日经特稿：住友商事借英国Gresham House经验扩张日本电池储能（BESS），2030年目标超500MW

TOKYO/LEICESTER, England -- In the leafy outskirts of Leicester, a city in England's East Midlands, an unassuming land houses 30 shipping containers. The long rows of boxes are filled with a combination of batteries and inverters, which have the capacity to store enough energy to power 160,000 homes for two hours.
The site is operated by Gresham House, one of the U.K.'s largest developers and operators of battery energy storage system (BESS) assets and an early mover in a sector becoming critical to the renewable energy transition. BESS is responsible for distributing the electricity stored in batteries when it is needed.
For Sumitomo Corp., one of Japan's five major trading houses, the Leicester site offers both a glimpse of what Japan could become -- an electricity market where BESS plays an increasingly important role in balancing a grid powered by more renewable energy -- and lessons in how to get there.
Sumitomo announced in May that it had partnered with Gresham to develop five BESS projects in Britain, taking a 25% stake in each. "The U.K. is probably five years ahead of Japan in terms of using BESS in electricity wholesale markets," said Shigenobu Hamada, head of the energy storage business unit at the Tokyo-based company.
"By getting directly involved in the market, we want to learn firsthand how BESS is being utilized and optimized," he said. "If the U.K. is where Japan could be five years from now, we can bring those lessons back to Japan and put them into practice ahead of the market."
Those lessons could be valuable as Sumitomo rapidly expands its battery business at home. The company currently operates around 10 megawatts of BESS connected to the electricity grid in Japan, but expects capacity to reach 100 MW by 2027 and aims to have a portfolio of more than 500 MW by 2030. Hamada said that could give it a 10% to 15% share of the domestic market.
As part of the push, the company is now developing one of Japan's largest grid-scale BESS projects in the southern Kyushu region, according to sources.
Sumitomo's expansion comes as Japan looks to battery storage to accommodate more renewable power. Japan is aiming for solar and wind to account for 30% to 40% of electricity generation in fiscal 2040, up from around 10% now. Because their output fluctuates with the weather, increasing their share will require more batteries to store excess electricity and return it to the grid when needed.
Yet while applications for new BESS projects have surged to more than 170 gigawatts by the end of 2025, according to the Institute for Energy Economics and Financial Analysis, or IEEFA, a think tank, only 0.62 GW of capacity has actually been physically connected to the electricity grid. In contrast, the U.K. has more than 8 GW.
"Japan is still an early-stage market despite an enormous pipeline, since very little capacity has passed through so far," said Chris Wilkinson, senior analyst at Rystad Energy, a consultancy.
One lesson from Britain is how quickly the ways batteries make money can change. The frequency response market, which pays batteries to rapidly charge or discharge to help keep the power grid stable, was initially profitable, Wilkinson said. But as more batteries entered the market and prices fell, "optimisers had to switch strategies towards arbitrage and [power] trading."
Wilkinson expects Japan to undergo a similar shift. "Operators in Japan should plan for arbitrage and trading to be the long-term core revenue," he said.
That is something Sumitomo hopes to learn from its U.K. operations. Hamada pointed to Britain's booming intraday power market, where electricity is bought and sold close to when it is needed, as an important source of revenue for BESS operators. In Japan, the market has yet to take off.
"I believe Japan will inevitably move in this direction eventually," Hamada said. "By investing in the U.K. market ourselves and gaining hands-on experience in generating revenue through intraday power trading, we believe we can contribute to the effective use of battery storage within Japan's electricity system."
However, multiple challenges remain for BESS operators in Japan. Congestion in connecting to the grid "remains the primary bottleneck," spurred in part by speculative project proposals, IEEFA said in a March report.
It added that high battery costs compared to other markets "present an additional challenge for new investment," with costs remaining 2.5 to 3 times higher than global benchmarks.
Power market participants have also pointed to the lack of negative pricing as a barrier.
In Europe, power prices frequently turn negative when electricity supply outstrips demand, often during periods of high renewables generation. BESS operators can take advantage of such price crashes, storing energy at times when prices are extremely low or negative -- effectively getting paid to store energy -- and discharging it when prices are higher.
Japan, meanwhile, has a floor price of 0.01 yen, or a fraction of a cent, per kilowatt-hour.
For a BESS developer, negative pricing is "a very important signal," said Camilla Larsen, vice president of enterprise sales at European energy technology company Volue, adding that in Europe, it has been a "strong incentive" to invest in batteries.
"If we allow the market to work, it will eventually converge towards [electricity supply and demand] balance because we will have necessary investment [on things like BESS]. Yes [BESS developers] do it to make a profit but at the same time it is helping the power system," she said.