Comparison of Thermal Efficiency Curvers of Solar Collector Tested in Outdoor Conditions
Abstract
The Solar Thermal Testing Laboratory (LEST) of CENER has been performing durability and efficiency tests on solar collectors since 2004 according to the European Standard EN 12975-2. This standard describes different testing methods to determine the thermal efficiency curve of solar collectors. The LEST is an, by the Spanish Accreditation Entity (ENAC), accredited laboratory for performing thermal efficiency curves in steady and quasi-dynamic states according to parts 6.1 and 6.3 of the standard EN 12975-2, respectively. In this paper, we focus our work on tests carried out in outdoor conditions under both methodologies. We will analyze the differences of thermal efficiency curves for two different kinds of solar collectors. In 2010, the LEST conducted different thermal efficiency tests on one flat plate collector and also on an evacuated tube collector. Both solar collector technologies were tested under quasi-dynamic and steady state conditions according to EN 12975-2 requirements. We will analyze the differences obtained by testing the same collector with both methodologies. Another important objective of this paper has been to know the influence of selecting different data sets in order to characterize the optical and thermal properties of two solar collectors tested under quasi-dynamic conditions. The aim of this paper is to confirm that the present outdoor efficiency test methodologies proposed by the EN 12975 are fully compatible with flat-plate and evacuated tube collectors.