Market Coupling in Electricity Trading

Market coupling combines buy and sell bids submitted on multiple electricity exchanges and clears them through a common algorithm. It replaces exchange-specific price discovery with a uniform market-clearing price for a coupled market segment, subject to transmission constraints and market splitting.

How the common price is discovered

The designated Market Coupling Operator pools bids received from participating exchanges for the relevant delivery period. The clearing algorithm jointly considers these bids instead of allowing each exchange to discover its own price.

• Aggregated buy bids form the demand side, while aggregated sell bids form the supply side of the coupled market.
• The algorithm selects feasible trades to maximise economic surplus, while considering bid conditions and available transmission capacity.
• Where the network is unconstrained, accepted transactions clear at a common equilibrium price across the coupled exchanges.
• The operator communicates the clearing price and cleared volumes to the exchanges, which continue to interface with their members.

Role of transmission congestion

Electricity cannot always move freely between locations because transmission capacity is finite. Under market splitting, a congested market may be divided into price areas, producing different area-clearing prices even though participating exchanges remain coupled.

• A surplus area may obtain a lower price, while an import-constrained deficit area may face a higher price.
• The price difference signals the economic value of the constrained transmission corridor.

Economic significance

• Coupling improves liquidity by bringing fragmented exchange order books into a common price-discovery process.
• It reduces price differences arising merely from the choice of exchange and promotes efficient use of transmission infrastructure.
• It separates price discovery from competition among exchanges in services such as trading interfaces, member support and settlement arrangements.
• Coupling does not eliminate scarcity or congestion; these remain reflected in clearing volumes and, where applicable, area prices.