Thermal storage: From low-to-high-temperature systems

Different technologies of cold and heat storages are developed at Fraunhofer ISE. This paper provides an overview of ongoing research for sensible and latent thermal energy storages. Phase change emulsions are developed supported by molecular dynamic simulations. A narrow temperature range of the phase change is crucial for the applicability. By the simulations a nucleation additive is identified that reduces supercooling by up to 9 K. The long-term stability of phase change material is investigated by degradation experiments. Thermal cycling and ageing of materials at elevated temperature are applied. The change of melting enthalpy and characteristic temperatures are evaluated. Among erythritol, adipic acid and myristic acid, the smallest degradation was observed for the latter. For sensible storages, the reduction of thermal oil by low-cost filler materials and their compatibility is investigated at elevated temperature. It can be concluded that the materials are compatible up to 320 °C. At the component level, different macroencapsulations and immersed heat exchanger are tested for phase change materials. The investigated configurations achieve similar values of thermal power during (dis-)charge. Compared to water as storage medium, the capacity increases by a factor of 2.2 and 4.1 for the macroencapsulation and the immersed heat exchanger, respectively.