T. Tomson

Department of Materials Science, Tallinn University of Technology, Ehitajate tee 5, 19086, Tallinn, Estonia, e-mail: teolan@staff. ttu. ee

Abstract

Two-positional exposure (discrete tracking) of PV-modules (or flat-plate solar thermal collectors) allows increased efficiency mainly due to a prolonged daily interval of performance. A stand-alone PV-module in the regime of the two-positional tracking is the most effective. If such PV-modules are concentrated into a farm, they will mutually shadow each-other during some transient shading interval in the sunny morning and in the sunny evening. For that reason a tracked PV-farm performs somewhat less effectively than the said stand-alone PV-module and its usage may be problematic. Therefore, the use of a tracked PV-farm is analyzed and discussed in this paper. In the farm the gain (increased efficiency) of discrete tracking depends on the relative distance between the tracked modules and the deflection angle. A PV-farm with a two-positional exposure is beneficial if the distance between the neighbor modules surpasses the two-three values of their width.

Keywords: PV-farm; two-positional exposure; shading interval; gain; deflection angle; relative distance

1. Introduction

Performance and profit of a stand-alone solar collector with two-positional tracking was analyzed in [1]. Such a collector has an axis around which it can be deflected (rotated) into two positions: eastward (AM) and westward (PM). In the conditions of Nordic region (~60° N) and maritime climate, the average statistical gain (increased efficiency or the profit) may reach up to 130%, depending on the initial tilt angle, deflection angle and share of direct radiation. Due to the positive correlation of the gain on the ratio of the direct and the diffuse radiation, the average gain is evidently higher for the continental climate. As a stand-alone solar collector is usually an exception, it is important to analyze the performance of the collector in a solar farm, which consists of several tracked collectors installed in parallel. Due to mutual shading their performance is somewhat less effective, therefore it is required to find out what the extent of difference is and which circumstances influence the gain. This study has focused on these issues. Principally, there is no difference between the behavior of tracked solar-thermal collectors or tracked PV-modules, but we will look at PV-modules first. Tracking solar-thermal collectors are complicated to use due to their (usually rigid) piping. Therefore we concentrate on the PV-modules. The theoretical analysis was done by a self-created computer simulation model. Experimental testing was performed by help of the physical model.