In a 2023 study in San Severo, six medicinal crops grew beneath tracking solar panels; deep shade cut evapotranspiration by 81.1% but reduced biomass by up to 48.8%

During a 2023 field trial in San Severo, Italy, researchers grew six crops under solar panels that tracked the sun. The results were mixed. The deep shade helped stop water loss from evapotranspiration by 81.1%. However, that same shade also reduced fresh plant biomass by as much as 48.8%. If you have ever wondered whether solar farms and farmland must compete for the same land, this study offers a clear answer. The study is relevant because it connects crop production, water use, and solar energy.

Why a herb farm in southern Italy is suddenly relevant to your grocery bill

Researchers at the University of Foggia conducted a study at a working site near San Severo in Italy's Puglia region. Solar panels rotate up to 45 degrees to follow the sun. Six perennial medicinal species: lavender (Lavandula angustifolia 'Royal Purple'), lemon thyme (Thymus citriodorus), common thyme (Thymus vulgaris), rosemary (Rosmarinus officinalis), spearmint (Mentha spicata 'Moroccan'), and sage (Salvia officinalis) were planted in three zones: ground that was always shaded by panels, ground shaded only between the rows of solar panels, and a full-sun control plot. Researchers tracked radiation, temperature, water use, biomass, and essential-oil content throughout the growing season from April to August 2023, publishing their results in the peer-reviewed journal Plants. The study took place on a working solar farm, which makes the results relevant to anyone considering how U.S. farmland might handle solar development.

Water use fell by 81.1% under deep shade

Water scarcity is not just an Italian issue. Big parts of the American West and Southwest have spent years under drought warnings, and every drop saved on a farm reduces irrigation costs. Scientists measured crop evapotranspiration, the water lost from soil evaporation and plant transpiration, with a corrected Turc method. The plots under the panels saw crop evapotranspiration fall by 81.1% compared with the open-sun plot, mainly because ground-level solar radiation dropped by 84.1%. Even the rows that were partly shaded between panels, which still got strong midday sun when the panels were horizontal, cut water loss by 13.1%. The U.S. Department of Energy's National Renewable Energy Laboratory says shade from panels cuts direct sunlight on crops, cools the daytime microclimate, and tends to increase soil moisture, which is especially helpful in hot, dry areas.

The trade-off: smaller plants

When conditions were most shaded, five of the six plants, lavender, lemon thyme, common thyme, rosemary, and sage, saw their weight drop by between 40.1% and 48.8% compared with the plants in full sun. Lemon thyme lost the most at 48.8%. Common thyme was right behind at 48.7%. Only spearmint stayed about the same. The plants in the shade between the panels kept their biomass steady. These plants did not show a drop compared with the full-sun plants. This suggests that how much shade a crop gets matters more than shade alone. Dry matter content stayed the same across all plants and zones. This means the shaded plants were smaller, not less dense. A 48.8% loss in weight is a significant hit for a working farm; for a grower who sells herbs by weight alone, that's a serious financial squeeze. But weight isn't the only thing buyers pay for: as the next section shows, the same shaded plants produced meaningfully more essential oil per gram, which is what actually drives value for crops like lavender and rosemary.

The upside: Higher essential oil content

Even though the plants grew smaller in shade, the essential oil content was much higher in the shaded zones than in the full-sun area. Higher essential-oil content is what makes lavender, rosemary, and thyme valuable crops. For farmers who sell herbs for essential oil, a smaller plant with higher essential-oil content can help offset the smaller size.

What this means if you are watching solar development in the US

Ground-mounted solar is spreading over the United States. People are constantly asking how much farmland can actually share space with farming. The U.S. Department of Energy has looked into this through its InSPIRE research initiative, which has studied the costs and benefits of agrivoltaics at more than 25 sites across the country, covering crop production, livestock grazing, and bee habitats since panel height, spacing, and sun-tracking all change results for a specific crop.

The San Severo data gives us a clearer picture of this situation. Crops that like shade and have value because of their oil content might work well with tracking solar systems. This may be a better fit in states like Arizona, Nevada, and parts of California and Texas. However, crops that need full sun to grow to a size are probably not a good fit. For herbs, the San Severo data suggests a real trade-off, not a dealbreaker: it cuts water demand by 81.1% and may shrink fresh yield by up to 48.8%, a loss partly offset by higher oil concentration.