The vanguard of decentralized energy for sonnen

Eight years ago, Christoph Ostermann and Torsten Stiefenhofer noticed the need for a market for energy storage systems, and sonnen was born. Communications spokesperson Mathias Bloch spoke to Decentralized Energy about the evolution of the company over the past decade and its ambition to be a hub of decentralised energy technologies into the future.

The straplines on the sonnen website reveal much about the benefits of the company’s products and services ” ‘It’s time to declare your independence ” sonnenBatterie’ and ‘A clean, fair and affordable energy supply for all is finally here’ indicating its main calling cards ” cheaper energy and more consumer control of that energy.

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  • The company has its roots in the realisation that while many people in Germany possessed residential rooftop solar photovltaic (PV) systems at the turn of the decade, it was universally being fed into the grid with no capability for self-consumption.

    “This new approach with the offer of self-consumption was the first step,” says Bloch. “In 2011 the first sonnen battery was introduced- it was a fully integrated storage battery system that stored the energy from day time that couldn’t be used at the time for later use at evening and night. People were then able to cover their energy needs 70 to 80 per cent per year by clean self-produced energy.”

    The sonnen battery is now firmly established as a leading storage system, with smart home functionality controlling self-consumption in the household. It’s grid-friendly and, crucially, has smart charging attributes that allow it charge at a time when grids are under high stress, relieving the grid by being an active component of the energy infrastructure.


    The emergence of digital technologies has increased that functionality since 2015.

    “All sonnen batteries are online so we can see production, consumption, storage and other factors in real time. We found out, among our customers, there are people who always produce excess energy and similarly people who are always in need of energy, so we though it would be good to connect those two so they could equalise their different energy levels or their own and not have to rely on a conventional energy supplier any more ” it’s the basic idea behind the sonnen community.”

    The sonnen community is an online virtual power platform, which facilitates connection of households that produce and share energy to do so with other members. True to the purest sense of decentralized energy, it dispenses with the need for a conventional energy provider altogether.

    Because of regulatory reasons individuals cannot trade energy directly between each other, but the platform makes the transactional process entirely legal.

    “Members get a certain amount of money for the electricity they put into the community. It’s around the same amount of money they would get for their normal feed-in tariff (FIT) and even a bit more, but the energy they get from the sonnen community- that’s free energy.”

    Participants sign up to membership by paying the ‘sonnen flat’, a flat fee for electricity, with a current price of EUR19.99 a month, after which all member energy is free from the community.


    The Bavarian firm has a diverse business, which now includes playing a part in managing the massive influx of renewables on the national grid.

    “The complex technology involved allows us to connect digitally the storage systems of our customers to form a large battery pool that can equalise fluctuations in the power grid, balancing power,” says Bloch.

    “For example, the German grid has a frequency of 50 Hz, but is always a bit under or over that. If it’s too far either way the grid operators must do something to bring the frequency back towards the 50 Hz mark and ca use our battery pool for the purpose. If there is too much energy they can store it in the battery pool and if there is too little they can take it out of the storage system. It is only for a few minutes normally and doesn’t impact the customer much because the energy amounts from each storage system are not high.”

    For this grid service, sonnen receives money from the grid operators, amounting to another revenue stream or channel for re financing the company’s batteries and services. Community customers also profit because they offer their storage to the grid operators and receive energy for free in exchange.

    The biggest revenue for the company continues to be its home battery storage system, which along with sonnen community services and service to grid operators makes for a strong, diverse business.

    “It’s a sustainable concept because we are not dependent on only one from a market that is developing very fast, where you see a lot of competition and price decline. In the future we have to continue to distinguish ourselves and provide new services and possibilities to profit from the energy market. With our battery pool, we opened a revenue stream for the energy market, that hadnt’t been a possibility for residential customers before.”

    In addition the sonnen community is tailored, offering tariffs for all kinds of users, whether PV owners, or people without either PV or storage systems.

    The company is also operating communities in Australia, Austria, Italy as well as Germany. A new sonnen community in Arizona is to see 3,000 newbuild houses complete with PV and storage installations. That community will can offer services to local utilities, such as battery storage for load shifting purposes.

    As it stands, sonnen’s customers are producing enough power to supply 100,000 people worldwide. With digitalization a relatively new addition it looks like a model replicable around the world particularly in the most energy deprived regions.

    “The sonnen community is a blue print for the decentralised energy system because many small producing and consuming elements are involved with all you need in terms of components ” in terms of production storage, smart metering and digital platform to manage all the energy and keep it in balance.”

    “It is of course interesting for countries that haven’t built up a big central energy system such as in Africa.”


    sonnen is self-sufficient and doesn’t require subsidies to make it a viable tool in continuing to enable Germany’s Energiewende. Grid balancing, and managing the enormous extent of distributed and renewable energy on the German grid is a top priority at the moment and Bloch says structural clarity is the company management’s main concern, in fulfilling that role and others into the future.

    “The Energiewende has been ongoing since 2000, but it has been a hardware and analogue Energiewende up until today. What we are doing is adding software and intelligence and creating a digital Energiewende.”

    “There is no doubt that the energy future will be decentralized and connected and that should be of interest to any government that wants a clean and sustainable energy infrastructure. What we need a is a stable political frame, especially regulation, that makes it easy to establish that decentralised energy system.”

    The company has drawn the attention of some strong operators keen to engage with sonnen’s offerings. Among current investors are GE Ventures and China’s Envision Energy, the world’s third largest wind turbine maker. Last month European trailblazer Engie combined with sonnen to offer customers in France residential battery storage installations under the residential ‘My Power’ solar solution it launched last year.

    For now sonnen is happy to remain independent, and retain its own voice, within the growing milieu in the decentralized energy space.

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