For renewables to work, they need batteries—otherwise, the lights go out when the sun goes down or the wind isn’t blowing. Companies like Tesla and Hyundai are addressing the problem by developing football-field-size lithium-ion batteries in Australia and South Korea.

These massive batteries, however, are expensive.

“There’s a cost floor to lithium-ion, which is dictated by the components that are used,” says William Woodford, the chief technology officer of Form Energy. “No matter how cheaply you put it together, you still have a certain set of active ingredients, and those have costs.” So while Elon Musk can build bigger, cheaper batteries, there’s a limit to how cheap they’ll ever get. Lithium carbonate, for example, can cost as much as $20,000 a ton.

To address this problem, Woodford has identified metal-sulfur chemistries that could beat lithium-ion technologies for long-term storage and cost. As a bonus, sulfur is cheap and abundant: it often goes unused as a waste product of oil and gas production.

—Dan Solomon