Thermochemical energy storage and synergies with hydrogen

Kurzfassung

Energy systems that are primarily based on renewable energies require flexible energy storage and conversion options to balance production and consumption needs. Thermal storages can play a significant role in such systems in order to match available electricity production with actual thermal requirements. Among the different types of thermal energy storages, thermochemical storage based on reversible gas solid reactions shows two specific features: an almost loss-free principle that allows to store large amounts of energy over long storage durations as well as an intrinsic and flexible heat pump functionality. However, few systems are ready for applications, as the required gas management is usually quite complex, especially with regard to system integration. In case of thermochemical reactions based on metal hydrides, the system complexity can be significantly reduced, if the storage unit is integrated into an already existing hydrogen infrastructure [1]. Such an infrastructure not only provides and takes-up hydrogen, but could thereby also offer different pressure levels, which form the basis for our innovation thermochemical conversion technology. An open metal hydride system has been demonstrated for the first time for mobile applications. By utilizing the pressure difference between the tank and the fuel cell, a cooling system was operated that does not require additional energy consumption onboard. The technology has been demonstrated on a Technology Readiness Level of 4 that the fuel cell operation is not affected by the integrated open metal hydride system [2]. At the same time, specific thermal powers of >0,5 kW/kgMH have been achieved, that can be translated into an increase in overall system efficiency of 5-14%. As hydrogen infrastructure is expected to increase in the upcoming years, the applicability of this kind of system can be extended to a variety of stationary applications. Here the technology can benefit from decades-long development of metal hydrides for hydrogen storage: the tremendous a variety of metal hydrides allows to utilize the same principle as heat pump applications in any temperature range from -20 °C to 400 °C with a H2 pressure range of 1-10/50 bar. Thus, the system enables the development of new, efficient heat pumps, which assist the defossilization of industrial and – at the same time – increase the efficiency of hydrogen-based systems as the compression work can be partially re-utilized.