Is a battery the same wherever you put it?

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Frequency restoration is the same anywhere within the same area. What matters is which area, whether the lines are congested, and — for the voltage role — exactly where.

Does a battery just need to be near a power line? Is it fine to scatter units far apart? On frequency, the answer is that anywhere within the same area is the same. Electricity travels at close to the speed of light, and in a single connected grid the frequency measured anywhere is essentially the same value once things have settled (in the few seconds right after a plant trips, it does differ by location). Eastern Honshu is one grid at 50 Hz, western Honshu one at 60 Hz. Hokkaido connects to Honshu by direct-current link, so its frequency is separate, and Okinawa is an independent system. Tokyo can use power from a plant in Niigata, and surplus solar in Kyushu can push frequency up as far as Kansai, for the same reason: it is one grid. A battery's frequency-restoration work likewise reaches the whole area, regardless of where it sits. Voltage support (48-3), on the other hand, is about the pressure pushing electricity out, so it only works near where the battery sits.

Constraint 1: the links between areas are thin

Japan's grid is divided into nine areas (ten including Okinawa), linked by interconnectors. Each interconnector has a limit on how much it can carry, and that limit sets both how much surplus can be sent to a neighbour and how much balancing power can be borrowed from one. So the balancing market procures across areas subject to interconnector constraints, with different operating scopes by product, and seats (the capacity market) carry area constraints too. Because east and west run at different frequencies, only what passes through the frequency converters between them can move. Interconnectors are being thickened, but it takes time.

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Fig. 1 — Japan's nine areas and its interconnectors. Within a single AC grid, frequency is essentially one value. Cross-area volume is set by interconnector thickness: east–west through the frequency converters, Hokkaido through the DC link (Hokkaido–Honshu). Sources: interconnector reinforcement plans in OCCTO, 103rd Wide-Area Grid Development Committee, Material 3 (1 September 2026); Agency for Natural Resources and Energy, "On the Next-Generation Power Network," 31 October 2023.

Constraint 2: even within an area, some lines get congested

Within an area, transmission lines also have carrying limits. Lines in regions where solar clusters get congested at midday, and batteries connected there can be told not to discharge (or not to charge) during congested hours (non-firm connection). OCCTO publishes annually which lines are congested and by how much; for FY2031, congestion is projected to increase on Hokkaido's bulk system and on local systems in eastern Japan and Chubu (103rd Wide-Area Grid Development Committee, Material 3, p.24). Location may not matter to frequency, but it matters to how much room is left on the line.

Spreading units out is, if anything, good

Precisely because of those two constraints, dividing batteries into smaller units and spreading them out has value. You can pick uncongested lines. One incident does not stop everything. And generally, siting near demand reduces transmission losses. Within a single area, spread units across places where there is room on the line. That is the basic approach to choosing a site.

How an investor should read this

Frequency restoration works the same wherever you put it. So "where to site" is decided by three things: ① which area (how free the seats are, the day–night price gap, whether there is nuclear — 48-7), ② whether the lines are congested (the FY2031 congestion outlook is published), and ③ whether it is before or after the interconnectors thicken. Within a single area, we see spreading units out as a strength from the standpoint of avoiding congestion and incidents.

The questions in this series

I. Why the grid ran without batteries in the past

II. Why thermal, nuclear and pumped storage are not enough

III. Where demand and the generation mix are heading

IV. The money, and what the state really wants

48-14Does the government actually want more batteries?
48-15What does battery storage resemble as an infrastructure investment?
48-16They say the earnings will thin out. Is that true?
48-17Can you copy the overseas playbook and make money in Japan?
48-18How much battery storage will Japan ultimately need?
48-19Is a battery the same wherever you put it? (this article)

The one question beyond the 1848-20 What do you pay, and what comes back?The answer differs by project, so we have built a calculator whose dials are made only from published figures. You can move unit price, clearing rate, seat fee, arbitrage spread and construction cost yourself.

Sources

OCCTO, 103rd Wide-Area Grid Development Committee, Material 3, 1 September 2026 (p.24 number of congested facilities; p.55 interconnector reinforcement plans: Hokkaido–Honshu 900 → 1,200 MW in March 2028, Tohoku–Tokyo November 2027, Tokyo–Chubu frequency converters FY2027, Chubu–Kansai June 2030)
Agency for Natural Resources and Energy, "On the Next-Generation Power Network," Material 6, 31 October 2023 (frequency converters 2.1 GW → 3 GW; Tohoku–Tokyo 10.28 GW)
OCCTO, "On Grid Connection and Use Rules — Non-Firm Connection," 10 July 2026
Balancing market (EPRX): area-level tendering and the cross-area procurement mechanism

Supervised by

Shinya Nakashima(Representative Director, Science X Inc.; Ph.D. in Engineering)

Works on the development, sale and technical due diligence of grid-scale battery storage plants. This column is written and supervised on the basis of hands-on transaction and evaluation practice.