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- SIDC: What it is and why it matters
- How the SIDC mechanism works
- Rising intraday liquidity
- Upcoming market changes
A solar forecast looks solid at noon, then cloud cover rolls in two hours before delivery. By the time the discrepancy is clear, the day-ahead market has long since closed. Without a mechanism to correct the position, that mismatch flows directly into costly balancing actions.
This scenario plays out across Europe multiple times daily. The share of renewables in Europe’s power mix keeps climbing, and with it, the challenge of staying balanced after the day-ahead market closes. Solar generation in particular can swing forecasts within hours, creating the need for trading closer to real time.
That’s where the Single Intraday Coupling (SIDC) comes in. SIDC extends the market coupling principle, enabling traders to adjust positions continuously up to one hour before delivery. In its first five years, it facilitated more than 240 million transactions, with trade volumes in 2025 roughly double those of 2022.
This article explores how the SIDC works, why intraday liquidity is rising, and what it means for short-term power traders.
SIDC: What it is and why it matters
To understand SIDC, it helps to start with the familiar Single Day-Ahead Coupling (SDAC). SDAC operates on the principles of single-price coupling and welfare maximization, connecting European power markets through a single coordinated auction. We covered the mechanism in depth in our article ‘How SDAC works and what happens when it fails’.
The Single Intraday Coupling (SIDC) extends that concept into real time. It links European markets for continuous cross-border trading up to one hour before delivery.
SIDC was established under the EU Capacity Allocation and Congestion Management Guideline (2015), which constitutes the legal basis for both SDAC and SIDC. Its goal: to enable continuous matching of cross-border trades while respecting grid constraints. SIDC is built around the XBID (Cross-Border Intraday) platform, launched in 2018.
The image below from the ENTSO-E platform offers an overview of the countries that have joined the mechanism since 2018:
Day-ahead coupling delivers clear economic benefits by linking markets with different generation mixes, for example, hydro-rich regions exporting competitively priced power to areas with higher marginal costs.
Intraday coupling adds a new layer of efficiency when renewable generation fluctuates. Short-term weather effects are often local, and SIDC enables market participants to correct those deviations through near-real-time trade rather than relying solely on costly balancing energy.
Consider a simple case: a cloud front reduces solar output in the Netherlands just as southern Germany sees unexpected sunshine. Through SIDC, traders can, in principle, buy and sell power across zones shortly before delivery – one covering a shortfall, the other monetizing excess generation. Without such cross-border intraday trading, these imbalances would later be resolved through balancing actions at much higher prices.
How the SIDC mechanism works
To understand how continuous trading operates in practice, we identify the key players and mechanisms, then zoom in on the XBID system and operations.
Key players and mechanisms
For starters, the main actors within SIDC are:
- NEMOs (Nominated Electricity Market Operators): power exchanges, responsible for running the national/regional electricity markets and operating the SDAC and SIDC.
- TSOs (Transmission System Operators): capacity providers responsible for grid operation.
- DBAG (Deutsche Börse AG): operates the core software infrastructure.
- RCCs (Regional Coordination Centres): calculate and coordinate available cross-border capacities.
- JAO (Joint Allocation Office): handles explicit capacity auctions when needed.
SIDC is jointly governed by NEMOs and TSOs through the SIDC Steering Committee (formerly XBID), ensuring equal access and operational harmonization.
SIDC integrates Europe’s intraday markets through two mechanisms:
- Intraday Auctions (IDAs): periodic centralized auctions similar to those in the day-ahead market.
- Continuous Intraday Trading: the more dynamic component, built around a continuous limit-order book.
We focus on the latter, as it represents the distinctive feature of SIDC operations.
Continuous intraday: The XBID system
Unlike SDAC’s single-auction clearing, continuous trading uses a limit order book in which bids and offers are matched instantaneously as they arrive, much as in financial markets. Thus, there is no single clearing price for everyone; each transaction may have a different price.
This continuous model, without a central clearing algorithm, offers distinct advantages over periodic auctions. It makes supply and demand partly visible in real time, supporting transparent, self-organizing price discovery.
Of course, the key difference with financial markets lies in physics. In financial markets, a buyer in New York can seamlessly match with a seller in London without worrying about the physical path between them. Power markets face a different constraint: electricity must flow through transmission lines with finite capacity.
To meet this requirement, the Available Transfer Capacity (ATC) between bidding zones constrains these trades. The calculation of this capacity is gradually evolving toward a flow-based approach, which better reflects how electricity physically flows through the grid. Since June 2024, a version of flow-based intraday calculation has been live for the Core region (Central-Western Europe), with further development underway.
In short, to manage the physical nature of the market, SIDC maintains a single consolidated order book for each product across Europe, but what traders see locally is filtered by available transmission capacity. We return to this point further down the article.
An order book example
The table below illustrates a simplified limit order book in the continuous intraday market. Each row represents aggregated buy (bid) and sell (ask) orders at different price levels. Traders place “bids” for the maximum price they are willing to pay and “asks” for the minimum price they are willing to accept, each with a corresponding volume.
The gap between the highest bid (€50/MWh) and the lowest ask (€51/MWh) serves as a simple measure of transaction costs and market liquidity. However, the spread alone doesn’t tell the complete liquidity story.
Market depth at the best prices and the book’s ability to refill after trades matter more than the simple bid-ask spread, while being harder to estimate. Moreover, algorithmic trading can tighten order book spreads in normal conditions, while during shocks and major information updates, liquidity can vanish very quickly, leading to wider bid-ask spreads.
Technology and operations
The XBID platform underpins SIDC and is composed of two main modules:
- Capacity Management Module (CMM): tracks and updates the global state of cross-border capacity (ATC).
- Shared Order Book Module (SOB): aggregates all tradable orders for a given contract across Europe into a consolidated order book.
What traders actually see, however, is filtered through their Local Trading Solution (LTS), the interface provided by their local NEMO. The LTS presents only the orders that are accessible, given the available transmission capacity to their zone.
For example, for a 16:00–16:15 contract, bids and offers from Germany and Austria are matched according to available transmission capacity. If ATC is exhausted, cross-border orders become invisible until new capacity is released or traded volumes decrease.
Gate opening and closure times
Cross-border intraday trading opens at 15:00 CET on D–1 and closes one hour before delivery.
National markets may continue trading closer to delivery (typically 5–30 minutes before), but with thinner liquidity. Some TSOs can still update capacities up to 15 minutes before the delivery period, creating last-minute trading opportunities.
The end-to-end SIDC flow
To summarize the above complexity, the SIDC process is as follows:
- Transmission System Operators (TSOs) provide capacity data (AAC, NTC) to Regional Coordination Centres (RCCs), which compute Available Transfer Capacity (ATC).
- The Capacity Management Module (CMM) and the Shared Order Book (SOB) – both part of the XBID platform – integrate ATC with local NEMO order book views. This enables continuous cross-border trading under capacity limits.
The image below visualizes the process:
System incidents
Like SDAC, SIDC operations occasionally face system incidents. On 6 September 2025, a critical event followed scheduled maintenance on the XBID system. Market participants were temporarily unable to connect to certain XBID components, leading to a total interruption of 10 hours and 50 minutes (including the planned maintenance window).
The root cause was a network infrastructure issue managed by the XBID service provider. Once resolved, normal operations resumed. More information in this post and report.
Rising intraday liquidity
As mentioned at the beginning of this article, intraday trading in Europe is expanding rapidly. This trend is clearly illustrated in the graph below from the latest SIDC stakeholder report. The number of SIDC trades and order events has grown steadily since go-live, reaching record levels in 2025, roughly doubling since 2022. Cross-border intraday traded volume exceeded 300 TWh in 2025, up ~40% year-on-year.
Several reinforcing factors are driving this momentum while supporting overall economic welfare:
- More intermittent generation and stronger incentives for market participants to stay balanced.
- Greater digitalization of trading desks, enabling faster and more precise position management via algorithmic trading solutions.
- Ongoing improvements in market design, interoperability, and automation.
As a result, liquidity is deepening, and that matters. With more renewables in the system, market participants increasingly depend on intraday markets to manage balancing risk. Liquidity, in turn, attracts more liquidity: narrower bid–ask spreads reduce trading costs, drawing in both hedgers and speculators.
Hedgers close open positions to stay balanced. Speculators assume short-term risk and provide liquidity – especially around public forecast updates – helping stabilize price discovery when risk preferences differ across participants. In moderation, such speculation contributes to a healthier market.
Finally, as intraday liquidity grows, market participation itself is changing. A rising share of trades is now executed automatically, with algorithms continuously responding to evolving prices and forecast signals across borders.
Upcoming market changes
Europe’s power markets are evolving toward a near-real-time, fully coupled system, a crucial step for integrating higher shares of renewable generation. Notable changes include:
- Increasing trading volumes on Intraday Auctions (IDAs) will complement continuous trading by strengthening price formation and congestion management.
- Cross-border capacity in SIDC is expected to remain available until 30 minutes before delivery (down from 60 minutes today), with full roll-out depending on TSO readiness.
- In parallel, flow-based allocation is being developed for intraday trading, extending the proven day-ahead method to make cross-border capacity use more efficient and dynamic.
At Dexter Energy, we’ve built our forecasts and trading signals around the reality of continuous markets: hourly-updated forecasts, machine-learning models that capture weather-driven volatility, and near-time optimization aligned with SIDC’s continuous trading window. With these capabilities, trading teams can adapt faster, reduce balancing costs, and make the most of Europe’s increasingly dynamic intraday market.