Correction for the absorber edge effect in analytical models of flat plate solar collectors

• The efficiency of non-ideal absorbers was calculated by two-dimensional simulations.
• From the results, a new correlation for the fin efficiency was derived.
• The new correlation is easy to use for engineering purposes.
• The correlation allows for more accurate efficiency/cost optimization.
• One of the major uncertainties of analytical models is eliminated.

Analytical models based on the theory of Hottel and Whillier (1958) overestimate the efficiency of solar collectors with single plate absorbers because the absorber tubes of real absorbers are usually not bonded up to the edge of the absorber plate. Based on two-dimensional numerical simulations, a correction factor has been derived. This correction factor, multiplied to the standard fin efficiency defined by the analytical model, takes the edge effect into account within 0.5% when compared to the numerical results.The advantage is twofold: The extended analytical model enables more rigorous cost- and efficiency optimization of the absorber, which is the most expensive part of a flat plate solar collector. Since one of the major uncertainties of the analytical model is eliminated by the addition of the correction factor, parametric studies will be more accurate. If the efficiency characteristics, the geometrical data and the material properties of a sufficient number of collectors are known, the enhanced model could be used to derive more accurate correlations for the heat loss coefficients.