Energy conversion and thermal energy storage processes for industrial process and power plant technology

The DLR Institute of Engineering Thermodynamics conducts research into energy storage, heat management and heat transfer. It is pursuing storage concepts for different heat transfer media in the 100 – 1000°C range: sensible (that is, without phase change) storage based on liquids and solids, latent heat storage and thermochemical storage.

In addition to applications in the felds of industrial process heat, combined heat and power, and conventional power plant technology, thermal energy storage is being developed and validated for solar-thermal power plants. While DSG-Store (Direct Steam Generation Storage) is essentially suitable for numerous applications, it was originally developed for thermal solar power plants. These are able to supply energy round the clock, almost like a conventional power plant. Optimised heat management also improves the operating characteristics, reduces partial-load operation and uses the power plant hardware in a more effcient way. Overall, this increases its proftability. A solar-thermal power plant works particularly effciently and cost-effectively if it is operated at the highest possible temperature. This can be achieved with direct solar evaporation of water, whereby the superheated steam for the steam turbines is generated in the collector. At a pressure of 120 bar, it reaches temperatures of over 500°C. This almost matches the steam parameters common in conventional power plants.

Approximately 65% of the solar energy is used for the evaporation process alone. The latent heat storage that absorbs this type of energy plays an equally important role. The storage medium is sodium nitrate, which melts at 306°C. It is located in a thermally insulated container that is in direct contact with heat exchange tubes, through which the steam flows during the charging process. In doing so, the steam cools down and condenses. For discharging, the feed water flows through the transfer tubes. The liquid salt solidifes and transfers its solidifcation energy to the feed water, which evaporates.

Both the geometrical structure and the individual components have been optimised in terms of their technology and cost-effectiveness in a pilot-scale test storage facility within the DSG project. In the process, the scientists have built upon the insights gained from the previous DISTOR and ITES research projects, as well as the parallel TESIN project. The project’s funding code is 0325333A,D.

German Aerospace Center (DLR)
Dan Bauer · E-Mail: dan.bauer@dlr.de · DLR.de