Nontoxic nanomaterials for luminescent solar concentrators in agrivoltaic systems

Abstract

Agrivoltaic systems combine agriculture and photovoltaics (PV) to meet the growing global needs of both renewable energy and sustainable food production in one plot of land. Greenhouses provide a controlled environment for year-long crop production, but demand significant amounts of energy, often stemming from non-renewable sources. This dissertation focuses on developing nontoxic luminescent solar concentrators (LSCs) for agrivoltaic greenhouses to offset or meet these high energy demands. LSCs utilize luminescent films to absorb, emit, and concentrate both diffuse and direct sunlight toward nearby PV cells, acting as solar windows. There is a wide, complex LSC design space with ample opportunity for exploration because the luminescent material, its film loading, and the film’s size/shape can be optimized for both plant growth and energy production. We first demonstrate the preparation of air-stable silicon quantum dots (Si QDs), which are attractive luminescent materials due to their biocompatibility and silicon’s earth abundance. We applied high-pressure water vapor annealing (HWA) to plasma-synthesized Si QDs to form silicon/silica core/shell QDs. Varying the steam pressure controlled the photoluminescence quantum yield (PLQY) and peak wavelength. Optimized conditions resulted in an environmentally stable PLQY of >40%. Tuning Si QD surface chemistry both pre- and post-HWA improved their dispersion in polar solvents as well, a necessary step toward their implementation in LSC films. We next model the potential of additional nontoxic QDs as passive, spectral-shifting sunlight filters for improving crop yields. By simulating films with nine different QDs, we calculated a concentration-dependent yield improvement of up to 45%. QDs that strongly absorb blue/green light and downshift it to red/far-red light resulted in the highest yields. Despite this strong absorption, QD films can be utilized broadly in the United States as demonstrated by outdoor sunlight maps. In contrast to trends in QD research, increasing the PLQY or film outcoupling efficiency did not further increase lettuce yield. Then, we establish LSC design rules for agrivoltaic greenhouses. By building a comprehensive model, we evaluated 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 determined the energy offset provided by the LSC. We demonstrated 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. Further analysis of roof-only LSC greenhouses shows that partially covering the greenhouse with luminescent films hinders the photosynthetic benefits of spectral shifting. Lastly, we conduct both single- and multi-objective optimization of agrivoltaic LSCs to determine optimal luminescent materials and LSC configurations. We find that one LSC layer best optimized crop yield, as this configuration allowed for the transmission of the optimal spectrum and light intensity for plant growth. To balance both crop yield and electricity generation, we produced Pareto fronts that showed all solutions resulted in crop yield gains of 35% - 50%, with a trade-off between crop yield and electricity generation. This work showcases the broad design space for LSCs in agrivoltaic systems and the strong potential of integrating LSCs into greenhouses.