TOKYO – According to a recent Japanese study, installing solar panels above rice paddies could increase total earnings for farmers by more than five times, thanks to additional income generated from the sale of solar power.
However, the team led by University of Tokyo agricultural science professor Yoichiro Kato also found that this solar power generation-farming method reduces rice yields by roughly 20% and worsens qualities including flavor, among other issues.
“Solar sharing,” the practice of generating solar power on farmland, is hoped to promote the use of renewable energy while also enabling boosted food production to support a growing global population. As such, it will be necessary to develop cultivation and management technology that can minimize yield reductions and stabilize crop quality.
In late March, the team’s discoveries were made available online in an agricultural science journal published by Elsevier, a prominent academic publisher from the Netherlands.
Over a span of six years beginning in 2018, the group of researchers carried out studies with assistance from a farm located in Ibaraki Prefecture. Their investigation involved comparing crop outputs and overall earnings—encompassing revenue generated through power selling—between a rice field wherein 27 percent of the space was occupied by solar panels and an ordinary plot without such installations.
In the paddy field covered with solar panels, the annual sunlight exposure decreased by 21-30% when compared to traditional paddies, and the average peak temperature dropped by 0.8 degrees Celsius. Due to these conditions, rice cultivation faced obstacles leading to an approximate reduction of 23% in the overall crop yield.
In the meantime, solar power production stayed consistent annually irrespective of the weather. Despite the declining purchase prices set by Japan’s fixed-priced feed-in tariff system for renewables each year, calculations revealed that with the rates projected for 2025, revenue from the solar sharing arrangement would be fivefold higher compared to cultivating rice exclusively.
Nonetheless, obstacles persist. The quality of the rice declined as the endosperm became white and opaque. Additionally, the amounts of amylose and proteins rose, leading to a less desirable flavor. The research underscores the necessity for developing rice strains and farming methods appropriate for solar-sharing systems.
Kato remarked, “A decrease in rice quality reduces its grading by approximately one step; nonetheless, solar sharing remains more profitable despite this factor.” Looking ahead, he continued, “Our initial objective is to implement this technology in Japan’s paddy fields to boost farmer earnings before extending it internationally, particularly into other parts of Asia.”
(Originally written in Japanese by Yuki Ogawa for the Lifestyle, Science & Environment News Department)