Tool around in a Tesla Roadster with the top down, and the sun can be a good friend. Now, Tesla Motors co-founder Elon Musk is finding an even better use for it.

Musk, who's also chairman of home solar-panel installer SolarCity, is joining the technologies of the two companies to create solar-powered rooftop energy-storage systems that would make the two companies eligible to receive rebates from the state of California, GigaOm reports. The systems would combine Tesla's lithium-ion battery packs with SolarCity's photovoltaic systems.

The two companies have filed 70 applications for systems under the California Public Utility Commission's (CPUC) Self-Generation Incentive Program (SGIP) that would supply energy in areas served by Pacific Gas & Electric (PG&E). The CPUC had previously awarded the two companies $1.8 million for their research on the energy-storage system now being proposed.

SolarCity was founded in 2006 and says it has more than 30,000 projects either completed or in the process throughout states such as California, Hawaii, Massachusetts, New York and Texas.