Boosting agrivoltaics in Japan

In countries like Japan, where mountainous terrain limits space, balancing clean electricity production with agricultural land use can be a challenge.

Researchers from the University of Tokyo have turned to the practice of agrivoltaics — ie, combining solar panels with agriculture — in order to address this problem. Their findings have been published in the Journal of Photonics for Energy.

For their pilot project, the researchers set up a dual-axis sun-tracking photovoltaic (PV) system above a rice paddy in Miyada-mura, Nagano Prefecture. Positioned three metres above the ground, the solar panels generated electricity while allowing rice cultivation to continue underneath. The system was designed to adjust panel angles daily and seasonally, prioritising rice growth during the planting season and maximising energy production during the off-season.

Over two growing seasons, the agrivoltaic system achieved rice yields of 75% and 85% when compared to the average crop yield in the surrounding area. The yield improved significantly in the second year after the team fine-tuned the amount of sunlight reaching the crops. Importantly, the rice also met Japan’s highest grain quality standards, the scientists said.

Meanwhile, the PV panels generated nearly 44,000 kilowatt-hours of electricity annually, with an energy yield (961.4 kWh/kW) that compared favourably to similar systems in Europe, according to the researchers. Over a projected 20-year lifespan, and without government subsidies, the estimated cost of electricity production was about 27 yen per kilowatt-hour — roughly equivalent to Japan’s household electricity rate at the time.

The study examined the trade-offs involved in balancing crop productivity with solar energy output. Ultimately, it showed that careful management of shading, including adjusting the panels’ angles throughout the day and season, can help in achieving both goals.

In addition, the researchers highlighted potential future directions such as using AI to optimise sunlight-sharing in real time, and experimenting with high-efficiency or semi-transparent solar panels to further reduce crop shading.

With Japan aiming to dramatically increase its solar capacity by 2030, the researchers hope their results will inform broader adoption of agrivoltaics — particularly in rural areas where preserving food production is essential. By combining energy and agriculture, they argue, it may be possible to support both sustainability and economic resilience on the same piece of land.

The original Gold Open Access article by Y. Okada et al., ‘Case study of rice farming in Japan under agriphotovoltaic system’, can be read at doi: 10.1117/1.JPE.15.032704.

Image caption: Solar panels used for clean energy generation among rice paddy fields, Japan. Image credit: iStock.com/mith_67