The CHEST (Compressed Heat Energy STorage) concept for facility scale thermo mechanical energy storage

Electric energy storage is considered to become a key element of the future electricity infrastructure. PTES (Pumped thermal electricity storage) represents an emerging thermo mechanical storage technology based on the transformation of low temperature heat by surplus electricity. After transformation, the high enthalpy heat is stored. During the discharge process, this heat is used to drive a thermodynamic cycle generating electricity. This concept allows storage of energy in the multi-MW range for several hours without any specific geographical requirements. Various combinations of thermodynamic cycles and storage types have been suggested for implementation using either low temperature storage (<200 °C) or high temperature storage (>500 °C). In contrast to these PTES concepts, the Compressed Heat Energy STorage (CHEST) concept presented in this paper is based on a medium temperature conventional Rankine cycle combined with a latent heat storage unit according to the current state of the art. This concept attains an efficiency of 70% while the maximum temperature is below 400 °C. The integration of heat provided by low temperature sources during the charging process represents an additional option of the CHEST concept; losses can be compensated, the electric work delivered during the discharge process might even outweigh the work needed during the charging process.