What are Cross-Border Interconnectors?

In order to exchange electricity between the transmission grids of two countries, these countries must set up so-called cross-border interconnectors. These are, in the case of three-phase alternating current high-voltage lines, visually indistinguishable from normal high-voltage lines - only that they cross the borders of two countries and the shape and design of the masts sometimes change behind the borderline. To transport electricity in HVDC transmission lines, however, special facilities have to be built because the electricity first has to be rectified for transport in the cable and then rectified again for feeding into the grid. However, these measures are also necessary for HVDC transmission lines that do not cross national borders.

Cross-border interconnection points are nodes in the Continental European Interconnected System (EV) and should enable the smoothest possible border traffic of electricity from one country to another. However, the expansion of existing capacities and the construction of new cross-border interconnectors is very costly in financial and administrative terms. New high- and extra-high-voltage lines have to be laid in partly densely populated areas, and neighboring countries have to agree on how to bear the costs. Efforts towards a fully integrated electricity grid are coordinated centrally by the European Commission's TEN-E (Trans-European energy networks policy) regulation, which also envisages projects beyond the UCTE member states, for example with Great Britain and the Baltic States.

However, there is no real alternative to increase cross-border electricity transmission capacity. Just like at a motorway border crossing where vehicles gather in long queues at peak times, the capacity of the border interconnectors is limited - the lack of transport capacity means that the electricity cannot flow in the quantity that is required under contractual agreements.

On the contrary, if more electricity is sold on the exchange than can actually be delivered, several unfavorable effects occur. One of these is market distortion: the difference between contracted and actually physically delivered electricity must be offset.

Loop flows are a concrete grid-related problem. Here, too, the metaphor of a motorway border crossing is useful: if the crossing is overloaded, the vehicles swerve to the surrounding country roads and clog the cross-town thoroughfares. Similarly, electricity also follows the principle of least resistance (Kirchhoff's laws) and uses the network capacity of other countries. This was the case, for example, between Germany and Austria until 2018: because the electricity there could not pass through the undersized border interconnectors, it diverted to the neighboring countries of Poland and the Czech Republic and caused annoying costs there - a major reason for the eventual separation of the common electricity price zone of Germany and Austria.

The image of the motorway border crossing is applicable to the seasonal utilization of the border interconnection points again. During the holiday season, there is a huge rush, and in November, which is not very holiday-friendly, less vehicles want to cross. The situation is very similar at the border interconnection points: here, the "travel demand" also depends on the national energy infrastructure, the volume of cross-border electricity trading and, last but not least, on the weather. Thus, meteorological factors have a direct impact on border traffic - for example, on cold winter days at the border interconnection points to and from France. The country relies primarily on nuclear energy and heats houses and apartments with electricity. This pushes nuclear power plants to the limits of their capacity in winter - France has to increase the import of electricity from neighboring countries.

The Alpine countries also have a seasonally strong fluctuating electricity demand, which has an impact on cross-border electricity exchange: During the snowmelt in spring and early summer, Austria and Switzerland export electricity to the rest of Europe, while in the winter months the countries in the Alpine region import electricity. In summer, a regular interplay has developed between the so-called solar belt of Baden-Wuerttemberg and Bavaria and the Alpine countries on a daily basis: While on a sunny day, electricity flows from German solar panels into the Austrian and Swiss grids during the day, at night they supply electricity from hydropower to the lightless solar regions.

Since little will change in the near future regarding the problem of insufficient capacities of the border interconnection points, the European states of the grid network are called upon to use the existing capacities as efficiently as possible. This is currently taking place primarily in the so-called Central European Market Coupling (CWE Market Coupling), which optimally uses the transmission capacities between two markets through cooperation between the national electricity trading centers and the TSOs.