What every source found
A solar panel over a field blocks light a plant would otherwise use, but it also cools the soil underneath and cuts how much water evaporates from it. Four independent sources, on 3 continents, checked what that trade does to real crops, and all 4 agree on which crops gain and which lose. Crops that mostly need water gain yield under the panels. Crops that mostly need light lose yield under the panels.
The trial is small, 0.01 hectares at 2 sites, so the direction of the change matters more than the exact size.
Show the numbers
| Onion, yield lost | 20.3 |
| Garlic, yield lost | 19.4 |
| Eggplant, yield lost | 14.7 |
| Tomato, yield lost | 14.3 |
| Coriander leaves, yield lost | 14.3 |
| Red spinach, yield lost | 10.7 |
| Ginger, yield gained | 12.3 |
| Turmeric, yield gained | 8.7 |
The clearest evidence comes from a 2 growing season field trial in Narayanjot and Ranachandi, Bangladesh, where researchers grew 8 crops under solar panels and compared each one against an identical plot in the open. Onion lost 20.3% of its yield under the panels, and garlic lost 19.4%. Turmeric gained 8.7%, and ginger gained 12.3%. The trial plots were small, 0.01 hectares each at 2 sites, so the exact percentages could shift in a larger trial, but the direction of the split matched every other source checked for this article.
Why some crops gain
Shade slows evaporation, so the soil under a panel holds more water for longer. A crop model built for United States growing regions, calibrated against real field measurements, found that shading raised the amount of grain produced for every unit of water used by 14% for maize and 16% for soybean in a dry region. The same model found soybean grown in that dry region was the only crop and region combination in the whole study that gained yield under the panels, up 6%, because water, not light, was already the scarcer resource there before any panel was added.
This is a crop model calibrated against 2 real field sites, not a field trial across all 3 regions. Every value here is a loss except soybean in the semiarid region, which gained 6% and is not plotted, see the stat tile instead.
Show the numbers
| Semiarid | 12 |
| Semihumid | 22 |
| Humid | 24 |
Why some crops lose
Where light, not water, is the limit on a crop, the same shade only takes away what the plant needed more of. In the Bangladesh trial, eggplant lost 14.7% of its yield, tomato and coriander leaves each lost 14.3%, and red spinach lost 10.7%. In wetter years, a long running German trial site at Heggelbach, near Lake Constance, recorded yield losses of up to 20% on wheat, barley, rye, triticale, potatoes, celery and clover grass grown under panels.
Shade intolerant crops, such as cereals, onion, garlic, and tomato, showed yield reductions, whereas turmeric, ginger, leafy vegetables, and other tuber crops performed better under partial shading.
Shahana Afrose Chowdhury and colleagues, a document quote, researchers at the University of Liberal Arts Bangladesh who ran the trial. Source 3.
The water numbers and the land law
In a Chinese trial that paired solar panels with a new drip irrigation system against plain dryland farming with no drip system, soil water content directly under the panels measured 91.7% higher at the seedling stage, 151% higher at flowering and 153% higher at the filling stage, compared with the dryland plot. Because the panels and the irrigation upgrade were installed together, that increase measures the whole new system, not shade by itself.
This trial paired new drip irrigation with the panels, so the rise also reflects the irrigation upgrade, not shade by itself.
Show the numbers
| Seedling | 91.7 |
| Flowering | 151 |
| Filling | 153 |
Germany writes a limit into the law that governs these systems regardless of the shading question. Under the standard called DIN SPEC 91434, a solar array mounted high enough to farm underneath may take up no more than 10% of a field, and a ground mounted array no more than 15%, so most of the field stays farmable by law regardless of what the shade does to any single crop.