Electric Thermal Energy Storage within the Decarbonization of Energy Supply: A challenge-driven study

The intermittent nature of many renewable energy sources certainly poses challenges to today’s energy system. But while many energy storages hence facilitate the integration of variable energy generation, only a few have significant potential to act as a key lever to a decarbonization of energy supply across all sectors at the same time.
Electric thermal energy storage describes a set of technologies which convert electricity to heat at charge, store the thermal energy and, at a later stage during discharge, reconvert heat to electricity or supply it directly to consumers. Due to their inherent but unique asset of readily available thermal energy storage not accessible to other electric energy storage technologies, electric thermal energy storage can play a pivotal role in future low-carbon systems. Their charge process can either be based on direct electric heating or on a heat pump cycle. Whereas the first option typically leads to a system with a high-temperature storage, the latter one operates at low temperature but using complex machinery.
This thesis addresses the technical challenges for these key components of electric thermal energy storage at scale through experimental methods as well as numerical simulation. Field and system simulations of different spatial dimensions and simulated time span are validated by means of academic and industrial facilities. The main outcomes include a novel 1 MWh_th partially underground rock bed solving issues regarding the bed temperature distribution and mechanics, as well as evidence on a fast-reacting CO₂ heat pump, as demonstrated by load changes of 7 MW_el in under 30 seconds. Finally, the implementation of electric thermal energy storage for both power and heat supply has been assessed from a techno-economic perspective on a local as well as national level, guiding future work towards bridging the gap between research and far-reaching commercialization.