Sonnen Charger, the latest product from Germany’s home battery market leader, is about more than anticipating a customer trend. By matching EV power demand and renewables output, Sonnen wants to address problems at both grid distribution and transmission levels.


Ahead of shipping in April, Sonnen is registering plenty of interest for its new 22kW wall-mounted charger, launched in Germany last month.

Around 10% of Sonnen’s existing customers in Germany already own an electric car. That number is expected to rise fairly briskly, reflecting the wider e-mobility transition, both at home and throughout western Europe.

“There are around 50,000 electric cars being driven in Germany and what we are seeing is many homeowners already installing the necessary cabling to make their homes EV-ready. This reflects the feedback we have been gathering from our customers, where the remaining 90% plan to make their next car purchase electric,” says Mathias Bloch, spokesman for the company.

Bloch also anticipates that the retrofit solar PV market could also be another source of demand for both the charger and Sonnen’s core offering, the Eco energy storage system, which wraps up lithium ion batteries, bidirectional inverter technology, energy management and automation within a single unit.


A new breed of energy supplier

In the fast growing global residential battery storage market Sonnen’s investment in self-learning software and digitalisation technologies has elevated the firm beyond simply being a hardware provider. As solar subsidies wane, in markets where energy prices for residential consumers are very high, or are continuing to rise, it now makes sense for households to install a battery with solar PV to increase self-consumption.

Sonnen initially launched its home energy storage system in 2011. In late 2015 the company expanded into the business of energy retail, via its Sonnen Community peer-to-peer energy trading market based on a proprietary virtual power plant (VPP) platform.

Those signed up as members, who consist mainly of homeowners with a solar PV system and a Sonnen battery installation, can pool, trade and share surplus electricity online with other members. By largely bypassing the wholesale power market, the cost of electricity the members buy from the Sonnen Community marketplace is often cheaper than the tariffs traditional energy companies are able to offer.

Providing services in combination with a robust, simple to operate, albeit premium priced, energy storage system has helped Sonnen become the largest supplier of these types of appliances in Germany. Various market studies attribute Sonnen’s share of its home market to be somewhere between 22-25%.

Germany remains Europe’s largest residential battery market, dwarfing all other EU markets combined, including Italy, the UK, France, Norway and Sweden.

The cumulative installed capacity of home storage systems in Germany stands at well over 60,000, which would suggest that there are at least 12,000 Sonnen batteries installed across the country.

If each system comprises an average of 4-5kWh, that’s tens of megawatts of pooled electricity that can be traded and marketed among the residential energy customers that have joined the Sonnen Community platform.

Extending its virtual power plant functionality further, in 2017 Sonnen launched its Sonnen Flat service for its Sonnen Community members.

In return for surrendering control of a small portion of their battery’s capacity to provide grid balancing services, those signed up to Sonnen Flat pay nothing for additional electricity they need that cannot be provided by their solar-plus-battery system. The proviso is their demand does not go over an agreed limit based on which tariff they opt for, which cap at 4250kWh, 5500kWh, or 6750kWh.

The charger rounds out Sonnen’s offering. “We already have a battery pool and now EVs can be connected into this as well,” says Bloch.

An app makes it easy to manage EV charging at home (Courtesy Sonnen)

Sonnen’s approach has always been about integration, sourcing lithium ion batteries and bidirectional inverters from third party suppliers, while assembling and testing these to work together within its Eco battery product, all controlled by the company’s own energy management software. A third party firm makes the charger hardware while Sonnen has developed the software controls.

Avoiding peaks on the low voltage network

The wall-mounted smart charger allows owners of EVs that also have solar PV installed to use solar power, or energy stored in their battery system, to ‘refuel’ their cars at home.

The charger is either optimised for speed, or it maximises the amount of self-generated solar energy directed into topping up the car’s battery. These settings can be controlled using an app.

If a member from the Sonnen Community does not have enough battery-stored solar energy to charge their EV they can use energy available via the VPP to cover the shortfall.

Owners of EVs that install the charger can also benefit from a special Sonnen Flat tariff that provides households with up to 8000kWh of free electricity a year. Based on an estimated consumption of 5000kWh, the household has the remaining 3000kWh for their electric car. This corresponds to a driving distance of 15,000-17,000km.

By integrating with the Sonnen battery the charger enables peak shaving. Rather than draw electricity from the grid at peak time the car tops up with electricity from the battery.

Even without a battery the smart charging capability relieves pressure on local grids by time shifting when the EV tops up to avoid several cars on the same feeder all drawing power from the grid at the same time.

Easing transmission bottlenecks

Integrating smart charging into Sonnen’s virtual power plant platform allows EVs to optimise use of renewable energy within grids and could help relieve transmission-based bottlenecks that are commonplace in Germany’s power grid.

When there is an oversupply of wind power, wind farm owners are paid to curtail generation by switching off turbines.

In 2016, the cost of curtailment and other measures to alleviate grid bottlenecks ran to €800 million in Germany, which is paid for by electricity consumers through grid charges. Besides building more high voltage cables to expand the transmission portion of the grid, creating more flexible capacity to absorb surplus generation limits costly curtailment.

A few hundred Sonnen battery systems in Germany are participating in a breakthrough pilot run by transmission system operator (TSO) Tennet. Via blockchain technology the home energy storage systems are being integrated into Tennet’s grid. The pilot ends in mid-2018.

Curtailment has been Germany’s approach to date to overcome the effect of too much wind in the transmission system

The networked fleet of batteries are controlled to absorb or discharge excess power in a matter of seconds based on location and time-specific requirements of Tennet.

To do so requires layers of software and digitalisation technologies, combining Sonnen’s own VPP software, with blockchain technology, developed by IBM. In the pilot Blockchain technology is being used to create a transparent virtual environment for distributed energy resources, like home energy storage systems, to participate in providing grid services.

If this and other pilots are successful, Tennet will no longer need to rely on curtailment or firing up large power stations to balance supply
and demand, reducing costs.

Smart charging is seen as crucial to managing the challenge of more EVs plugging into the low voltage distribution network. Studies show that while EV owners tend to plug in their cars at home overnight, the cars only draw electricity from the grid for just a few hours to in order to top up. This behaviour provides a window for charging periods to be moved around without coming into conflict with most owners’ car use.

It becomes easy to see how the project between Sonnen and Tennet might also pave the way for a future where EVs connected to the grid, via smart chargers, are called upon by TSOs to absorb fluctuations in supply-demand at the transmission system level, topping up with clean energy that would otherwise be wasted.


Other markets

Sonnen’s charger is only available in Germany, for now. Bloch agrees that changes to regulations in markets such as the UK where a new law proposed could make it mandatory for home charge points to enable charging management will act as drivers for smart chargers. In places like the UK, other energy storage system providers are only starting to integrate third party home charger products with their technology.

As Germany is much further ahead in terms of installed battery units, the market is instructive of how others might also evolve. Australia may not be far behind. The combination of many sunshine hours, high energy prices and an unstable grid are creating perfect storm conditions that have triggered demand for home storage systems in some states. In a recent deal with the South Australia government Sonnen is supplying 50,000 of its Eco batteries down under over the next five years.

In other markets closer to Germany, the EV transition could in turn drive demand for energy storage. For example, in the UK, which in some respects is a big car market crowded onto a relatively small island, a percentage of EV owners will want to use clean energy to provide electricity for their car so may consider a solar-plus-storage investment.

Norway is already exhibiting the side effects of what rapid EV take-up is doing to distribution networks. Owners in regions where local networks are at capacity face paying thousands of euros in grid connection fees to install a home charger. A battery presents a cost-effective alternative.

In these new markets, once Sonnen has enough batteries installed it will be able to roll out its Sonnen Community VPP platform and services enabled by it. In the UK, in addition to selling its Eco battery to private home owners, Sonnen is also supplying the unit to social housing landlords, which include local councils, in Scotland, Wales and London.

The systems installed in properties, with solar PV, reduce energy bills for tenants and give them more visability over their consumption. In future, as more systems are installed they can be networked into the VPP that can be connected to the electricity balancing market, helping to keep it stable at times of high levels of wind or solar generation. Income earned can be made available to social housing landlords, as well as their tenants, in the form of cheaper or free electricity.

As older power stations are mothballed and more intermittent renewable generation is added, for stressed grids, EVs threaten to be the last straw to break the camel’s back, because their load corresponds with peak demand. Smart charging turns this burden into much needed flexible capacity, enabled by self-learning software and digitalisation technologies, like VPP platforms and Blockchain.

Sonnen represents just one approach that’s out there. But the company knows success depends on offering a compelling alternative to customers, not just batteries, or chargers, but a whole service that guarantees cheaper, cleaner energy, whilst creating flexible capacity that can be manipulated at the click of a mouse to address problems facing grid and distribution system operators.