SustainableEnergyScience andEngineeringCenterSimplified Collector Performance ModelPrediction of the thermal output of various solar collectors: The quantity of thermal energy produced by any solar collector can be described by the energy balance equationwhere = rate of thermal energy output= rate of optical energy absorbed by receiver= rate of thermal energy lost from receiver.Q⋅out=Q⋅opt−Q⋅lossQ⋅outQ⋅optQ⋅lossSource: Solar energy Fundamentals and Design, William B. Stine & Raymond W. Harrigan, John Wiley 7Sons, 1985
SustainableEnergyScience andEngineeringCenterOptical Energy Absorbed by the ReceiverQ⋅opt=Aaρs,mτgαrRSIaAa= specular reflectance of concentrating mirror, if any (1.0 for non-concentrating flat-plate collector)ρs,m= transmittance of any glass envelope covering the receiver (e.g. glass cover plate in a flat-plate collector)Aa= aperture area of the collectorS= receiver shading factor (fraction of collector aperture not shadowed by the receiver; 1.0 for a flat-plate collector)R= receiver intercept factor (fraction of reflected beam intercepted by receiver; 1.0 for a flat-plate collector)αr= absorbance of the receiverIa= isolation (irradiance) incident on collector aperture (W/m2)S, R, αr, ρs,mand τg are constants (in a more detailed model, the dependence of the angle of the incident insolation can be considered) dependent only on the materials used and the structure accuracy of the collector - they can be lumped into a single constant term ηopt, the optical efficiency of the collector. For a flat-plate collector utilizing no reflectors, S, R and ρs,mare set equal to 1.0.
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