The Kinokawa Energy Storage Plant, established by Kansai Electric Power and ORIX, in Kinokawa, Wakayama Prefecture (Courtesy of Kansai Electric Power).
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12,500 times—that is how many times JERA, Japan's largest thermal power operator, started and stopped its gas-fired power plants in fiscal 2024. This is 2.5 times what it was a decade ago. In fiscal 2025, the figure rose further to 13,500 times.
Why has the number of start-stop cycles increased so dramatically? The background is the rapid expansion of renewable energy. Electricity requires that generation and consumption match; otherwise, frequency becomes unstable, potentially leading, in the worst case, to a large-scale blackout.
Because renewable energy output fluctuates with weather conditions, adjustments are needed to match consumption. Gas-fired thermal power plants play the leading role in what is called "smoothing"—adjusting the gap in electricity supply and demand caused by fluctuations in renewable output.
As renewable energy adoption has expanded, the burden of smoothing carried out by gas-fired plants has grown, sharply increasing the number of start-stop cycles.
Curbing Sharp Output Fluctuations
The problem is that frequent starting and stopping, along with sharp fluctuations in output, place strain on gas-fired plant equipment. Equipment malfunctions have in fact been on the rise, and if this continues unchecked, it could disrupt the electricity supply. For this reason, JERA is moving forward with a new countermeasure to ease the burden: building battery storage facilities.
As the name suggests, a battery storage facility is a site that stores electricity. It typically involves installing dozens of containers housing lithium-ion batteries, the same type used in electric vehicles. Also known as grid-scale batteries, these facilities connect directly to the transmission network, charging when there is an excess of electricity and discharging when there is a shortage, thereby helping balance supply and demand.
Battery storage facilities are expected to curb sharp fluctuations in gas-fired power output. For example, in the evening, when solar power generation drops rapidly, gas-fired plants need to sharply raise their output—but if battery storage facilities discharge at the same time, the rise in output can be made more gradual.
"Thermal power is needed as an adjustment tool to bring in renewable energy. If solar power increases further, operating thermal power will become even more difficult," said Kenji Takahashi, an executive officer responsible for the operation, maintenance, and management of thermal power, voicing his sense of urgency.
JERA has been running repeated simulations to determine where and at what scale battery storage facilities should be installed, taking into account cost-effectiveness and stable supply, and aims to introduce them as soon as possible.
Subsidies and full operation of the electricity adjustment market provide a tailwind
The government is also supporting the development of battery storage facilities. Subsidy support began in fiscal 2021. The full-scale operation of the Supply-Demand Adjustment Market, which trades adjustment power sources including battery storage, started in April 2024, providing a further tailwind—and battery storage development plans have been announced one after another as a result.
Kansai Electric Power is a leading company working on battery storage development. In December 2024, it opened the Kinokawa Energy Storage Plant (Kinokawa City, Wakayama Prefecture) with Orix, with an output of 48,000 kilowatts.
The company is also proceeding with six other locations and seven projects in Hokkaido, the Kanto region, the Chubu region, Kyushu, and elsewhere, and has decided to invest ¥20 billion (approximately $135 million) over the three years from fiscal 2026.
The combined output of the eight projects, including Kinokawa, comes to 416,000 kilowatts. The company plans to expand this further to 1 million kilowatts—equivalent to one nuclear reactor—as early as the 2030s.
Government Targets Renewables as Top Power Source
In the Seventh Strategic Energy Plan, adopted by the Cabinet in February last year, the government set a target of raising the share of renewable energy in overall power generation to around 40–50% by fiscal 2040, positioning it as the leading power source.
However, no matter how much renewable energy is introduced, its potential cannot be fully realized if there is a shortage of adjustment capacity. Solar power generation has been increasing year by year, but balancing electricity supply and demand during the daytime has become increasingly difficult in recent years. As a result, "output curtailment" of renewable energy has been increasing.
To maintain the supply-demand balance, transmission and distribution companies affiliated with major power utilities have been asking renewable energy operators to halt generation.
Output Curtailment Up Sevenfold in Five Years
According to the Organization for Cross-regional Coordination of Transmission Operators, which coordinates electricity supply and demand nationwide, output curtailment (excluding remote islands) occurred 426 times in fiscal 2025—a sevenfold increase over five years.
The frequency has continued to rise so far this fiscal year. If battery storage facilities spread nationwide, surplus daytime electricity could simply be stored. This is expected to help reduce the curtailment of renewable energy output.
Toshiki Oda, general manager in charge of the battery storage business at Kansai Electric Power, emphasized the importance of developing battery storage facilities, noting that expanding solar power requires a power source to support it and that such facilities can help expand renewable energy.
Renewable energy has been promoted as a power source that contributes to decarbonization. At the same time, it is classified as a purely domestic energy source. Now that Japan has experienced the closure of the Strait of Hormuz, the importance of renewable energy for the country's energy security is growing, given that it relies on imports for nearly all of its fossil fuels.
How to make up for renewable energy's weak point and put it to effective use as a stable core power source—battery storage facilities are poised to become a key piece of that effort.
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(Read the article in Japanese.)
Author: Shunichi Takahashi, The Sankei Shimbun
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