Situations can occur where the volume of electricity that market participants in France, Austria or Switzerland want to transport across the border exceeds the load capacities that TransnetBW can provide. On this page we explain the causes of this congestion or “bottlenecks” and how the transmission system operators calculate capacities of their network elements.

Bottleneck in the grid

The transmission system operators make transport capacities of their grid available to each market participant at the same conditions. This includes cross-border transport capacity. It is required mainly by electricity traders who want to buy electricity in one country and resell it in another one. In order to be able to transport electricity from one national grid to a neighbouring grid via international interconnectors – power lines that connect two national grids to one another – the necessary capacities must be acquired first.


Congestion Management

TransnetBW GmbH
Energy and Balancing Markets (SM)
Pariser Platz
Osloer Straße 15-17
70173 Stuttgart Germany 711 21858-3333

A situation where the volume of electricity that traders want to transport across a border exceeds the capacity that transmission system operators can make available is known as congestion. The reasons are of a technical nature, the transport capacity of power grids is limited by definition. It is important that free capacities are allocated efficiently and free of any discrimination.

TransnetBW provides cross-border transport capacities to France, Switzerland and Austria. Together with the transmission system operators in the neighbouring countries, the available capacities are calculated (capacity calculation) and then passed on to the various market participants (capacity allocation).


Security of supply

Die innovative Stromdrehscheibe im Herzen Europas

The innovative electricity hub in the heart of Europe.

Die TransnetBW GmbH betreibt das Strom-Übertragungs­netz in Baden-Württemberg. Mit diesem Transportnetz sichern wir die Stromversorgung in der Region, in Deutschland und in Europa.
TransnetBW GmbH operates the electricity transmission system in Baden-Württemberg. With this transmission grid we ensure security of supply in the region, in Germany and in Europe.

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Capacity calculation

The transmission systems in Europe are closely interlinked. Electricity flows through the grid according to Ohm’s laws, also across national borders. The transmission system operators calculate jointly how much transmission capacity is available to the market participants. In the process, they make assumptions about how much electricity power plants will generate and how much will be taken off the grid at which points. The available transmission capacity is calculated on the basis of capacity utilisation of the grids. The transmission operators consider different time horizons.

Cross-border capacity – long term

Using joint set processes, transmission capacity available in the long term is calculated. This is used as the basis for annual or monthly rights that traders can acquire at auctions. Today, most auctions are conducted by the Joint Allocation Office JAO.

Cross-border capacity – short term (“day ahead”)

In the Core capacity calculation region (Core CCR), a joint process taking into account capacity utilisation of grid elements is used (flow based). The transmission system operators in France, the Netherlands, Belgium, Luxembourg, Austria, Germany, Poland, the Czech Republic, Slovakia, Slovenia, Hungary, Romania and Croatia are closely interlinked in this context. Via a centralised system, the relevant information is consolidated in order to achieve a maximum of transmission capacity for the markets. Technological limitations are always taken into account, thus ensuring system security.

Cross-border  capacity – within one day (intraday)

The remaining intraday tranmission capacity is made available to the markets via central platforms (e.g.

Capacity allocation

There are two main methods for placing capacity on the markets.

Explicit auction

Traders acquire the right to utilise a certain volume of cross-border tranmission capacities within a set period of time at an auction. This method is mostly used for allocating long-term rights, i.e. month- or year-ahead products. The capacity right can be availed physically or by means of financial compensation.

Implicit auction (market coupling)

Here, a central unit receives the information on the local market price (before the exchange between markets) and the transport capacity between the markets at the same time. The central unit keeps exchanging electricity between the markets until either the prices have become identical or the transport capacity is exhausted. This approach ensures that a maximum of transport capacity is utilised and is employed mostly in short-term trading (day-ahead and intraday). The process also provides for a maximum of price harmonisation between the markets.

Groups in Europe

In Europe, groups have been set up by region, ensuring optimal capacity calculation and capacity allocation. The transmission system operators of the Core CCR collaborate closely within the framework of the flow-based process. You can find more information on the website of the Joint Allocation Office (JAO).

Additional details on the Core capacity calculation region are available on the ENTSO-E website (Capacity Calculation Regions (

Single day-ahead coupling (SDAC) and single intraday coupling (SIDC) projects are continuously optimising the allocation processes with the electricity exchanges. More information is available on the ENTSO-E website (Single Day-ahead Coupling (SDAC) ( and Single Intraday Coupling (SIDC) (