Performance Investigation of Bifacial PV Modules in the Tropics

Abstract

ABSTRACT: Bifacial photovoltaic modules can convert solar energy to electrical energy from both sides of the module. This means that light reflecting off the rooftop and hitting the rear side of the module can also be converted. Tropical climates such as Singapore have plenty of sunlight to produce power from photovoltaics, with diffuse content of more than 50% of the total irradiance. Our interest is to know the behaviour and performance of bifacial modules under these conditions. In the present study, commercially available bifacial and monofacial modules of the same cell technology were installed in Singapore on a rooftop at the National University of Singapore (NUS) and data for various electrical parameters are being collected. The performance ratio with respect to the horizontal-plane irradiance has been measured to find the optimum tilt angle of the bifacial modules for Singapore. The gain in short-circuit current has been studied with respect to the diffuse/global irradiance ratio and the time of the day. The results from this study will provide guidelines for the optimal installation of these modules in the tropics, and will also help to improve the design of bifacial modules for tropical climate conditions. Keywords: Bifacial PV module, diffuse radiation, tropical climate 1 INTRODUCTION In contrast to monofacial PV modules, which only convert light which enters the module via the front side into electricity, bifacial PV modules can convert light which enters the module from either side. This means that bifacial modules can perform better than monofacial modules when installed under the same conditions. This module type can enhance the power density (power per unit area) and thus area related costs such as land, cabling, installation structure etc. can be reduced [1]. A power gain of 50% from bifacial modules as compared to monofacial modules has been reported in the literature for specific installation conditions [2]. The potential applications of bifacial modules such as noise barrier along highways, fence integrated PV system, component of building architectures, static concentrating system, multifunctional bifacial PV sun shading element etc. have been reported by various authors [3-6]. The energy gain of a bifacial module over a monofacial module depends on a number of factors, including the installation parameters as well as the characteristics of the incident irradiance, since these factors affect the amount of light which can enter via the rear side of the module. To estimate the gain from bifacial modules, various simulation and experimental methods have been proposed in the literature [7, 8]. The solar radiation in tropical climates like Singapore can be characterised by large diffuse content in the global irradiance. Hence, to know the performance and behaviour of bifacial modules in the tropical climate of Singapore, it is necessary to have the experimental data for the bifacial modules in these climatic conditions. This experimental data can help in optimising the bifacial PV modules and the PV installations for the tropical climate of Singapore. 2 OUTDOOR INSTALLATION SET-UP AND MEASUREMENTS Commercially available bifacial and monofacial modules of the same silicon solar cell technology were installed in Singapore (on a rooftop at the National University of Singapore, NUS) in December 2011. Prior to this, their I-V characteristics were measured under standard test conditions (STC) at the Solar Energy Research Institute of Singapore (SERIS), NUS. For the first experiment, the installation was South facing, at elevation of 100 cm above the flat roof surface. All performance indices like maximum power (P