represents a fourfold increase in annual capacity from the current approximately 5 gigawatts to an average of 21 gigawatts between 2026 and 2035.
Hilden has set itself the goal of becoming climate-neutral by 2035, ten years earlier than the national target. This requires a massive expansion of renewable energies at the local level. Currently, the existing photovoltaic systems in Hilden cover only about six percent of the city's electricity needs. The planned solar park would increase this share to approximately ten percent.
The Hilden municipal utilities are pursuing a comprehensive climate protection strategy and are working on decarbonizing the city's energy supply. In addition to the solar park, this also includes municipal heat planning and the expansion of other renewable energy sources.
Economic aspects and financing
The lease agreement between the city of Hilden and the municipal utilities has a term of 30 years with an annual lease payment of €8,000. This amount is fixed for the first ten years and subsequently adjusted every five years to reflect the company's profitability, but it may never fall below the original amount.
The economic viability of solar parks has improved considerably in recent years. The levelized cost of electricity (LCOE) for ground-mounted photovoltaic systems has fallen continuously, while the efficiency of the modules has increased. Modern solar parks can now produce electricity at a cost of three to five cents per kilowatt-hour, making them one of the most cost-effective energy sources.
The investment costs for a solar park of this size typically range between 4 and 6 million euros, depending on the specific design and local conditions. The amortization period is generally between ten and fifteen years, meaning that substantial returns can be achieved over the 30-year contract term.
Role of battery storage for grid stability
A special feature of the Hilden project is the integration of a battery storage system with a capacity of 4 megawatt hours. Battery storage systems are becoming increasingly important in the integration of renewable energies, as they can compensate for fluctuations in electricity production and contribute to grid stability.
Storage technology makes it possible to store excess solar power during periods of high production and feed it back into the grid when needed. This is particularly valuable for providing ancillary services such as frequency control and voltage regulation. Modern battery storage systems can react to grid fluctuations within milliseconds and are therefore significantly faster than conventional power plants.
The combination of a solar park and battery storage, also known as a hybrid power plant, represents an optimal solution for modern energy supply. It not only maximizes the self-consumption of the electricity produced, but also contributes to relieving the strain on the transmission grid.
Citizen participation and social acceptance
The discussions surrounding the solar park in Hilden have demonstrated the importance of comprehensive public participation in energy projects. Over a period of almost a year, various information events were held in which citizens, the local administration, the municipal utility company, and external experts examined the project from different perspectives.
Citizen participation can take various forms, from simply providing information and consultation to financial involvement. Models that not only inform the local population but also allow them to benefit economically from the project are particularly promising. This could include energy cooperatives, subordinated loans, or discounted electricity tariffs.
Experience from other projects shows that financial participation models can significantly increase acceptance. When citizens share in the profits, attitudes often shift from skepticism to support. Successful examples can be found in communities like Tuningen and Maßbach, where local participation models have been implemented.
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At the heart of this technological advancement is the deliberate departure from conventional clamp fastening, which has been the standard for decades. The new, more time- and cost-effective mounting system addresses this with a fundamentally different, more intelligent concept. Instead of clamping the modules at specific points, they are inserted into a continuous, specially shaped support rail and held securely. This design ensures that all forces occurring—be they static loads from snow or dynamic loads from wind—are evenly distributed across the entire length of the module frame.
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The future of solar parks: Innovative technologies and regional opportunities until 2027
Project development and scheduling
Developing a solar park is a complex process that typically extends over several years. Hans-Ullrich Schneider, Managing Director of the Hilden municipal utility company, outlined the further timeline: The building application is to be submitted in autumn 2025, followed by the tender for construction. The contracts and awarding of the contract could be finalized in autumn 2026, with planned commissioning in the first half of 2027.
This timeframe is typical for solar park projects. The actual construction time is relatively short, lasting only a few weeks to months, but the preceding planning and permitting phase takes considerably longer. Project development can be divided into five main phases:
The search for suitable land and initial discussions with landowners and municipalities typically take about six months. This is followed by the complex planning and permitting phase, which can take up to two years for large solar parks. During this time, technical assessments are carried out, permits are applied for, and the public is involved.
Preparing the site, including developing access roads and cabling, takes another six months to a year. The actual construction of the plant then takes place within eight to ten weeks, depending on the size and complexity of the project.
Technological innovation and future trends
Modern solar parks utilize the latest generation of photovoltaic modules and inverters, which are significantly more efficient than those of just a few years ago. Power density has continuously increased, allowing more electricity to be generated on the same area.
Bifacial modules, which also utilize their backsides for power generation, are becoming increasingly important. They can increase yield by ten to 25 percent, depending on the substrate and mounting system. Tracking systems, which allow the modules to follow the sun's path, can also significantly increase output.
The integration of battery storage into solar parks is a relatively new trend driven by falling storage costs and improved technologies. Lithium-ion batteries have experienced a dramatic cost reduction in recent years and now achieve cycle lives of over 6,000 full cycles.
Environmental and nature conservation aspects
An important aspect in the planning of ground-mounted photovoltaic systems is their impact on nature and the environment. The first solar package therefore introduced minimum environmental protection criteria that must be observed for all systems subsidized under the Renewable Energy Sources Act (EEG).
This includes the aforementioned maximum area coverage of 60 percent, which ensures that sufficient space remains for the development of vegetation and habitats. In addition, measures to promote biodiversity must be implemented, such as the creation of wildflower strips or the establishment of biotope structures.
Many studies show that well-planned solar parks can even have positive effects on biodiversity. Extensive land management and the avoidance of intensive agricultural use create habitats for various animal and plant species. Particularly important is the permeability for smaller animal species, which can be ensured through appropriate fencing.
Regional value creation and municipal benefits
Solar parks can significantly contribute to regional economic development. In addition to direct lease income for landowners, local tradespeople involved in construction and maintenance also benefit. Business tax revenue flows to the host community and can be used for municipal projects.
Furthermore, municipalities can benefit from the so-called Citizen Energy Act, which allows operators of renewable energy plants to provide affected municipalities with 0.2 cents per kilowatt-hour fed into the grid. For a solar park the size of Hilden, this would mean annual payments of approximately 10,000 to 20,000 euros.
Challenges and solutions
Developing solar parks is not without its challenges. One of the biggest hurdles is the availability of suitable land and its development under planning law. The land requirement for the energy transition is considerable: To achieve the national expansion targets, an additional 80,000 to 100,000 hectares will be needed for ground-mounted photovoltaics by 2030.
At the same time, conflicts with other land use claims must be avoided. The competition between energy production, agriculture, and nature conservation requires intelligent solutions such as agri-photovoltaics, which combines agriculture and solar power generation.
Another critical point is network integration. Many potential locations lack sufficient network capacity, which can lead to long waiting times and high connection costs. Innovative approaches such as flexible network connection agreements and local marketing concepts are needed here.
International context and best practices
Germany is not alone in developing solar parks. Internationally, there are numerous examples of successful projects and innovative approaches. In countries like Spain, France, and the Netherlands, large solar parks with citizen participation have been under construction for years.
Particularly interesting are models in which solar parks are developed as part of regional energy systems. These systems not only produce electricity, but also consider heat and mobility. Such integrated approaches can significantly increase efficiency and foster public acceptance.
Digitalization and Smart Grid Integration
Modern solar parks are no longer just passive power generators, but active participants in the energy system. Digital control systems allow them to respond flexibly to grid demands and provide various system services.
Integration into smart grids makes it possible to optimally match electricity production with consumption and avoid grid overloads. Artificial intelligence and machine learning help to improve production forecasts and control the systems proactively.
Solar park and battery storage for a resilient energy system
The solar park in Hilden is more than just an energy project – it's a symbol of the transition to a sustainable energy supply at the municipal level. The city council's decision demonstrates that even challenging projects can be successfully implemented with sufficient public participation and transparent communication.
The experience gained in Hilden will also be valuable for other municipalities planning similar projects. In particular, the combination of technological innovation, ecological responsibility, and economic participation of citizens could serve as a model for future energy projects.
With its planned commissioning in 2027, Hilden will have taken an important step towards achieving climate neutrality by 2035. The solar park will not only contribute to the local electricity supply but also serve as a building block for a resilient and sustainable energy system.
The integration of battery storage makes the project future-proof and demonstrates what modern energy infrastructure can look like. If other municipalities follow this example and implement similar projects, Germany could actually achieve its ambitious climate goals.
The path to achieving this is not always easy, as the months of discussions in Hilden have shown. But the result – a democratically legitimized decision for a sustainable energy future – demonstrates that the effort is worthwhile. Hilden is thus becoming a role model for other municipalities that want to take the step towards a renewable energy future.
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