Offshore wind: how energy travels from the sea

When you look at an offshore wind farm, you’re watching the wind become an element of the infrastructure. The white blades stand out against the horizon, seemingly thin yet powerful enough to transform the motion of the air into electricity. This is one of the iconic images of the energy transition, a technology which is young in Italy but which is destined to play a decisive role in the country’s future.

The idea of harnessing offshore wind to generate electricity originated at the end of the twentieth century, but it wasn’t until the early 2000s that the technology began to establish itself in earnest. The first large modern offshore wind farm, Horns Rev 1, became operational in Denmark in 2002: 80 turbines capable of generating 160 MW, the project that first proved the possibility of producing renewable energy industrially in the open sea. Since then, the trend has never lost momentum: in just over twenty years, the size of plants has continuously increased — including the turbines, which today exceed one hundred metres — as has the capacity, which now reaches 10-15 MW. At the same time, wind farms have multiplied in number: Europe, a pioneer in the sector, has seen a series of projects emerge in the North and the Baltic Seas, such as Hornsea One and Hornsea Two in the UK, with capacities of 1,218 MW and 1,386 MW respectively. Even more ambitious is the Dogger Bank facility, also in British waters, which will exceed 3.6 GW once completed, making it the largest offshore wind farm in the world.

In 2025, global offshore wind capacity exceeded 83 GW, an amount sufficient to power approximately 70 million residences. It is a steadily growing sector, which aims to become one of the cornerstones of global energy policies. Behind these figures are state-of-the-art infrastructures employing technologies which are innovative in both engineering and environmental terms: submarine cables which can stretch hundreds of kilometres, offshore conversion stations, and HVDC connections capable of transmitting large amounts of electricity. Though hidden, this is the side of wind power that allows the wind captured by the blades to reach all of us, industries and citizens. It’s a long and complex journey, starting with offshore turbines, going through production and transformation, followed by transport, connection and, finally, integration into the grid.

From wind to electricity. Offshore turbines, anchored to the seabed or mounted on floating structures in deep waters, are designed to harness winds which are stronger and more consistent than those on land. In fact, each one can be seen as its own little power plant, capable of producing up to 10 MW. The rotor converts the wind’s kinetic energy into mechanical energy, the generators convert this into electricity, and the conversion units stabilise its power. An offshore farm, with dozens of turbines, can produce hundreds of megawatts: enough to power entire cities. But this freshly generated energy must embark on a journey beneath the surface of the sea.

Submarine cables: “invisible” arteries. This is where submarine cables come into play: nothing short of “electricity highways” laid on the seabed that connect the turbines to offshore stations and on to the coast. Each cable is manufactured to have specific characteristics allowing it to withstand high pressures, marine currents, coastal erosion, and even the threat of accidents involving anchors or fishing nets. For this reason, laying these cables is a delicate engineering operation: specialised ships install the cables on the seabed following meticulously planned routes. The cables are not just conductors of energy: they are strategic arteries that ensure the continuity of flow and the security of the network.

HVDC technology. When wind farms are located near the coast, alternating-current connections are the most commonly used solution. Over long distances, high-voltage direct current (HVDC) technology is more reliable. Thanks to HVDC, energy can travel as many as several hundred kilometres while maintaining its efficiency and stability. This is the technology Terna is adopting for the construction of major electricity transmission backbones such as the Tyrrhenian Link, which will connect Sicily to Sardinia and Campania, the Adriatic Link, which will link Abruzzo and Marche, and the Elmed project for the interconnection of Italy and Tunisia via submarine cables. This strategy, which is outlined in the 2025-2034 Development Plan, makes Italy a cutting-edge laboratory for electrical interconnections.

As it approaches the coast, the energy produced by the wind farms arrives at onshore conversion stations. Here, direct current is transformed back into alternating current so that it can be brought into the national grid, a crucial step marking its transition from the realm of the sea to the land-based electricity grid.

Integration into the electricity system. Every kilowatt-hour produced at sea becomes part of the bigger national energy picture. This is made possible by the high-voltage grid: a network which already stretches over 75,200 km and which Terna plans to expand further to absorb increasing flows of renewables in the coming years. Investments of over 23 billion will also be made for the increasing integration of green energy, through submarine infrastructures and interconnections. The journey taken by offshore wind is the story of an energy source that starts out “light” and is made “solid” thanks to innovative, strategic infrastructures, made up of submarine cables and conversion stations. Italy, with its strategic position in the Mediterranean, is ready to rise to the challenge of establishing itself as an energy hub.