Design and performance analysis of compressed CO2 energy storage of a solar power tower generation system based on the S-CO2 Brayton cycle

Abstract

Two kinds of S-CO2 Brayton cycle tower solar thermal power generation systems using compressed CO2 energy storage are designed in this paper. The energy storage system uses excess solar energy to compress CO2 near the critical point to a high-pressure state for energy storage during the day, and the high-pressure CO2 is heated by a gas-fired boiler or the heat of stored high-temperature molten salt at night, so that it enters the turbine for work and drives the generator to generate electricity. The traditional molten salt heat storage scheme and the proposed compressed CO2 energy storage system model are established with Ebsilon software, and then the equipment selection, structure layout, and parameter design processes are carried out for the energy storage and heating systems. The thermoeconomic and technoeconomic indexes of the three energy storage schemes are calculated under the operating conditions of a typical day. The results show that the efficiency of the combined cycle is higher than that of other organic working fluids when T-CO2 is used as the bottom cycle working fluid. The integrated scheme of compressed CO2 energy storage and auxiliary combustion has the highest average daily efficiency (26.62% on summer solstice and 23.04% on winter solstice) and the lowest initial equipment investment. However, due to the additional cost of natural gas, the scheme has the highest levelized cost of energy (LCOE) at $0.1168/kWh. The LCOE of the integrated scheme of compressed CO2 energy storage and molten salt heat storage was the lowest at $0.1046/kWh.