Conceptual design of a thermo-electrical energy storage system based on heat integration of thermodynamic cycles – Part B: Alternative system configurations

Thermo-electrical energy storage (TEES) based on thermodynamic cycles is currently under investigation at ABB corporate research as an alternative solution to more consolidated but site-dependent electricity storage technologies such as pump-hydro or compressed air energy storage. During charge electricity is converted into thermal energy by means of a heat pump and during discharge a thermal engine converts thermal energy into electricity. The synthesis and the thermodynamic optimization of a TEES system based on hot water, ice storage and on transcritical CO2 cycles is discussed in two papers (part A and part B). A methodology for the conceptual design of a TEES system based on Pinch Analysis tools was introduced in part A together with the results of a thermodynamic optimization of a base case. The overall synthesis problem was solved by implementing in the optimization a heuristic procedure for the synthesis of the heat exchanger network and the storage tanks thus letting the optimal complete system structure and its design parameters to be found for given values of cycle parameters. In part A, basic topologies for the CO2 heat pump (HP) and thermal engine (TE) were considered, and no alternative cycle configurations were investigated through the optimization. A larger synthesis problem involving the change of cycle topologies is addressed in this second paper. Different system configurations were generated by modifying the base case configuration through an organized procedure and were optimized separately following the objective of maximum roundtrip efficiency only, as done for the base case in part A. The optimization results of the new configurations are discussed and compared with the base case scenario. A complete picture of the impact of design choices on the maximum system performances is obtained.