Calculate instantaneous and daily efficiency of flat plate solar thermal collectors using the Hottel-Whillier equation.
Input Parameters
Results
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Instantaneous Eff
%
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Heat Output
BTU/hr/ft²
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Heat Loss
BTU/hr/ft²
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Stagnation Temp
°F
Note: FR(τα) is the y-intercept and FR UL is the slope of the efficiency curve. Higher FR UL means more heat loss at high temperatures.
Reference
Hottel-Whillier Equation:
η = FR(τα) - FR UL x (Ti - Ta) / G
Heat Output = η x G [BTU/hr/ft²]
Heat Loss = FR UL x (Ti - Ta)
Stagnation Temp = Ta + FR(τα) x G / FR UL