A research team at Spain's University of Jaén demonstrated a novel agrivoltaics concentrator PV module, featuring rear-side crossed compound parabolic concentrators (CCPC) and crystalline silicon solar cells emulating a bifacial configuration. To suit agricultural applications, it was designed to balance high efficiency and optical transparency with minimal panel shading.
“Our research presents the first semi-transparent photovoltaic (STPV) module that uses rear optical concentrators specifically to enhance the contribution of reflected irradiance, a resource that has traditionally been underutilized in both agrivoltaics and building-integrated photovoltaic systems,” co-corresponding author of the research, Álvaro Valera-Albacete, told pv magazine.
Unlike earlier STPV designs, the prototype, RearCPVbif, concentrates and redirects albedo light to the rear of bifacial cells for a “substantial increase” in power generation without compromising optical transparency, according to Valera-Albacete.
“The main motivation was the growing need to reconcile solar energy production with limited land availability,” explained Valera-Albacete, noting that, in agrivoltaics, increasing electrical output “typically comes at the cost of reducing the quality and quantity of light” that reaches the crops due to shading by the PV modules.
The researchers fabricated a prototype module and developed a modelling framework for testing. The proposed design integrates low-concentration optical components on the back side, aligned and bonded to small, interspaced crystalline silicon solar cells. The geometric concentration had a targeted transparency factor (TRF) of 60%, which is “adequate for most horticultural crops,” according to the researchers.
To emulate the bifacial cells required for the design, the scientists used two electrically independent monofacial crystalline silicon solar cells. These were placed in 3 × 3 arrays and mounted on an 8 mm thick transparent polymethyl methacrylate (PMMA) substrate. The module was 42.8 mm thick and weighed 0.4767 kg, or 34.15 kg/m2.
Tests of optical performance of CCPC power output gain, light quality, average photosynthetic transmittance (APT), average visible transmittance (AVT), and thermal performance were completed. The results showed a bifacial response, with the “rear side generating more than twice the power of the front, showing clear gains over monofacial and bifacial references,” according to the research.
The system also provided “good transmission of diffuse light” and visible transmittance of close to 60%. Thermal performance remained stable, with “predicted cell temperatures below 70 C, “with the insulating capacity “comparable to that of double-glazing systems,” reported the researchers.
They said that the experimental and numerical results were in “good agreement for light transmission and uniformity,” but they also noted discrepancies in non-uniformity, indicating the need to further refine the model and to perform outdoor testing.
The work is described in “Study on the potential of a novel semi-transparent rear concentrator photovoltaic system for agrivoltaics,” published in Results in Engineering.
Currently, the researchers are in discussions with private sector organizations to accelerate development and transfer the technology to the market, according to Eduardo F. Fernández, co-corresponding author of the research.
“This also includes a detailed assessment of the benefits that the technology provides for crop growth, based on an experimental campaign in which different types of crops are investigated,” said Fernández.
In addition, the research team is building on its experience with optics and solar cells by researching wireless energy transfer applications with high-power photovoltaic receivers and monochromatic laser light sources.
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