Universal Experimental Methods for Evaluating the Performance of Radiative Cooling Materials

The achievable cooling temperature and cooling power of a radiative cooling material are highly affected by time, location, and environmental conditions (e.g., the amount of radiatively participating gases in the atmosphere and incident solar radiation). Such influences cause deviations in the material's performance. To introduce more universal values for the cooling temperature and cooling power, a well-controlled setup is developed to experimentally evaluate the material's performance. In contrast to the total emissivity of the atmosphere varying from 0.409 to 0.975 with 0%-100% relative humidity, the total emissivity of the experimental setup in this study is fixed at approximately 0.001, which clearly indicates the elimination of atmospheric radiation. A solar simulator is used to replicate the solar flux at air mass 1.5. The obtained time-dependent temperature profiles suggest that the proposed measurement setup can be utilized to evaluate the material's performance independent of time, location, and environmental conditions.