SAPEI

Sixteen hundred metres under the Tyrrhenian Sea, a cable about 12 cm across carries up to 1,000 MW between Sardinia and the Italian mainland. When SAPEI was inaugurated on 17 March 2011, no power cable anywhere lay deeper.

The ends are two converter stations. In Sardinia the link starts at Fiume Santo, near Sassari, on a site of 48,000 square metres; on the mainland it ends at Latina, in Lazio, on 35,000. About 15 km of land cable connect them to a 420 km submarine section. The SAPEI article on Wikipedia gives these figures and a cost of more than €730 million. Terna owns and runs it; Prysmian made the cable and ABB the converters.

Building it took five years. The project was launched in 2006, followed by scientific studies and geophysical surveys of the seabed. The first cable went down in 2008, the converter stations were working in 2009, and the second cable was laid at the end of 2010. The BEST PATHS project’s own report on the world’s top undersea HVDC cables, written in 2017, describes how the cable was held in place: on rocky seabed it was anchored with collars fixed by hand, and in sediment it was protected by burying it about a metre deep.

Why so much effort for one island? Sardinia had only one other link to the mainland, the small and ageing SACOI line through Corsica. SAPEI more than tripled the capacity between the island and the peninsula in one step. Because it is DC, it can cover the long distance and the great depth without the charging losses that would cripple an AC cable of that length.

SAPEI’s depth record did not last. In December 2025 Nexans laid a cable for the Tyrrhenian Link at 2,150 metres, and that project will give Sardinia a second high-capacity DC connection, this time to Sicily.