Batteries are everywhere these days: in our phones, our cars and increasingly, our electric grids. A report by the Energy Information Administration shows rapid growth in utility-scale battery energy storage as a source of electricity. Around 5 gigawatts have been added so far this year out of about 21 gigawatts total. So how exactly are these batteries being used?

Big batteries play three major roles on the electric grid, said Sam Huntington with S&P Global Commodity Insights:

A flexibility role, “balancing second-to-second, you know, variations in the grid,” Huntington said. A reliability role, helping the grid meet peak power demand, and a clean energy role, “extending the reach of renewables into the market.”

In sunny states like Texas and California, batteries move clean energy produced from solar panels during the sun-shiny part of the day “into nonrenewable hours, so starting to eat into the market share of gas,” Huntington said.

By 2030, he expects the grid will have roughly four times the battery storage it has now.

In California, policy changes have driven the increase in storage, said Caitlin Smith with Jupiter Power. “We have these renewable goals. Oh, no. Oh, wait. Now we need dispatchable energy. Now we need storage,” she said.

Whereas in Texas, she said, it’s more market driven, because there’s money to make from storing renewable energy.

Ömer Karaduman, a professor at Stanford University, said the batteries charge when the electricity prices are low — like when the sun is shining. But when it’s dark, electricity prices will be high, which is when these companies will sell power to turn a profit. 

Still, batteries can’t yet replace fossil fuels, said Ramteen Sioshansi with Carnegie Mellon University.

“The handful of hours when the wind and solar is not producing enough, well, we still have gas generators that can basically fill that gap,” he said.

And Doug Lewin, author of Texas Energy and Power newsletter, said it’s important to note it’s not just green energy that can be stored by these batteries.

“Batteries are well suited to renewables, but frankly, they can kind of work with almost anything,” he said, like natural gas or nuclear power. As the technologies evolve, he said the market applications are still TBD.