A six-year field trial in Japan examined how solar panels affected rice production and electricity generation. Researchers from the University of Tokyo studied an agrivoltaic system in Chikusei, Ibaraki Prefecture, from 2018 through 2023, comparing rice grown beneath the panels with rice in a nearby open-field control plot. The panels covered about 27% of the field. Across the six growing seasons, rice yield under the panels averaged 6.5 tonnes per hectare, compared with 8.5 tonnes in the control plot, a reduction of about 23%. However, when the researchers combined the value of the rice and electricity; the agrivoltaic system produced a gross return about 14 times higher than the rice-only comparison. The 2025 study in Field Crops Research also found that shaded rice grew in slightly cooler daytime conditions and showed changes in grain quality.
The experiment is notable because it did not hide the downside of putting panels over a crop. Less sunlight reached the rice, and that affected growth. The researchers found that the yield gap varied from year to year. In wetter growing seasons, the drop was larger, suggesting that the relationship between weather and shading mattered. The completed trial was designed to assess both the agricultural and energy performance of solar sharing rather than judging the system only by rice yield.
What the panels changed in the rice field
The solar array did more than simply make the field darker. Maximum air temperature under the panels was about 0.8°C lower than in the open plot, although minimum temperatures were similar. The shade also affected the crop's growth. Lower biomass and fewer panicles, the flowering structures that produce grains, helped explain why the rice yield fell under the panels. The researchers found that the yield penalty was particularly noticeable in rainy years, when sunlight appeared to matter more.
The changes went beyond the amount of rice harvested. Grain quality was also affected. The shaded rice had more chalky grains, which are more prone to breaking during milling and contributed to a lower proportion of whole rice after processing. It also had higher protein and amylose levels. The shaded rice also had higher protein and amylose levels. Those details matter for farmers because a field can produce a reasonable amount of grain while still producing a product that behaves differently during milling or cooking. In this case, the six-year experiment showed that judging agrivoltaics only by tonnes of rice would miss part of the story.
At the same time, the panels were doing something the open rice field could not: generating electricity throughout the year. That changed the economics of the comparison. A rice-only field earns money from the crop, while an agrivoltaic field can earn from both the crop and the power produced overhead. In the researchers' calculation, the difference was large enough for the combined gross return from the agrivoltaic system to reach roughly 14 times the return from rice alone. The figure is an economic comparison for this particular setup, not a promise that every rice field with solar panels will produce the same return.
Why the economics looked so different
The economic result should not be read as evidence that the panels improved rice production. The rice itself became less productive, on average, under the panels. The calculation instead measured the combined value of crop production and electricity generation on the same land. The researchers also pointed to several limitations. The system covered a fixed share of the field, and the amount of sunlight reaching the crop could not be ignored. Rice varieties, panel arrangements and farming practices may change the outcome elsewhere. The study therefore calls for better management of shading and crop production rather than implying that solar panels can be installed over any rice field without reducing yield. A recent review of agrivoltaic research notes that crop response varies with the amount of shade, local climate, panel design and management practices.
The Japanese trial was valuable because it covered six growing seasons. Short experiments can miss the way weather changes from one growing season to the next, while a longer study gives researchers a better chance to see whether a result holds up under different conditions. Here, the answer was mixed: the rice consistently faced a production cost from reduced sunlight, but the wider farm system gained another source of income through electricity.
That trade-off may be the main lesson from the field. Agrivoltaics is not simply about growing the same amount of food beneath solar panels. It is about deciding whether a reduction in crop output can be offset by the value of electricity produced on the same land. In this Japanese rice field, the answer looked surprisingly favourable when both were counted together. Solar panels reduced average rice yield by 23%, and they also affected grain quality. But the field was producing something else at the same time, and that extra output changed the economics dramatically.
© Copyright 2025 The SSResource Media.
All rights reserved.