IN Brief:
- HEXA Energy Services has confirmed a 50MWac export rating for its planned Oyabe battery in Toyama Prefecture.
- The developer’s project register identifies 200MWh of energy storage capacity, equivalent to four nominal hours at maximum rated power.
- Shirokuma Power is the EPC partner and commercial operation is targeted for May 2028.
HEXA Energy Services has detailed plans for a grid battery in Oyabe City, Toyama Prefecture, following a joint presentation with the municipality on 8 October 2026. The developer has confirmed a 50MWac export rating, while its project register identifies 200MWh of storage capacity. Shirokuma Power is responsible for engineering, procurement and construction, with the facility scheduled to begin commercial operation in May 2028.
The installation is planned for the Ishinada area of Oyabe, where a groundbreaking ceremony was held on 6 September ahead of the October public presentation. Site preparation and the municipal engagement establish progress in development, although installation of the complete battery equipment and its network connection remain ahead. Those works, followed by electrical testing and operating approvals, must be completed before the proposed 50MWac can become available to the surrounding electricity system.
Using the two published ratings, the proposed battery has a nominal duration of four hours when 200MWh of energy is divided by 50MWac of maximum output. That comparison assumes the full nameplate energy is available and does not account for conversion losses or limits on the permitted state of charge. The actual energy delivered during a commercial dispatch period will consequently depend on how the installed system is controlled and the usable capacity available at the time.
Battery modules store energy through direct current electrochemical processes, whereas the grid connection carries alternating current electricity. Power conversion equipment controls the exchange between the two, allowing the plant to absorb electricity when charging and return it during discharge. A central controller must coordinate the response of the individual storage and conversion units so that the site’s overall power exchange remains within its connection limit and the batteries’ permitted operating conditions.
Because the plant is designed for nominally four hours of output at rated power, it could deliver electricity over longer intervals than installations configured mainly for short frequency response. The service portfolio has not been specified, however, and every discharge period will require sufficient stored energy and time for subsequent charging. Scheduling will therefore depend on available state of charge, market instructions and the conditions under which the project is ultimately allowed to import or export power.
Oyabe has obtained support through Japan’s long-term decarbonisation power source auction arrangements, which provide a commercial framework for investment in qualifying electricity capacity. HEXA reports 13 successful bids across the 2023 and 2025 auction rounds, including this development. Those awards support the financing case for future storage, while each facility must still meet the local connection and operating requirements before its power can be dispatched.
As the design progresses, transformers, switchgear, earthing and protective devices will have to accommodate both charging and discharging through the electricity network. Protective relays must respond to faults while coordinating with the power conversion and battery control equipment, whose operating limits also constrain the electrical response. Detailed product selections, protection settings and the final grid connection voltage remain undisclosed, so these arrangements are engineering requirements rather than confirmed equipment specifications for Oyabe.
The intended battery installation will also need thermal management and monitoring to supervise temperatures, cell conditions and charging limits, together with suitable protection against electrical faults. HEXA has identified safety in its engagement with Oyabe City, although the detailed fire protection design and equipment selection have not been published. Construction and subsequent commissioning will determine how the chosen safety systems interact with the storage enclosures and site electrical controls.
Once connected, Oyabe could contribute flexibility by increasing electricity demand while charging and releasing stored energy during periods when export is required. The effect on the wider network will depend on connection location, dispatch arrangements and participation in the relevant electricity markets. Neither a four-hour nameplate ratio nor a 50MWac rating establishes the exact balancing services or market contracts under which the completed facility will operate.
HEXA’s wider Japanese project register identifies battery developments in Hokkaido, Mie, Kyoto and Fukuoka as well as Toyama, each with its own capacity and delivery programme. Supported by infrastructure investor I Squared Capital, the company is building a portfolio of proposed storage assets through a series of individual projects. Their planned capacity should remain separate from electricity storage already commercially operating, and Oyabe is still undergoing its development and construction stages.
Shirokuma Power will coordinate construction of the site infrastructure and installation of the equipment needed to connect the battery assemblies with the power conversion and grid systems. Civil work, cabling, protection, communications and testing will have to be completed in the sequence required by the approved design. In particular, grid connection commissioning will need to demonstrate how the combined plant responds to network conditions before commercial dispatch is authorised.
The confirmed May 2028 target leaves HEXA and Shirokuma Power with the remaining construction, equipment integration and commissioning programme at Oyabe. The 50MWac export rating and 200MWh energy capacity define the planned facility, while its eventual availability depends on the installed equipment and grid approval. The September ceremony and October presentation document development progress, with operating capacity to be established after the plant enters service.
