We have investigated the influence of the spectral albedo on the power output of bifacial solar cells. We adapted the Shockley-Queisser radiative flux balance framework to account for a variation of the spectrum and intensity of the incoming light. We find that the ideal band gap and the maximum efficiency depend on the spectral albedo of the surroundings and that optimal cell performance cannot be assessed when only accounting for a spectrally independent albedo. With a spectral albedo model, we predict that the power output for a bifacial silicon solar cell surrounded by green grass is 3.1% higher than for a wavelength-independent albedo, and even 5.2% higher for white sand. We experimentally verify this trend for silicon heterojunction solar cells and we derive the ideal spectral albedo.
We have performed a computational study on the enhancement of the power output of bifacial solar modules with effectively transparent contacts (ETCs). ETCs are triangular crosssectional silver grid fingers that redirect light to the active area of the solar cell, therefore mitigating grid finger shading losses. Furthermore, ETCs can be spaced densely leading to light trapping. We modeled bifacial silicon heterojunction solar modules with varying front and rear illumination and ETC coverages. We determined that shading losses can be almost fully mitigated and that light absorption can be increased by up to 4.7% compared with state-of-the-art screen-printed bifacial modules. Furthermore, we calculated that grid resistance and silver usage can be improved when using ETCs.
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