Passive sun tracking of a single evacuated tube collector with the focusing mirror

摘要

Evacuated tube solar collectors with a heat pipe is one of the most widely used solar collectors types. Although they are characterized by a very high energy conversion efficiency there are still possibilities for improvements. One of the available options is the use of mirrors focusing the solar radiation. In order to maximize the efficiency of absorbing solar energy with the focusing mirrors their manufacturers recommend the use of the tracking system for the apparent movement of the sun. Nevertheless, such a solution has several disadvantages which include: higher investment costs and energy consumption as well as potentially higher risk of faultiness. This paper presents the results of the experimental research, on the basis of which it was possible to determine the reduction of the radiation amplification factor in the case of system without solar tracking in comparison with the maximum theoretically attainable amplification factor. The research was conducted for a single evacuated tube collector with and without the focusing mirror. The parabolic focusing mirror, made of bent aluminum sheet, was selected for this analysis. As the result of these analyses the daily amplification factor was determined and this factor emphasizes the benefit of using the focusing mirror. Moreover, it was concluded that the amplification factor is insignificant when the solar hour angle is greater than 15° while azimuth of focusing mirror is direct south at the same time.