One approach for renewable energy not always being available is molten salt: https://insideclimatenews.org/news/16012018/csp-concentrated-solar-molten-salt-stor

One approach for renewable energy not always being available is molten salt: https://insideclimatenews.org/news/16012018/csp-concentrated-solar-molten-salt-storage-24-hour-renewable-energy-crescent-dunes-nevada https://insideclimatenews.org/news/16012018/csp-concentrated... It heats the salt up to 1050 degrees where it is essentially a liquid and uses that to produce steam to turn a turbine.