By Lisa Mcdonald
Last August, I looked at a concept gaining increased attention among agriculturists—the concept of agrivoltaics.
Agrivoltaics refers to the practice of co-locating photovoltaic infrastructure and agriculture by planting crops under photovoltaic panels. The technique was originally conceived in 1981, and it became more attractive in recent years as photovoltaic prices dropped, interest in renewable energy rose, and financial pressures on small farmers grew.
Supporters of agrivoltaics note numerous benefits to both photovoltaics and crops, including creation of a favorable microclimate under the solar canopy for plants (e.g., protected from wind, less variation in temperature) and reduced heat stress on the solar panels due to localized cooling from water evaporation.
There is a downside to agrivoltaics, though—lower crop yield of certain plants.
Because solar panels absorb light, they naturally reduce the amount of light reaching underlying plants. And while some plants grow well in the partial shade cast by solar panels, other plants experience detrimental effects.
“For example, for lettuce, the total biomass yield under agrivoltaic installation in Montpellier (France) was 15–30% less than the control conditions (i.e., full-sun conditions). When growth of tomato was tested in Japan, the yield in an agrivoltaic regime was about 10% lower than for conventional agriculture,” researchers write in a recent open-access paper.
The researchers come from several universities in the United Kingdom and Italy and are led by postdoctoral researcher Paolo Bombelli from the University of Cambridge. And in their recent paper, they investigate a possible way to circumvent this limitation.
The key, they propose, is not simply to let more light through—the key is customizing which wavelengths of light get through.
In conventional agrivoltaics, opaque and neutral semitransparent solar panels absorb electromagnetic radiation uniformly across the entire visible spectrum. However, visible wavelengths are not absorbed uniformly by the underlying plants.
Chlorophylls, the main photosynthetic pigments in plants, absorb wavelengths mostly in the red (≈600–700 nm) and blue (≈400–500 nm) regions of the electromagnetic spectrum; wavelengths in the green region (≈500–600 nm) are rarely absorbed (giving chlorophylls, and plants, a green appearance).
At the same time, other pigments such as carotenoids and anthocyanins absorb wavelengths in the blue and green regions, respectively, with the purpose of dissipating excess/harmful solar energy to protect the photosynthetic apparatus.
Taken together, “part of the solar energy absorbed in the blue and green portions of the electromagnetic spectrum is dissipated without contributing to photosynthesis,” the researchers write.
Based on this knowledge, a solar panel that absorbs blue and green wavelengths while allowing red wavelengths to pass through may mitigate the detriments of shade because the wavelength most important to photosynthesis is still reaching the underlying plants.
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