How does tilting solar panels more vertically affect rice yield and electricity production in the University of Tokyo study?

Tilting panels more vertically increases light available to plants, boosting the probability of meeting harvest targets. This adjustment comes at the expense of some electricity production, balancing crop and energy needs.

What was the average yield reduction measured in the six-year Japanese rice field study by the University of Tokyo team?

The study measured an average yield reduction of 23% under solar panels. Production was 6.5 tons per hectare with modules, compared to 8.5 tons for crops grown without them.

What minimum harvest retention target does the research aim to meet for agrivoltaic rice farms in Japan?

The target is to retain at least 80% of the harvest obtainable without panels, aligning with Japanese requirements. Simulated yields ranged from 66% to 94% of conventional levels, highlighting the need to account for weather variability.

Rice and solar panels in the same field: Japanese study reveals optimal panel tilt to boost crop yield (and energy production)

A team from the University of Tokyo and the International Rice Research Institute has developed a system to jointly estimate the rice and electricity produced by an agrivoltaic rice farm. In the simulations, tilting the panels more toward the vertical increases the light available to the plants and the probability of meeting harvest targets, at the expense of some electricity production.

The research, presented by the University of Tokyo and published in Field Crops Research, addresses a specific problem: using the same land for both crop growth and energy generation requires distributing light between two activities that both require it.

Rice grown beneath solar panels may suffer in both yield and quality.

A previous study conducted by the same group, carried out over six years in a Japanese rice field, measured an average yield reduction of 23%. Production under the panels was 6.5 tons per hectare, compared to 8.5 tons for the crop without modules.

The shade had limited biomass and the number of panicles, the inflorescences on which the grains form. Quality issues also emerged: more grains with opaque and whitish areas, a defect known as chalkiness, and a lower yield of brown rice after processing.

These results are specific to that system and the conditions studied. However, they show why, when designing agrivoltaic energy in rice fields, focusing solely on kilowatt-hours overlooks an essential part of the budget.

Three models and thirty years of meteorological data

The new method connects three instruments: one reconstructs the light reaching the plants, ORYZA simulates rice growth and yield, and PVsyst estimates photovoltaic production. This allows for an evaluation of how changes in panel configuration affect both agricultural and energy outputs.

The experimental site is located in Chikusei, Ibaraki Prefecture, where the panels cover 27% of the projected surface area on the ground. After validating the model against field measurements, the researchers used meteorological data from 1994 to 2023 to explore the system’s behavior across different years.

A preliminary scientific report on the work, presented to the Japanese Society of Crop Science, reports simulated yields ranging from 66% to 94% of conventional levels. The target considered is to retain at least 80% of the harvest obtainable without panels, in line with Japanese requirements. Therefore, weather variability means that considering only the average is insufficient.

How much does the outcome change when the panels are tilted?

In the initial configuration, the simulated average yield was 82% of the conventional level, but the probability of falling below the target was 26%. Increasing the tilt by 7 degrees toward the vertical from the initial configuration raised the probability of meeting the threshold to 80%, with an estimated 0.1% decrease in global annual revenues.

With an additional 30 degrees, the probability reached 90%, while rice yield improved by 4.2% and electricity production decreased by 3.2%. Total revenues fell by 2.7%. At 53 degrees above the initial position, the probability reached 95%. In this case, rice yield increased by 10.3%, accompanied by a 9.4% reduction in electricity production and an 8% drop in revenues.

Therefore, more light for the plants means a greater chance of safeguarding the harvest. However, progressively tilting the panels entails increasingly significant sacrifices in terms of energy and economics. The percentages describe simulated scenarios for the system studied. Revenue, which includes income from the sale of rice and electricity, also depends on the economic assumptions adopted.

According to the researchers, the method could also be used to evaluate the size and density of the panels, the climate, and the characteristics of the cultivated varieties. A system that would allow for the design of installations taking agricultural needs into account, even before installing the modules. To apply it to Italian rice paddies, local data and field verification would be required. Meanwhile, a tool from Japan addresses one of the most delicate issues in agrivoltaics: producing electricity without unnecessarily sacrificing the crops growing under the panels.

I am a passionate environmental journalist. Originally from the vibrant city of Medellín, Colombia, I have dedicated my career to highlighting stories of resilience and ecological innovation in Latin America. At Aconcagua.lat, I have the privilege of collaborating with a team committed to inspiring positive change through in-depth and insightful reporting.