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.

Tesla executives were unwilling to publicly put figures on expected sales for the company’s stationary storage products or for near-term cost reduction objectives, but said that production is on track.

Tesla boss Elon Musk has claimed that his company is already sold out of stationary storage products for next year before the first ones have even been shipped to customers.