Interview with ECO STOR about the battery storage facility in Bollingstedt/Gammellund

Morning Mr Niewierra, you put a large battery storage facility into operation in the municipality of Bollingstedt in the district of Gammelund in northern Schleswig-Holstein back in May. Can you tell us a bit about the technical data and mode of operation?

"It is a standard storage facility covering 1.2 hectares and comprising two container blocks with an output of 103.5 MW and a capacity of 238 MWh. The containers are arranged in two rows with 64 containers containing the batteries and another 32 containers with converters and other technology. Its module-in-module design enables the replacement of individual battery elements in blocks without having to switch the entire container. We see this model as a blueprint for additional projects. Not far from the site, we are constructing an identical storage facility in Schuby. This year we also started construction on a project three times the size in Förderstedt, which will have an output of 300 MW and a capacity of 714 MWh. "

How many charging cycles are slated per year?

"We run up to two complete cycles a day, with feed-ins and feed-outs usually happening early in the morning and in the evening, so up to approx. 730 cycles a year. "

What can you tell us about the battery cells and their chemistry? Is second life a relevant factor?

"The lithium-ion batteries at the Bollingstedt site were sourced from the manufacturer BYD. In total, 212,992 battery cells are installed there in 512 battery cabinets, pooled into groups of eight in 64 battery stations. Viewed individually, second-life batteries are certainly safe and reliable. However – as I outlined above – large storage facilities require thousands of cells to work together, and they need to be as identical as possible. Even minor variance in the age status or performance can lead to efficiency losses or failures. This means that the necessary uniformity is lacking, as used batteries are very different and their remaining service life is difficult to predict. That is why we do not use second-life batteries in major battery storage facilities."

What about the efficiency and service life of the cells?

"We are clocking efficiency at 90 percent. Given the load profile I mentioned earlier, we anticipate that the cells will last ten to 15 years in total. We would consider replacement when the residual capacity dips below 70 percent. To assess the status, we operate a variety of sensors for tight monitoring.

Which aspects need to be considered when creating a battery storage facility?

As a rule, installing a storage system is generally hinges on the availability of a grid connection. This is provided by Schleswig-Holstein Netz at Bollingstedt. Aside from this factor, selecting the ideal site is naturally relevant as well. It was not an issue with this project, although the site’s topographical attributes can always play a role, for example if you have to overcome elevation differences on slopes. But even after a suitable site has been identified and the formal measures such as obtaining the land and applications, as well as approval for the grid connection contract have been completed, there are a still a number of things to do before we can start with the actual construction.

These include various preliminary investigations, as well as studies relating to animal welfare, environmental protection and immission control for all infrastructure projects. We erected a six-meter noise wall in Bollingstedt. A low hum would be an apt description of the background noise inside the facility – at a volume comparable to road traffic. But it is actually louder in the environs outside the complex.  

Overall, it should be emphasised that we are talking about an important part of the supply infrastructure. This entails significant responsibility, which we seek to fulfil with the greatest possible care, expertise and our long-standing know-how. Projects in this magnitude depend on smooth interaction between a large number of stakeholders – service providers and partners in the planning, construction and also in the operation and marketing of the facility.

Broadly speaking, storage sites face the challenge that some grid operators may not be prepared for the requirements of energy storage systems, even despite their ability to stabilise the grid. They then demand that we take action to slow down the output of the storage systems, for instance using time delays – known as ramps – when the storage system is started up or the electricity is fed into the grid.

Specifically which stakeholders need to be involved? Where do you normally encounter resistance?

"That really depends on the balance of political power in the region. The geographical situation on the ground also plays a role in that current wind farms, for example, can boost acceptance due to the prior experience with renewable energies. At least if they are well received and a benefit to the local population. Since 2025, municipalities have also benefited financially from battery storage facilities, as 90 percent of the business taxes payable for these systems are transferred directly to the municipalities where they are located. It is worth noting that we played a leading role in endorsing the necessary legislative amendment. Apart from this, we also need to address safety concerns in direct dialogue with the local communities."

Can you describe the process of applying for grid connection?

"The starting situation in Bollingstedt was actually favourable. Schleswig-Holstein-Netz, the grid operator, was generally interested in connecting grid-serving storage systems so that the renewables in the grid – such as wind farms and solar plants – would not have to be shut down and that the electricity they generate could be temporarily stored at the site. But you cannot take this kind of progressive openness for granted. Irrespective, though, the procedures involved are really quite intricate, starting with the application and various subsequent checks through to the planning and technical clarification of aspects such as routes, transfer stations and controllability etc."

How do the projects usually come into being? Can you describe the legwork?

"We do our own scouting for good locations close to substations. Naturally, adequate connection capacity needs to be available as well. In some cases, however, municipalities, project developers or individual companies approach us with enquiries, which we check and evaluate according to strict criteria."

How much waste heat do the batteries generate? Could the neighbouring municipality even put this waste heat to use?

"It can make perfect sense to consider these options from a sustainability and holistic perspective. But it is not yet feasible in practice if the storage facilities are located at a distance from built-up areas. There we are simply lacking the consumers or infrastructures to accept the heat. Transport over long distances would not be economical. What’s more, the waste heat tends to be generated in a low temperature range, which places additional limits on its use. Although this aspect will remain interesting moving forward, we are currently unable to put it to good use."

The groundbreaking ceremony took place when the CDU, SPD and Green Party coalition was still in power. How is your business now faring in the new legislative period?

"We are currently dealing with an open market that is not yet regulated, one that will continue to grow and evolve. There is no doubt as to its necessity, as we are currently dealing with a storage shortfall that is placing a burden on our electricity infrastructure. This leads to some turbulence in the system, which is manifested in severe price fluctuations and a market that often suffers from overheating. As a ballpark figure, we will need around 500 of these ‘Bollingstedt’ facilities in future. So it is absolutely imperative to introduce new regulations that are designed to ensure that all stakeholders can generate reasonable revenues. In our view, this should not be about maximising individual profits and focus instead on achieving a sustainable livelihood in the interests of the common good. Unfortunately, we believe that the Ministry of Economic Affairs and Energy drew the wrong conclusions in its interpretation of the Monitoring Report, which cannot be justified from a technical and market perspective. We will continue to campaign actively for regulations that will pave the way into a bright future based on technical, market and sustainability needs."

What is your opinion on different electricity price zones (North/South)?

"Generally speaking, regional price signals should be welcomed. They visualise bottlenecks and oversupply in the electricity grid and also indicate where flexibility is particularly needed. Proceeding in this way creates targeted incentives for storage facilities and flexible consumers to align their behaviour according to actual demand. Without these signals, flexibility would be deployed with less coordination and effectiveness. Accordingly, regional price signals are a mainstay and basic requirement for a functioning flexibility market, as highlighted in the Study on Grid Serviceability by the analyst firm NEON.

Furthermore, I would also point to our position paper The 7 BRIDGES TO THE FUTURE OF STORAGE, which we would like to build between the current electricity market and the emerging storage market. We use this paper to make offers, but also to propose our own compromises in the interests of the common good, for example by using the grid-friendly ramps during feed-in."

Outlook: Do energy storage facilities embody the future here in the north, or will they be built predominantly in the south of Germany in the long term (assuming the power lines are built)? Would it not be more sensible to build the storage facilities where the electricity is actually needed?

"Storage systems are most beneficial when they are located close to consumers, as they contribute directly to grid stability and avoid transmission losses. However, storage facilities can also be useful in places where a particularly large amount of renewable electricity is generated that would otherwise have to be curtailed. So the location actually depends on the specific goal: security of supply, integration of renewable energies or relief from intermittent grid bottlenecks. Economic factors such as available space, grid connections and regional price signals are also significant factors. Given the overall need for considerably more storage facilities, every new one should be viewed as an important contribution to the success and irreversible establishment of the energy transition. Therefore, the best-case scenario would be to ensure equal distribution of storage facilities across the entire country."

Thank you very much!