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 v(wind), ambient temperature T-amb 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 theta(in), while at other times of day optical losses are nearly the same due to only small changes of transmission for theta(in) < 45 degrees. 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 unencapsulated and encapsulated Si solar cells are investigated by simulation. Comparing the results indicates that TiO2 as ARC reduces the reflective optical loss within lambda = 0.4-1.1 mu m after encapsulation, while SiO2 as ARC increases the loss by similar to 5%. Energy allotment analysis shows that from 9:00 to 15:00, the reflective and transmissive optical losses are relatively steady at similar to 26% and similar to 13% of the incident energy, while the convective and radiative heat losses account for a further similar to 30% and similar to 24%, respectively. Thus, only similar to 7% of incident energy is converted to electrical power. (c) 2006 Elsevier Ltd. All rights reserved.