Residential solar developer Sunrun Inc. is rolling out its "BrightBox" battery storage system in California after sales in Hawaii exceeded internal projections, a spokeswoman said on Dec. 14.

The move comes as California utility customers shift to time-of-use rates, which are based on electricity supply and demand and will likely make power more expensive late in the day when solar systems drop offline. Customers with solar-plus-storage systems can save some of the electricity they generate at midday for use later when prices rise.

"I think what we're just excited about is, finally, for the first time, we have quality product at a low cost being manufactured at scale by a number of companies who are all rapidly growing their manufacturing capability and rapidly increasing their energy density and rapidly lowering their costs," Sunrun Chairman Edward Fenster said of the battery storage market on an earnings call in November. "So the overall picture there is just awesome, and we're very excited to see where it's going to go in 2017."

Sunrun introduced the BrightBox product in Hawaii after the state's Public Utilities Commission ordered the elimination of net energy metering for new solar customers of Hawaiian Electric Industries Inc. utilities. That has left new solar customers to depend on PUC-approved credits for excess power they send to the grid or a self-supply program that relies heavily on energy storage.

The changes were a blow to the state's solar industry. "We're just not seeing the economics there pencil" for the self-supply program, Enphase Energy senior business analyst Katherine Hsia-Kiung said in an interview in November.

Sunrun and its partners have sold more than 500 BrightBox systems in Hawaii in the past three months, according to the company.