Japan's Organization for Cross-regional Coordination of Transmission Operators (OCCTO) has signed off on six days of curtailment orders that Chubu Electric Power Grid issued to solar and wind generators in July 2026, after finding there was no other resource on the congested line that could have been cut instead.
The congestion sat on a 154kV transmission line in the Chubu area, identified in OCCTO's filing only by its Japanese line designation. On July 3, 7, 8, 9, 10 and 12, Chubu Electric Power Grid ordered variable renewable generators, meaning solar and wind, to reduce output because forecast power flow was expected to exceed the line's operating capacity.
The cuts were not large by grid standards but they were frequent for a single month on one line. The heaviest curtailment came on July 3, at 4,100 kW between 9:00 and 11:00. The other five days ranged from 1,100 kW to 3,500 kW, with most curtailment windows also falling in the mid-morning hours, consistent with a solar-driven congestion pattern; July 7 ran a short afternoon window and July 12 shifted into an 11:00 to 13:00 slot.
| Date | Max curtailment | Curtailment window |
|---|---|---|
| July 3 (Fri) | 4,100 kW | 9:00-11:00 |
| July 7 (Tue) | 1,100 kW | 13:00-13:30 |
| July 8 (Wed) | 3,400 kW | 10:00-11:00 |
| July 9 (Thu) | 3,400 kW | 9:00-11:00 |
| July 10 (Fri) | 3,200 kW | 9:00-11:00 |
| July 12 (Sun) | 3,500 kW | 11:00-13:00 |
OCCTO's review, carried out under Article 180, Paragraph 2 of its business rules, asks two questions before it will call a curtailment order valid. First, could adjustable power sources, non-firm or firm-connected non-adjustable generators, or biomass plants have been cut first? On this line, OCCTO confirmed none of those facility types exist, so there was nothing ahead of solar and wind in the queue. Second, was the curtailment actually necessary? OCCTO checked the forecast power flow at the moment of each day's peak curtailment, built in an allowance for forecast error, and still found it would have exceeded the line's operating capacity. On that basis it ruled all six days' orders valid.
The finding matters less as a one-off event than as a structural signal. Solar and wind operators connected to this line have no adjustable generator, storage system, or biomass plant sharing the constraint, so they sit first in line whenever the line runs tight. Six curtailment days inside a single month suggest that congestion on this line is a recurring feature of summer operating conditions in that part of the Chubu grid, not an isolated incident. OCCTO's report does not say when or whether reinforcement work on the line is planned.