Developments of CPC solar evacuated glass tube collector with a novel selective coating

Abstract

This paper describes the development of a novel CPC (compound parabolic collector) evacuated tube solar collector, using a medium-temperature selective coating. The medium-temperature selective coating was obtained by co-sputtering titanium and aluminum targets. The absorptance and the thermal emittance of the heat treated coating is 0.95, and 0.04 at 80℃ respectively. The collector was optimized, using a manifold of copper U-tube with anti-oxidized coating and aluminum fin. An anti-reflection layer is added on the cover glass tube, and non-flash getter are used for maintaining the vacuum of the collector tubes. Thermal test results shown that the instantaneous efficiency based on gross area ηG can reach 0.46 at the temperature of 150℃ and the normalized temperature difference Tm* is 0.13 [(m2-°C)/W]. The experimental steam system application showed that the novel CPC solar collector can produce steam from water with temperatures about 108–145 °C during sunny days. It was also shown that the thermal performance of the solar collector did not degraded significantly.