The researchers installed photovoltaic panels three meters above a rice paddy, enabling the system to follow the sun throughout the day and across seasons. During the planting season, the panels were adjusted to allow more sunlight to reach the rice, while in the off-season, the configuration was optimized for energy output.
Rice yields under the panels reached 75 percent and 85 percent of those from conventional paddies during the first and second years, respectively. Improvements in the second year were attributed to better sunlight calibration. Crucially, the rice met Japan's top grain quality benchmarks.
The solar array produced nearly 44,000 kilowatt-hours annually, achieving an energy efficiency of 961.4 kWh per kilowatt - comparable to leading systems in Europe. The cost of production over 20 years was estimated at 27 yen per kilowatt-hour, aligning with typical household rates in Japan, even without subsidies.
The team emphasized the importance of dynamic shading management to strike a balance between crop productivity and solar output. They proposed future enhancements such as real-time sunlight optimization using AI and the use of high-efficiency or semi-transparent PV materials to minimize shading.
As Japan targets substantial solar expansion by 2030, the study advocates for agrivoltaics as a means to harmonize clean energy goals with food security, particularly in space-limited rural regions.
Research Report:Case study of rice farming in Japan under agriphotovoltaic system
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