An experimental study on evacuated tube solar collector using supercritical CO2

A solar collector using supercritical CO2 as working fluid is proposed in this paper. In order to investigate and estimate the CO2-based solar collector, an experimental set-up was constructed. Of particular interest of this paper are the basic collector characteristics, such as CO2 temperature and pressure in the collector, CO2 flow rate, and collector performances. The collector has been tested under various weather conditions. The results show that the CO2 temperature, CO2 pressure and mass flow rate increase with the solar radiation, which is different from those of traditional solar collector using liquid as working fluid. The solar radiation has influence on the CO2 states, being liquid, liquid-gas or supercritical state in the test, furthermore, affects the CO2 mass flow rate. The annually-averaged collector efficiency is found to be above 60.0% in the case of supercritical CO2 as working fluid, which is much higher than that of water-based solar collector. This study shows the potential of the supercritical CO2-based solar collector in the field of solar thermal utilization.