Assessment of the annual performance of solar collectors by means of the utilizability method

Abstract

This report presents some results from a comparative analysis of the long-term efficiency of flat-plate and evacuated tube solar collectors under different operating conditions. The analysis involves calculation of the daily utilizibility factor, which is defined as the fraction of total monthly solar radiation over an inclined surface that exceeds the critical value. The monthly values of the critical radiation and the daily utilizability factor for the solar collectors are determined under different climatic conditions and different temperatures of the heat transfer fluid. The obtained results are used to compare the annual performance of the solar collectors.