The output from renewable energy sources fluctuates massively. But when the grid needs power, it needs it instantly.
Megawatt Storage Farms wants to build at least 4 GW of storage in California, about 5% of the total load. All sorts of regulatory and turf war hurdles are in the way that hopefully will be resolved soon. Then California can store renewable power to use as needed.
Storage technologies include compressed air, pumped hydro, batteries, flywheels, super-capacitors, and more.