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Glossary · Energy industry & energy transition

Core CCR

Core CCR Capacity calculation region EU Electricity Market bidding zone flow-based market coupling transmission grid congestion management

Core CCR stands for Core Capacity Calculation Region. It refers to a European capacity calculation region in which transmission system operators calculate cross-border trading capacities jointly and in a coordinated manner. Legally, the region relates to bidding zone borders and not to states. Under ACER Decision 06/2016, it comprises the borders between the bidding zones of Austria, Belgium, Croatia, the Czech Republic, France, Germany, Hungary, Luxembourg, the Netherlands, Poland, Romania, Slovakia and Slovenia. Germany and Luxembourg form a single joint bidding zone. Sixteen transmission system operators are involved, including the four German ones (50Hertz, Amprion, TenneT and TransnetBW) as well as RTE, Elia, APG, PSE and ČEPS.

A capacity calculation region is not a market zone, not a grid area and not a trading platform. It is a coordination area in which the capacities between bidding zones are calculated. The reason lies in network physics: in a meshed alternating current grid, electricity does not follow trading contracts. If a trader sells electricity from France to Germany, the physical flow is spread across many parallel paths. Lines in Belgium, the Netherlands or further east may also be loaded as a result. Such unplanned circular or parallel flows are referred to as loop flows. The Core CCR is meant to take these interactions into account already during the calculation, rather than only compensating for them afterwards in grid operation.

Origin and legal framework

The Core CCR was established in June 2016 by ACER Decision 06/2016. The basis was a proposal by the transmission system operators on the configuration of the capacity calculation regions. In essence, the former regions Central West Europe (CWE) and Central East Europe (CEE) were merged. The legal basis is the CACM Regulation, i.e. Regulation (EU) 2015/1222. Under its Article 20, the flow-based method is in principle to be applied in highly interconnected regions. The Core transmission system operators submitted their day-ahead methodology to the regulatory authorities in September 2017. The authorities of the region approve the methodologies. If they cannot reach agreement, ACER decides.

The Electricity Market Regulation (EU) 2019/943 is also decisive for the outcome. Under Article 16(8), where flow-based calculation is used, at least 70 percent of the capacity of critical network elements must be available for flows resulting from cross-border trade. This applies to cross-border lines as well as to internal network elements, in each case taking contingencies into account. The remaining maximum of 30 percent is left for safety margins, loop flows and internal flows. The 70 percent is a lower limit and not an upper limit. For Member States with action plans or temporary derogations, a transition path with annually increasing values applies. The minimum level must be reached by 31 December 2027 at the latest.

How the calculation works

In the past, border capacity was often set bilaterally as a fixed megawatt value per border and direction, as so-called Net Transfer Capacity. In a highly meshed grid, this reflects the actual effect of trade only roughly. Depending on generation, load, grid topology and trade at other borders, the same exchange can cause very different loadings on lines. In the CWE part of today's Core region, a flow-based method was therefore already introduced in 2015. Since 8 June 2022 (delivery from 9 June 2022), flow-based market coupling has applied in the day-ahead market for the entire Core region. It is embedded in the Europe-wide day-ahead coupling SDAC. With this launch, market coupling was also introduced at the border between Croatia and Hungary.

Instead of border limits, the calculation delivers a set of constraints for critical network elements under contingency conditions, the so-called CNECs. These can be overhead lines, cables or transformers. For each of these elements, PTDF factors indicate what share of a changed trading position of a bidding zone arrives as flow on that element. A PTDF of 0.1 means, for example: of 1000 megawatts of additional export, roughly 100 megawatts flow over this element in calculation terms. The remaining available margin (RAM) results from the permissible loading minus the safety margin and expected base flows. It determines how much trade is still possible. How changes in the net position are distributed across the power plants and loads of a zone is determined by the GLSK data. The methodology for the intraday timeframe requires that only elements that are noticeably loaded by trade within the Core region be taken into account. Elements whose highest zone-to-zone PTDF is below 5 percent are screened out. Calculation is done in megawatts, i.e. in terms of power per market time unit and not energy quantities.

In organisational terms, the process involves the national transmission system operators, the regional coordination centres TSCNET and Coreso as coordinated capacity calculator, and the Joint Allocation Office (JAO), which publishes the results. Each calculation is based on a common European grid model that contains forecasts for load, renewable generation, power plant schedules, grid topology and outages. Before release, each transmission system operator checks the results for its own area. If operational security is at risk, it may reduce the capacity with justification.

Extension to intraday trading

For the intraday market, flow-based calculation was introduced gradually. The capacities there go to the European intraday coupling SIDC. In spring 2024, the processes IDCC(a) and IDCC(b) started, providing capacities on the previous day until 15:00 and until 22:00. Since 25 June 2025, IDCC(c) has been added, with capacities on the delivery day until 04:30. According to ENTSO-E, IDCC(d) (until 10:00) followed in spring 2026 and IDCC(e) (until 16:00) in autumn 2026. An important difference from the day-ahead market remains: in intraday, calculation is flow-based, but the intraday platform cannot yet process flow-based parameters directly. Limits in ATC format are therefore derived from the result and made available to the market.

Distinction from related terms

  • Bidding zone: a market area with a uniform wholesale price. The Core CCR, by contrast, is a calculation framework spanning several bidding zones. It does not set prices, but provides the capacity limits within which the coupling algorithm forms the prices.

  • Interconnector: a single physical connection. The Core calculation, by contrast, covers many network elements, including internal lines that are loaded by cross-border trade. This very inclusion is contentious from a regulatory perspective, because internal congestion could otherwise restrict trade.

  • Market coupling: it brings the bids together and optimises the trade flows. The capacity calculation of the Core CCR is an input for this. Without it, it would not be possible to check which exchanges are compatible with secure grid operation.

Significance for market and grid

In the Core region, major generation hubs and load centres lie close together: wind power from north-western Europe, nuclear power from France, hydropower from the Alpine region, conventional power plants in Central and Eastern Europe and large industrial centres. The more cross-border capacity is available, the more often the prices of neighbouring zones converge. If capacity is scarce, prices diverge. Congestion income then arises, and the need for redispatch may increase. More market capacity does not automatically mean better grid operation, however. If internal congestion is opened up to trade via the 70 percent rule without reinforcing the grid, part of the congestion costs shifts to redispatch. Capacity calculation therefore does not alone determine costs. It does show where the market area and the physical grid diverge. It thereby provides arguments for debates on grid expansion, flexibility and the configuration of bidding zones.

Typical misunderstandings

  • Border capacity is not a fixed line value. The tradable capacity depends on the overall grid situation and is recalculated for each market time unit. Maintenance, outages, generation patterns and safety margins change it continuously.

  • The Core CCR does not cover all of continental Europe. Italy, Switzerland, the Iberian Peninsula and the Nordic countries are not part of it. Their borders are handled in other regions or cooperations. Switzerland is, moreover, not part of EU market coupling.

  • Congestion is not purely national. A country's power plant fleet, grid expansion or redispatch rules affect the trading possibilities of its neighbours via PTDF coupling. Conversely, congestion abroad can limit the capacity of a German, French or Polish zone.

In short, the Core CCR is the place where physical grid limits, electricity trading and European regulation are translated into concrete trading capacities. Anyone who wants to understand European electricity price differences, redispatch or the debate on bidding zones needs this term. Many visible market outcomes arise precisely in this translation.

Sources

Related glossary entries

Edited by eCMS on 11.11.2026 18:04

© 2026 Erik Schmidt. All rights reserved. Quotations with a link to the source are welcome.