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Kyushu Electric considers cutting off renewable energy feed-ins due to oversupply

A solar farm is seen in Itoshima, Fukuoka Prefecture, on the southwestern Japanese island of Kyushu. (Mainichi/Takashi Kamiiriki)

Electricity from the Kyushu Electric Power Co. regional utility service area was sent to five other regional power providers on Oct. 1 to prevent a potential blackout caused by an oversupply of renewable energy, it has been learned.

The power transfer was carried out between 9 a.m. and 2:30 p.m. that day by the economy ministry-certified Organization for Cross-regional Coordination of Transmission Operators (OCCTO), which manages power supply and demand across Japan.

According to the organization, as much as 1.125 million kilowatts was sent from the southwestern island of Kyushu across transmission lines to the main Japanese island of Honshu, to the grids run by Kansai Electric Power Co., Chubu Electric Power Co., Hokuriku Electric Power Co., and Chugoku Electric Power Co., and to Shikoku Electric Power Co. on the western Japan island of Shikoku. It was the first such transfer made due to renewable energy oversupply since the system for inter-utility power sharing was introduced in 2015.

Solar power has been widely adopted in Kyushu, and the OCCTO's move has prompted worries that Kyushu Electric may call for renewable producers to temporarily halt their power output in times of oversupply. The idea has gained particular traction with the onset of autumn, a season of sunny days but also of decreased power demand.

It was sunny all across Kyushu on Oct. 1, and the expected rise in solar-generated electricity risked creating such a severe supply-demand imbalance that, in the worst-case scenario, the entire Kyushu grid could have been blacked out. In response, Kyushu Electric restricted output from its thermal power plants, and increased power consumption at its pumped storage hydroelectric plants. However, these measures proved insufficient to completely allay the risk of a grid-wide power outage, like the one that struck the northernmost prefecture of Hokkaido in the wake of a major earthquake there on Sept. 6.

OCCTO then stepped in to transfer excess electricity to the five other regional utilities. Exactly how much power was sent to each utility was not revealed, but an OCCTO official said that "there was just enough demand for them to take the surplus electricity."

Kyushu's plentiful sun and cheap land make it ideal for solar farms. Since the feed-in tariff (FIT) system, under which utilities buy up power from renewable producers, was introduced in Japan in fiscal 2012, solar power generation has spread quickly across the island. There was some 8.07 million kilowatts of renewable energy being produced in Kyushu as of the end of August this year, equivalent to the output of eight nuclear reactors and over 10 times the amount generated at the end of fiscal 2011, just before the FIT system was introduced.

However, during periods of low power consumption in Kyushu Electric's service area such as early spring, daily demand slips below 10 million kilowatts. While solar power output fluctuates depending on weather conditions, there were three days this past spring when the energy source filled more than 80 percent of total demand. Furthermore, Kyushu Electric's total power supply got a 4.14-million-kilowatt boost in August with the restart of a total of four reactors at the utility's Sendai and Genkai nuclear plants.

In future, should there be an electricity oversupply that cannot be dealt with by the measures taken on Oct. 1, Kyushu Electric appears ready to restrict feed-ins from the some 24,000 solar power stations and 60 wind power units on the island producing 10 kilowatts or more each. Should the utility take this course, it would be a national first (except for remote islands).

According to Kyushu Electric, it may impose the temporary feed-in restrictions "at the start of this autumn as power demand from cooling systems falls." If these instances become frequent, they could impact the viability of renewable energy businesses on the island. Meanwhile, with the government looking to boost renewable power generation as a pillar of Japan's energy policy, the Kyushu situation highlights the urgent need to improve the country's electricity transmission network.

(Japanese original by Takayuki Hakamada, Business News Department, and Taiki Asakawa, Kyushu Business News Department)

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