A correlation model to compute the incidence angle modifier and to estimate its effect on collectible solar radiation

Abstract

Radiation transmittance and absorptance of materials vary according to the angle of incidence of the incoming solar radiation. Therefore, the efficiency of most solar converters (thermal or photovoltaic) at a given radiation amount is a function of the sun's position through the angle of incidence. This problem is accounted for by the Incidence Angle Modifier, which is considered in this paper. An analytic expression for the incidence angle modifier, based on meteorological data or on geographic and geometric parameters, has been developed; this expression includes the effect of beam and diffuse radiation as well as the global influence. A comparison between measured data and computed from our model has given a very good correlation, the results being within a ±3% of difference for horizontal and tilted planes, and within ±17% for vertical surfaces, on average. The method also computes the collectible solar energy within a 5% error for thresholds up to 300 W m −2. The method has been validated for more than 30 locations of south and west Europe.