Thermo-economically optimal design = optimal molecule + optimal process + optimal equipment.

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Higher shares of renewable energy increase the need for electricity storage. A promising storage technology is Pumped‐Thermal Electricity Storage (PTES): PTES systems transform electricity into heat using a heat pump (HP) and reconvert the heat into electricity using a heat engine. Since both HPs and heat engines require working fluids, maximum performance requires the optimal combination of PTES process and working fluids. Herein this work, the thermo‐economic potential of an Organic Rankine Cycle (ORC)‐based PTES system is analyzed by simultaneously designing both the PTES process and the working fluids used in the HP and the ORC. To rigorously explore the molecular design space, the 1‐stage Continuous‐Molecular Targeting ‐ Computer‐Aided Molecular Design method is employed. Detailed models for costing and sizing of the equipment allow for a thermo‐economic design of the PTES. The computer‐aided molecular design formulation integrates the working fluids as degrees of freedom into the process optimization. For the investigated ORC‐based PTES system with an input power of 60 MW, the optimal process and working fluids minimize the specific investment cost to SIC = 929  € kWh out − 1 . The analysis of cost drivers shows that with decreasing compressor cost, the investigated ORC‐based PTES system can become a competitive storage technology.

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