A few days ago, the electric grid in California hit a new milestone: At 7pm on March 29, batteries provided 12.3 gigawatts of power—roughly as much as six Hoover Dams, or around 43% of the total demand on the grid. Nearly all of that battery storage was built in the last five years. “Until 2020 or 2021, battery storage was still quite expensive, but we’ve seen huge price drops over the last few years,” says Nicolas Fulghum, senior energy and climate data analyst at Ember, a global energy thin...