Browsing by Subject "Luminescent Solar Concentrator"

Now showing 1 - 3 of 3
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    Light Management and Optical Loss Mitigation for Photovoltaics: Downshifting, Downconversion, and Tandem Solar Cell Designs
    (2023-07) Keil, John
    The efficiency of single-junction Si photovoltaic cells has continually increased over the past several decades, but is approaching fundamental thermodynamic limits. Holding over 95% of the solar module market share, Si modules will continue to be an integral part of the rapidly expanding photovoltaic industry, so different device technologies that increaseSi cell efficiencies beyond thermodynamic limits, or that expand the available installation sites for solar cells, are needed. In this thesis, three types of technologies are discussed that use optical design to more efficiently use the high energy solar spectrum for Si PV: downshifting, downconversion, and tandem solar cells. We first discuss the design of downshifting and concentrating devices called luminescent solar concentrators (LSCs). Tandem LSC architectures, which combine multiple luminophores to broaden the absorption spectrum, are one potential route to increase the efficiency of these devices. We first describe an analytical model to develop luminophore selection criteria for tandem LSCs. We find that luminophores with high photoluminescent quantum yield, minimal overlap between the absorption and photoluminescence spectrum, and an absorption onset closely matched to the band gap of the chosen photovoltaic cell yield the best LSC performance. We then create bilayer LSCs, which combine CdSe/CdS and Si nanocrystals in a monolithic waveguide. Through a combination of transmission measurements, position-dependent photoluminescence measurements, and ray-tracing simulations, the bilayer LSC was found to sensitize Si nanocrystal absorption and enhance the optical efficiency by 30% relative to a single layer LSC. We discuss the use of the bilayer device in agrivoltaic applications, and then explore this use further using a thin-film stack optimization methods to direct emission out one LSC side toward the plant species. The LSC extraction efficiency is increased from 13.9% to 15.1%. We next consider optical designs for downconversion, a process by which one high energy photon is converted into two lower energy photons. We consider the coupling efficiency from the downconverter to a realistic Si solar module in several different configurations, finding an optical coupling efficiency of 95.25% by placing the downconverting film directly on the Si cell. This enhances the power conversion efficiency by 2% absolute. Lastly, CdTe/Si four-terminal tandem solar cells are studied to improve the sub-band gap transparency of CdTe solar cells. We find that the surface texture of the CdTe significantly impacts light transmission into the Si bottom cell, and that the losses are dominated by the transparent conductive oxide absorption. An optical design solution is proposed that mitigates transparency loss and enhances the short circuit current density of the Si cell by 2.5 mA/cm2 , which enhances the tandem efficiency by a relative increase of 5.6%.
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    Supporting Data for Design Guidelines for Luminescent Solar Concentrator Greenhouses in the United States
    (2024-11-21) Loh, Kristine Q; Harbick, Kale; Eylands, Nathan J; Kortshagen, Uwe R; Ferry, Vivian E; veferry@umn.edu; Ferry, Vivian E
    Agrivoltaic greenhouses combine controlled environment agriculture and photovoltaics in one plot of land to simultaneously address the global challenges of renewable energy and sustainable food production. Luminescent solar concentrators (LSCs) can benefit these systems by providing additional design flexibility, granting the ability to tune light transmission for plant growth while generating electricity. Herein, we determine design guidelines for the implementation of LSCs in agrivoltaic greenhouses given the two competing priorities of light used for crop yield or for energy generation. Using a comprehensive model, we evaluate the impact of LSC design choices on the greenhouse environment, energy generation, crop yield, and economic value in 48 locations across the contiguous United States. We show the PV coverage ratio and the greenhouse’s heating demands determine the energy offset provided by the LSC. For improving crop yield, luminophore selection should maximize transmitted red light. We demonstrate the sensitivity of the economic value to crop yield, thus dictating luminophore selection for optimizing plant growth. Based on current project technology costs, LSC greenhouses are as profitable as conventional greenhouses generally for states below 40 °N. Future improvements to LSC manufacturing may allow previously unprofitable LSC greenhouses to become economically viable in northern states. This work showcases the broad design space for LSCs in agrivoltaic systems and the strong potential of integrating LSCs into greenhouses.
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    Supporting Data for Luminescent Solar Concentrator Greenhouses for Concurrent Energy Generation and Lettuce Production in the United States
    (2024-05-23) Loh, Kristine; Harbick, Kale; Eylands, Nathan; Kortshagen, Uwe; Ferry, Vivian; veferry@umn.edu; Ferry, Vivian; University of Minnesota Department of Chemical Engineering and Materials Science
    Meeting the needs for both renewable energy production and increased food supply to sustain growing communities remains a global challenge. Agrivoltaic greenhouses can meet these dual needs in one plot of land, mitigating land competition. Luminescent solar concentrators (LSCs) benefit these systems by providing additional design flexibility for crop-specific spec-trum modification while allowing sufficient light transmission for crop growth. Silicon quantum dots (Si QDs) have received growing interest as a material candidate for LSC greenhouses as well. We present an investigation into the impact of Si QD film concentration on the energy demands of an LSC greenhouse in Phoenix, Arizona through a comprehensive modelling framework. We then expand upon one Si QD concentration and simulate LSC greenhouses in 48 locations across the United States. We demonstrate LSC greenhouses can supply their annual energy demands in warm climates, where greenhouse heating demands remain low. LSC greenhouses can also be as profitable as the conventional glass greenhouse if the crop yield remains comparable or if the greenhouse can benefit from net metering.