Rachel Harper used to work in the oil and gas industry in Texas and never thought she'd be working next to solar panels all day.

"It's a much more peaceful environment," Harper said. "I like this way better."

She's now at a startup in California called B2U that takes the still-usable batteries out of older electric vehicles, slides them into large racks and then plugs them into solar panels so they can store solar power.

"We're basically a retirement home for these EV batteries," Harper said.

Battery storage allows renewable energy to provide power even when the sun isn't shining or the wind isn't blowing. It's key to making the electrical grid reliable as the U.S. transitions away from coal and gas and their planet-warming emissions. Batteries also help keep the lights on when heat waves put a strain on the power grids.

As director of energy storage and systems at the University of California, San Diego, Mike Ferry is at the forefront of the next generation of battery technology.

He says batteries are getting better and costs are dropping. That has allowed California to install more than 10,000 megawatts of battery storage, which is equivalent to the output of about five nuclear power plants, according to the U.S. Energy Information Administration.

California and Texas account for 85% of the battery storage in the nation, according to Ferry. The two states combined have more than any other country except China, which has 31,400 megawatts of battery storage, according to the China National Energy Administration.

"This year, 81% of all new capacity on our national grid is going to be solar and storage. And these two technologies go hand in hand, sort of like chocolate and peanut butter," Ferry said.

Nationwide, solar power is the fastest growing form of renewable energy, but it still accounts for only about 5% of electricity generated. In California, it's nearly 30%, thanks to massive new projects like one in the Mojave Desert, where an array of 2 million solar panels near Edwards Air Force Base can be seen from space.

The 4,000-acre site is the largest solar storage facility in the country and has enough energy to power about a quarter million homes.

"Without this, I think renewable energy would hit a limit fairly quickly," said Gus Luna, the chief development officer for Terra-Gen, the company that built the site.

California, the fifth largest economy in the world, aims to run on 100% renewable energy by 2045.

"You'll probably need something like another 20, maybe 30, more of these projects to be able to reach that," Luna said.

That's because to truly make all those panels and turbines work, you need batteries included.

In:
• Renewable Energy
• Climate Change
• Environment
• Solar Power
• Wind Power