New Publication from the SUNLAB: Optics Express

SUNLAB has published a new paper in Optics Express, first-authored by MASc candidate Trevor Coathup. This paper quantifies the impact of torque tube reflections in tracked bifacial photovoltaic systems over a typical meteorological year in Livermore, California, USA.

Among the racking elements of bifacial photovoltaic single-axis tracked systems, the torque tube introduces the most shading and reflection, increasing irradiance nonuniformity and electrical mismatch loss. Ray tracing bifacial PV modeling software can capture these effects at a high computational cost, and two-dimensional or three-dimensional view factor models can estimate their impacts with shading factors to iterate through simulations more quickly. DUET, SUNLAB’s three-dimensional view factor model, which accounts for detailed shading using ray-object  intersection, can be expanded to include reflections from racking elements, specifically the torque tube, and balance the accuracy-computational intensity tradeoff. 

We simulate the impact of torque tube reflection on irradiance, electrical mismatch, and total energy yield based on sun position and sky condition for central bifacial photovoltaic modules on one-in-portrait (1P) and two-in-portrait (2P) single-axis trackers. We extract the torque tube reflection using a ray tracing model and introduce it as an additional irradiance source in DUET to assess the impact of torque tube reflection in such a model. 

Despite the gap between modules allowing for more incident illumination on the torque tube in the 2P system, the relative impact of the torque tube reflection is similar, and can be larger in the 1P system for low irradiance conditions. Torque tube reflection increases annual irradiance in 1P and 2P systems by 0.17% and 0.30%, respectively. Overall, torque tube reflection increases the predicted instantaneous energy yield by up to 0.8% and 0.4%, and the annual energy yield by 0.11% and 0.18% in 1P and 2P system, respectively.

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T. J. Coathup, M. R. Lewis, A. C. J. Russell, J. E. Haysom, C. E. Valdivia, and K. Hinzer, Impact of torque tube reflection on bifacial photovoltaic single axis tracked system performance, Optics Express 31(4) (2023).  DOI: 10.1364/OE.481301