New system design for spectral-splitting concentrator Agrivoltaics

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Researchers in China have build a 10 kW spectral-splitting concentrator agrivoltaic system that accomodates small farming equipment below it. The installation relies on 128 concentrator modules integrating each an ultra-white and toughened concentrating curved glass (CCG), a multilayer polymer film (MPF) and 23%-efficient interdigitated-back contact (IBC) crystalline silicon solar cells provided by Sunpower.

Researchers at the University of Science and Technology of China have developed a new system design for spectral-splitting concentrator agrivoltaics (SCAPV)

The system is based on the spectral separation of sunlight based on the difference in the spectral response of photovoltaics and photosynthesis. According to this principle, red and blue wavelengths are used for photosynthesis as they match the absorption peaks of plant chlorophyll, while all other wavelengths are used for concentrated power generation.

In the study “Large-scale and Cost-efficient Agrivoltaics System by Spectral Separation,” published in iScience, the scientists explained that the proposed system utilizes a dual-axis tracking technology with concentrator modules that optimize the cell components and the concentrating curve.

The 10 kW system occupies a surface of 400 m2 and consists of 128 concentrator modules, each integrating an ultra-white and toughened concentrating curved glass (CCG), a multilayer polymer film (MPF), which the researchers said is the key component for achieving spectral separation. Furthermore, 23%-efficient interdigitated-back contact (IBC) crystalline silicon solar cells with a concentration ratio of 6% were provided by Sunpower.

“These cells were cut into 1/3 strip PV cells (41 mm × 125 mm) and then connected in series using ethylene vinyl acetate (EVA) along with PV glass and a backboard, resulting in the formation of PV modules consisting of 24 such strip PV cells,” the scientists said, noting that solar cells with a higher concentration ratio would have resulted in higher system costs. Their selection process also took into account the spectral shift characteristics of the MPF, processing cost, module size, and holder height.

The concentrator photovoltaic panel consists of a back side receiving concentrated sunlight from the concave screen and a front side receiving direct sunlight. The tracking system uses two motors to control the angle of the spotting module for both azimuth and altitude angle tracking.

“The concentrator modules on the entire main beam square tube are driven via a drive shaft,” the researchers explained. “Integral brackets on the lower part of the concentrator module support the weight of the concentrator modules and wind/snow loads, and the weight is transferred to the primary beam through the north-south swing arm rotation shaft and the swing arm weldment.”

The SCAPV system was placed horizontally at a height of 2.5 m to allow small farm machinery to pass below it.

The system was tested in outdoor conditions in Anhui, China, and was found able to produce 107 MWh of electricity per hectare. Its overall system efficiency reached 11.6%, which the scientists said is the highest efficiency ever recorded for the spectral separation technology.

“Field planting experiments showed that five crops (ginger, peanut, sweet potato, bok choy and lettuce) had an average yield increase of 18.4% under SCAPV compared to open-air systems,” stated the research group. “The microclimate at the bottom of the SCAPV system, especially the soil moisture retention capacity in the daytime, was better than in the open air.”

The scientists believe that the costs of the system may decrease by 18.8% if around 1 GW of SCAPV capacity is deployed globally. They noted that the cost of the MPF currently accounts for around 50% of the system costs.

“Nevertheless, the laboratory’s four-pronged plan – mass production of an autonomous film processing process, optimization of mechanical structures, development of lightweight modules, and the realization of scale effect – points towards heightened economic viability,” they concluded.