California is experiencing a surge in renewable energy generation from the sun and wind. But the state will face long-term economic and environmental challenges relying on these intermittent resources without deploying more energy storage, such as batteries, compressed air, and pumped hydro facilities. Of the options available, only large-scale energy storage technologies can capture enough surplus renewable energy during times of low demand for later dispatch at the scale needed to decarbonize our electricity supply over the coming decades.