Thermal energy storage FTWThe Solana solar station in the Arizona desert is one of the first large-scale solar plants with thermal storage that allows it to keep producing power even when the sun doesn't shine, allowing it to better match output to peak demand. The three-square-mile facility near Gila Bend uses concentrated solar power (CSP) technology to heat up oil that is piped through the solar collectors (up to 735 degrees Fahrenheit). That heat transfer fluid is pumped to steam boilers, where it heats water to create steam. The steam drives two 140-megawatt turbines to produce electricity, much like a traditional power plant.
But what's special is that "in addition to creating steam, the heat transfer fluid is used to heat molten salt in tanks adjacent to the steam boilers. The thermal energy storage system includes six pairs of hot and cold tanks with a capacity of 125,000 metric tons of salt, and the molten salt is kept at a minimum temperature of 530 degrees Fahrenheit. When the sun goes down, the heat transfer fluid can be heated by the molten salt to create steam by running it through the tanks instead of the field of parabolic mirrors."
It's not hard to understand why this kind of storage is important; one of the big problems with renewable energy is that power isn't always available when you need it. This can mitigate the problem, along with other technologies like hydro storage, smart grids that can better match supply and demand, and things like V2G for electric cars (storing renewable energy surplus in batteries, and using it when there's a deficit).
The Arizona Public Service (APS) has this promo video about Solana, explaining some of the main features of the solar plant: