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The new Capri power line reported by those who built it

The technological challenges, archaeological and environmental context and lessons learned during construction reported by Terna engineers.

“Why is the new power line important? Because, naturally, it helps Capri. Because it is not an end in itself but it also allows for the restructuring of the grid in all of the Sorrentine peninsula. Because keeping a refrigerator or an air conditioning unit running will no longer be a problem. Because it improves the lives of people that live on the island and the tourists that visit. Because it improves the environment. Because...”.

There are thousands of reasons that, whilst the sun sets on the inauguration of the new invisible power line between Capri and Sorrento, hosted by the electrical substation on the island on 14 October 2020, highlight the historic scope of a day which the Capresi have been long-awaiting. Riccardo De Zan and Francesco Perda speak proudly about the project as those who saw it being born and growing step by step. De Zan is the Terna representative for the HVDC & Submarine Cable Projects unit. And Perda works alongside him. The first step was taken in 2012 with the launch of plans for the first undersea cable between Torre Annunziata and Capri through the building of a new substation, which went into operation in 2017.

The electrical cable placing operations in Sorrento in December 2019 (photo by Terna)

This is a truly historic milestone for the island which, until recently, was aided by a private diesel plant that was insufficient to guarantee coverage to consumers, very polluting and opposed by environmentalists. The new step, activation of the second undersea cable, closes the circle of the definitive connection between Capri and the Italian mainland: a bidirectional connection (to and from the peninsula), which carries an electrical current of 100 megawatts in the face of a demand that for the island reaches around 20 MW in the summer and it also allows Sorrento and the area all the way to Torre Annunziata to have stable electricity and a reliable grid, along with a significant decrease in CO2 emissions.

Capri is probably the most beautiful island in the Mediterranean and one of the most beautiful in the world; the island which the emperor Tiberius chose for his stunning Villa Jovis and that since then has attracted intellectuals, directors, actors and every kind of celebrity, mixing history, culture, environment and the good life. It wasn’t easy to work on an infrastructure project that on one hand must offer the maximum technological quality and efficiency, and on the other must guarantee the highest respect for the sea, fauna, flora and archaeological finds. “Its management was also complex due to interaction with the Superintendence Departments”, explains Riccardo De Zan who monitored and continues to monitor great undersea power cables from Terna, “but then the building was less tiring and after having started work in October 2018 we finished building them exactly two years later”.

The Italian Prime Minister Giuseppe Conte and the CEO of Terna at the inauguration of the new Capri electrical connection on 14 October 2020 (photo by Terna)

If it is true, the engineer again highlights, that “each construction site has its own story”, this has confirmed the expertise of Terna in the field of undersea work. There are few undersea cables even if they are spreading throughout Europe due to their reduced visual impact”. The Torre Annunziata-Capri-Sorrento ring has therefore added to the great experience of the national TSO with record undersea power lines: the Italy-Greece sea cable a thousand metres below sea level which was inaugurated in 2002, the Sapei, between Sardinia and Lazio (more than 400 km of cable and 1600 metres deep) operating since 2010, the Sorgente-Rizziconi power line between Calabria and Sicily in operation since 2016, the Italy-Montenegro “bridge”, which is 1200 metres deep, inaugurated at the end of 2019.

The Capri construction site had its own peculiarities. “The possible archaeological findings in the area identified in the beginning by the electrical substation”, adds Francesco Perda, “forced us to move the building to lower ground, close to the ecological zone. And the design of the plant was curated in such a way as to integrate it with the style of the island. The activity of the Marina Grande landing site required specific archaeological security for the rocky coast and steel pipes which carry the cables from the landing site to the substation, almost vertically, are green and are now covered by vegetation making them practically invisible even under the lens of Google Maps".

The new Terna substation in Capri (photo by Terna)

A separate discussion regarding the Poseidonia. “In order to avoid damaging the underwater grasslands we made use of directional drilling”, De Zan explained, “which allowed us to build a microtunnel underneath the plants with a specific tunnel boring machine, in which the cable was housed”. In order to do this divers that had experience working in areas 30 metres deep were hired, and so with very limited time they worked underwater with a hyperbaric chamber for them when they came back up. The undersea cable was then protected or laid down in an undersea trench excavated to contain it (the operation is called jetting) or covering it with piles of rocks. This second solution was chosen for the section in the port of Sorrento. “One Saturday night, the Lazio-Atalanta game was on”, remembers the engineer, “and the captain of the port interrupted, fearing that the rocks which we were unloading could cause problems for the port's dock. It was a moment of intense phone calls in the middle of the night but then by sunrise everything was resolved; we had all of the necessary authorisations!”.

"The undersea cable was protected or laid down in an undersea trench excavated to contain it (the operation is called jetting) or covering it with piles of rocks".

Episodes followed one after another and Capri will be remembered as a construction site that was contributed to by many local institutions and the population. “We have had a very warm welcome after years of discontinuous power supply, with moments of genuine emotion; I remember the reaction of an old man when he saw the cable arrive which would have ensured the certainty of a stable power supply for the future”. The outages should now improve even if the Terna grid ensures transmission up to the distribution switchboards: from there on the competence and responsibility of any power disconnections lies with the individual local distributor.

The divers busy with laying down the undersea cable between Capri and Sorrento (photo by Terna)

When one chapter closes, many more of them open. For the connection on other smaller islands with undersea cables- such as Favignana in the Aegadian archipelago, Ischia or even Elba, new projects are currently in the study phase or are already ready to be added to the next Terna Development Plan. More relevant works are in sight for the larger islands, such as Sacoi 3 (a Sardinia-Corsica-Italian mainland triangulation) or in the study phase such as the Thyrrenian link between Campania, Sardinia and Sicily which was pre-announced as the most important undersea cable project ever done by Terna, fundamentally for the phase out of coal in Sardinia foreseen for 2025. In addition, strategic and of geopolitical relevance is Tunita, an undersea cable between Italy and Tunisia that aims to connect the North African market with the European market. The project was included in the third list of Projects of Common Interest (PCI) published by the European Commission.