Wiring The World.

The energy transition is the biggest economic and investment trend in the world today. It is likely to endure for the next two decades as the world rewires itself and builds the infrastructure required to move away from fossil fuels. One of the key challenges of the transition is the process of moving energy from place to place.

If energy is generated by the wind or sun, storing it and transporting it is a different challenge altogether. Companies can either build giant batteries and move these around the world, which would be prohibitively expensive and incredibly dirty, or they can move the energy to where it needs to be via giant wires.

The latter option is far easier and an incredibly efficient way of transporting energy. There’s no need for giant supertankers powered by dirty diesel fuel, or any requirement to super-cool gas into a liquid. The wires are laid, infrastructure is switched on and there is very little additional input necessary aside from regular maintenance.

Most underwater cables are designed to operate for a maximum of 25 years, although there are examples of cables lasting much longer.

The first international undersea cable was laid in 1850 between England and France by the English Channel Submarine Telegraph Company of Jacob and John Watkins Brett.

It was a simple copper wire with insulation, just 11mm thick, designed to carry simple
telegraph signals. The cable was wound on a drum mounted on the deck of the paddle steamer Goliath, which set off from Dover on 28 August 1850.

There were two problems with the cable set-up. Firstly, it wasn’t heavy enough, so lead weights had to be attached every 100 metres to make it sink. Secondly, the cable wasn’t armoured and it snapped almost as soon as it was connected on both sides of the channel. By the end of September 1850, sections of the cable were being sold as souvenirs.

The early pioneers didn’t give up. By 1851, a new cable was in place. By the end of the decade, one had been laid between North America and England and from there, the business boomed. The cables of the late 1860s were nearly 70mm thick, with a 2mm thick copper wire at the centre surrounded by several layers of steel armour bound together with a mix of tar and gutta-percha (a form of rubber).

Today, there are around 400 underwater telecommunications cables in operation around the world, spanning a length of over 1.2 million kilometres.

The submarine power-cable market is young. In 1954, the world’s first submarine HVDC Cable (High Voltage Direct Current), Gotland-1, was installed. This was 98km long, from Gotland Island to the Swedish mainland, and had a capacity of 20 megawatts (MW).

The biggest hurdle with transporting electricity large distances underwater is converting power from alternating current (AC) to direct current (DC).

In most countries (including the UK), AC is the dominant power supply. Unlike DC power, AC current frequently changes direction, whereas in DC, electrons flow steadily in a single direction. According to the National Grid, AC offshore cable voltages are limited to 200 kilovolts (kV), whereas HVDC cables can take three times as much power or more.

What’s more, there’s no technical limit on the length of cable or overhead line that can be used in HVDC connections.

AC cables are far more brittle and require more maintenance, making installation over long periods prohibitively expensive and complex.

However, there needs to be a converter station installed at each end of the cable to convert the power back from DC to AC in order to get it onto the grid. These converter stations take up a lot of land and are very technically complex, which is where complications can arise.

Demand for undersea power cables is set to explode over the next couple of years, led mostly by the wind industry.

Data from consultancy 4C Offshore shows that total length of HVDC cable installed worldwide for wind projects was nil until 2009. That year, the first 660km of cable was installed. There was no more installed until 2017, when the total jumped to 750km.

But then, in 2019, the total length began to rise exponentially. The figure hit just under 5000km at the end of 2023 and will rise to 6000km by 2025. By 2030 it is projected to hit 23000km. In 2035, the consultancy predicts, 56000km of underwater HVDC will be in operation around the world. And these numbers only relate to the wind industry.

The UK, with one of the world’s most developed renewable-energy sectors (thanks to our unique position as an island surrounded by the North Sea), has one of the most mature HVDC cable markets.

In December 2023, the world’s longest undersea land and power cable was switched on between the UK and Denmark. The £1.7bn Viking Link interconnector stretches 764km and is just one of six cables connecting the UK grid with its European neighbours.

A series of other cables are planned around the UK and between Europe, including NeuConnect, the first direct power link between Germany and Britain, with a cost of £2.1bn.

National Grid plans to spend a total of £21bn by 2034 on 14000km of high-voltage cables connecting the wind industry and different parts of the UK transmission system.

That’s just the UK. The rest of the world is also charging ahead with plans to rewire. This year alone, several firms have announced plans to construct factories to feed the booming market.

Between 2015 and 2020, around $3bn dollars of new projects were awarded per year to cable manufacturers. In 2022, this figure was $11bn, and analysts have pencilled in further growth to around $20bn of orders per annum for the next decade. The major manufacturers have been caught off guard. Order books are full until the end of the decade. In some cases, backlogs stretch out for over 12 years.