Question

How to calculate the efficiency for the different thermal energy storage mediums like 1)Water 2)Water-Glycol mixture 3)Mineral Oil 4)Synthetic Thermal fluid 5) Molten inorganic salts 6)Molten Metals 7) Solid Storage like concrete.

Answer 1

Storage Efficiency : - The ratio of the energy delivered by the storage system to the energy supplied to the storage

Water is the most available and cheapest fluid to use, but the problem with water is that it has very limited temperature range when it is liquid. Keeping water in liquid state above 100 ^oC requires high pressure, which adds significantly to system complexity and cost. Oils and other synthetic liquids are commonly used in CSP plants, as they have a much wider working temperature range. Molten salts are probably the most common storage medium but are not the best heat transfer medium, because salt tends to solidify in tubes at lower temperatures, blocking transport. Additional heating will need to be provided in that case to start up the plants.