Davis, California, USA
September 23, 2024
Pepper plants growing on campus, part of an experiment examining the effects of agrivoltaics. Photo by: Jael Mackendorf, UC Davis
Growing beside sleek vertical solar panels, lush green pepper plants flourish at the height of summer. A team of UC Davis researchers are analyzing an agrivoltaics system that combines farming with solar technology to boost crop growth and promote sustainability.
This innovative approach, according to UC Davis Associate Professor Majdi Abou Najm with the Department of Land, Air and Water Resources, could be a valuable solution as California faces a hotter, drier climate.
“This could be the future of agriculture as we adapt to climate challenges,” he said. “If we want to continue to lead in agriculture, we need solutions that think of the sun as our friend.”
Andrea Alsup tracks height of pepper plant while Rufaidah Labban writes down measurement at the agrivoltaics system at UC Davis. Photo by: Jael Mackendorf, UC Davis
On a one-acre plot on the edge of campus, rows of pepper and tomato plants have been growing since mid-May. In the experiment, plants grown in full sun with ideal irrigation serve as the control group. Other plants experience varying combinations of light, water and soil conditions to evaluate how these factors impact their growth. Some plants are partially shaded by vertical solar panels, while others are fully shaded or placed under red panels that filter red light to the plants. All panels generate electricity while altering the light conditions for the crops.
Given recent droughts and heat waves, Abou Najm said California growers are interested in agrivoltaics for its various benefits, including reducing heat stress on plants.
UC Davis student Sonal Agarwal uses a light bar to measure photosynthetically active radiation, or the range of light plants use for photosynthesis. This helps paint a picture of how the different light conditions affect plant growth and the plant’s ability to convert light into energy. Photo by: Jael Mackendorf, UC Davis
Measuring key factors
Researchers, including undergraduate and graduate students, gather data on light, water, air, soil and plant growth. Sonal Agarwal, a junior majoring in environmental science and management, oversees the database in which all the numbers are being recorded.
She regularly visits the site to measure photosynthetically active radiation – the range of light plants use for photosynthesis – using an instrument called a light bar. She waves the light bar above the plants and jots down the readings. By doing this, the team can compare how different light conditions affect plant growth and its ability to convert light into energy.
Kelly Mae Heroux, a Ph.D. student in soils and biogeochemistry, takes reading with an instrument known as a pump-up pressure bomb to see how plants manage water stress under varying light conditions. Photo by: Jael Mackendorf, UC Davis
“It’s basically measuring how much light is reaching the plants so we can tell what the solar panel is actually doing, what effect it is having on the light that the plant is able to access,” Agarwal said.
Light is just one piece of the puzzle; understanding how plants grow under these conditions is equally important. Andrea Alsup, who graduated with a bachelor’s degree in sustainable agriculture, monitors plant development from seedlings to harvest, comparing growth and fruit development among the different treatments.
During one observation in August, Alsup noted that the pepper plants shaded by solar panels appeared taller and healthier compared to the control group.
“It’s been cool to see all the differences between the treatments,” Alsup said. “The controls may be growing at the right rate, you see a normal amount of fruit you would see on a pepper plant, but with the panels, I feel like they’re taller and there’s way more fruit in the crown that you don’t see on the control.”
Researchers are also focusing on soil health. Students measure soil compaction under the different light treatments to understand how these conditions affect soil health, carbon levels and microbial communities, plus how these factors together influence the overall ecosystem.
“We want to see how introducing different light treatments basically impacts soil structure, improves soil health and enhances its resilience, function and biophysical interactions,” Abou Najm said. “We are looking at the big picture.”
UC Davis Associate Professor Majdi Abou Najm with the Department of Land, Air and Water Resources is leading a team of researchers to analyze how agrivoltaics affects crops as California faces a hotter, drier climate. Photo by: Jael Mackendorf, UC Davis
Testing water efficiency
Just as light and soil conditions are critical, understanding water usage is key to maximizing the benefits of agrivoltaics. Researchers are testing three irrigation levels: 100%, 90% and 75% to see how different amounts of water affect plant health under varying light conditions.
Kelly Mae Heroux, a Ph.D. student in soils and biogeochemistry, takes on one of the more demanding tasks. She uses a special tool to meticulously measures the water pressure needed for plants to transport water through its tissues.
“It’s called a pump-up pressure bomb, and it gets its pressure by physically pumping,” Heroux explained. “You put a seal on it, pressure builds in the box and then you understand how much pressure is required to push the sap through.”
This hands-on work reveals how plants cope with water stress under different shading setups, offering insights into whether agrivoltaics can support healthy crop growth with less water. These findings could help farmers adapt to a changing climate while conserving water.
Abou Najm believes all this data will paint a complete picture of agrivoltaics and highlight the potential benefits for plants, growers and the environment.
“We’re trying to show that plants are responding to different light setups, even under the same prevailing weather,” Abou Najm said. “When we show that, we can communicate with the growers that you can actually change the conditions favorably in your fields, the plants will love it and you will gain extra benefits like clean energy, favorable micro-climate for the plants and water savings.”
The research team assessing the benefits of agrivoltaics (L-R): Cailin Gervin, Alden Hughes, Kelly Mae Heroux, Sonal Agarwal, Yuanxin Ji, Associate Professor Majdi Abou Najm, Rufaidah Labban, Muhtarima Tabassum and Andrea Alsup.
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