Market coupling (SDAC + SIDC)
Market coupling is the European mechanism that runs every day-ahead and intraday auction across the continent as a single matching problem. SDAC (Single Day-Ahead Coupling) handles the noon auction; SIDC (Single Intraday Coupling) handles continuous intraday trading. Instead of each country clearing its bidding zone in isolation, one algorithm takes all bids, all offers and all available cross-border capacities and computes prices for every zone at once. Estonia is fully coupled into both.
Market coupling is the European mechanism that runs every day-ahead and intraday auction across the continent as a single matching problem. Instead of each country clearing its own zone in isolation, one algorithm takes all bids and offers from all participating zones, all available cross-border capacities the TSOs have made available, and computes the clearing prices for every zone in every market time unit at once. Power flows from cheap zones to expensive zones automatically until the prices equalise or the connecting cable saturates.
SDAC vs SIDC
The two pieces are SDAC (Single Day-Ahead Coupling) and SIDC (Single Intraday Coupling). SDAC is the noon auction: one matching run per market time unit, EUPHEMIA algorithm, prices published a few minutes after gate closure. SIDC is the continuous intraday market: bids and offers cross the border in real time through the XBID matching engine, until the gate closes shortly before delivery. Day-ahead is one-shot pricing for tomorrow; intraday is continuous re-pricing as forecasts shift.
Why this matters
Without market coupling, every country would clear in isolation and cross-border flows would be auctioned separately by each TSO, leading to inefficient routing. With it, the whole connected European grid behaves as if it were a single market for matching purposes — the cheapest available megawatt anywhere in the network is offered to the demand that values it most, subject to the physics of the cables. The economic gain is enormous: ENTSO-E estimates SDAC alone produces several billion euros of consumer welfare per year.
Estonia
Estonia is fully coupled into both SDAC and SIDC. The EE bidding zone clears alongside FI, SE, NO, DK, LV, LT and the rest of Continental Europe in the same SDAC run, and EE bids and offers can match against any other coupled zone in real time on SIDC, subject to available cross-border capacity. Since 1 October 2025 SDAC clears in 15-minute market time units (previously hourly), tightening the alignment with imbalance settlement and balancing markets.