Optimum coupling of thermal energy storage and power cycles for carnot batteries

To enable the widespread exploitation of intermittent, low-cost, and non-dispatchable renewable energytechnologies, energy storage plays a key role in providing the required flexibility. In the spectrum ofenergy storage systems, one out of a few geographically independent possibilities is the storage ofelectricity into heat, so-called Carnot batteries. For thermal-to-electricity reconversion, depending onthe operating energy storage temperatures, conventional or advanced power cycles can be integratedinto the system, yielding different techno-economic performances. This work proposes a methodologythat enables decision-making in selecting the adequate power cycle and Thermal Energy Storage (TES)type for a wide range of operating temperatures between 200 and 800 °C. To select the optimumcoupling of TES and power block, a techno-economic optimization has been conducted aimed atminimizing the Levelized Cost of Storage (LCOS) for different plant capacities and charging costs. Thestudy explores various power block configurations, including Organic Rankine Cycle (ORC), steamRankine cycle, and supercritical CO2 (sCO2) Brayton cycle. Additionally, it evaluates different TESoptions such as molten salt, particle, and air packed bed TES. Results highlight that, for a charging costof 50 EUR/MWh, the most cost-effective combination of TES and power block involves sCO2 powerblocks with recompression and intercooling, along with particle-based TES operating at temperaturesbetween 600 to 800 °C and a temperature difference of 200 °C. ORCs are suitable for low temperatures(up to 350 °C) and high temperature differences, while the steam Rankine cycle is considered optimalbetween the low-temperature and the sCO2 preferred regions. Air-packed bed TES is suggested as aviable option when TES represents a large share of the capital cost, with low charging costs, low hottemperatures, or low temperature differences. Molten salt TES is ideal when its design temperaturesalign with the operating limitations of the salts. Particle-based TES is the most cost-effective choiceacross a wide range of temperatures, at small (10 MW) and large scales (100 and 200 MW).