OPTIMAL SIZE AND POSITION OF THE PLANAR BACK REFLECTOR MOVEABLE ONLY IN THE DIRECTION NORMAL TO THE BIFACIAL SOLAR COLLECTOR PLANE

Abstract

In this paper, the concept of a collector-reflector system consisting of a bifacial solar collector and a single flat-plate reflector separated and placed in parallel below the collector but moveable only in the direction normal to the collector plane is investigated. The developed mathematical model was used to optimize the size and position of the planar back reflector. The optimal hourly, daily, monthly and annual distances between the collector and reflector were determined. In addition, the daily, monthly and annual energy performance of the optimized bifacial collector-reflector system was estimated and compared with that of the corresponding monofacial solar collector. Based on the obtained results, two ways of use of the reflector are recommended, either according to the optimal hourly (moveable reflector) or optimal annual (fixed reflector) reflector positions. With optimally positioned moveable or fixed reflector the total solar radiation incident on the bifacial solar collector can be significantly higher than that for a monofacial solar collector. Its largest daily and monthly as well as average annual increase is: 74% (59%), 65.91% (46.21%) and 54% (39.4%), respectively. The proposed model can be applied to evaluate the energy performance of flat-plate bifacial thermal, photovoltaic or photovoltaic-thermal solar collector, of arbitrary size and position, which is in this arrangement with a planar reflector.