A Realistic Approach of the Maximum Work Extraction from Solar Thermal Collectors

Evangelos Bellos,Christos Tzivanidis

doi:10.3390/asi1010006

Evangelos Bellos, Christos Tzivanidis

Open Access

https://doi.org/10.3390/asi1010006

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Abstract

In this study, the maximum work extraction from the incident solar energy on solar thermal collectors is investigated by coupling solar collectors with a Carnot machine. A simplified thermal model for the solar collector performance is developed in which the radiation losses play a significant role. In every examined case, the optimum operating temperature that leads to maximum work extraction is calculated. The final results are presented parametrically, covering a great variety of real solar collectors. Moreover, the validation procedure of the developed model proves high accuracy. The results show that non-concentrating collectors should operate up to 400 K while concentrating collectors in higher temperature levels. More specifically, a parabolic trough collector can operate efficiently in temperature levels up to 850 K, while solar dish collectors can operate efficiently in temperature levels up to 1100 K. The results of this study can be exploited for the preliminary design and optimization of solar thermal systems. Moreover, a clear and realistic upper limit concerning the exergy production of solar irradiation with solar thermal collectors is given.

Highlights

Solar energy is a promising renewable energy source that is able to substitute the use of fossil fuel to a large degree [1,2]
The heat convection losses are negligible in this model, because the receiver is assumed to be inside a huge dome
In concentrating collector the convection losses have a minor influence of the thermal losses, something that enforces the main assumption of this study

Summary

Introduction

Solar energy is a promising renewable energy source that is able to substitute the use of fossil fuel to a large degree [1,2]. The most important parameter in the solar Plants is the operating temperature, because this parameter influences the collector efficiency and the thermodynamic cycle efficiency. Higher temperature levels make the solar collector have greater thermal losses, but the efficiency of the coupled thermodynamic cycle is greater. The selection of the solar collector kind is dependent on the operating temperature levels. Evacuated tube collectors are usually selected for applications as solar coolers, with industrial heat in the low-medium temperature range up to 150 ◦C [7]. At higher temperature levels, concentrating collectors are the only possible choice. Fresnel collectors [12] and solar towers are promising concentrating technologies for medium (up to 400 ◦C) and high temperatures (up to 600–700 ◦C), respectively

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