Intraday market

What it is (precise)

The three CACM definitions are precise in a way that matters. Article 2(38) defines the intraday cross-zonal gate opening time as the point when cross-zonal capacity between bidding zones is released for a given market time unit and a given bidding zone border.

Article 2(39) defines the intraday cross-zonal gate closure time as the point where cross-zonal capacity allocation is no longer permitted for a given market time unit. Read that again before relying on it: what closes is cross-zonal capacity allocation, for one market time unit, on one border. It is not a blanket statement that all trading stops at that instant.

Single intraday coupling is defined at Article 2(27) as the continuous process where collected orders are matched and cross-zonal capacity is allocated simultaneously for different bidding zones in the intraday market.

The matching engine is the shared order book, defined at Article 2(24) as the module in the continuous intraday coupling system collecting all matchable orders from the NEMOs participating in single intraday coupling and performing continuous matching of those orders. ENTSO-E states the consequence plainly: orders entered for continuous matching in one country can be matched by orders submitted by market participants in any other coupled country.

Why it matters in a real grid-scale project

For storage, intraday is the correction layer. The day-ahead schedule is committed on forecasts; wind, solar and demand then move, and intraday is where the resulting position error is traded out or exploited. A battery is well placed here because it can change position quickly and because the value of doing so rises as delivery approaches. The design consequence is that state of charge headroom has to be reserved deliberately for intraday action — a plant optimised to exhaust its energy against the day-ahead schedule has nothing left to sell into the closer, often more volatile market.

The gate timings are changing, which makes any hard-coded number a maintenance liability. Under the Electricity Market Design Reform the intraday cross-zonal gate closure time is being reduced from 60 minutes to 30 minutes before delivery. ENTSO-E records that the first window of European borders went live on 14 January 2026, and that most European borders are expected to apply the 30-minute closure by 2029. So the statement that the European intraday market closes 60 minutes before delivery is now border-specific and date-specific rather than a general fact about Europe.

Typical values and standards

Alongside continuous trading, SIDC runs three intraday auctions. ENTSO-E gives their gate closure times for market parties and their allocated periods: IDA1 closes at D-1 15h with an allocated period of D 0h–24h; IDA2 closes at D-1 22h, also allocating D 0h–24h; IDA3 closes at D 10h, allocating D 12h–24h. Use ENTSO-E's own term — allocated period — rather than delivery period. The allocated period is the cross-zonal capacity allocation window, which is the concept CACM Article 2(39) actually regulates, and IDA3's window covers only the second half of the delivery day.

Scale, from ENTSO-E's SIDC page: 31 TSOs and 18 listed NEMO entries (17 distinct — ENTSO-E's list repeats BRM), launched on 12/13 June 2018 across 15 countries, with 25 countries coupled as of the page's current state. Compare the two coupling processes deliberately, because the difference drives everything downstream.

CACM Article 2(26) makes single day-ahead coupling an auctioning process; Article 2(27) makes single intraday coupling a continuous process. One produces a cleared price per market time unit; the other produces continuously matched trades against a shared order book, with no single reference price.

How it shows up in specs, studies and contracts

In systems terms, the trading interface has to handle both shapes: continuous order entry against the shared order book, plus three auction submissions per day. In a revenue model the intraday layer is usually modelled as an uplift on the day-ahead position rather than as a standalone price series, and the assumption that deserves scrutiny is how much volume can genuinely be traded at the modelled spread close to gate closure. In contracts, be explicit about who holds intraday rights — a tolling or offtake structure may reserve them to the offtaker even where day-ahead rights are shared.

Operationally, write the gate structure into the dispatch procedure with dates attached: which border, which gate closure applies today (60 or 30 minutes), and which market time unit. The day-ahead side moved to 15-minute intervals in SDAC in September 2025, so a model or procedure that mixes hourly day-ahead blocks with finer intraday products carries an internal inconsistency that surfaces as unexplained imbalance volumes rather than as an obvious modelling error.

Common pitfalls

The first trap is reading the cross-zonal gate closure as the end of all trading. CACM Article 2(39) defines it as the point where cross-zonal capacity allocation is no longer permitted for a given market time unit — the constraint is on capacity allocation across a border, per market time unit, not on every trade in the market. If a procedure assumes the market is simply shut after that point, verify it against your NEMO's actual product terms before relying on it for dispatch or for imbalance management.

The second is hard-coding 60 minutes. That figure is being replaced by 30 minutes under the Electricity Market Design Reform, starting with the first window of borders on 14 January 2026 and expected on most European borders by 2029, so it is a per-border, per-date parameter now. The third is treating an IDA allocated period as a delivery period: IDA3 closes at D 10h and allocates D 12h–24h, so assuming it covers the whole day overstates the cross-zonal capacity available for morning delivery hours.