The effects of spectral albedo on bifacial silicon heterojunction photovoltaic cell performance is explored in six locations in North America using an optoelectronic drift-diffusion model. We model seven spectral albedos using the scaled rear irradiance method and compare to broadband values. Cell performance varies geographically, with the maximum efficiency of 22.6% calculated for Cambridge Bay (69°N) with snow ground cover, and maximum output power of 216 W/m2 for Mexico City (20°N) with white sand. Neglecting spectral effects of albedo can under or over-estimate power by >2%, which can significantly impact system-level energy yield.
Non-uniform irradiance on the rear side of bifacial photovoltaic (PV) modules causes electrical mismatch between cells and energy loss across the module. Racking structures increase this non-uniformity through shadows and reflections that vary throughout the day. However, commercial software typically use constant values to estimate mismatch losses in annual simulations. We investigate the impact of torque tube shading and reflection on rear side irradiance mismatch in bifacial PV modules in one-in-portrait (1P) and two-in-portrait (2P) horizontal single-axis trackers with a range of ground albedos over a typical meteorological year in Livermore, California, USA. Irradiance simulations use a version of bifacial_radiance, the National Renewable Energy Laboratory’s python wrapper for the RADIANCE ray tracing software, which we modified for arbitrary 2D irradiance sampling of the module(s) under investigation. For a torque tube reflectivity of 0.745, torque tube reflection accounts for 3.0% and 5.5% of the annual rear insolation in 1P and 2P configurations, respectively, for a 0.2 albedo; or 2.9% and 3.1% for a 0.6 albedo. Torque tube reflection decreases annual rear insolation mismatch from 11.8% to 10.7% in 1P configurations, and from 11.5% to 9.8% in 2P configurations with 0.2 albedo. Similarly, with 0.6 albedo, annual rear insolation mismatch decreases from 12.6% to 11.6% in 1P configurations, and from 11.9% to 10.4% in 2P configurations. However, we demonstrate that annual figures are insufficient for capturing the impact of torque tube reflection; seasonal and diurnal variations must also be considered.
Bifacial photovoltaics present a clean and cheaper alternative to diesel generators for high-latitude remote communities; however, solar cells are tested at air mass 1.5, while average air mass increases with increasing latitude. For example, Cambridge Bay (69ºN) has an irradiance-weighted average air mass of 3.1. We demonstrate improved efficiency of bifacial silicon heterojunction modules under high air mass spectra due to reduced incident UV light. We implement air mass correction in our bifacial PV modelling software, and we quantify the impact of air mass on energy yield for fixed-tilt and tracked systems in high latitude locations.
Bifacial photovoltaics present a clean and cheaper alternative to diesel generators for high-latitude remote communities; however, solar cells are typically tested at 0° angle of incidence, 25°C, and AM1.5, from which high-latitude conditions vary greatly. A bifacial silicon photovoltaic cell optimized for high-latitude conditions will improve energy yield for these systems. We integrate experimentally-derived cell parameters with a systems-level model capable of fixed-tilt and tracked energy yield predictions. We optimize to find the most efficient cell design for high-latitude environments in Sentaurus and SunSolve and determine the resulting improvement in energy yield for an entire panel in MATLAB.
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