Overview
According to trading data published by the Japan Electric Power Exchange (JEPX), the trading volume in the intraday market for September 2026 averaged 35,733,308 kWh per day [1]. This is reported to be a 16.2% increase from the previous month, marking a record high for the third consecutive month [2]. There were 12 days where the daily trading volume exceeded 40 million kWh, and it reached the 50 million kWh range on September 22 and 24 [1][2]. These two days coincide with days when spot prices in the Tokyo and Chubu areas rose to the 50 yen/kWh range in the evening [3]. In this article, we will organize the reasons for the expansion of the intraday market, along with the price differences between east and west in the spot market, changes in trading by major power companies, and the revision of imbalance charges implemented in October.
In short, ‘bulk buying on the previous day’ is no longer sufficient for electricity, and there is a sudden increase in ‘additional buying on the day.’ This is because businesses that could not finish buying in the previous day’s trading or those that want to fill gaps in their plans at the last minute are gathering in the intraday market. Not only the level of electricity rates but also the way power companies procure electricity itself is beginning to change.
Background and History
JEPX has two main ‘markets for buying and selling electricity on the spot.’ The first is the day-ahead market (hereinafter, spot market). It divides the electricity to be used the next day into 48 products in 30-minute units and matches everyone’s bids to determine a single price [4]. The second is the intraday market. JEPX positions the intraday market as a ‘market for responding to unforeseen supply-demand mismatches’ and adopts a ‘continuous trading’ method where transactions are concluded one after another as soon as the conditions of the seller and buyer match [4].
To use an analogy, the spot market is like a ‘regular order’ where you buy ingredients for the next day in bulk the night before. The intraday market is closer to an ‘additional order’ where you buy extra items at a nearby store after seeing the number of customers on the day. However, actual electricity cannot be kept as inventory. Therefore, if the additional order is not in time, the discrepancy is filled by the transmission and distribution system operator and settled later.
This discrepancy is called an ‘imbalance.’
> Terminology Note: Imbalance
> The difference between the plan submitted in advance by a retail electricity provider or power generation business and the actual usage or generation amount. The transmission and distribution system operator adjusts for the difference, and the business pays (or receives) an imbalance charge.
The intraday market has long been a ‘supporting role.’ According to the compilation by the Electricity and Gas Market Surveillance Commission (hereinafter, the Commission), the ratio of JEPX trading volume to domestic electricity demand was 49.6% in June 2026 [5]. Of this, the intraday market accounted for only 1.2% [5]. As of April 2025, the ratio was 34.1% for the entire JEPX and 0.9% for the intraday market [5].
The trend changed in April 2026. In the materials for the 24th System Design and Surveillance Expert Meeting (September 29), the Commission cited four factors for the price increase in the April-June 2026 period [5]. These are the soaring fuel prices due to the situation in the Middle East, the termination of long-term power purchase contracts between major operators, the suppression of operational capacity toward Tokyo on the ‘Tohoku-Tokyo’ interconnection line, and a decrease in supply capacity [5]. With the end of long-term contracts, a large number of sell and buy orders entered the market [5]. As a result, the trading volume in the spot market for the April-June period was 83.5 billion kWh, and the intraday market was 2.16 billion kWh, both of which were 1.3 times the same period of the previous year [5].
Details of Current Trends
Since July, the growth of the intraday market has exceeded that of the spot market. Looking at the monthly daily average trading volume in JEPX data, it has continued to increase from 24.59 million kWh in June to 29.26 million kWh in July, 30.74 million kWh in August, and 35.73 million kWh in September [1]. On the other hand, the daily average trading volume in the spot market decreased by 13% from 1.24453 billion kWh in August to 1.08042 billion kWh in September [3]. This means that the spot market decreased while only the intraday market increased (author’s calculation).
Why did buying gather in the intraday market? The Denki Shimbun points out the possibility that retail electricity providers who ‘lost out on buying’ in the spot market procured in the intraday market [2]. In the spot market, buy orders with a bid price lower than the clearing price are not concluded. If a higher price is set than expected on the previous day, businesses that submitted lower buy orders will face the day without securing electricity. Such businesses choose to either buy back in the intraday market or settle as an imbalance.
This view is consistent with the daily data for September. There were 10 slots (30-minute products) in September where the spot price in the Tokyo area reached 50.01 yen/kWh [3]. All of them were between 16:00 and 19:00 on September 22 and 24 [3]. The trading volumes in the intraday market for the same two days were 53.14 million kWh and 55.16 million kWh, which were the top two days in September [1]. The evening is a time when solar power generation drops and demand remains high. Looking at the intraday market trading volume in September by time slot, 16:00-20:00 was the highest at an average of 8.66 million kWh per day, accounting for about 24% of the total (author’s calculation) [1].
Another change is the players in the market. According to the Commission, the amount sold by former general electricity utilities (major power companies including JERA; hereinafter, former utilities) in the intraday market in the April-June period was 1.20 billion kWh, 1.6 times the same period of the previous year [5]. The amount bought by new power companies and others was 840 million kWh, an increase of 1.7 times [5]. Also, for former utilities as a whole, buying exceeded selling, and for new power companies, selling exceeded buying [5]. It can be seen that both major and new power companies are shifting to a way of using the intraday market where they ‘both sell and buy.’
On October 1, the system revision for imbalance charges was also implemented. The upper limit of the supplementary imbalance charge when supply and demand are tight was raised from 200 yen/kWh to 300 yen/kWh [6]. Since the payment for leaving plan discrepancies unaddressed has become heavier, the role of the intraday market in filling discrepancies at the last minute will become even greater (author’s opinion).
Data and Numerical Analysis
Comparing the monthly trends with the same month of the previous year, it is as follows [1][3]. The average price of the intraday market was calculated by the author as a weighted average by trading volume.
The daily average trading volume of the intraday market in September is 1.88 times that of the same month last year (author’s calculation) [1]. The ratio to the spot market trading volume is 3.31%, up 1 point from 2.31% in the same month last year (author’s calculation) [1][3]. There was only one day in the entire fiscal year 2025 when it exceeded 40 million kWh per day (author’s calculation) [1]. In fiscal year 2026, it has suddenly increased to 5 days in August and 12 days in September (author’s calculation) [1]. The total monthly trading volume of the intraday market in September is approximately 1.07 billion kWh (author’s calculation). This means that nearly half of the three-month total for April-June (2.16 billion kWh) was traded in one month [5].
The price gap between East and West also widened further in September. While the monthly average area price in September was 23.78 yen/kWh for Tokyo and 23.77 yen/kWh for Chubu, it was 16.45 yen/kWh for Kansai, 14.06 yen/kWh for Kyushu, and 12.92 yen/kWh for Shikoku [3][7]. The difference between Tokyo and Shikoku is 10.86 yen/kWh [7]. The number of time slots where the price in the Tokyo area differed from the Kyushu area accounted for 95.2% of all slots in September (author’s calculation) [3]. In September of the previous year, this was 82.1% (author’s calculation) [3]. It can be said that in East Japan, a state continued where the risk of failing to purchase due to the previous day’s clearing price exceeding expectations remained high (author’s view).
The situation on days with price surges can be summarized as follows [1][3].
There is a point to note. The annual data for the intraday market published by JEPX does not include prices by area [1]. Therefore, the average price of the intraday market is a value that aggregates all areas. The fact that the average intraday market price (around 35 yen) fell below the Tokyo spot price (50.01 yen) on the evening of September 22 is considered to be because cheaper transactions from West Japan are mixed in (author’s view).
Compared to overseas, Japan’s intraday market can still be considered small. At the European power exchange EPEX SPOT, the trading volume of the day-ahead market in 2025 was 676.3 TWh [8]. The intraday market was 241.2 TWh, an increase of about 12% from the previous year’s 214.5 TWh [8]. The ratio to the day-ahead market is about 36% (author’s estimate) [8]. There is a 10-fold gap with Japan’s September ratio of 3.31%. In Europe, it is said that renewable energy, storage batteries, and algorithmic trading supported the growth of the intraday market [8].
Impact on Stakeholders
The impact of the expansion of the intraday market varies greatly depending on the position [1][3][5][6].
The impact is greatest on retail electricity providers that procure electricity from the market in East Japan. If they fail to buy on the previous day, they have two choices: buy back in the intraday market on the day, or settle as an imbalance. From October, the upper limit during tight supply was raised to 300 yen/kWh [6]. There are more situations where buying at a slightly higher price in the intraday market is cheaper than leaving an imbalance (author’s view). As a result, buying tends to concentrate in the evening intraday market, making it easier for a cycle that pushes up prices to occur.
For businesses with storage batteries or demand response (initiatives where the demand side adjusts usage; hereinafter, DR), the intraday market becomes a new sales destination. If they discharge and sell in time slots where evening prices are high, they can change the plan decided the previous day to match the situation on the day. However, at present, the most common example of sell orders in the intraday market from former general electricity utilities is raising them within ‘more than 1 hour and less than 2 hours’ before the transaction deadline (gate closure, hereinafter GC) [5]. According to the Electricity and Gas Market Surveillance Commission’s aggregation, out of 622 sell orders on three characteristic days in the April-June period, 189 were raised within 1 hour of GC [5]. Although this is an increase from the previous quarter (158 out of 611), it cannot be said that a sufficient amount is being put up for sale until just before [5].
Future Outlook and Action Points
Short-term (until January 2027)
Entering October, the trading volume in the intraday market has calmed down compared to September. The daily average from October 1 to 13 was about 23.3 million kWh (author’s calculation) [1]. This is seen as being because temperatures dropped and evening demand decreased (author’s view). There are three points of attention. The first is whether the way the intraday market is used will change after the increase in the upper limit of imbalance charges [6]. The second is how the Surveillance Commission will evaluate the intraday market in its monitoring report for the July-September period [5]. The third is whether the spot price in East Japan will jump again in the evening during the winter demand season.
Medium-term (FY2027-2028)
The mechanism of the intraday market itself is also in the process of being reviewed. In its second interim summary on October 15, 2025, the national ‘Study Group on the Ideal State of Simultaneous Markets’ showed the overall picture of a ‘simultaneous market’ that clears electricity (kWh) and adjustment power (ΔkW) at the same time [9]. There, the basic direction is to open the intraday market after the day-ahead market ‘once in the evening of the previous day and twice on the day’ [9]. Furthermore, there is also a plan to establish a ‘pre-closing market’ just before GC to trade electricity to be delivered about one hour later [9]. Regarding the current continuous trading, it is stated that ‘there are certain needs,’ and its opening will be considered even after the introduction of the simultaneous market [9].
Summarizing the outlook in scenarios, it is as follows (author’s view).
Action Points for Industry Stakeholders
First, retail electricity providers in East Japan should review how they determine their buy bid prices in the spot market. When they fail to buy in an evening time slot, they are required to decide in advance the upper limit of how much they will buy in the intraday market. Now that the upper limit of the imbalance charge has been raised to 300 yen/kWh, this judgment is directly linked to profitability.
Second, storage battery/DR businesses and aggregators should include the intraday market in their calculations as one of their revenue sources. It is necessary to prepare operations to compare whether to submit to the supply-demand adjustment market or the intraday market in high-price evening time slots.
Third, all market participants should prepare to provide input on the detailed design of the simultaneous market. The number of times the intraday market is held and whether to keep continuous trading will greatly affect the procurement methods of businesses that rely on last-minute transactions [9]. The rapid increase in trading volume in September will be an important material for that discussion.
