Modeling, Design, and Fabrication of Spectrally-Selective Mirrors for Photovoltaic Thermal Management
2020-07
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Modeling, Design, and Fabrication of Spectrally-Selective Mirrors for Photovoltaic Thermal Management
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2020-07
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A typical c-Si photovoltaic module will operate 20-30K above ambient temperature due to waste heat generated as it converts incident sunlight into electrical power. As temperature increases, the conversion efficiency drops by ~0.4%/K, reducing overall power output. Reducing the total amount of waste heat generated during operation would both lower the module operating temperature and improve its efficiency and energy yield. Waste heat is generated in the module in part due to parasitic absorption of sub-bandgap light that does not have enough energy to be useful for power conversion. Sub-bandgap reflection offers a method of preventing parasitic absorption, cooling the module, and increasing its efficiency. In this thesis, a time-independent matrix model is introduced to calculate module energy yield and waste heat generation through parasitic absorption, recombination, and electronic losses. The model considers the spectral and angular dependence of the optical properties of the module including modification by photonic structures, and is used to characterize and optimize the design of aperiodic photonic mirrors which selectively reflect sub-bandgap light from the module and enhance its energy yield. Importantly, these mirrors are designed considering weather and irradiance conditions typical for outdoor fixed-tilt module installations. As a result, it is shown that these mirrors are omnidirectional, achieving the required spectral selectivity regardless of the angle of incidence of sunlight or the geographic location of installation. Low-complexity mirror designs which are simple to fabricate offer the most potential for reducing the cost of energy. These designs are primarily anti-reflection coatings, but also avoid a rise in operating temperature while increasing energy output. Two simple designs are fabricated, integrated into modules, and tested outdoors. The fabricated mirrors have the desired spectral selectivity, and reduce module operating temperature by over 1K. Alternative strategies to reject sub-bandgap light, including reflection from the cell surface or cell rear contact, and backscattering from near the cell are also modeled and compared to result for reflection from the glass. Designing for the glass interface in particular allows maximization of the dual benefit, optical and thermal, of the mirrors.
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University of Minnesota Ph.D. dissertation. July 2020. Major: Chemical Engineering. Advisor: Vivian Ferry. 1 computer file (PDF); xvi, 153 pages.
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Slauch, Ian. (2020). Modeling, Design, and Fabrication of Spectrally-Selective Mirrors for Photovoltaic Thermal Management. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/220621.
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