Energy analysis of silicon solar cell modules based on an optical model for arbitrary layers

An optical model for arbitrary layers is developed and a one-dimensional steady-state thermal model is applied to analyze the energy balance of silicon solar cell modules. Experimental measurements show that simulations are in good agreement, with a maximum relative error of 8.43%. The wind speed vwind, ambient temperature Tamb and irradiance G are three main factors influencing the temperature of a photovoltaic panel. Over the course of a day the electrical output is reduced by the module temperature to only 32.5% of the rated value. Optical studies reveal that before 8:00 hours and after 16:00 hours, significant incident energy is lost by reflection because of the large angle of incidence θin, while at other times of day optical losses are nearly the same due to only small changes of transmission for θin < 45°. In addition, some optical losses result from the mismatched refractive indexes of encapsulating materials, especially at the ethylene-vinyl-acetate (EVA)/anti-reflection coating (ARC) and the ARC/Si interfaces. The uses of SiO2 and TiO2 as ARC materials for un-encapsulated and encapsulated Si solar cells are investigated by simulation. Comparing the results indicates that TiO2 as ARC reduces the reflective optical loss within λ = 0.4–1.1 μm after encapsulation, while SiO2 as ARC increases the loss by ∼5%. Energy allotment analysis shows that from 9:00 to 15:00, the reflective and transmissive optical losses are relatively steady at ∼26% and ∼13% of the incident energy, while the convective and radiative heat losses account for a further ∼30% and ∼24%, respectively. Thus, only ∼7% of incident energy is converted to electrical power.