French power grid operator RTE has started work on a new 190 km power interconnection across the Alps to Italy, in an effort to ease congestion on the existing lines to the largest importer of French electricity.

The 320,000 volt direct-current line will cost about 1 billion euros, spread evenly between RTE and its Italian counterpart Terna, and will be the longest subterranean high-voltage power line when it goes into service in 2019, according to Euractiv.com.

With capacity of 1,200 megawatts – roughly equivalent to one nuclear reactor – the line will boost the saturated 2,700 MW connections between the two countries, according to RTE, which is owned by state-controlled French utility EDF.

Last year Italy imported more than 19 terawatt-hours (TWh) of power from France, nearly a third of France’s 65.1 TWh net power exports.

Like the new France-Spain line across the Pyrenees, the new France-Italy line runs completely underground to limit the visual impact on the mountain landscape and address public concern over the addition of new electricity pylons.

Boosting electric interconnections between European Union member states is one of the EU’s top priorities to improve security of supply, minimise the impact of the intermittent nature of solar and wind energy and cut electricity prices.

The EU has set a target for all member states to have interconnection capacity of at least 10% of power generation capacity.

The bloc wants to boost interconnection capacity between countries to 15% of generation by 2030. Many countries, including Britain, Spain and Italy, are still well short of that target with interconnection capacity around or below 5%.

RTE and Terna are Europe’s two largest electricity transmission network operators, with grids of 105,000 km and 64,000 km respectively.