The Gemasolar solar thermal plant in Spain uses molten salt to store excess heat from the sun to power turbines at night. It recently produced electricity day and night for a record-breaking 36 days. Solar thermal uses heliostatic mirrors to reflect the heat of the sun to a central tower to heat water which powers the turbines. Many solar thermal system convert the steam back to water, thus hugely cutting water usage.
Molten salt is used in solar power tower systems because it provides a low-cost medium to store thermal energy and operates at temperatures that are compatible with steam turbines as well as being non-toxic and non-flammable.