Effect of spectral response of solar cells on the module output when individual cells are shaded

Solar cell characterization is carried out by current-voltage (I-V) and spectral response measurements. These characteristics of the solar cell depend on solar cell design, fabrication, material properties, junction depth and optical coatings. Generally, during module manufacturing, solar cells of similar wattage are used and spectral response (SR) including external quantum efficiency (EQE) and internal quantum efficiency (IQE) characteristics are not given any attention. It is observed that similar wattage rating crystalline solar cells have slight variation in their spectral response behavior over the wavelength range (300-1100 nm). In this paper, the effect of shading on the crystalline solar cells of the module having same power output and slight difference in spectral response are experimentally investigated. The maximum and minimum drop in short circuit current of the module is observed to be 84.2% and 34.6% when the solar cells of high and low spectral response are shaded. Minority carrier diffusion length and dead layer thickness parameters of solar cells are also calculated from the short and long wavelength region of the spectral response curve. It is found that the effect on module output is high in case of shading a cell having maximum diffusion length and minimum dead layer length. It is concluded that spectral response of a solar cell is an additional parameter that must be considered apart from cell I-V characteristics in module fabrication for superior and uniform performance in the field.