In a Biosphere 2-linked Arizona study, cherry tomatoes grew beneath solar panels with 50% less irrigation; midday water stress was about 40% lower across crops

Plants can experience what scientists call midday depression, a period when photosynthesis slows during the hottest part of the day. High temperatures, dry air and strong sunlight can make it harder for leaves to keep taking in carbon dioxide, even when water is still available in the soil. A 2025 study by University of Arizona researchers examined whether the shade created by solar panels could ease some of that stress in crops grown in Arizona's dry climate. The findings, published in npj Sustainable Agriculture, suggest that agrivoltaic systems can change the growing conditions around crops and help some plants maintain productivity under reduced irrigation.

The experiment was conducted at the Biosphere 2 Agrivoltaics Learning Lab, an outdoor research site operated by the University of Arizona north of Tucson. Researchers planted Genovese basil, Anasazi bush red beans, and cherry tomatoes in open-sun plots and beneath a raised photovoltaic array. The panels were positioned 3.3 metres above the ground at their lowest end and tilted at 32 degrees. The researchers tested both normal irrigation and a treatment receiving 50% of the usual irrigation.

Why the solar panels changed the growing conditions


The panels created a noticeably cooler microclimate. Between 9:30 am and 4:30 pm, air temperatures under the agrivoltaic array averaged 1.3 ± 0.3°C lower than in the full-sun plots, according to the study. The researchers also recorded lower vapour pressure deficit, a measure of how strongly the atmosphere draws water from plants. Between 7:30 am and 6 pm, VPD averaged 0.50 ± 0.04 kPa lower under the panels.

The cooler and less drying conditions affected how the crops behaved during the day. In the morning, plants in full sun generally had higher instantaneous photosynthetic rates. But from about 1 pm to 6 pm, the pattern reversed, with plants beneath the panels maintaining higher photosynthetic rates. Basil and red beans growing in full sun reached photosynthetic rates of zero or below zero during the hottest part of the day, while tomatoes continued photosynthesising at about 33% of their peak morning rate.

The response also varied from crop to crop. Under normal irrigation, cumulative daily carbon uptake was 25.5% higher for red beans and 11.7% higher for tomatoes under the panels than in full sun. Basil showed no significant difference in cumulative daily carbon uptake between the two growing conditions.

The researchers also measured midday plant water stress. Across the three crops, average midday water potential was 40% greater under the agrivoltaic system than in the full-sun treatment, which corresponds to lower water stress. The effect was strongest in basil and weakest in tomatoes. When irrigation was reduced by 50%, the difference in plant water stress between the agrivoltaic and full-sun conditions increased to 60%.

What happened when the researchers cut irrigation in half

The most striking results appeared when the researchers supplied only half the usual amount of irrigation. In the full-sun plots, cutting irrigation by 50% reduced cumulative daily carbon uptake by 43% in basil, 40% in tomatoes and 26% in beans. Under the solar panels, however, the same reduction in irrigation had no detectable effect on cumulative daily carbon uptake in tomatoes or beans, although basil's uptake fell by 48%.

The yield results were similarly crop-specific. Tomato plants beneath the panels produced the same yield when irrigation was cut by half, while tomatoes growing in full sun experienced a 59% reduction in yield. Red bean production under the panels actually increased by 14% with the 50% irrigation treatment. Basil behaved differently, with production falling by 21% under the panels when irrigation was halved, although that decline was smaller than the 39% reduction recorded in full sun.

For gardeners, the findings offer a useful but limited lesson. Many plants can struggle when intense heat and dry air combine, and the study shows that partial shade can alter that microclimate. A shade cloth, patio umbrella or taller companion plant can provide some of the same basic cooling and light-reduction effects, although a home garden will not reproduce the exact conditions of the Arizona experiment.

The study does not show that every crop will automatically need less water under shade. Instead, it highlights how differently plants can respond to the same growing conditions. Tomatoes, beans, and basil each reacted differently when irrigation was reduced, which is why the researchers emphasised crop-specific responses.

Agrivoltaics combines solar electricity generation with agriculture on the same land. The Arizona experiment suggests that, in hot and dry conditions, the shade from panels can do more than create electricity. It can also change temperature, atmospheric dryness, soil moisture and the daily pattern of photosynthesis around crops. For gardeners considering shade or ornamental structures over edible plants, the practical takeaway is to observe how individual crops respond rather than assuming that more sun or less water will produce the same result for everything growing in the garden.