Self-protecting concave microstructures on glass surface for daytime radiative cooling in bifacial solar cells

As a passive and compact cooling mechanism, radiative cooling is lightweight and does not consume energy. Especially for the new popular bifacial PV modules, the traditional cooling method, containing air cooling with heat sink, water cooling, phase change cooling etc. would not be suitable, and the passive radiative cooling is attracting extensive attention. In PV radiative cooling field, high emissivity materials with high visible transparency are usually used to improve the radiative heat dissipation capacity of solar cell. Most of them are polymer materials with micro-nano structural surface, which have the defects of oxidation yellowing and structural loss, and the radiative cooling film itself adds an extra thermal resistance. Hence, a variety of concave micro-nano structures based on photovoltaic glass are proposed in this work, which are protected on the inner surface of glass, making the slender structure possible, and a strong heat dissipation effect while retaining self-cleaning characteristics without covering radiative cooling films. Moreover, the spectral properties of seven kinds of structures are numerical studied, and the solar cell temperature is calculated, as well as photoelectric conversion efficiency and cooling power. The results show that the visible light transmittance of these structures is basically higher than 0.9, the emissivity of some structures between 4 and 25 μm can reach more than 0.95, the solar cell can be cooled by 2–6 °C under common environmental conditions. When T_a = 30 °C and h_c = 12 W/(m²·°C), electrical efficiency is improved by 0.47% absolutely by the hemisphere, P_cooling can reach about 330 W/m². As they are designed inside the glass, the hardness and life are greatly improved compared with previous study achievements, allowing large application potential in glass packaging PV field.