What is the molten salt heat storage technology?

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Molten salt is used both as a heat transfer fluid (HTF) as well as a thermal energy storage medium.

The molten salt mixture is both non-toxic and inert. the use of molten salt represents the most flexible, efficient and cost-effective form of large scale energy storage system deployed today. This storage feature enables stable and dispatchable power delivery without the need for any backup fossil fuel such as the natural gas needed for many other CSP technologies.

Molten salt is one of the thermal energy storage methods that can be used by retain thermal energy collected by solar tower or solar trough to generate electricity in bad weather or at night when the sun is not shine. The mixture of molten salt vary, the most extended mixture contains sodium, potassium and calcium nitrates. The salt will be melted (using solar energy) at 131 C (268 F) and it is kept liquid at 288 C (550 F) in an insulated storage tank. The liquid salt will be pumped through panels in a solar collector where the focused sun heats it to 566 °C (1,051 °F).Then it well be sent to a hot storage tank. This is so well insulated that the thermal energy can be usefully stored for up to a week.When the electricity is needed, the hot salt is pumped to a conventional steam-generator to produce super heated steam for a turbine/generator as used in any conventional coal, oil or nuclear power plant. 

It is the mixture of Potassium  nitrates and Sodium nitrates.. 60%Sodium Nitrates and 40%Potassium Nitrates. This Mixture has many properties such as, it can store the heat energy in the isothermal tanks up to 15 hours, it acts as the water in volume. This mixture can transfer its` heat into the water which transfer to steam, the steam can generate electrical energy with a suitable turbine. The molten-salt technology can be used in the Central Solar Power "CSP" especially in the Solar Power Tower "SPT".