BY YURIY HUMBER
Since the start of Japan’s solar boom in 2012, the power grid serving the Tokyo metropolitan area has never been forced to turn off solar or wind farms due to excess supply. In March, it happened not once but five times.
The curtailments have so far been confined to weekends, when electricity demand is lower, but they have already formed a recurring pattern that extended into April. With flexibility in the TEPCO Power Grid area increasingly constrained, the combination of weather and demand conditions that trigger curtailment is more frequent.
This suggests the issue is no longer incidental but structurally embedded, according to Japan NRG analysis of grid, weather and plant maintenance data.How the Tokyo grid absorbs the return of nuclear power will be a key test for renewable integration. While in western Japan nuclear generation has largely displaced coal- and gas-fired output, the Tokyo system appears more tightly balanced.
Curtailment patterns in March suggest that the availability – and inflexibility – of thermal and nuclear generation is already influencing when renewable output must be reduced, as Kashiwazaki Kariwa NPP Unit 6 moved in and out of service during the month. TEPCO’s operating approach has also shifted since the first curtailment on March 1, and is likely to continue evolving.
Curtailing renewable output when supply exceeds demand is becoming a broader feature of Japan’s power system. Almost all ten of the regional grids faced curtailment conditions in March, with Kyushu the most affected, at times curtailing roughly a sixth of its solar output.
Beyond the immediate loss of zero-carbon electricity, curtailment highlights a deeper challenge: renewable capacity is expanding faster than the system’s ability to absorb it, increasing pressure on storage, transmission and flexible generation.