Numerical Modeling of Bifacial PV String Performance: Perimeter Effect and Influence of Uniaxial Solar Trackers

Abstract

The bifacial photovoltaic (PV) systems have recently met large interest. The performance of such systems heavily depends on the installation conditions and, in particular, on the albedo radiation collected by the module rear side. Therefore, it is of crucial importance to have an accurate performance model. To date, in the scientific literature, numerous models have been proposed and experimental data collected to study and optimize bifacial PV system performance. Currently, 3D and 2D models of bifacial PV devices exist. Though the former are more mathematically complex, they can lead to more accurate results, since they generally allow to fully consider the main aspects influencing a bifacial PV system performance. Recently, we have proposed and validated through experimental data a 3D model tested as a function of module height, tilt angle, and ground albedo. In this work, through such a model, we studied the role played by the perimeter zones surrounding the PV string, by considering PV strings of 30 or 60 modules. We considered the cases of fixed installation with optimal PV module tilt and of installation with uniaxial horizontal solar tracker. We evaluated the PV energy yield as a function of the size of the perimeter zones for the two cases, i.e., both with and without the solar tracker. In optimal perimeter conditions, we then studied the behavior of bifacial and mono-facial PV strings by varying the geographical location in a large latitude range.

The Effects of Module Temperature on the Energy Yield of Bifacial Photovoltaics: Data and Model

“…In summary, the problem of predicting the PV module temperature in BPV is a crucial aspect which needs further analysis. In this paper, we report an experimental study focused on this problem, and on the basis of the experimental results, we refine the physical model that we have previously proposed [10,11] which calculates the BG in three-dimensional system geometry.…”

“…In refs. [10,11], we have proposed a model to evaluate the I-V characteristics and energy yield of PV bifacial modules and strings. The model assumes a complete threedimensional (3D) geometry, that is, no simplification to a bidimensional (2D) approximation is carried out.…”

“…More specifically, Isc,front was calculated as the convolution of the front side external quantum efficiency (EQE) with the spectrum of the solar radiation incident to the front, while Isc,back was calculated as the integral over all the underlying ground elements of the radiation diffused by each element, proportional to the solid angle under which it sees the solar cell back. Further details of the model are reported in [11]. In the calculation, we took into account the wavelength dependence of ground albedo, back-side EQE, and the spectrum of the Figures 5-7 also report the calculated best-fit curves of the quantitative model described below, which allows performing quantitative evaluations of the energy yield of bifacial PV systems.…”

“…Therefore, to take into consideration the large observed temperature difference, we refined the model of refs. [10,11] as follows: in a conventional monofacial PV module the temperature is evaluated as…”

“…Sun et al [9] studied the optimisation of a stand-alone bifacial module for various geographic locations. In our previous works [10,11], we have proposed an analytical model which considers the spectral content of the solar radiation incident on the front and back surfaces of PV modules. This model has been validated on experimental data and applied to evaluate inhomogeneous illumination on large PV strings and energy yield of BPV systems, either with fixed-tilt installation or uniaxial trackers.…”