Japan's new intraday market (Oct 2026)

What changed on 1 October 2026

• API-only trading. JEPX's own intraday (時間前) trading screen was retired. Orders now go through the JEPX member API, either from a member's own system or through one of the trading-system providers JEPX lists. Trading still opens at 17:00 the day before delivery and closes one hour before each 30-minute slot; the trading fee for FY2026 is ¥100/MWh.
• A dedicated line. A direct API connection needs a JEPX dedicated line (専用接続線). It is open to Japanese companies and costs ¥500,000 to install plus ¥250,000 a month (before tax). Members can instead connect through a provider that already has a line. For a small portfolio the fixed cost is material, which pushes smaller players towards aggregators and software providers.
• 13 listed providers. As of 5 October 2026 JEPX lists 13 trading-system providers (取引システム提供事業者のご紹介). Some offer a browser trading screen and their own web API; others focus on automated trading and battery optimisation. At least two say intraday support arrives during FY2026, so check each provider's status.

Five area groups, and why

• Members now see the intraday order book in five area groups: Hokkaido; Tohoku–Tokyo; Chubu–Hokuriku–Kansai; Chugoku–Shikoku; Kyushu. The groups are fixed in JEPX's API specification.
• Why show areas at all: before the switch, the order book did not show which area a sell order came from, so a trade matched on price could still fail when an interconnector was full.
• Why five groups rather than nine areas: the regulator, the Electricity and Gas Market Surveillance Commission (EGC), chose groups so that the former regional utilities' marginal costs and fuel prices cannot be inferred from their orders.
• The book shows buy and sell volume at each price level. Completed trades show price and volume but no area, so even members do not get an area-level intraday price. JEPX's trading rules (取引規程 第112条) bar members from sharing this information outside the membership.
• What is still public: only the national summary for each 30-minute slot: open, high, low, close and weighted-average price, total volume and number of trades. JEPX does not publish area or area-group intraday prices or volumes. That is why every area intraday figure on this site is labelled derived from national data: the national intraday spread applied to the area's day-ahead schedule.

Imbalance price cap: ¥300/kWh

• From the same date the cap on the corrected imbalance price (補正インバランス料金, C値) rose from ¥200 to ¥300/kWh. The change was moved from April so that it would start together with the new intraday system. Shortage pricing on tight evenings can now run higher, which raises the cost of under-forecasting for FIP and merchant plants and the value of fast-responding batteries.
• JEPX Pulse shows the new cap on the Imbalance panel, and the calculator includes a ¥300-cap stress. Since the end of August 2025 only three half-hours reached the old cap (Tokyo 1, Hokuriku 2), so history alone says little about how often the new cap will bind.

Series break in the analytics

• Intraday and imbalance analytics on this site treat 1 October 2026 as a series break: a Pre / Post 1 Oct toggle keeps the two periods apart, and an early-days caveat is shown while fewer than 30 post-change days exist. This is the same approach we use for the balancing-market regime change of 14 March 2026.

What it means for renewable and BESS players (JEPX Pulse analysis)

• FIP and merchant generators: intraday repositioning now needs an API connection or a service provider. The ¥300 cap raises the penalty for being short, so forecast quality and updates before gate closure matter more.
• BESS operators: members can now see where intraday liquidity sits by area group; outsiders, including investors, cannot. Public national data remains a fair guide to the average intraday-vs-day-ahead spread, not to differences between areas.
• The groups don't follow how prices actually separate. In FY2025 day-ahead results, Chugoku and Shikoku (same group) had the same price in 66% of half-hours, while Kansai and Chugoku (different groups) did in 90%. Chubu and Kansai (same group) matched in 64%. A group's order book can still hide congestion inside the group.
• Analysts: compare pre- and post-October periods separately. Early figures: 1–4 October averaged 27.1 GWh and about 9,000 trades a day, against 35.7 GWh and about 11,800 a day in September. Four days is too few to draw conclusions.

Sources

• JEPX: 取引システムの更改について (8 Sep 2026); システム更改のスケジュール他について (26 Nov 2025); API仕様書（時間前市場取引システム） v1.0.3 (1 Dec 2025); 専用接続線 接続技術書 v2.1 and 通信線利用規約; 取引システム提供事業者のご紹介; 取引規程. All at jepx.jp.
• EGC, 制度設計・監視専門会合 第15回 資料6 (21 Nov 2025): 時間前市場におけるエリア別表示とインバランス料金制度の改正時期について
• JEPX day-ahead and intraday market data; area-pair and liquidity figures calculated by JEPX Pulse.