“Low voltage is the easy route” does not hold for a storage station

"At low voltage, a notification is all it takes." The more experience someone has with low-voltage solar, the more likely they are to walk into batteries believing this. It is wrong. At the same 49.5 kW, solar is a small-scale business-use electrical facility, while a storage station (蓄電所) is a business-use electrical facility whatever its output, which means a safety regulations filing and the appointment of a chief electrical engineer. The applicant is not you either, but the retail electricity provider; the grid connection cost contribution is fixed only after you have applied; and a single unit can sell nothing into any market. A low-voltage storage station is not a small version of low-voltage solar.

Low-voltage battery resources (receiving capacity under 50 kW) became eligible for the balancing market from the delivery date of 14 March 2026 (EPRX). In the six months since, subdivided lots and packaged products advertised at "49.5 kW, about six tsubo (roughly 20 m²), in the ¥20 million range" have spread through the market, and the land enquiries reaching us increasingly involve small parcels that fall short of the minimum for a high-voltage project. Yet when the assumptions being repeated in the field are checked against the statutes, the government's Q&A and the application rules of the ten general transmission and distribution utilities (TDSOs), five of them fail. This column is written strictly within what could be confirmed in documents published by the Agency for Natural Resources and Energy (ANRE), the Organization for Cross-regional Coordination of Transmission Operators (OCCTO), EPRX and the ten TDSOs, as of 22 August 2026.

In order: where the lines are actually drawn (01), the applicant is not you (02), the price is set after you apply (03), the "4-year rule" does not exist (04), one unit sells nothing (05), choosing between low and high voltage (06), what takes effect from here (07), and five checks before you file (08).

The five assumptions — what you were told, and what is actually the case

Scope of this column

01Where the lines are drawn — 50 kW, 2,000 kW, and the "storage station"

Grid interconnection classes are drawn by receiving capacity. Under 50 kW is low voltage; 50 kW to under 2,000 kW is high voltage; 2,000 kW and above is extra-high voltage. High-voltage projects are designed at 1,990 kW or 1,999 kW because crossing the 2,000 kW line brings extra-high-voltage receiving equipment and procedures with it, and low-voltage projects are designed at 49.5 kW for exactly the same reason. Up to this point, batteries behave like solar.

The Electricity Business Act draws a different line. Electrical facilities fall into three classes — general-use, small-scale business-use and business-use — and the only things inside the small-scale business-use class are solar at 10 kW to under 50 kW and wind under 20 kW. A storage station — equipment that takes in electricity from outside the site, stores it, and sends it back out at the same voltage and frequency — is a business-use electrical facility whatever its output (METI, "Guide to Installing Electricity Storage Devices (Batteries) and Storage Stations", 14 November 2025). Low-voltage solar gets by on a notification because the small-scale business-use category exists. Storage stations have no such category.

Three things come with that. First, the duty to maintain conformity with technical standards (Article 39 of the Electricity Business Act), the safety regulations filing (Article 42) and the appointment of a chief electrical engineer (Article 43). For facilities under 5,000 kW connected at high voltage or below, safety management can be outsourced under the external outsourcing approval scheme, so you do not have to be the chief engineer yourself. The outsourcing fee, however, lands as a fixed annual cost per unit. Second, electricity storage devices above 20 kWh have been subject to incident reporting since 20 November 2025 (amendment to the Ordinance on Reporting of Electricity-Related Matters: fire, explosion or damage to major equipment must be reported in outline within 24 hours and in detail within 30 days). Every low-voltage storage station in the 100–200 kWh class is caught. The Interpretation of the Technical Standards for Electrical Installations was amended the same day, incorporating the lithium-ion battery standard JIS C 8715-2. Third, the Fire Service Act. The amendment to the ministerial ordinance on fire-use equipment, in force from 1 January 2024, changed the unit of regulation to kWh: above 10 kWh a system is regulated, and above 20 kWh a filing with the fire department is required. Fire-prevention ordinances are set municipality by municipality, and outdoor installations must as a rule sit at least 3 m from buildings (relaxed with fire-spread prevention measures or a cubicle-type enclosure). If the volume of electrolyte exceeds the designated quantity under the Fire Service Act (1,000 L for Class 4, Petroleums Class 2), a separate hazardous-materials regime can apply alongside the fire-use equipment ordinance. Pre-consultation with the local fire department cannot be skipped, even at low voltage.

Some things, on the other hand, you genuinely do not need at low voltage. Notification as a power generation business is triggered at an aggregate connected capacity above 10,000 kW; the construction plan notification and pre-service self-inspection apply at 10,000 kW or more of output or 80,000 kWh or more of capacity. A standalone low-voltage unit needs neither. In an urbanization control area, however, the question of whether the facility is a Category 1 Designated Structure (MLIT notice of 8 April 2025, COLUMN 43) applies at low voltage too.

The reading is this. The "notification is all it takes" instinct learned from low-voltage solar does not transfer to storage stations on the safety side. The lightness of low voltage lies in the grid interconnection procedure, not in the treatment under the Electricity Business Act.

02The applicant is not you — the counterparty to the supply contract is the retailer

A low-voltage storage station that discharges (exports) is filed with every TDSO under the category of the Generation Output Adjustment Supply Contract (発電量調整供給契約, "hatsuchō" contract). And the party to that contract is not the owner but the retail electricity provider — the generation contract holder. TEPCO Power Grid states expressly that where reverse power flow occurs a generation-side application is required, that the generation contract holder applies to TEPCO PG for the contract, and that applications go through its web application system. You are the owner, not the contracting party. Hokkaido Electric Power Network, Chubu Electric Power Grid and Kyushu Electric Power Transmission & Distribution require a "letter of consent from the generator" to be attached to the retailer's application form. The owner is not the party who applies; the owner is the party who signs the consent.

The channel differs by utility (Table 1). Kansai has "Takusō-kun", Kyushu has "Takusō Net", Chugoku has its "Wheeling Web New/Expanded Works Application", Shikoku has a "Works Application Reception System" (paper still accepted for now), Hokuriku has its "Wheeling New/Expanded Application System", Chubu and Hokkaido take internet applications, and Tohoku takes applications by e-mail and internet while grid interconnection applications go by post. It is not only the names that differ: the forms, the required documents and the standard processing times differ too.

The caps come from each TDSO's own calculation (11th Next-Generation Power Grid Working Group, 10 June 2026, Document 2) and their published pages. Because the scheme applies to "connection studies" for grid-scale batteries, there is no express text applying it to low-voltage grid batteries, which have no connection study (see §07).

Let us be precise about agency. You sometimes hear that "low voltage cannot be filed by an agent", but that is not what the utilities' application rules say. That the contracting party is fixed as the retail electricity provider, and that the mechanics of filing can be delegated under a mandate, are two different things. Chugoku Electric Power Network states expressly that new/expanded applications (including the Wheeling Web application) may be filed by an electrical contractor acting as agent, provided the connection supply contract and the generation supply contract are already concluded. Tohoku Electric Power Network runs two tracks — low-voltage grid interconnection applications from "the generator (including an application agent)", and supply contract applications from the retailer that will buy the power — and Hokuriku Electric Power Transmission & Distribution likewise assumes in its FAQ that applications come from "an application agent (electrical works / electrical contractor / architectural design)". For the remaining six utilities (Hokkaido, Tokyo, Chubu, Kansai, Shikoku, Kyushu), no page could be found that states verbatim whether a third party may file the supply contract application under mandate ❓. No utility allows a dedicated permitting agency to sign the supply contract in its own name, so if you want to use an agent, the starting point is a power of attorney from the retailer.

One more. From 1 June 2026, filing the generation side (discharge) and the demand side (charging) simultaneously became a condition of accepting a contract application for grid-scale batteries ✅. Low voltage is covered as well. TEPCO PG introduced a new technical-consultation request form for low-voltage supply contracts on 15 May 2026, adding a field for whether grid charging and discharging occur. Kyushu Electric Power T&D requires a non-firm connection consent form with the supply contract application, and, for storage equipment connected at low voltage with reverse power flow, a PCS specification sheet covering power factor and ramp rate.

The reading is that the order is inverted. The solar instinct is "land → equipment → application". For a low-voltage storage station it is "retail electricity provider (and aggregator) → land and equipment → application". Until the generation contract holder is settled, you cannot take the first step.

03The price is set after you apply — there is no connection study at low voltage

The better you know high-voltage development, the more likely you are to trip here. At high voltage you apply for a connection study, receive a response within three months as a rule (two months for units under 500 kW using inverters), and move to the contract application after seeing the estimated grid connection cost contribution written in it. At low voltage there is no such connection study ✅. Under OCCTO's "Flow of Grid Access for Generation and Related Facilities" and TEPCO PG's grid access rules, the TDSO carries out a technical review in connection with the contract application, and the cost contribution is fixed only after the design is complete. Kyushu Electric Power T&D's low-voltage procedure page likewise states that where a contribution arises, the amount is as a rule calculated after design completion. "Decide once you have seen the estimate" is not structurally available. Time, on the other hand, is short: the response to a contract application is one month as a rule at low voltage, against six months or an agreed period at high voltage and above.

The easy confusion here is between "no connection study" and "no technical review". Even at low voltage you must submit interconnection documentation — single-line diagram, PCS ratings, protective relay settings, CT locations — and the feasibility and conditions of interconnection are judged on that basis. It is only the timing of that judgment that moves behind the application.

What about the deposit? OCCTO's "Methodology for Calculating Deposits on Contract Applications for Generation and Related Facilities" (updated 18 March 2026) sets the deposit for grid-scale batteries at 10% of the estimated cost contribution stated in the connection study response (for applications received from 1 April 2026), and states in a footnote that for applications where no connection study is required, the estimated contribution is treated as zero. Followed literally, the formula puts the low-voltage deposit at zero. However, TEPCO PG's notice on the deposit increase expressly scopes it to [high voltage and extra-high voltage], and no notice could be found on any utility's site stating either that low voltage is subject to a deposit or that it is exempt ❓. There is no document that lets you conclude "no deposit at low voltage"; you have to ask each utility's wheeling desk.

The level of the cost contribution is unknowable in advance for the same reason. Some utilities, such as Chugoku Electric Power Network, apply a unit-price schedule to low-voltage interconnection contributions (since February 2021), but those are common unit prices for low-voltage generation facilities including solar. No published case could be found giving an actual contribution figure for a standalone low-voltage grid battery ❓.

Two readings follow. If your funding plan requires the contribution to be fixed before you apply, low voltage is structurally unsuited to you. Conversely, the advantage of low voltage is that it avoids the connection queue that has stretched to 18–24 months at high voltage (COLUMN 09). It is a trade: price later, time sooner.

04The "4-year rule" does not exist — but the rules do name storage stations

Two claims are circulating in the market. "If the landowner is the same going four years back, it is a split project." And "1 MW — that is, about 21 units of under 50 kW — is the lot size for applications." Neither appears anywhere in ANRE's Q&A, the enforcement ordinance under the Electricity Business Act, or the TDSOs' application guidance ❓. That does not mean there are no rules. There are, and they name storage stations expressly. Let us set it out.

The basis is not FIT. The prohibition on splitting solar sits in Article 5(1)(ii) of the enforcement ordinance under the Renewable Energy Special Measures Act (in force April 2014), which is a certification requirement for FIT and FIP. It does not reach non-FIT storage stations directly. What applies instead is the proviso to Article 3(2)(ii) of the Enforcement Ordinance of the Electricity Business Act. The amendment of 1 April 2022 added to the definition of "a single demand location" an exclusion to the effect that where multiple generation-and-storage electrical facilities are installed on adjacent premises without a special reason, they are not treated as separate demand locations (they are aggregated); the amendment of 1 April 2023 widened the scope to "generation and storage electrical facilities" — that is, both generating and storage equipment. ANRE's "Q&A on Countermeasures Against the Segmentation of Generation and Related Facilities" (last updated 11 June 2026) expressly lists "grid-scale batteries (storage stations)" among the concrete examples in scope ✅.

The elements of the test are set out in the same Q&A. That the installer of the new facility and the installer of an existing adjacent or nearby facility are the same. That, even where the installers differ, the landowner of the new site and the existing site is the same. That the same installer is building several facilities on adjacent or nearby land. That, even where the installers differ, the land is recognised as substantively one location. And that even where names differ formally, the judgment is made on substance — "substantively the same". The judging party is the TDSO, and it happens during the review of the connection study or the technical review. Low voltage has no connection study, but the technical review seen in §03 plays that role.

The look-back period is "as a rule, where the landowner is the same within one year back from the fiscal year of the application" (same Q&A, A4-1). Only for low-voltage solar of 10 kW to under 50 kW does the look-back extend as far back as FY2014, on the grounds that deliberate splitting was common there (A4-2). Because item 2 is confined to solar generation facilities, on the face of the text the one-year rule applies to storage stations (there is no passage in the Q&A that names storage stations and sets a look-back period for them). And neither contains "four years". Nor could "1 MW = 21 units" be found: the figure of 1 MW appears as the minimum bid size in the balancing market (§05), not as an application lot or a unit for the segmentation test.

The examples that count as a "special reason", and therefore do not amount to segmentation, are in the same material. A road, river, historic footpath or waterway — public property outside the statutory categories — has always sat in between, so the sites cannot physically be combined. Land subject to objectively recognised restrictions on other uses, such as farmland or protection forest, lies in between. Even if split, each part would still be extra-high voltage. The facilities are of different types. A private line is run from the existing facility so that everything is combined into one demand location. The number of service connections from the grid is unchanged (except where the purpose is to avoid safety regulation). A battery installed as ancillary equipment is not a storage station, so placing a storage station adjacent to it is not segmentation (Q10). The Q&A also states, however, that even where a case formally meets a "special reason" it may be judged as segmentation on the substance — for instance where the purpose is to avoid stepping up voltage — that splitting high voltage into high voltage is also in scope (Q11), and that the test may be applied again at the change-of-name procedure on a transfer. These rules bite on the buyer too.

Enforcement comes in two stages. If segmentation is found at the application stage, the several sites are treated together as one demand location, and an application under 50 kW cannot stand. Chubu Electric Power Grid states expressly that it will not accept applications judged to be split projects. As for cases discovered after interconnection, Chubu Electric Power Grid states in its notice of 7 March 2022 that where it requests remediation to a proper generating state and the operator does not comply, it may terminate the contract ✅. That said, no case of a storage station being rejected, revoked or terminated on segmentation grounds could be found in METI's published enforcement actions, or in notices from ANRE or the TDSOs ❓. Every published action concerns solar. FIT/FIP certification revocations in FY2025 numbered 55 (against 13 the previous year), and among them the Tajima-Minami No. 1 power plant (revoked March 2026) was a case of forging official documents to make a project appear not to be a split one (published by METI on 6 April 2026). Split the names to evade the test and it stops being a segmentation problem and becomes a forgery problem.

The background to the rules is worth holding onto as well. The body of the Q&A takes as its starting point the sharp increase, from April 2021 onwards, in projects split below 50 kW in order to apply for connection contracts while avoiding safety regulation — safety regulations, construction plans, chief engineers — and lists three concerns: the unfairness of escaping regulation that ought to apply, the pass-through of TDSO management costs into wheeling charges, and the inefficiency of unnecessary poles and meters. As §01 showed, a storage station is a business-use electrical facility whatever its output, so slicing below 50 kW does not escape safety regulation. Even so, the pattern of one landowner or installer placing many units on nearby land is precisely the pattern these rules are aimed at. From January 2026, newly built generation and storage facilities requiring a connection study must submit documentation of the results of checking the land register for the installation site (on the face of the text, low voltage, which has no connection study, is not covered).

The reading is this. "Four years" may be gone, but the pattern of one landowner filing several applications at the same time is the archetype of segmentation, and the look-back period never comes into play. The contested point shifts to whether a "special reason" applies — whether a road, footpath or farmland has always sat between the parcels, whether the service connections are separate per parcel and can be explained as having no safety-avoidance purpose. Consult the connecting utility early in the planning phase, and if it does not qualify, change the design. Splitting the names is the worst move available.

05One unit sells nothing — a 1 MW minimum bid, and 49.5 kW is a twentieth of it

The minimum bid size in the balancing market is 1 MW (1,000 kW) (EPRX, "Introduction to the Balancing Market"). Resources below 1,000 kW are bundled before bidding. The capacity market likewise sets 1,000 kW as the minimum, with anything below that bundled as a dispatch-instruction resource. 49.5 kW is roughly one twentieth of 1 MW. A low-voltage storage station can sell nothing into any market on its own.

How low-voltage resources became eligible is clear enough. Per EPRX's FAQ, completion of the market management system (MMS) update made trading possible for resources meeting the entry requirements from the trading date of 13 March 2026 (delivery date 14 March). OCCTO's 57th Balancing Market Subcommittee (26 September 2025) established that low-voltage resources metered at the receiving point can participate in all products under the list and pattern method — registering multiple resources as a "list" and bidding, evaluating and settling on a list basis — and the TDSO-side registration ceilings were raised to 100,000 resources and 500 lists/patterns. The framework on the bundling side is in place.

The party doing the bundling is an aggregator registered with the Minister of Economy, Trade and Industry as a Specified Wholesale Supplier. Connection to the simplified command system, compliance with the cyber-security guidelines for ERAB (energy resource aggregation business), responsibility for planned-value balancing, and absorbing the penalties for non-performance — the party accountable to the market is the aggregator, and the owner is a resource provider.

Here is the state of disclosure on intake terms. RE100 Denryoku advertises a 5% management fee, but conditional on a bundled aggregation-plus-O&M package (advertised figure). FPS uses a combination of a revenue share and a fixed monthly fee (rate undisclosed), and states on its own site that it has suspended new intake of low-voltage batteries, including residential and self-consumption types. Digital Grid states in its own FAQ that it takes on low voltage from 30 units. WATT-TUNE (basic agreement announced 14 March 2026 under a four-way tie-up with Eco-Kaku, GoodWe Japan and REVIX JAPAN) and Tensor Energy (which announced the start of its business on 14 March 2026; 500 units by 2028 and 1,000 by 2030 are targets) disclose neither fee rate, nor contract term, nor whether the contract survives a change of owner. Not one aggregator in the scope of our search discloses whether the operating contract can be assigned when the owner changes ❓.

Treat the yield figures the same way. "Over 20%" and "payback in five to six years" are sellers' advertised figures; commentary sites present ranges such as annual gross revenue of ¥2.63–6.32 million and a pre-tax IRR of 5.8–17.4%, but market operation at low voltage only began in April 2026 and no full-year record exists ❓. On top of that, the price cap in the balancing market falls to ¥10 from the delivery date of 1 September 2026, with further conditional step-downs already signalled (COLUMN 41). The initial cost of ¥12.5–27 million and the footprint of about six tsubo are advertised figures too, and exclude land acquisition, the grid connection cost contribution, site preparation and ground improvement.

There is one reading. Revenue at low voltage is determined not by the performance of your battery but by the aggregator's bidding and operating capability and by how it takes its fee. The gap between gross and net described in COLUMN 17 bites harder at low voltage, where each unit is small and the fixed-cost ratio is high, than it does at high voltage. Choose the aggregator before the equipment. That is the order.

06Low voltage or high voltage — the table of the dividing line

"Advertised figure" means a number from sellers' material or commentary sites, not a regulatory or operating figure. Low-voltage procedures are per OCCTO's "Flow of Grid Access for Generation and Related Facilities" and each utility's low-voltage pages; deposits are per OCCTO's calculation methodology (18 March 2026).

Here is the reading. The conditions under which low voltage becomes rational come down to three. You already own a small idle parcel and do not need to pay for land. You want to avoid the high-voltage connection queue. You want to spread your exposure in units of tens of millions of yen rather than hundreds of millions. Conversely, if you have concentrated capital and a site, and want a single location you can hold at arm's length, high voltage is the answer. A design in which "2 MW-equivalent spread across 40 low-voltage units matches a high-voltage project" is also being marketed (advertised figure), but that is also 40 supply contracts, 40 safety regimes, 40 fire-department filings and 40 access roads — and it takes the segmentation test in §04 forty times.

Scale adds up. The work does not.

07What takes effect from here — the 2026–27 rules and how they reach low voltage

The run of new rules introduced during 2026 is designed to tighten the connection study process in order to stop speculative queue-holding. Much of it does not reach low voltage, which has no connection study, but three things certainly do: parallel filing (1 June), land use title documents (1 October) and JC-STAR ★1 (October 2027).

Two of these deserve detail. On land use title, the ten TDSOs have applied for approval of amendments to their wheeling service tariffs, with implementation planned for 1 October 2026. Non-FIT and non-FIP sources are covered, and unless a copy of the land register or the lease agreement is submitted within two months of interconnection consent, the interconnection reservation is cancelled. A low-voltage storage station falls within that category of "non-FIT, non-FIP source". Land rights have become something you settle before you apply.

JC-STAR ★1 becomes mandatory with the April 2027 revision of the grid interconnection technical requirements; products connecting at low voltage (under 50 kW) get a transitional six-month lag, applying to contract applications from October 2027 (7th Next-Generation Power Grid Working Group, 9 February 2026, Document 2, "On the Grid Code"; 20th Grid Code Study Group, 16 December 2025). The trigger is the contract application date, not the interconnection date (COLUMN 14, COLUMN 27). In scope are PCS, EMS, gateways and other equipment involved in control over IP communications. ★1 is a self-declaration of conformity, valid for at most two years. Low-voltage projects filing from October 2027 need to check the IPA's list of products holding conformity labels before ordering equipment.

08Five checks before you file

1. Are the retail electricity provider and the aggregator settled? As §02 and §05 show, you cannot take the first step until the generation contract holder is fixed, and there is no revenue until you have someone to bundle with. Get in writing: the minimum intake unit (a 1 MW bundle? from 30 units?), how the fee is taken (success fee, fixed monthly, any up-front charge), the contract term, whether the contract survives a change of owner, and where liability sits for imbalance and outages. Most operators publish none of this, so asking before you sign is the only way to find out.
2. Is the safety regime in place? As §01 shows, a storage station is a business-use electrical facility whatever its output. Line up the external chief electrical engineer, the safety regulations, and the fire-department filing and incident-reporting arrangements required above 20 kWh — for every unit. The "notification only" routine you used on low-voltage solar does not transfer as it stands.
3. Have you built into your funding plan that the cost contribution only emerges after design completion? As §03 shows, "decide once you have seen the estimate" is not available at low voltage. Whether a deposit applies is not written down either, so ask each utility's wheeling desk. Do not lock in decisions on land, equipment and finance ahead of the application.
4. Is there a facility on adjacent or nearby land with the same installer or the same landowner? As §04 shows, "four years" does not exist but the rules do. If there is, consult the connecting utility early in the planning phase about whether a "special reason" — a pre-existing road, footpath or farmland, separate service connections — applies. Do not take the route of splitting names to change how it looks.
5. Will you make October 2026 and October 2027? As §07 shows, land use title documents are due within two months of interconnection consent, and JC-STAR ★1 applies to contract applications from October 2027. Confirm land rights and equipment conformity before you file.

ENDA low-voltage storage station is not a small version of low-voltage solar

To restate the five. A storage station is a business-use electrical facility whatever its output, and needs safety regulations and a chief electrical engineer. The applicant is not you but the retail electricity provider, and from June 2026 the charging side must be filed in parallel. There is no connection study at low voltage, and the grid connection cost contribution is set after design completion. The "4-year rule" appears in no document, but the segmentation rules under the Electricity Business Act name storage stations expressly, and the test turns not on a look-back period but on identity of installer and landowner and on "special reason". And 49.5 kW is one twentieth of the 1 MW minimum bid: a single unit sells nothing.

The advantages of low voltage are real. You can start on a small parcel, avoid the high-voltage connection queue, and spread your exposure in units of tens of millions of yen. But those advantages come from the lightness of the grid interconnection procedure — not from any lightness in the treatment under the Electricity Business Act, in the unit of market participation, or in the segmentation rules. When you look at low voltage, the order is not land, and not equipment, but the retailer and the aggregator. Only once those are settled can you go back to land and equipment.

❓ Unconfirmed — the limits of this column

Null finding: No detailed operating rules on segmentation specific to low-voltage grid batteries — look-back years, or a unit expressed in capacity or number of projects — exist in ANRE's Q&A or in the TDSOs' application guidance. As far as can be confirmed, the segmentation test for batteries is carried out by the TDSOs on the basis of the proviso in the Enforcement Ordinance of the Electricity Business Act, applying by analogy the test elements built up in the solar context.