Solar Engineering a Condensed Course

365.5 Collector CharacterizationDB 6.15-16Measured collector performance and performance calculated according to the principlesmentioned above agree very well. The collector is also well described by the (stationary)Equation 5.1.3, possibly complemented by the collector's dynamic performance.This equation contains three parameters, ULand FRwhich are constant or varies withtemperature, and (τα ) that is constant or varies with incidence angle θi.The collector's instantaneous efficiency ηiis given byQ F U ( T − T )uR L i aηi= = FR( τα ) −(5.5.1)AcGTGTIn the next section, the incidence angle modifierK= τα ) /( τα ) f ( θ )(5.5.2)τα(n=bwhere the parameter bois part of the expression, will be explained. This leaves us with threebasic solar collector parameters:F (τα ) indicating how energy is absorbed;RnF RULindicating how energy is lost; andboindicating the dependence of the incidence angle θ b.