Solar thermal power plants are already in use in sunnier climes such as southern Spain, and salt has long been used as a storage medium in such plants - just not as a heat transfer medium. Such power plants generate heat from concentrated sunlight, which is then transferred in oil to a salt tank, where it is stored as heat before being turned into electricity. While the technology is not suitable for electricity generation in Germany, it could potentially be used to supply industrial process heat and therefore contribute to decarbonisation.
This is the background behind the Évora Molten Salt Platform, a pilot plant that has just launched as a joint venture between the German Aerospace Centre (DLR) and the Portuguese . It’s also one of the first of its kind to use molten salt in place of thermal oil for heat transfer.
“The Évora Molten Salt Platform is an important step towards advancing solar thermal power as a technology for the energy transition,” said Karsten Lemmer, the DLR executive for Innovation, Transfer and Research Infrastructure, . “This facility enables us to test the use of molten salt at the power plant scale for its reliability and operational safety. Both are important criteria for moving quickly from laboratory scale to industrial application and increasing competitiveness.”
The solar heat is collected in parabolic troughs – two rows of curved mirrors covering 700 metres – and channelled into pipes containing molten salt where it is kept liquified at high temperatures. The thermal energy can either be stored (for up to 12 hours) in tanks or used to evaporate water, which turns a steam turbine and generates electricity – with a total output of 3.5 MW.
The benefit of salt is not only that its cheaper and greener than thermal oil, but it can be heated up to 550°C-celsius, whereas the limit is 400°C-celsius for oil. This results in significantly cheaper electricity. Solar thermal systems can’t beat photovoltaics on price yet but they have the advantage of being able to generate power when it’s cloudy and at night when combined with storage.