On a hot, flat, empty stretch of desert in Lancaster, California, a company is trying to solve two of renewable energy’s biggest problems at once.

Problem one: The dearth of clean energy sources in the evening, when the demand for that energy is at its highest.

Problem two: Electric vehicle batteries contain a lot of precious metals that need to be extracted from the Earth — a very energy-intensive process. But as they get older, the battery’s mileage range drops, and they may be replaced. In other cases, drivers get new cars long before the batteries stop working completely.

B2U Storage Solutions is using the excess supply of used batteries to meet the high demand for stored clean energy. “It’s pretty simple: Take it out of the car, put it in, cable it up, and it’s ready to go,” says Rachel Harper, B2U’s operations project manager. 

There are dozens of trailers in the area that hold old EV batteries stacked on top of each other. Each battery still has 60% to 70% of its original charge capacity. They sit right next to countless rows of solar panels, soaking in the harsh, unmitigated desert sun. The used car batteries — 1,300 of them in total — are hooked up to wires, using the juice they have left to store energy that the solar panels generate during the day.

The idea is the company can sell solar power back to the grid in the evening, when Californians need it most.

“This is exactly the type of market-based solutions that we’re looking for,” said manager Yamen Nanne of the Los Angeles Department of Water and Power.

An EV driver might decide to replace their battery once their car can’t drive as far as it used to. That’s happening more every year, and Nanne sees the potential.

“As more and more EV batteries become available to the secondary market, I think we’re gonna see more and more of this,” he said.

The project makes money for B2U Storage Solutions because solar energy that gets stored is more profitable, and L.A. is willing to pay the price to meet its ambitious renewable energy goals.

“That, of course, then would lead to much higher prices in periods when the sun is not shining, but where the demand for power is still high,” said B2U co-founder Freeman Hall.

B2U gets old batteries from automakers like Nissan and Honda that might have been replaced by warranty or that were in old leased cars. The batteries get a second life storing solar power for five or six years. Once they’re completely dead, they get recycled.

But there aren’t a lot of solar farms storing energy like this. It hasn’t happened at scale, and that’s partly because there aren’t that many old EV batteries out there. A decade ago, carmakers sold just tens of thousands of EVs annually.

“Now we’re selling over 2 million EVs a year, and that is a number that’s rising rapidly, of course,” Hall said.

Some energy researchers think it’s a great idea too, including Antoni Tong, who used to test battery technology for the Department of Energy and the California Energy Commission. He said it’s far better than other storage options, including the most common technology today: hydroelectric.

“Hydro doesn’t really meet the requirement because … the controllability of this is very limited. The capability of building new sites for environmental reasons are also very limited nowadays,” Tong said.

Tong was so convinced by his research and testing that he’s founded a company that specializes in using old batteries for energy storage, just like B2U.

“The be-all-end-all option for storage today is the lithium-ion batteries,” he said.

Lithium-ion batteries power electric vehicles. And since they’re so expensive and the metals inside are difficult to mine, it’s cheaper and more environmentally conscious to use batteries that have already been produced.