California’s law mandating 100% carbon-free electricity has a big hole in it. It fails to address energy storage. Batteries as well as other longer-duration energy storage solutions are absolutely essential for a reliable supply of electricity that relies largely on energy resources such as solar and wind, which are available only some of the time. Ordinarily, one might assume the state’s utilities would invest in large storage projects such as pumped storage, an efficient technology allowing the capture and storage of excess renewable energy so we don’t have to waste it. When the sun is shining or the wind is blowing during the day, it pumps water uphill.