Household battery energy becomes tradeable

German household-scale battery maker Sonnenbatterie will soon enable buyers of its systems to trade energy with each other over the grid. It'll save clients money, and it's another step toward a clean energy future.

Deutsche Welle, 26 Nov 2015

Solar PV systems on houses in Germany

On Wednesday in Berlin, Sonnenbatterie co-founder and CEO Christoph Ostermann presented "SonnenCommunity," a way for buyers of the company's household-scale electricity storage batteries - most of whom also have solar photovoltaic panels mounted on their rooftops - to automatically buy and sell energy from each other directly through a shared online platform.

Launching in January, the platform will allow members who have more stored power than they need on a given day to sell electricity to others who are short of electricity.

Sonnenbatterie's wall-mounted batteries, which the company calls "Sonnen" units - Sonnen is the German word for "suns" - are similar to the "PowerWall" batteries presented this summer by California-based Tesla, which the car- and battery-maker plans to start selling in Germany in early 2016.

However, Sonnenbatterie claims its Sonnen system is better than Tesla's Powerwall system.

Sonnenbatterie's wall-mounted household-
scale unit combines energy storage,
regulator and smart-grid connectivity in
a single rather elegant package

Friendly rivalry

"Tesla's technology is nothing special," said Mathias Bloch, Sonnenbatterie's public relations officer. "Its Powerwall unit is just a battery module, so it's only one component of an energy storage system."

Sonnenbatterie's Sonnen unit, in contrast, includes the battery module, a power regulator, and the software allowing the system to buy and sell power from other SonnenCommunity members over the electricity grid, all integrated into a single package, making it very easy for installers and clients to work with, Bloch said.

Both Sonnen and Powerwall battery modules are based on the same kinds of batteries used in mobile phones, with Tesla using a grid composed of hundreds of small Panasonic batteries in each Powerwall unit, linked into a tightly packed grid, and Sonnenbatterie using Sony batteries.

"Sonnenbatteries's Sonnen units still retain 70% of their charging capacity after 10,000 charge-discharge cycles," Ostermann said, suggesting this was superior to the performance expected of Tesla's Powerwall units.

Sonnenbatterie's wall-mounted
Sonnen power storage unit comes
in white as well

Money talks

Sonnen buyers who join SonnenCommunity will directly benefit in financial terms, the company said. For one thing, new Sonnen unit buyers will get a discount of 1,875 euros off the retail price of the battery, in exchange for having to pay a 20 euro per month members' fee.

Members will also get 1,000 kWh of free electricity per year - power SonnenCommunity will acquire from grid operators at times when excess solar or wind power, due to bright sunshine or strong winds, is flooding Germany's wholesale electricity market to such an extent that the spot price of electricity goes to zero. That's an increasingly frequent event in a country where 30 percent of total electricity produced in 2015 was renewable electricity - much of that from wind and solar power.

Buying and selling

Under German law, the electricity grid operator must buy any solar power offered to it by anyone in the country, and pay a regulated "feed-in tariff" that sets a firm price for solar power sold over a 20-year contract period starting when the solar panels are first installed and connected to the grid. At the moment, the grid operator must pay about 11 cents per kWh for new solar power installations.

SonnenCommunity members who instead sell power to other members will get 0.25 euro cents more per kWh than they would get from the grid operator for solar-generated electricity.

A much more significant benefit will accrue to members of SonnenCommunity who are short power on a given day. They'll pay a flat rate of 23 euro cents per kWh to buy electrictiy from other members of the Community, a much lower rate than the roughly 32 euro cents flat rate they pay to grid operators for electricity.

Solar PV Panels on the Roof of an Ikea
 store in Rothenburg, Germany. Eventually,
solar PV fields and wind farms will be
 combined with interconnected smart
energy storage systems to form
microgrids

Ostermann mentioned some other benefits for SonnenBatterie battery owners associated with becoming members of SonnenCommunity, but the price advantage for electricity buyers seemed to be the strongest benefit.

More developments to come

Electricity markets are heavily regulated - they have to be, since the electricity system is fundamental to the functioning of modern civilization and the government has to ensure systems are reliable, resilient and affordable, even under extreme loads or weather conditions.

For that reason, the details of regulations affect business models heavily, and there's a reciprocal relationship between new technologies driving evolution in regulations, and new regulations driving technological evolution.

For example, Germany's legally mandated generous 20-year flat-rate contracts for electricity produced using solar or wind power generation, or "feed-in tariffs" (FiTs), first introduced in the year 2000, caused a huge boom in solar and wind power.

That in turn drove rapid technical evolution. Wind and solar power generation units today are dramatically cheaper, more reliable and more efficient than they were 15 years ago as a direct result of Germany's FiT law of 2000.

Sonnenbatterie's Sonnen unit has a
 competitor from California, also wall-
mounted: the Tesla Energy Powerwall

Household energy storage is the next frontier

As energy storage units like those of Sonnenbatterie have come onto the market, they've begun to change the financial incentives consumers face. At some point, when all costs are taken into account and "levelized" on a price per kWh basis, it will probably become cheaper for most owners of single-family households to buy something like a Sonnen unit or a Powerwall unit, plus some solar rooftop panels, rather than buy power from the grid. SonnenCommunity helps move things in that direction.

The marketplace for household-scale energy storage systems is still in its early stage. Sonnenbatterie has sold 8,500 Sonnen units so far - out of a total of 25,000 household-scale battery packs that have been sold in Germany to date. It's the market leader in a small market.

But with solar and wind power generation unit prices continuing to drop year-on-year, and regulations continuing to evolve, the market for household-scale energy storage units is sure to grow.

Sonnenbatterie sales and marketing chief Philipp Schröder, who left his position as head of Tesla Germany to join Sonnenbatterie, told DW he expects new business cases to emerge - for microgrids, for example. "The renewable energy business promises to stay exciting for years to come," he said.

Elon Musk, the chief executive of Tesla Motors, announces the company’s
entry into the energy market

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