Spectrally selective agricultural solar module

Abstract

The present disclosure provides a translucent solar module that allows a portion of direct and scattered light in the visible wavelength range to pass through the module to the crops below, while redirecting direct and scattered near-infrared light to planar photovoltaic cells. The module includes a strip of opaque photovoltaic cells dispersed in a transparent substrate and an embedded optical element characterized by a thin-film interference filter applied to a non-planar geometry.

Description

Technical Field

[0001] The present invention relates to photovoltaic modules, and more particularly to a photovoltaic module that allows some portions of direct and diffused visible light to pass through and reach crops located below the module, while redirecting direct and diffused near-infrared light to photovoltaic cells dispersed in the plane of the module for power generation. Background Technology

[0002] Photovoltaics (PV) offers the lowest-cost energy source of any power source and will become the largest contributor to large-scale energy in the future. As the global energy system transitions to zero-emission renewable energy, most solar PV deployments will be on agricultural land. This is primarily due to several reasons: agricultural land is largely cleared, flat, unprotected, and close to existing transportation infrastructure, allowing for minimized deployment and operating costs. Most importantly, most solar PV deployments will be located close to existing power grid transmission infrastructure, situated around and between major population centers. This is the same area as high-yield agricultural land. For many densely populated countries or regions, the proportion of agricultural land required for solar PV deployment is at a level that will have a significant impact on local food production.

[0003] The expanded use of photovoltaics combined with agricultural activities (agricultural photovoltaics) can provide for the sharing of high-value land near grid infrastructure, benefiting crops themselves and diversifying income for rural communities. Agricultural photovoltaics, in particular, utilizes structures in fields (open-field protective cultivation) or greenhouses to protect crops in protective growing environments, demonstrating the most favorable relationship for agricultural photovoltaic use in the horticulture sector.

[0004] In agricultural photovoltaics, the design of PV systems must be tailored to maintain the desired level of sunlight reaching crops. Semi-transparent PV modules that allow the required amount of photosynthetically active radiation (PAR) to pass through will be a key start-up technology in this adaptation. (See reference...) Figure 11 PAR (partial near-infrared) light is a wavelength in the solar spectrum that crops can use to drive photosynthesis and growth. This wavelength is limited to 400-700 nm, roughly the same range as visible light (PAR and visible light are often used interchangeably in this article). Crops do not utilize wavelengths above 700 nm in the near-infrared (NIR) spectrum for photosynthesis and require only a very small amount of NIR for growth. However, NIR constitutes a significant portion of the solar spectrum. Furthermore, NIR light heats crops and the soil surface, increasing crop transpiration and thus water use, especially in semi-arid regions.

[0005] Some thin-film photovoltaic technologies, such as amorphous silicon (a-Si), organic photovoltaics (OPV), or dye-sensitized solar cells (DSSC), can make the entire PV module area semi-transparent by reducing the thickness of the absorber layer and using transparent electrodes and substrates. Although they generate electricity almost entirely in the visible light region, they have low power generation efficiency and low visible light transmittance. Many also have severely limited durability and lifespan.

[0006] Crystalline silicon (c-Si) is the mainstream photovoltaic technology, and modules using wafer-type c-Si cells currently account for over 94% of the global PV market. It boasts low manufacturing costs, relatively high efficiency, and a long lifespan. However, c-Si wafers are opaque to PAR (parameters used in photovoltaics), requiring spacing between them and the use of transparent films or back glass to allow PAR to pass through, thus creating semi-transparent modules. Even with this dispersed structure, the performance and lifespan of c-Si semi-transparent modules far surpass current thin-film technologies. Furthermore, as... Figure 11 As shown, c-Si cells are the most efficient in the NIR portion of the solar spectrum up to its 1110 nm bandgap.

[0007] NIR rays passing through the gaps in a semi-transparent c-Si panel can be collected and redirected to c-Si cells for power generation, thus creating a spectrally selective agricultural photovoltaic module. The effective increase in power generation is significant, with more efficient increases achieved while maintaining lower cell coverage (larger cell spacing). Furthermore, crops can be protected from NIR light.

[0008] Previous attempts to introduce spectral selectivity in semi-transparent c-Si photovoltaics relied on three approaches: The first used medium- to high-concentration systems (reflector troughs or dish concentrators) and separate c-Si receivers, where the reflective surfaces were composed of dichroic materials that transmit a portion of visible light. This approach was complex, expensive, required solar tracking equipment, and was not compatible with typical protective crop growing environments or infrastructure. The second used luminescent solar concentrator (LSC) arrangements, where c-Si cells were located at the edges of a flat-panel module or within a plane within the module, with fluorescent dyes interspersed in the gaps. This approach was extremely inefficient due to inherent losses in the photoluminescent materials themselves, including low absorption efficiency, quantum efficiency, and energy loss during redshift, as well as optical losses, including light emitted at angles smaller than the critical angle in the "escape cone" and waveguide losses. The third approach used selective light-scattering materials in the form of embedded nano- or micron-sized rare-earth metal particles that could scatter a portion of UV or IR light. This scheme remains inefficient due to low scattering efficiency and optical losses, including light emitted at angles smaller than the critical angle in the "escape cone" and waveguide losses.

[0009] In view of the rapid global expansion of agricultural photovoltaics and the above observations, the present invention disclosed herein has come into being. Summary of the Invention

[0010] This disclosure provides a spectrally selective agricultural solar module for use above crops in an agricultural photovoltaic system. Within this solar module, photovoltaic (PV) cells are situated on a highly transparent substrate and regularly dispersed to allow visible light to pass through them. The optical elements are characterized by thin-film interference filters, including those on a structured non-planar geometry, being placed on the back side of the substrate or within the substrate in a plane containing the PV cells. Visible light with wavelengths in the range of approximately 400-700 nm, which contributes to photosynthesis, is transmitted through the optical elements to the crops below, while near-infrared (NIR) light with wavelengths in the range of approximately 700-1100 nm is directly reflected or waveguided by the substrate to the PV cells, thereby increasing the light density on the PV cells and thus increasing power generation.

[0011] The thin-film interference filter of the optical element can be a multilayer polymer film, a multilayer silver dielectric coating, or other suitable thin-film interference structure composed of repeating thin film layers with a high refractive index contrast.

[0012] Optical elements require structured nonplanar geometry to properly redirect NIR light to the PV cell according to the law of reflection. This can be a set of linear trenches, a two-dimensional trench pattern, or a surface with Lambertian properties.

[0013] The coverage (CR) of the opaque PV cells above the module opening area can be selected based on the required level of shading for the crops below. For protective agricultural PV applications, a useful CR value range is 35%–65%.

[0014] The use of semi-transparent crystalline silicon (c-Si) PV modules in agricultural photovoltaics enables the dual use of agricultural land, providing crops with the necessary photosynthetically active radiation while protecting them from severe weather. Furthermore, the spectrally selective agricultural solar modules disclosed herein significantly increase power generation while protecting plants from excessive NIR radiation, thereby reducing water consumption.

[0015] A key innovation lies in characterizing the optical layer by incorporating thin-film interference filters onto a structured, non-planar geometry. This enables high optical redirection efficiency across a wide spectral range, thereby significantly increasing power generation while maintaining higher visible light transmittance for crops compared to existing methods.

[0016] Based on annual averages, the spectrally selective agricultural solar module with 50% of the open area covered by opaque PV cells disclosed in this paper can increase power generation by 27% compared to a typical semi-transparent module with the same PV cell coverage, while maintaining 91% visible light transmittance to crops. If the desired PV cell coverage is reduced to 38%, an additional 40% of annual power generation can be obtained while still maintaining 91% visible light transmittance.

[0017] The disclosed spectrally selective agricultural solar module is a static concentrator that maintains a monolithic flat-plate structure, ensuring compatibility with existing protective crop infrastructure and solar module systems. Unlike some existing methods, it does not require solar tracking infrastructure.

[0018] The disclosed spectrally selective agricultural solar module can redirect both direct and scattered light in the NIR wavelength range to the PV cells, while allowing both direct and scattered light in the visible wavelength range to penetrate to the crops below. Unlike some existing methods, it is not limited to transmitting or scattering visible light. Attached Figure Description

[0019] Preferred embodiments will be described in detail with reference only to the accompanying drawings, in which: Figure 1 This is a schematic diagram of a spectrally selective module that allows direct and diffuse visible light to pass through to reach the crops below, while redirecting direct and diffuse near-infrared (NIR) light to planar photovoltaic (PV) cells.

[0020] Figure 2 An embodiment of the spectral selectivity module is illustrated, wherein the optical layer is located on the back side of the substrate, showing the redirection of NIR light to the PV cell. Important geometric parameters, including substrate thickness, PV cell width, and PV cell spacing, are indicated.

[0021] Figure 3 An embodiment of a spectrally selective module is illustrated, wherein the optical layer is located in a plane containing a PV cell.

[0022] Figure 4 The figure shows the calculated reflection and transmission characteristics at the normal incident point of a suitable thin-film interference filter characterized by multilayer polymer films.

[0023] Figure 5 The graph shows the calculated reflection characteristics of a suitable thin-film interference filter, characterized by a multilayer polymer film, as a function of the incident angle when immersed in a glass medium.

[0024] Figure 6The graph shows the calculated reflection, transmission, and absorption characteristics of a suitable thin-film interference filter characterized by a multilayer silver dielectric coating.

[0025] Figure 7 The graph shows the calculated reflection characteristics of a suitable thin-film interference filter characterized by a multilayer silver dielectric coating as a function of the incident angle when immersed in a glass medium.

[0026] Figure 8 An example of a non-planar geometry required for the proper redirection of NIR light is illustrated, characterized by a set of linear trenches.

[0027] Figure 9 The image shows a small, spectrally selective agricultural photovoltaic module that uses a multilayer polymer film as a thin-film interference filter.

[0028] Figure 10 The graphs and tables show the annual average power generation performance gains and visible light transmittance, derived from spectrally selective optical elements characterized by multilayer polymer films incorporated into a linear trench nonplanar geometry. The results are for a single site in Armidale, Australia, with three different PV cell coverages and two different module orientations.

[0029] Figure 11 The chart shows the operating spectra of crops and monocrystalline silicon solar cells, as well as the solar spectrum at standard atmospheric mass 1.5. Detailed Implementation

[0030] This document discloses an embodiment of a spectrally selective agricultural solar module, indicated as 100. First, refer to... Figure 1 and Figure 9 A photovoltaic (PV) cell 104 is located within a nearly transparent substrate 102 and is dispersed to allow visible light to pass through it. A continuous optical element 106, characterized by thin-film interference filters comprising a structured non-planar geometry, is placed on the back side of the substrate. Visible light with wavelengths ranging from approximately 400 to 700 nm, which aids in photosynthesis, is transmitted through the optical element to the crops below; while near-infrared (NIR) light with wavelengths ranging from approximately 700 to 1100 nm is directly reflected or waveguided by the substrate 102 to the PV cell 104, thereby enhancing the light intensity on the PV cell and thus increasing power generation.

[0031] The use of semi-transparent crystalline silicon (c-Si) PV modules in agricultural photovoltaics enables the dual utilization of agricultural land, providing crops with the necessary amount of shade and protection against severe weather. Furthermore, the spectrally selective agricultural solar module 100 disclosed herein significantly increases the module's power generation while protecting plants from excessive NIR light, thereby reducing water consumption.

[0032] A key innovation is the characterization of the optical layer 106 through thin-film interference filters incorporated on a structured non-planar geometry. This enables high optical redirection efficiency across a wide spectral range, thereby significantly increasing power generation while maintaining high visible light transmittance. On an annual average basis, the spectrally selective agricultural solar module 100 disclosed herein, with opaque PV cells 104 covering 50% of the opening area, generates 27% more power than a typical semi-transparent module with the same PV cell 104 coverage, while maintaining 91% of the original module's visible light transmittance reaching crops.

[0033] The spectrally selective agricultural solar module 100 disclosed herein serves as an ultra-low concentration solar energy device with a large receiving angle. Therefore, both direct and diffused visible light can be transmitted to crops through the optical element 106, while direct and diffused NIR light are redirected to the PV cell 104 by the optical element 106. Furthermore, the spectrally selective agricultural solar module 100 disclosed herein functions as a static concentrator, eliminating the need for any solar tracking equipment.

[0034] Reference Figure 2 The coverage ratio (CR) of the opaque PV cell 104 can be selected based on the shading requirements of the crops below. For protective agricultural photovoltaic applications, a useful CR value range is 35%–65%.

[0035] Reference Figure 2 The illustrated spectrally selective agricultural solar module embodiment 200 includes a transparent battery sealant layer 208 within a substrate 102. Based on the front and rear substrate 102 thicknesses (T) and considering the typical range of solar incidence angles throughout the year, the cell width (W) for the desired PV cell CR can be selected. C ) and gap width (W G To optimize NIR light direction efficiency. In this embodiment, the optical element 106 is continuous and located on the back side of the substrate 102, so that the reflected NIR light can directly reach the back side of the PV cell 104, or, in the case that they are bifacial cells, waveguide to the front side of the PV cell 104.

[0036] Reference Figure 3 The illustrated spectrally selective agricultural solar module embodiment 300 includes a plurality of optical elements 106 and a PV cell 104 located within a sealant layer 208. This embodiment can be used when the PV cell 104 is single-sided, or when reducing costs or extending lifespan by positioning the optical elements 106 within the sealant layer 208. In this embodiment, reflected NIR light must pass through a waveguide on the substrate 102 to the front side of the PV cell 104.

[0037] To provide optimal wavelength selectivity, the optical element 106 can be constructed from a multilayer polymer film placed on a structured nonplanar geometry. For example... Figure 4 As shown, the multilayer polymer film can provide broadband transmission of visible light wavelengths and broadband reflection of NIR wavelengths with minimal absorption. Considering the non-planar geometry used and the typical range of solar incidence angles throughout the year, the position of the strip edge 410 at normal incidence is chosen to maximize the amount of NIR redirected to the PV cell 104 while largely preserving visible light transmitted to the crop.

[0038] Multilayer polymer films consist of multiple alternating layers of two polymer films with different refractive indices. Due to this periodic alternating structure, as the optical path difference of the reflected light decreases and the incident angle increases, the wavelength at the 410° band will shift towards shorter wavelengths, such as... Figure 5 As shown in the diagram. This should be taken into account when selecting the location of edge 410.

[0039] The optical element 106 may be composed of a multilayer silver dielectric coating placed on a structured non-planar geometry. For example... Figure 6 As shown, the silver dielectric coating provides the desired wavelength selectivity but also introduces some light absorption. Considering the non-planar geometry used and the typical range of solar incidence angles throughout the year, the location of the strip edge 612 at normal incidence was chosen to maximize the amount of NIR redirected to the PV cell 104 while largely preserving the visible light transmitted to the crop. Figure 7 As shown, for a multilayer silver dielectric coating, the shift of the band edge 612 towards a shorter wavelength is minimized as the incident angle increases.

[0040] According to the law of reflection, optical element 106 requires a structured non-planar geometry to properly redirect NIR light to PV cell 104. Figure 8 An embodiment of a structured nonplanar geometry 814 is illustrated, characterized by a set of linear trenches on which a thin-film interference filter may be included. The pitch and angle (θ) of the trenches can be optimized to provide optimal NIR light redirection, taking into account the substrate 102 thickness (T) and the typical range of solar incidence angles throughout the year. Other embodiments of the structured nonplanar geometry may be used, including two-dimensional structures or surfaces with Lambertian characteristics.

[0041] To realize the optical element 106, the required structured nonplanar geometry 814 can be formed in one or more surfaces of the substrate 102 by an appropriate process, and then a thin-film interference filter can be applied to that surface. Alternatively, the structured nonplanar geometry can be formed in a separate thin film and then applied to the surface of the substrate 102.

[0042] Figure 10 The illustration shows, for example, Figure 4 The multilayer polymer film shown and such Figure 8 The structured nonplanar geometry 814 shown includes Figure 2 The average annual performance gain is calculated for an embodiment of the spectrally selective agricultural solar module disclosed herein, when considering the optical element 106 in the spectral selective agricultural solar module 200. It is assumed that the site is located in Armidale, New South Wales, Australia, and typical meteorological year data is used to characterize solar resources. A greater power generation gain is obtained when the PV cell 104 coverage is low, with a CR of 38%, and an additional 40% annual power generation is obtained when the module is tilted northward at a 35° angle to the horizontal.

[0043] While specific embodiments of the invention have been described, those skilled in the art will understand that the invention can be embodied in other specific forms without departing from its essential characteristics. Therefore, these embodiments and examples should be considered exemplary in all respects, not restrictive, and thus all modifications that are obvious to those skilled in the art should be included therein.

Claims

1. A spectrally selective photovoltaic module, comprising: A substrate, said substrate being at least partially transparent to light in the visible wavelength range, wherein the photovoltaic cell is located within or on the back side of said substrate and is dispersed to allow transmission of light in the visible wavelength range; and One or more optical elements are defined on or within the back surface of the substrate, the optical elements being used to reflect and redirect direct and scattered light with a wavelength range of about 700-1100 nm toward the photovoltaic cell, while transmitting direct and scattered light with a wavelength range of about 400-700 nm to a large extent. The optical element is characterized by including a thin-film interference filter on a structured non-planar geometry.

2. The photovoltaic module as described in claim 1, characterized in that, The thin-film interference filter is a multilayer polymer thin film.

3. The photovoltaic module as described in claim 1, characterized in that, The thin-film interference filter has a multilayer silver dielectric coating.

4. The photovoltaic module as described in claim 1, characterized in that, The thin-film interference filter has a multilayer structure and is composed of transparent metal oxides such as Al2O3, SiO2 or TiO2.

5. The photovoltaic module as described in any one of claims 1 to 4, characterized in that, The structured non-planar geometry is generated on the surface of the transparent substrate.

6. The photovoltaic module as described in any one of claims 1 and 2, characterized in that, The structured nonplanar geometry is generated within the polymer film.

7. The photovoltaic module as described in claims 1 to 6, characterized in that, The non-planar geometry is a set of linear grooves.

8. The photovoltaic module as described in claims 1 to 6, characterized in that, The non-planar geometry is a two-dimensional groove pattern.

9. The photovoltaic module as described in claims 1 to 6, characterized in that, The non-planar geometry is a Lambertian surface.

10. The photovoltaic module as described in claim 1, characterized in that, The optical element is located on the back side of the substrate.

11. The photovoltaic module as described in claim 1, characterized in that, The optical element is located in the plane containing the photovoltaic cell on the inner side of the substrate.

12. The photovoltaic module as claimed in any one of the preceding claims, characterized in that, Considering the typical range of solar incidence angles throughout the year, the size of the photovoltaic cells and the distance between them were optimized for PV cell coverage of 35%-65% and substrate thickness of approximately 2.0-7.0 mm.

13. The photovoltaic module according to any one of the preceding claims, characterized in that, Considering the typical range of solar incidence angles throughout the year, the band edge of the thin-film interference filter is selected in the range of approximately 750-950 nm at normal incidence to optimize power generation and visible light transmission.

14. The photovoltaic module according to claim 1, characterized in that, The module includes a spectrally selective static concentrator.

15. The photovoltaic module according to claim 1, characterized in that, The module includes a spectrally selective low-concentration light system.

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