Spectral Selectivity Surface for Both Solar Heating and Radiative Cooling

A spectral selectivity surface for both solar heating and radiative cooling was proposed. It has a high spectral absorptivity (emissivity) in the solar radiation and atmospheric window band (i.e., 0.2 μm–2.5 μm and 8 μm–13 μm), as well as a low absorptivity (emissivity) in other bands aside from the solar radiation and atmospheric window wavelengths (i.e., 2.5 μm–8 μm or above 13 μm). A type of composite surface sample was trial-manufactured using blue titanium-polyethylene terephthalate (BTPT). Sample tests showed that it has clear spectral selectivity in the spectra of solar radiation and radiation cooling wavelengths. More specifically, the absorptivity (emissivity) of the BTPT surface in the three spectra mentioned above is 0.92, 0.80, and 0.55, respectively. The equilibrium temperatures of it under different sky conditions or inclination angles of surface were tested. Numerical analysis was conducted to evaluate the heating and cooling performance of the BTPT surface. Comparisons among it and three other typical surfaces were performed. These comparisons indicated that the BTPT surface had a relative heat efficiency of 76.8% to the normal solar heating surface and a relative temperature difference of 75.0% to the normal radiative cooling surface, with little difference in cooling power.