Four giant cables are linking the electricity grids of Spain and France beneath the seabed

The construction of the electricity grid linking Spain and France beneath the Bay of Biscay has reached a significant stage. According to an announcement by Red Eléctrica, the operator of the Spanish electricity transmission system, work has begun on laying the subsea cables. This strategically important infrastructure project is being implemented by Red Eléctrica and the French system operator RTE through Inelfe, the joint venture they have established. 

Work on the construction of the undersea cable will be carried out in several phases between now and next summer

Work on the first 65-kilometre section of the subsea cable has begun in the Lemoiz area of the Basque Country. The cables are being transported and laid by the Danish company NKT using its specialised cable-laying vessel, the NKT Victoria.
The vessel is a veritable behemoth, 140 metres long and with a capacity of 11,000 tonnes; it is one of the few vessels capable of laying subsea power cables both at great depths and close to the coast. The works will take place in several phases between the Spanish and French coasts, continuing until the summer of 2027.

In some places, the cables will run at a depth of 140 metres 

The grid connection between the two European countries consists of four parallel electricity cables, alongside which optical cables are also being laid to facilitate the operation and monitoring of the infrastructure.
Along the 276-kilometre subsea section, NKT Victoria is laying the cables at depths of up to 140 metres in certain areas. Depending on the seabed conditions, the cables are buried in the seabed in sandy areas and protected by a stone cover in rocky sections.

In preparation for the underwater installation, four directional boreholes, each over a kilometre long, were drilled at Lemoiz. The tunnels were excavated beneath the coastal cliff face, with their exits located on the seabed, some 500 metres from the shoreline. This solution significantly reduces the impact on the coastline and its wildlife.

On the French side, a further 27-kilometre section of cable is being laid, this time underground. This is necessary so that the route can bypass the Capbreton deep-sea canyon on land, before the cables return to the sea.

The transmission capacity between the two countries could be almost double

Once the interconnector is commissioned, the electricity transmission capacity between Spain and France will increase from the current 2,800 megawatts to 5,000 megawatts. The development will strengthen security of supply, improve the efficiency of the electricity systems, and enable a higher proportion of energy from renewable sources to be integrated into the grid. The investment is expected to connect the Iberian Peninsula’s electricity system to the French grid – and, via this, to the European grid – from 2028.
The Red Eléctrica, in collaboration with the AZTI marine research centre, also monitors the region’s marine mammals and commercially important fish stocks.
The European Union has designated the interconnector as a project of common interest. The project is also supported by the European Climate Action, Infrastructure and Environment Executive Agency and the European Investment Bank.