Calorimetric testing of solar thermal absorbers for high vacuum flat panels

Among solar thermal collectors, the evacuated flat panel is emerging as a reference technology for operation at temperatures high 200 °C with an increased annual energy production owing to both direct and diffuse light capture. Accurate measurements of optical properties selective absorbers used in such devices are key reliable estimation overall performance. These must be measured under vacuum temperatures, conditions which panels meant operate. In this study, we accurately these using calorimetric technique. The measurement procedure based on power balance equation sample absorber suspended high-vacuum chamber minimized losses well adapted class devices. Calorimetric obtained Sun LED illumination revealed excellent reproducibility good agreement those traditional analysis low air. When extended up stagnation temperature, often exceeds 300 °C, started deviate from measurements, indicating importance measuring actual operating conditions.