Comparison of Solar Collector Thermal Efficiency Curves from Different Testing Methods
Abstract
The CENER Testing Laboratory has been performing durability and efficiency tests on solar collectors according to the European EN 12975-2 Standard since 2004. This Standard describes different thermal efficiency curve test methods. This laboratory is accredited for performing the thermal efficiency curve in indoor and outdoor test benches. In the paper, we analyze the difference of some efficiency curves found for some solar collectors using different efficiency tests according to both methodologies. We show the results of the factor analysis for estimation of tested solar thermal optical efficiency according to the European Standard. Indoor tests with a solar simulator involve controlling of the spectrum of its lamps to ensure that the difference from the solar spectral distribution does not significantly change the optical efficiency of the solar collector. Solar collectors tests are done according to Parts 6.1 and 6.3 of the EN 12975-2 Standard, indoors with the continuous solar simulator or outdoors on a fixed or sun-tracking test bench. This study estimated the differences observed in the efficiency curves of some solar collectors, with different selective materials. In this paper can be observed that the efficiency curves for the same collector have up to a 0,016 difference over the range tested (0 to 0,06 Km2/W) for indoor conditions, and 0,010 for outdoor conditions.