How does soiling affect the spectral transmittance of PV module glass, and what are the implications for energy yield in different environmental conditions?

Soiling, which is the accumulation of dust, dirt, pollen, and other particulate matter on the surface of PV modules, affects the spectral transmittance of the glass by selectively blocking certain wavelengths of light. Spectral transmittance refers to the fraction of incident light that is transmitted through a material at each wavelength. Soiling tends to have a greater impact on shorter wavelengths (blue light) than on longer wavelengths (red light). This is because smaller particles, which are common components of soiling, are more effective at scattering shorter wavelengths. The implications for energy yield vary depending on environmental conditions. In environments with high levels of dust and particulate matter, such as deserts or agricultural regions, soiling can significantly reduce energy yield, especially if rainfall is infrequent. The spectral selectivity of soiling can also affect the performance of different PV module technologies. For example, thin-film modules, which tend to be more sensitive to blue light, may experience greater yield losses from soiling compared to crystalline silicon modules, which are more sensitive to red light. In humid environments, the combination of moisture and soiling can create a hardened layer that is more difficult to remove and can further reduce light transmittance. Regular cleaning of the PV modules is necessary to mitigate the effects of soiling and maintain optimal energy yield. The frequency of cleaning depends on the severity of soiling and the cost-effectiveness of cleaning operations. The type of soiling also has an impact, with some types being easier to remove than others.