The Impact of Optical Properties on the Performance of Flat Plate Solar Collectors
Date Issued
June 2003
Author(s)
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.
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.
Subjects
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