The thermal energy storage system of one of Europe's first parabolic trough power plant, Andasol 1, has been successfully put into operation by Solar Millennium. The commissioning of the storage system and the turbine, along with the feeding of electricity into Spain's grid (on a test basis) will follow within the coming days. In a few weeks, Andasol 1 will then go into regular operation.

The Andasol 1 storage system absorbs part of the heat produced in the solar field during the day. A turbine produces electricity using this heat during the night, or when the sky is overcast. This process almost doubles the number of operational hours at the solar thermal power plant per year, the company said.

The heat generated in the solar field will be stored in a molten mixture of 60% sodium nitrate and 40% potassium nitrate. Both substances are used in food production as preservatives and are also used as fertilizer. The storage tank consists of two, 14-meter high tanks with a diameter of 36 meters and a capacity of 28,500 tons of molten salt.

During the pumping process from the cold to the hot tank, the molten salt absorbs additional heat at an outlet temperature of approximately 280°C, reaching a temperature of 380°C. A fully loaded storage system can keep the turbine in operation for 7.5 hours, which means almost 24-hour operation of the power plant in during high sunshine periods.