The Impact of Optical Properties on the Performance of Flat Plate Solar Collectors

Abstract

The impact of the optical properties of flat plate collectors on the annual performance in a typical Mediterranean climate is estimated with TRNSYS program. For this purpose the detailed collector model has been considered and the simulations were performed by using the TMY file for Nicosia, Cyprus. The factors considered are absorptance and emittance of the absorber and the number of collector glazing. The reference solar collector considered is one were the absorber is painted with ordinary blackmat paint with α=0.9 and ε=0.1. The results show that the increase in performance of collectors employing an absorber with improved properties is considerable. A simple way to obtain somewhat improved properties is by painting the absorber with selective paint (α=0.95, ε=0.1). This is not a very expensive method therefore this modification is expected to be economically viable. However other more high-tech measures like a collector with α=0.97 and ε=0.05, which is out of the manufacturing capabilities of the industry and considered only for comparison purposes, increases more the performance of the collector but their economic viability is questionable unless the collectors are used in hightemperature applications. The use of double-glazing is also questionable because at low temperature applications gives worse performance. However, at higher temperatures double-glazing is superior due to the better insulating properties and the minimization of the thermal top losses. Another point of interest is that at lower temperatures the use of advance coating materials can let to lower performance, as the temperature of the absorber plate is low and thus radiation losses are minimal.