Rice under panels in Japan and the 80% rule

In Japan, rice grown under solar panels must yield at least 80% of conventional fields. University of Tokyo researchers published in Field Crops Research a model combining radiation, rice growth and generation, calibrated in Chikusei from 2019 to 2022. Using 1994 to 2023 weather, average yield was 82%, with a 26% chance of falling below the floor.

The floor has consequences. In a January 2026 document, the Ministry of Agriculture, Forestry and Fisheries notes that since April 2024 the criteria sit in the Agricultural Land Act regulations: a yield drop of 20% or more blocks approval, and violations expose operators to revocation and temporary suspension of FIT and FIP payments.

That ties energy revenue to the harvest. The study prices the protection: tilting panels to 30 degrees raises the chance of meeting the floor to 90%, at a 2.7% loss in total income; at 53 degrees, to 95%, at an 8% loss.

Tilt works as insurance with a known cost, which a project can size against the revenue it protects.