Photo/Illutration A mega solar farm in Kyushu (Asahi Shimbun file photo)

Electric power companies even in major urban areas are increasingly resorting to a practice known as “output power control,” where power transmission is temporarily halted.

This helps maintain a balance between the supply and demand of electricity as an oversupply could lead to power outages.

But companies that generate electricity using renewable energy sources are often being asked to stop power generation, which could dampen enthusiasm for such energy sources because potential investors might find it difficult to make profit forecasts.

“Compared to Europe, Japan has been slow in taking various measures (about this), so there is a need for a quick response to also further promote renewable energy sources,” said Tetsuo Saito, a senior researcher at the Renewable Energy Institute.

Output power control has, until now, been limited to rural areas with lower electricity demand, but this spring Chubu Electric Power Co., which provides electricity to the region centered on Nagoya, implemented the measure.

Tokyo Electric Power Co. and Kansai Electric Power Co. are also preparing to one day utilize the practice. 

A potential oversupply of electricity is possible on weekends, when many factories that normally would use large amounts of electricity are not operating and when abundant sunshine means a lot of solar power generated.

The need for output power control also rises in spring and autumn when fewer people use air conditioners.

The government has a priority list of energy sources it goes to when the need for output power control arises. The first targeted are thermal power plants, which emit large amounts of greenhouse gases but can also most easily have their power output lowered and later raised.

When output power control is implemented, thermal power generation is reduced to the minimum level possible and surplus electricity is transmitted to other regions.

But because power transmission lines connecting the various regions are not extensive, there are limits to how much surplus electricity can be sent elsewhere.

This reflects the fact electric power companies in the past enjoyed a regional monopoly that, in turn, created no need for transmitting electricity to other regions possibly facing a shortage.

The other power generation methods targeted for output power control are biomass, solar and wind power. Nuclear power generation is not covered because output cannot be easily adjusted.

This year, Chubu Electric and Hokuriku Electric Power Co. implemented output power control measures for the first time in April.

Although Chubu Electric covers an area with a concentration of factories, a 60-percent increase in solar-power generation compared to five years ago meant it had excess supply, forcing it to use output power control.

Kyushu Electric Power Co., a frontrunner in the spread of solar power, began output power controls in 2018.

Other utilities began resorting to the measure from the spring of 2022 in line with renewable energy sources spreading in their regions.

So far, eight of the 10 major electric power companies have employed the measure.

TEPCO and Kansai Electric also announced this year that they would consider the measure if demand dramatically dropped.

Saito suggested electric power companies should have more automated power transmission rather than the current practice of asking power generators to manually stop generation to cut off the flow of power being transmitted.

(This article was written by Shiki Iwasawa and Hisashi Naito.)

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