Comparative study on solar flat-plate collectors coupled with three types of reflectors not requiring solar tracking for space heating

The existing reflector not requiring solar tracking used in solar flat-plate collector is mainly plate-type structure. This kind of structure is simple, but it is not the optimal one. To solve this problem, the new polyline-type and parabolic-type reflectors not requiring solar tracking were proposed for solar flat-plate collectors in this paper. A comparative study of the two types of reflectors and the existing plate-type reflectors under no sun-tracking conditions was carried out by theoretical and experimental methods. The reflected light losses under the off-design conditions were analyzed. The transient and annual operation characteristics were discussed. The results showed that under the design conditions the ranking of boost factor is parabolic-type, polyline-type and plate-type. But the reflection losses under the off-design conditions are just the opposite. Under the same reflective area with the collectors, when the reflection losses are considered, the increases of solar radiation on the collectors are 40.3%, 27.7% and 19.8% for the polyline, parabolic and flat-plate reflectors respectively in the heating season. In the coldest three months, the polyline-type always has the largest solar radiation. This paper is helpful to improve the efficiency and economy of solar space heating in cold areas.