German lithium-ion based energy storage system maker Sonnen says it achieved an undisclosed “seven-figure sales number” in the US in the first quarter of this year.

Sonnen said it sold 2,600 units of its SonnenBatterie energy storage systems worldwide, an increase of more than 100% over the previous quarter. The privately-listed company was coy about revealing specifics of the figures, but said the US is now its second-largest market outside Germany, with over 50 retailers signing up as partners to sell the products.

The US commercial space was the first segment of that country’s market Sonnen launched into in mid-2015. At that time, it had sold around 8,000 units in Germany, making it something of a market leader. Sonnen has now launched its residential products in the US as well after racing Tesla into that segment and launching just before Christmas 2015.

While a lot has been made of the rivalry with Tesla, including the fact that some senior employees have moved from one company to the other, Sonnen’s US chief Boris von Bormann told Energy-Storage.News at the time of the US launch that the company was pleased the EV maker’s stationary storage announcements had put pressure on Sonnen’s battery vendors to compete more aggressively on price.

In late November, the company launched SonnenCommunity in its homeland, a peer-to-peer energy trading concept where PV-plus-storage owners trade their surplus energy with one another. Sonnen has also launched distribution channels in Italy and the UK in recent months.

"Our sales figures show that global customer demand for energy storage is real. We began shipping product at the end of 2015 and have seen demand growing at a steady pace in the first quarter of 2016. We have over 54 sonnenBatterie partners selling our energy storage products to residential and commercial customers across the country and we are just getting started,” Boris von Bormann said of the latest financial announcement.