DLR has been operating the solar tower in Jülich, just under 60 kilometers from Cologne, as a solar thermal test facility for commercial tower power plants since 2011. In summer 2020, DLR expanded the test facility with a second tower with three test levels on which experiments can take place at the same time, made possible by the control software of the mirror field which can align subgroups of mirrors to the different target areas of both towers.
In solar tower power plants, many individual mirrors concentrate the solar radiation. At the Jülich site there are more than 2000 such movable mirrors (heliostats). The heliostats then direct the concentrated sunrays to a point at the top of the tower, the receiver. There, the radiation heats a circulating heat storage medium to very high operating temperatures (around 560 degrees Celsius for molten salt circuits, up to 900 degrees Celsius for particle systems and up to 680 degrees Celsius for air systems like here in Jülich). The heat is then used to generate steam that drives the turbines and produces electricity without CO2. Most of the energy from solar radiation is available in the Earth's sun belt, but Germany can also produce and use solar thermal energy, for example in high-temperature industrial processes.
In various projects, solar researchers at DLR and their cooperation partners in Jülich are testing new components and processes in order to further develop solar tower power plants. The aim of the research is to achieve higher temperatures and better efficiency in order to reduce electricity production costs, among other things. The focus is on mirror systems for directing and concentrating solar radiation, solar absorber and energy storage systems and their effective use, as well as theoretical and IT-supported analyzes and developments in the field of fluid mechanics and heat transfer. Depending on the development status and goal, individual components, functional groups or even a complete solar power plant system can be tested, evaluated and optimized. In addition, the DLR Institute of Future Fuels is investigating manufacturing processes for solar fuels (e.g. hydrogen) and the use of high-temperature solar heat for industrial processes.
The two solar towers
The larger tower in Jülich is a functioning solar tower power plant, meaning it can actually produce electricity. It is 60 meters high and includes a research level on which different experimental setups can be set up. The nominal electrical output of the system is 1.5 megawatts. The electricity generated in this way can be fed into the local medium-voltage network, even if the DLR does not use the system commercially for electricity production, but for research purposes. In the large-scale experiments carried out so far, the focus was on the further development of volumetric receivers and processes for the solar thermal production of hydrogen. There are still experiments taking place in the tower.
The new multi-focus tower has been in operation since 2020. It runs parallel to the existing tower and uses the same mirror field for irradiation. The second solar tower was built to increase research capacity and is purely a test facility. In the tower there are three levels with special equipment for the installation of certain experiments, on which various experiments can take place at the same time. A particle receiver is being built on the upper level. Experiments will take place there with ceramic beads as a heat transfer, storage and transport medium. In addition, at the middle level, which is specially equipped for process engineering applications, scientists are researching high-temperature processes for solar water splitting. On the lower level, current research revolves around molten salt as a carrier medium for high temperature heat. This is also where the pump, tank and heat exchanger for this system are installed and used.