To extend the operation beyond sunshine hours, a thermal energy storage system (TES), consisting of two molten salt storage tanks, the “cold” and the “hot” one, is integrated in the solar plant. As the solar field is oversized, the excess energy collected during the day can be transferred to this thermal storage. The molten salt mixture, which is 60% sodium nitrate (NaNO3) and 40% potassium nitrate (KNO3) can then provide the necessary heat to operate the power plant at night or during overcast periods.
During the pumping process from the “cold” to the “hot” tank, the molten salt mixture absorbs additional heat to be heated from approx. 290°C up to 390°C.
To discharge this heat when needed, the salt is pumped from the hot storage tank, through a shell and tube heat exchanger train, where the salt returns its thermal energy to the cold HTF.
A full storage tank can be used to operate a power plant turbine for about 7.5 hours which allows a 24-hour electricity production in the summer months. With its capability of operating at full capacity for seven and a half hours even after the sun has set, the plant can provide solar power for almost twice as long as a solar power plant without a salt storage.
