How Thermal Storage Works
In a power tower that uses molten salt as the heat transfer medium, cold molten salt is pumped up the tower to the receiver, where it is heated, then flows to a hot storage tank. The hot salt then flows through a heat exchanger, where heat is transferred to water to produce the steam that spins the turbine. The molten salt then flows back to the cold storage tank. This hot molten salt retains its heat so well that it can be stored and used to generate electricity at later times.
In a parabolic trough solar facility, the heat transfer fluid can be used not only to create steam, but also to heat molten salt stored in tanks near the power block. When the sun goes down, the hot molten salt (rather than the sun-heated fluid) generates steam and electricity.
In a CSP system with thermal energy storage, the heat transfer medium, such as molten salt, retains heat so well that it enables the plant to generate electricity for hours when the sun is not shining.
By placing the storage between the receiver and the steam generator, solar energy collection is no longer directly coupled to electricity generation. The sun remains a necessary component of the system, but the molten salt thermal storage enables the plant to continue reliably generating electricity for hours when the sun is not immediately available, such as in the evenings or during cloudy days.