SolarCity—a company that’s grown quickly by installing solar panels for free and charging customers for the solar power—announced a new business that will extend that model to providing batteries for free, too. SolarCity is a rare success story for investors in clean technology, and its business model has sped the adoption of solar panels.

The batteries could help businesses lower their utility bills by reducing the amount of power they draw from the grid. They could also help address solar power’s intermittency, which could prevent it from becoming a significant source of electricity. The batteries are being supplied by Tesla Motors, whose CEO, Elon Musk, is SolarCity’s chairman.

Other solar companies have failed in recent years. But SolarCity’s business model has helped it grow quickly. It had a successful IPO a year ago, and its stock price has risen from its IPO price of $8 to over $50 today.

CEO Lyndon Rive says that eight years from now, the company might not be able to continue selling solar panel systems unless it packages them with batteries, because of the strain on the grid that solar power can cause. “It could be that, without storage, you won’t be able to connect solar systems to the grid,” he says.