In eTES technology (electrical Thermal Energy Storage) electrical energy is stored in the form of internal energy of a fluid, to be later recovered in a steam turbine.

The fluid chosen for storage is a mixture of sodium nitrate and potassium nitrate, ideal for this application due to its high specific heat and stability over a wide temperature range.

The salts initially stored in the cold tank (around 300ºC) are passed through an electric heater to be stored at a high temperature (around 565ºC) in the hot tank. During the discharge process, the hot salt returns to the cold tank passing through a series of heat exchangers where the salt yields its energy to evaporate water. The steam thus generated is used in a conventional steam turbine to produce electricity.

TSK has managed to develop this technology by taking advantage of its experience in solar thermal power plants, since both the process and most of the components have been in use for years in this type of plant. The novelty lies in the electric heater that replaces the oil-salt exchanger, providing great flexibility to the system since the electricity consumed in the heater can come from any type of adjacent generation plant such as wind or photovoltaic, or directly purchased from the network.