Thermal performance of high temperature concrete thermal storage system for solar thermal power generation

The thermal performance of a concrete thermal storage system was investigated by the lumped parameter method. The application range of the lumped parameter method was extended to large Biot numbers by using the corrected heat transfer coefficient between the solid and the fluid. The development of the thermocline region and its influence on the thermal performance of the concrete thermal storage system were examined. The effects of three parameters on the discharging performance were explored. The results show that there exists a thermocline region along the flow path, and it moves downstream and the region area increases gradually. The thermal performance of the whole system can be improved by increasing thermal conductivity of concrete but the rate of thermal performance improvement will be smaller with an increase in the conductivity. The increase in the total length of series modules can effectively enhance the system thermal performance while the influence could be ignored when the total length is greater than 1 km. Increasing the equivalent ratio of the outer diameter of the heat storage unit to the inner diameter of the steel tube will reduce the temperature gradient of the thermocline region along the flow path and increase the thermocline region area.