Abstract
In this article, we present a solar trough system in which the receiver pipe is enclosed in a glass cover under vacuum. The dominant radiation losses from the receiver are reduced by the use of a ‘hot mirror’ on the glass cover instead of a selective coating on the receiver pipe. We present the results for a general heat transfer model and compare the performance of a selective coating with that of a hot mirror, using simulations. We determined that a hot mirror is a viable alternative to a selective coating, and certainly allows higher temperatures of the working fluid. We recommend the use of a hybrid system, in which a selective coating is used in the part of the receiver pipe in the low temperature region, and a hot mirror is used in the high temperature region to reduce radiation losses.
Highlights
Solar energy has been identified as a strong candidate for use as an alternative energy source
In this study we focused on the possibility of a substitute for the selective coating, namely a hot mirror coating on the glass cover, which could both decrease radiation losses and raise the operating temperature of the working fluid
The glass cover temperature is seen to be much lower than the receiver pipe temperature, and this allows the glass cover to be coated with a hot mirror, because the hot mirror coating can operate at these temperatures (~500 K)
Summary
Solar energy has been identified as a strong candidate for use as an alternative energy source. Numerous ways of extracting useful energy from the sun have been investigated in the form of applications ranging from domestic applications (such as flat-plate collectors,[1] cookers,[2] solar panels[3] and pool heating systems1) to those of industrial size (including power towers,[4] solar troughs,[4] solar panel arrays[3] and desalination plants[5]). Research in this field has largely focused on methods of efficiently converting solar energy into the desired energy form (such as thermal or electrical). The largest solar trough power plant in the world, the SEGS (Solar Energy Generating Systems) in California with a peak capacity of 364 MW, has been operational and studied in detail since the mid-1980s.6 Solar trough systems consist of long, cylindrical parabolic mirrors and a similar length of receiver unit (absorber tube) through which a ‘working fluid’ circulates (Figure 1)
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