Weird: Japanese Utilities Dream of 100% Nuclear Capacity Factor

This is a strange story, but it was the top article in yesterday’s Asahi Shimbun. Unfortunately, the online edition is hidden behind a paywall, so I won’t link to it.

As I learned from the article, some of the utilities still having monopoly status in Japan have set up “maximum wind power purchase goals”. The big utilities serving Tokyo and Osaka (Tokyo Denryoku and Kansai Denryoku) are not doing this, but those in Hokkaido, Tohoku and Kyushu are.

That means that wind developers in Tohoku only get to sell up to that amount, if that policy is allowed to stand.

The article in Asahi has done some research on how these numbers are calculated. Their justification in the first place seems to be that wind is not compatible with nuclear power. As long as the utilities run their nuclear power plants, which have no ability to reduce their output to follow the load, they can’t accept intermittent wind into their system above a certain level because that would cause them to get time slots where they have too much electricity.

That in turn means that those numbers depend on the amount of nuclear electricity in the system. And, as Asahi has learned, those utilities calculate the thresholds assuming that all their nuclear power stations are running all year long at 100% capacity factor.

This is of course quite far away from reality. Right now, only two nuclear power plants in Japan are running. Not really 100%.

But the utilities say they don’t plan to revise their numbers. Most of them say that they want to restart their nuclear power plants and therefore want to keep their unrealistic numbers.

Only Kyushu Denryoku answered that the thresholds have not been reached anyway, so there is no actual need to increase them.

That is actually true for all of the utilities that have thresholds in the first place.

This story is weird on several levels.

For one, under the new feed-in tariff system in place since July, utilities actually don’t get to choose unilaterally how much wind energy they want to buy. The law gives them an obligation to buy wind energy. I doubt very much that the excuse “we want to run our nuclear power plants instead” would be allowed in Japan right now.

And insisting on 100% capacity factor for nuclear in Japan right now? They really need to rethink their position. Right now that is another excellent point for opponents of nuclear energy in Japan to point to. If restarting nuclear power plants actually stands in the way of developing wind or solar power in Japan, that would be another reason for opposing and resisting such restarts.

Published by kflenz

Professor at Aoyama Gakuin University, Tokyo. Author of Lenz Blog (since 2003,

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