A diverse range of sustainable energy sources will play a crucial role in building a sustainable future and reducing greenhouse gas emissions. There is an increase in competition between food and energy production for land use and as such, interest in co-use of land for both agricultural and energy production has become an area of interest for research [1]. Multiple studies have been conducted that analyse various approaches for using silicon solar panels on greenhouse roofs and the effects on crop yields, energy production and microclimate. [2] [3] [4] [5] This study investigates the concept of using semi-transparent luminescent solar concentrators as greenhouse rooftop panels for the co-production of food and energy. Both the crops and luminescent dyes used in solar concentrators have a specific absorption spectrum for solar radiation. [6] Plants have a high absorption of light in the blue and red spectrum with peaks at 440 nm, 620 nm, and 670 nm [7] which it uses for photo morphological/phototropic responses and photosynthesis, respectively [8]. A luminescent concentrator that allows light of these wavelengths to pass undisrupted through while capturing energy for electrical conversion from other areas of the spectrum offers a promising solution to agrivoltaic applications. Photosynthetically active radiation (PAR) consists of solar radiation from between 400-700 nm which is used by crops to drive photosynthesis. Non-PAR, or non-photosynthetically active radiation, is light that falls outside these wavelengths such as infrared and UV radiation which can be captured and converted into electricity without impacting the photosynthetic rate of the crops. Luminescent dyes that absorb light in the PAR region and the IR region are integrated into the model. By carefully choosing a luminescent dye that absorbs radiation from the non-PAR spectral region and from the regions of low photosynthetic absorption in the PAR region, electricity can be generated while minimizing the effects of reduced solar irradiance on crop yield. By reducing the amount of light entering the greenhouse the crop experiences a shading effect and the micro-climate within the greenhouse is altered. Shading on greenhouses is commonly used in warm climates during summer [9] [10] [11]. An analysis of the literature on the effects of shading in greenhouses was done to assess the possible impacts of semitransparent roof material on the microclimates and crop yields in greenhouses. A reduction of solar radiation due to greenhouse shading was found to have a beneficial effect on crop yield and water use in climates/seasons with high solar irradiance and hot temperatures [3] [9] [10] [11]. Herein we perform numerical analysis to model a greenhouse made using semi-transparent roof-top panels that function as luminescent solar concentrators that direct non-PAR onto photovoltaic cells located at the edges of the panels. Our results show that by designing LSCs with optimal concentrations and types of dye the operation of a greenhouse can be greatly enhanced ...
Numerical calculations are performed to determine the potential of using one-dimensional transparent photonic crystal heat mirrors (TPCHMs) as transparent coatings for solar receivers. At relatively low operating temperatures of 500 K, the TPCHMs investigated herein do not provide a significant advantage over conventional transparent heat mirrors that are made using transparent conducting oxide films. However, the results show that TPCHMs can enhance the performance of transparent solar receiver covers at higher operating temperatures. At 1000 K, the amount of radiation reflected by a transparent cover back to the receiver can be increased from 40.4% to 60.0%, without compromising the transmittance of solar radiation through the cover, by using a TPCHM in the place of a conventional transparent mirror with a In2O3:Sn film. For a receiver operating temperature of 1500 K, the amount of radiation reflected back to the receiver can be increased from 25.7% for a cover that is coated with a In2O3:Sn film to 57.6% for a cover with a TPCHM. The TPCHM that is presented in this work might be useful for high-temperature applications where high-performance is required over a relatively small area, such as the cover for evacuated receivers or volumetric receivers in Sterling engines.
Herein we present an optical cavity in the form of a prolate ellipsoid that can greatly enhance the performance of solar thermophotovoltaic (STPV) systems. The geometrical parameters of the cavity can be designed to control the degree of photon recycling, the temperature of the emitter within the STPV system, gap distance and effective view factor between the PV cell and the emitter, and to minimize the emission losses. Numerical analysis shows the ellipsoidal optical cavity can be designed to achieve an effective view factor of 88.7% between the emitter and PV cell within a STPV system. Results show an efficiency of 5.62% in a STPV system with a GaSb PV cell and a black-body emitter under solar radiation at a concentration factor of 350X. Further, assuming the surface of the ellipsoidal optical cavity is capable of reflecting 99% of the radiation incident onto its surface, efficiencies of 15.54% can be attained when the solar concentration factor is 1400X. These results are attained for STPV systems without using selective absorbers, emitters or filters. The ellipsoidal optical cavity can be integrated into the design of advanced TPV systems and bring them closer to the high theoretical efficiencies TPV systems are capable of.
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