Mega solar park in Hilden – How a city wants to become climate neutral: A 40,000 square meter project is supposed to do it

City council votes for future-oriented energy supply

After months of intensive discussions and careful consideration of various interests, the Hilden City Council has made a groundbreaking decision. With 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 conducted by secret ballot, underscoring the sensitivity of the issue. Even the CDU parliamentary group lifted the party discipline to allow each council member to make a decision 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 site on An den Gölden Street. The plant is expected to achieve a peak output of 5.2 megawatts and will be complemented 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, corresponding to approximately seven percent of the electricity sales potential of Hilden's municipal utility.

The project will be implemented with an east-west orientation, which allows for optimal use of space while ensuring more consistent power 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 An den Gölden farm and hiking trail. This distance will be established as a sown flowering and protective strip, which not only provides ecological benefits but also improves landscape integration.

Legal framework and approval procedures

The construction of open-space photovoltaic systems in Germany is subject to a clearly structured approval process. Generally, such systems require a building permit, which is issued in accordance with the respective state building regulations. In most federal states, a permit is required for open-space systems with a height of three meters and a length of nine meters or more.

Building planning law generally requires the preparation of a development plan, as open-space photovoltaic systems are not eligible for privileged development under the Federal Building Code. This means that the municipality must conduct a corresponding development planning process, which 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 conditions for ground-mounted photovoltaics were significantly improved. The so-called disadvantaged areas are now generally eligible for EEG funding nationwide. This represents a reversal of the previous opt-in regulation, under which the federal states had to first approve these areas by regulation.

In addition, minimum nature conservation criteria have been introduced to ensure the sustainable development of solar parks. These include the requirement that the maximum area occupied by modules may not exceed 60 percent of the total area of the project.

Energy policy context and climate targets

The decision to build the solar park in Hilden is part of Germany's ambitious climate goals. A photovoltaic capacity of 215 gigawatts is to be achieved by 2030, with rooftop and ground-mounted systems accounting for half each. This represents a quadrupling of annual capacity expansion from the current level of 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 ahead of the national target. This requires a massive expansion of renewable energy at the local level. Currently, Hilden's existing photovoltaic systems only cover about six percent of the city's electricity needs. The planned solar park would increase this share to approximately ten percent.

Hilden's 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 heating planning and the expansion of other renewable energy sources.

Economic aspects and financing

The lease agreement between the City of Hilden and the municipal utility company has a term of 30 years, with an annual rent of €8,000. This amount will be fixed for the first ten years and then adjusted every five years based on profitability, but may never fall below the original amount.

The economic viability of solar farms has improved significantly in recent years. The levelized cost of electricity for ground-mounted photovoltaic systems has continuously declined, while the efficiency of the modules has increased. Modern solar farms 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 million and €6 million, depending on the specific design and local conditions. The payback period is generally between ten and fifteen years, allowing for significant returns 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 4-megawatt-hour battery storage system. Battery storage is becoming increasingly important in the integration of renewable energies, as it can compensate for fluctuations in electricity production and contribute to grid stability.

Storage technology makes it possible to store excess solar power during peak production periods and feed it back into the grid when needed. This is particularly valuable for providing system services such as frequency control and voltage stabilization. Modern battery storage systems can react to grid fluctuations within milliseconds, making them 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-use of the electricity produced but also helps relieve the load on the transmission grids.

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 administration, the municipal utilities, and external experts examined the project from various perspectives.

Citizen participation can take various forms, from pure information and consultation to financial participation. Models that not only inform the local population but also allow them to benefit economically from the project are particularly promising. These can include energy cooperatives, subordinated loans, or subsidized electricity tariffs.

Experience from other projects shows that financial participation models can significantly increase acceptance. When citizens share in the proceeds, attitudes often shift from skepticism to support. Successful examples can be found in communities such as Tuningen and Maßbach, where local participation models have been implemented.

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Project development and scheduling

The development of a solar park is a complex process that typically takes several years. Hans-Ullrich Schneider, Managing Director of Stadtwerke Hilden, outlined the further schedule: The building permit application is to be submitted in fall 2025, followed by a tender for construction. Contracts and awarding of contracts could be completed in fall 2026, with commissioning planned for the first half of 2027.

This timeframe is typical for solar farm projects. The actual construction period is relatively short, a few weeks to months, but the upstream planning and approval phase takes considerably longer. Project development can be divided into five key phases:

The site search and initial discussions with owners and municipalities typically take about six months. This is followed by the complex planning and approval phase, which can take up to two years for large solar parks. During this time, technical reports are prepared, permits are applied for, and public participation is encouraged.

Site preparation, including access roads and cabling, takes another six months to a year. The actual construction of the facility then takes eight to ten weeks, depending on the size and complexity of the project.

Technical innovation and future trends

Modern solar parks utilize the latest generation of photovoltaic modules and inverters, which are significantly more efficient than 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 the rear side to generate power, are becoming increasingly popular. They can increase yield by 10 to 25 percent, depending on the substrate and mounting arrangement. Tracking systems, which allow the modules to follow the sun's path, can also significantly increase output.

The integration of battery storage into solar farms is a relatively new trend, driven by falling storage costs and improved technologies. Lithium-ion batteries have experienced drastic cost reductions in recent years and now achieve cycle lifespans of over 6,000 full cycles.

Environmental and nature conservation aspects

An important consideration when planning ground-mounted photovoltaic systems is their impact on nature and the environment. Solar Package I therefore introduced minimum nature conservation criteria that must be observed for all systems supported by the Renewable Energy Sources Act (EEG).

This includes the aforementioned maximum area coverage of 60 percent, which ensures sufficient space for the development of vegetation and habitats. In addition, measures to promote biodiversity must be implemented, such as the creation of flower strips or the creation 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. Permeability for smaller animal species is particularly important, and can be ensured through appropriate fencing.

Regional added value and municipal benefits

Solar parks can contribute significantly to regional value creation. In addition to the direct rental income for the landowners, local tradespeople involved in construction and maintenance also benefit. Trade tax revenues flow to the host municipality and can be used for municipal projects.

In addition, municipalities can benefit from the Citizens' Energy Act, which allows operators of renewable energy plants to provide affected municipalities with 0.2 cents per kilowatt-hour fed in. For a solar park the size of Hilden, this would mean annual payments of approximately €10,000 to €20,000.

Challenges and solutions

The development of solar parks is not without 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 combine agriculture and solar power generation.

Another critical issue is grid integration. Many potential locations lack sufficient grid capacity, which can lead to long waiting times and high connection costs. Innovative approaches such as flexible grid connection contracts and local marketing concepts are needed here.

International classification and best practices

Germany is not alone in the development of solar parks. Internationally, there are numerous examples of successful projects and innovative approaches. Large-scale solar parks with citizen participation have been under construction for years in countries such as Spain, France, and the Netherlands.

Particularly interesting are models in which solar parks are developed as part of regional energy systems. This involves not only generating electricity, but also considering heat and mobility. Such integrated approaches can significantly increase efficiency and promote 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 enable them to respond flexibly to grid needs and provide various system services.

Integration into smart grids makes it possible to optimally coordinate power production with consumption and avoid grid congestion. Artificial intelligence and machine learning help improve production forecasts and proactively manage plants.

A resilient energy system with solar park and battery storage

The solar park in Hilden is more than just an energy project – it is a symbol of the transition toward a sustainable energy supply at the municipal level. The city council's decision demonstrates that even difficult projects can be successfully implemented with sufficient citizen participation and transparent communication.

The experiences from Hilden will also be valuable for other municipalities planning similar projects. In particular, the combination of technical innovation, ecological responsibility, and economic participation by citizens could serve as a model for future energy projects.

With its planned commissioning in 2027, Hilden will have taken an important step toward climate neutrality by 2035. The solar park will not only contribute to the local power supply but will 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 this goal isn't always easy, as the months of discussions in Hilden have shown. But the result – a democratically legitimized decision for a sustainable energy future – shows that the effort is worthwhile. Hilden is thus becoming a model for other municipalities that want to take the step into a renewable energy future.

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