The aim of the research project under the leadership of DLR is to examine the efficiency and reliability of parabolic trough power plants with molten salt as heat transfer medium. To date, commercial parabolic trough power plants use thermal oils for receiving and transferring the high-temperature heat generated from solar radiation. Compared to thermal oil, the advantage of salt is its lower procurement cost and the higher maximum temperature to which the salt can be heated.


“A key advantage of the molten salt is its good resistance at high temperatures,” says Project Manager, Dr. Michael Wittmann from DLR “For the thermal oil a temperature of 400 degrees Celsius is the limit. But the salt withstands temperatures above 500 degrees in continuous use. Depending on the salt mixture upper process temperatures of up to 560 degrees are possible.”


In an innovatively designed once-through steam generator, the salt transfers its energy to a connected water-steam cycle. The compared to state-of-the-art technology elevated steam parameters allow higher efficiencies of the power plant unit. In addition, the once-through principle allows supercritical steam parameters for commercial application.


Salt can be used in parabolic trough power plants not only as a heat transfer medium. Already existing solar power plants use huge tanks with molten salt as thermal heat storage. Such power plants run with a two-circuit system with synthetic oil in the collector field and liquid salt in the storage system. Where salt is used as storage and also as carrier medium, a two-circuit system is no longer necessary. This leads to a reduction in system complexity and investment.


Évora Molten Salt heat storage tanks. Source: DLR.


The research project “High Performance Solar 2 (HPS2)” is funded by the German Federal Ministry of Economic Affairs and  Energy and accompanied by the Project Management Jülich (PTJ).