Sonnen to provide primary balancing power to German grid from networked home storage

Transmission system operator TenneT has prequalified sonnen and its technology partner Tiko Energy Solutions to participate in Germany’s primary balancing power market.

This will be achieved by combining its country-wide network of residential battery systems into a large virtual storage unit. Among other services, it will help compensate for fluctuations in the power grid, says sonnen in a statement released.

Sonnen has long been working towards obtaining approval, Jean-Baptiste Cornefert, managing director of Sonnen E-Services tells pv magazine, with many employees traveling throughout Germany to negotiate with the distribution network operators. Now the deal has been upon and validated with all four transmission system operators in Germany, he says.

While the company eventually aims to combine all of the around 30,000 solar batteries it has installed in Germany into its virtual storage unit, it has initially been prequalified to deliver 1 MW, which can be used for primary control energy.

“The sonnen virtual battery takes a unique approach. It consists of thousands of individual energy storage systems installed across the entire country, each of which can be used to manage energy consumption for individual households,” said the company in a statement released.

It continues, “In addition, when fluctuations arise in the power grid, these batteries independently arrange themselves into a large-scale virtual battery. Since each sonnenBatterie has a different state of charge the large number of individual batteries will be aggregated into blocks starting at 1 MW, which are then made available to the energy market.”

TenneT's certification process required sonnen to discharge 1 MW of power to the grid and then recharge that amount back again within 30 seconds.

“… we are showing that our customers in Germany can assume all of the functions that were previously reserved for large power stations. They can create and store energy and also ensure the security of supply within the power grid. The shift from the old energy system with central power stations to a new distributed system with the people at its core, is finally coming about as a result,” said Cornefert.

The prequalification from TenneT was also important to sonnen with regards to its flat offer to customers. Indeed, homeowners who participate in this community, providing their home storage for network services, will receive free electricity in return.

“We're giving away around 30 percent of the remaining electricity when the owners provide their spare capacity,” says Cornefert. Sonnen can now also generate additional income from the pre-qualification on the primary regulation energy market.

However, Cornefert emphasizes that, in contrast to large storage facilities that would be used for primary or secondary control, home storage systems are installed primarily with a view to optimizing the self-consumption of PV. The revenues from the primary control market, therefore, are additional for the operators.

With a view to the not so distant future, sonnen wants to increase the performance of its home storage network for the provision of the grid service from 1 to 100 MW. Cornefert did not say when that would likely happen, however. “Certification by TenneT has certainly been the hardest part, especially considering the administrative overhead,” he says, adding that scaling the model is less complex.

Overall, sonnen has around 30,000 battery systems in Europe, each with a capacity between 5 to 15 kWh. “The total network has a capacity of up to 300 MWh and the potential to supply around 120,000 households with electricity for one hour,” continued the statement.