Retrofit of a coal-fired power plant with a rock bed thermal energy storage

Power production accounts for about one-fifth of the global final energy consumption and over one-third of all energy-related CO2 emissions. Low-cost, large-scale thermal energy storages are considered as solutions for the decarbonization of fossil-fired power plants by their conversion into power-to-heat-to-power systems, so-called thermal storage power plants. This paper investigates the retrofit of a Chilean coal-fired power plant with an innovative solid media storage from a techno-economic perspective. Selecting a storage capacity of 5.27 GWhth, corresponding to 8 h of discharge, and increasing the inlet steam generator temperature from 590 to 650 degrees C lead to the highest annual round-trip efficiency of 34.9% and to up to 3.4% lower levelized cost of electricity. Minimum levelized cost of electricity as low as 88.1 e/MWh is attained and considered as close to competitiveness with well-established molten salt storage systems. A sensitivity analysis shows that assuming even five times lower storage costs, initially the strongest driver of capital expenditure, only meant 4% lower levelized costs of electricity on average. On the other hand, the design of electricity purchase for charging, for example with green power purchase agreements, turns out to be the key lever to a successful implementation.