In solar tower power plants, up to several 10,000 movable solar mirrors reflect sunlight to a target surface at the top of the tower. There, the concentrated sunlight hits a receiver and heats a heat transfer medium that flows through the receiver. The solar power plant uses this heat to produce steam, which drives a turbine to generate electricity. While steam was still used as the heat transfer medium in the first tower power plants, new power plants rely primarily on molten salts. These allow high process temperatures of up to 565°C and enable cost-effective storage in large tanks.
The aim of the High Performance Molten Salt II (HPMS-II) project is to increase the upper process temperature of the salt circuit to 600 °C. This reduces the investment costs, as both the salt storage tank and the steam generator can be dimensioned smaller. In addition, the steam cycle achieves a higher efficiency. Both effects reduce the electricity generation costs.
Previous systems are designed to be open to the environment. A higher process temperature would cause the nitrate salt to continuously decompose and the salt-bearing metal pipes to corrode. One approach to increasing the process temperature to 600°C is therefore to close the salt circuit to the environment. To inhibit salt decomposition and metal corrosion, a gas jacket made of synthetic air is used in all components.
The aim of the project is to test the newly developed receiver, the associated salt circuit and the safety concept in a real environment. The researchers are also investigating how individual components such as salt pumps, valves, insulation and measurement technology react in operation at high temperatures and are testing the components for their resilience.
DLR and MAN Energy Solutions installed the developed system and receiver at the multifocus tower in Jülich from August 2021 and commissioned it from spring 2022, initially with water and later with liquid salt.
The companies involved in the project are MAN Energy Solutions, Flexible Industriemesstechnik FLEXIM and the Solar Institute Jülich at Aachen University of Applied Sciences. The companies Salzgitter Mannesmann Forschung, Mannesmann Stainless Tubes, HORA Regelarmaturen, PERSTA and Endress+Hauser are involved as associated partners.
The BMWK is funding the HPMS-II project, short for "High Performance Molten Salt Tower Receiver System" (funding code 0324327A-D). The Ministry for Economic Affairs, Innovation, Digitalisation and Energy of the State of North Rhine-Westphalia is funding the SALSA project - "Test Platform for Solar High Temperature Liquid Salt Receiver Systems".