The size and number of utility-scale bifacial photovoltaic (PV) installations has proliferated in recent years but concerns over modeling accuracy remain. The aim of this work is to provide the PV community with a validation study of eight tools used to simulate bifacial PV performance. We simulate real 26 kilowatt-peak (kWp) bifacial arrays within a 420-kWp site located in northern Europe (55.6° N, 12.1° E). The substructures investigated include horizontal single-axis trackers (HSATs) and fixed tilt racks that have dimensions analogous to those found in utility-scale PV installations. Each bifacial system has a monofacial reference system with similar front side power. We use on-site solar radiation (global, diffuse, and beam) and albedo measurements from spectrally flat class A sensors as inputs to the simulation tools, and compare the modeled values to field measurements of string level power, rear and front plane of array irradiance, and module temperature. Our results show that state-of-the-art bifacial performance models add ~0.5% uncertainty to the PV modeling chain. For the site investigated, 2-D view factor fixed tilt simulations are within ±1% of the measured monthly bifacial gain. However, simulations of single-axis tracker systems are less accurate, wherein 2-D view factor and 3-D ray tracing are within approximately 2% and 1% of the measured bifacial gain, respectively.

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One of the prerequisites for a reliable energy yield prediction of bifacial photovoltaic (PV) systems is the capability of modeling the backside irradiance of those systems with high accuracy. Currently, the most important optical models used to quantify the reflected irradiance on the backside of a bifacial solar panel are view factor and ray tracing. The MoBiDiG simulation tool has been developed at ISC Konstanz uses the view factor (VF) concept to model the rear irradiance. In addition to the VF concept, ray tracing (RT) has been adopted to determine the backside irradiance of bifacial modules by using the open-source tool bifacial_radiance that has been developed by the National Renewable Energy Laboratory (NREL). A customized monocrystalline silicon solar panel has been built in order to evaluate the accuracy of the existing optical models by locally resolved rear irradiance measurement. The performance of rear irradiance has been investigated along the rows of the customized PV module during sunny and cloudy days with typical back irradiance values of ≈50 and ≈ 150 W∕m 2 . The comparison of measured and modeled data has been carried out on hourly, daily, and monthly basis, and the results show lower deviations for solar cells located in the center of the PV module than on the edge. Moreover, the concept of decisive solar cells has been introduced and applied to both measured and modeled data, solar cells located in the center rows were found to act as the most decisive solar cells. Finally, considering the installation configuration studied here, ie, bifacial mounting with low clearance height (below 0.2 m), both hourly RT and VF approaches are able to model long-term cumulative irradiance received by decisive solar cells with a very high accuracy ranging from ±0.5% to ±2%.