Sandia has coded a view factor model that estimates back-side irradiance across a row of bifacial modules, accounting for the row’s shadow on the ground and assuming an isotropic model for sky diffuse irradiance. Figure 1 and Figure 2 show the modeled variation in back-side irradiance by cell at noon and 3 PM, respectively, for…
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NREL has formulated an array-scale model which assumes edge effects are not significant with respect to the overall energy production for large PV arrays. The figure illustrates the components of irradiance considered in the array scale model which include: sky diffuse irradiance from the visible wedge of the sky accounting for circumsolar, horizon and rest-of-sky…
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View factor models are used for radiative transfer calculations of the amount of radiation leaving one surface (A) that reaches a second surface (B). The view factor is the fraction of the radiation from surface A that hits surface B. In the context of bifacial PV arrays, the surface B is the back side of…
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Ray Tracing Work at the University of Iowa COMSOL is a finite element method (FEM) solver and the Ray Optics Module can be used to model electromagnetic wave propagation in systems in which the wavelength is much smaller than the smallest geometric detail in the model. The electromagnetic waves are treated as rays that can…
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Ray Tracing Work at NREL RADIANCE is a reverse ray tracing model typically used for lighting design of buildings. This simulation tool provides physically realistic image rendering and illuminance mapping, and has been used previously for the modeling of bifacial PV installations [Lo, Lim and Rahman, 2015]. We have conducted initial validation of this modeling…
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Ray tracing models follow light from the source to the surface of interest (forward ray tracing) or from the surface of interest back to the source (reverse ray tracing). These models are typically based on a Monte Carlo approach that simulates hundreds or thousands of different rays and uses optical physics to predict how each…
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The main challenge for modeling the performance of bifacial PV arrays and systems is the prediction of the irradiance hitting the array from the back side. Unlike the front side irradiance, which is usually assumed to vary little with position on the array, backside irradiance varies quite a lot with position, array design, and near…
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A standard module rating condition for bifacial PV modules would be a boon to the PV community as it would provide a common, accepted basis for measurement and nameplate rating of bifacial PV products. In particular, conditions that also harmonize with existing PV module rating standards are desired. Through simulation and experiment, we are investigating…
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Preliminary measurements were made at Sandia to demonstrate the process of measuring bifacial gains and to illustrate some of the challenges of designing bifacial experiments that are representative. In this short term test, we mounted two bifacial and two monofacial modules in two-up, landscape orientation at 35° tilt. It is worth noting that our setup…
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Sandia is building an outdoor bifacial PV performance test bed in Albuquerque, NM to collect data to be analyzed and shared with the community. This data will be used to develop predictive performance models that can eventually be included in commercial applications. Based on a review of literature on this topic, we designed our test…
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