Integrating cold thermal energy storage (CTES) into supercritical CO2-based solar power plants: Comprehensive evaluation of thermal performance under full operating conditions

Solar thermal power systems are typically installed in deserts to take advantage of high solar radiation, but they also face challenges due to extreme weather conditions, particularly large temperature variations between day and night. During the daytime, high ambient temperatures reduce the cooling capacity and, as a result, the system's efficiency and net power output. At night, low ambient temperatures increase the cooling capacity, leading to overcooling of the power cycles. To improve the cooling capacity throughout the day, this study investigates the integration of cold thermal energy storage technology into a solar tower power generation system using supercritical carbon dioxide as the working fluid. The system leverages diurnal temperature variations to store excess cooling energy in water tanks at night and release it during the day. First, the heat exchange characteristics and cooling capacity of the cold thermal energy storage system are evaluated under both design and off-design conditions. Subsequently, the dynamic performance of the solar power tower plant integrated with this system is analyzed over two typical days, revealing significant efficiency and stability improvements. The system initially uses cooling air to remove over 90 % of the waste heat from the supercritical carbon dioxide, and then uses cooling water to further reduce its temperature by 4–5 °C. With the enhanced cooling capacity, the power cycle can maintain efficient and stable performance across all operating conditions. For cold thermal energy storage systems with water tank capacities of 200, 400, and 600 tons, the temperature fluctuation coefficient is reduced by 51 %, 66 %, and 72 % on the summer solstice, and by 12 %, 15 %, and 16 % on the hottest day. Additionally, total daily power output increases by 0.5 MWh, 0.7 MWh, and 0.82 MWh on the summer solstice, and by 2.07 MWh, 2.38 MWh, and 2.51 MWh on the hottest day, respectively.