Design and simulation of a vacuum solar thermal flat plate collector prototype

This paper presents the design and a mathematical simulation model of a novel evacuated flat-plate solar thermal collector prototype. As it is known, for a typical solar thermal collector, the convective heat dissipation accounts for a large percentage of the overall thermal losses. These losses can be reduced by “insulating” the solar absorber with a suitable vacuum space (lower pressure than the atmospheric one) of the collector enclosure. The main problem of this solution is the high initial cost of the modifications required on the structure of the collector envelope (casing and glazing) to withstand the vacuum. Because of the reduced thermal losses, such a system is able to produce relatively high temperatures, compared to normal flat-plate collectors, but also retain their basic advantage which is the fact that there is no need to track the sun like the respective concentrating collectors, which can be used alternatively to produce the same level of temperatures. In this paper, an in-house mathematical model is developed for assessing the energy performance of such technology. A sensitivity analysis on the main parameters affecting the energy efficiency and the working fluid outlet temperature of flat-plate solar thermal collector is also presented. The aim of this analysis is to obtain useful design criteria for the fabrication of a novel evacuated collector prototype. Therefore, construction details about the improved prototype, as well as results about the calculation of the optimal system geometry and the selection of the considered collector materials are provided. In this regard, the description of the attempts carried out to obtain the best design options is also reported. Finally, a comparison between the optimized flat-plate solar collector against a typical one is also presented and encouraging results were achieved.