Katana had AI read the annual reports of 110 companies that write about storage batteries or storage plants, looking for those already booking sales or orders from grid-scale battery storage, where it makes up a large part of their revenue.
Grid-scale battery storage means large batteries connected directly to the power grid. They charge at midday, when solar power is in surplus, and discharge in the evening, when power runs short. The more renewable energy grows, the more of this balancing the grid needs.
On September 30, 2026, ORIX and others began building storage plants totaling 589 MWh of storage capacity in Oita and Yamagata, and on October 1 Sumitomo Corporation started construction of a 291 MWh plant in Namie, Fukushima. In Japan's Long-Term Decarbonization Power Source Auction, which promises new power sources long-term revenue, about 3.7 GW of battery output has been awarded across three rounds. Applications to study connection to the grid reached about 172 GW at the end of December 2025.
Yet grid-scale batteries actually connected to the grid came to only about 0.64 GW at the same point. Because of the flood of applications, the government capped from August 2026 the number of connection studies one company may hold at a time. Many large storage plants are scheduled to start operating in 2028 to 2030.
Battery stocks usually bring battery makers to mind. But for the cells used in storage plants, China's top six makers account for about 75% of global shipments. As batteries spread, much of the money for the cells goes abroad.
A storage plant, though, does not run just by placing batteries. Someone must secure the land and the right to connect to the grid, supply the equipment that links batteries to the grid and the system that controls charging, then build, operate and maintain the plant. This work is rooted in Japan's land and grid, so Japanese companies should have a role.
So we used Katana to search annual reports for companies that already report orders or sales from grid-scale battery storage, where it makes up a large part of revenue.
“We want companies that already report orders or sales for grid-scale battery storage, such as building, selling or equipping storage plants, and for which this business is a large part of revenue.”
Claude built and ran the screen through Katana's MCP connection. We used word conditions to keep companies whose main annual report sections use any of six terms for battery storage (such as grid-scale storage, storage plant, power conditioner and BESS, in Japanese), turned this profile into two questions entered in English, and had the AI read each report, question by question. We checked the supported and top-ranked companies against the report text. Claude checked the latest results and share prices in each company's earnings reports and presentations. Judgments and data as of November 3, 2026; share prices are November 2 closes.
Katana computes its metrics for every company.
AI reads each annual report and judges support and counterevidence.
The questions were entered in English and judged in order. For the first question, passages containing grid-scale storage, storage plant or BESS were read first.
read the filings and latest results, and picked 7.
Of 110 companies, 4 were supported on both questions (actual orders or sales, and batteries at 15% or more of revenue), 9 need review, and 97 had counterevidence. After checking the report text and the latest results we list 7: developers that sell storage plants, a storage system maker, builders and equipment makers, and newcomers.
As a result, it completed the development and sale of 10 grid-scale storage plants two years ahead of plan and greatly expanded its pipeline.Filing ↗
In its solar and grid-scale storage business, it sold 191.67 lots of solar facilities and 5 grid-scale storage plants.Filing ↗
Its BESS business mainly sells and maintains the large stationary storage system PowerX Mega Power and the mid-size PowerX Cube.Filing ↗
Sales rose as design-and-build work on the Shizuoka Kikugawa storage plant and on a grid-scale storage plant for a company formed by Tokyo Century progressed smoothly.Filing ↗
Monitoring and control systems for water treatment and large projects for grid-scale storage plants and data centers were firm; segment sales rose 9.4% and segment profit 118.4%.Filing ↗
Its infrastructure asset business began developing a storage plant in the fourth quarter, and construction progressed smoothly; it also booked sales from support for grid connection applications.Filing ↗
As a result, the grid-scale battery business posted sales of ¥2,234 million and segment profit of ¥477 million.Filing ↗
Note: of the 4 companies the AI supported on both questions, we left out Birdman, an advertising company that recently entered battery storage, because in October it disclosed worsening cash flow and the use of raised funds for purposes other than those disclosed. Instead we added 4: West Holdings, GreenEnergy & Company, TESS Holdings and Seiko Electric. West Holdings' storage segment was 12% of revenue in the year of the report, short of 15%, but grew 3.8 times in the results since. The other 3 report storage-plant sales together with solar or electrical work, so the report alone could not confirm the share for batteries. Large makers of the equipment and control systems that link batteries to the grid, such as Meidensha, Daihen, OMRON, Nichicon, Yaskawa Electric and Fuji Electric, were among the 110, but battery storage is a very small part of their business.
For the 7 companies, we list battery storage's share of revenue, the latest storage-plant figures and forward PER. PER is based on the November 2 share price and the company's own profit forecast for this year, lowest first.
| Company | Battery share | Latest storage figures | PER |
|---|---|---|---|
| West HD | 38% | Sales ¥21.7bn, 3.8x | 8.5x |
| Seiko Electric | Not disclosed | Related segment +66% | 9.5x |
| Star seeds | 22% | H1 ¥0.67bn | 14.3x |
| GreenEnergy | Over 40% | Q1 ¥1.96bn | 17.4x |
| TESS HD | Not disclosed | Backlog ¥43.3bn | 17.7x |
| GRID | 24% | Plan ¥1.5bn | 21.1x |
| PowerX | 89% | Backlog ¥84bn | Over 150x |
Battery share is battery storage's share of revenue. West Holdings uses the fiscal year to August 2026 and GreenEnergy & Company its latest first quarter; in the year of the report, West Holdings was 12% and GreenEnergy 40% together with solar. Seiko Electric and TESS Holdings do not disclose storage-plant sales alone (94.5% of TESS's construction backlog is batteries). Seiko Electric's figure is year-to-date growth through the third quarter in its service segment, which includes storage plants. PowerX gives a range for this year's profit forecast, so its PER is about 150 to 225 times.
West Holdings earned ¥8.4 billion of operating profit from storage plants in the fiscal year to August 2026, about two-thirds of the company total. It sources batteries mainly from Toshiba Mitsubishi-Electric Industrial Systems and sells finished plants to investors such as funds. Without making batteries itself, it earns the largest profit of the 7 by securing land and grid connection rights, turning them into storage plants, and selling them.
PowerX, which assembles storage systems at its own plant, has the largest backlog at ¥84 billion, and its PER exceeds 150 times. PowerX, often named as a battery stock, is priced for growth well into the future.
The company earning the most from storage plants today is the cheapest, while the company that makes storage systems is priced for growth well into the future.
Demand is clearly there. But while connection applications have flooded in, few storage plants are actually running. Which companies will win is not yet decided.
What seems to decide it is less the price or performance of batteries than whether a plant can be connected to the grid. At TESS Holdings, the grid connection work the client must pay for cost far more than expected, and about ¥4 billion of work was canceled. At JESCO Holdings, connection talks and work dragged on, and sales of solar and storage plants fell to about half the prior year. Since August the government has capped the number of connection study applications, and it plans to require documents proving land rights with contract applications. Piling up applications no longer turns into storage plants by itself.
Conditions are changing on the battery side too. From the next round, the government auction will give priority to batteries using cells from makers it has certified. GS Yuasa, which is certified, starts mass production in October 2028.
The winners are likely to be not those who buy batteries cheaply, but those who hold projects that can connect to the grid and can turn them into running plants on schedule. West Holdings has filed over 1,600 applications for connection talks and says it will reselect its projects. As applications turn into storage plants, the gap between companies that can connect and those that cannot will start to show in their results.
Katana narrows companies with its own metrics, and AI reads annual reports to judge qualitative conditions. For complex theses and company profiles, the selection you used to do one company at a time, AI now runs across the Japanese market.
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