World’s Largest Submarine Cable

The world’s longest submarine power cable will measure some 930 miles and will deliver energy from Iceland’s volcanoes and power plants to energy-hungry Britain.

Iceland is practically awash with untapped energy sources, sparking dreams of more of such cables in the future, which would guarantee the country a new and lucrative export commodity.

The volcanoes that lie beneath Iceland will soon be tapped for their bountiful energy by power-hungry Britons across the frigid North Atlantic, thanks to an agreement made last spring in which the United Kingdom and Iceland decided to establish a 930-mile power cable between the two countries.

When it is completed in 2020, it will be the world’s longest submarine power cable. But first, it must surmount the challenges of being laid deep below some of the world’s most treacherous waters.

Iceland’s plentiful natural energy

There are only 313,000 people living in Iceland — more than 60,000 fewer than live in the city of Honolulu — but the island is rich in natural energy sources, primarily hydroelectric power and volcanic heat. More than a third of the country is situated almost 2,000 feet above sea level, and in many places annual rainfall exceeds five feet a year. The rivers roaring to the ocean are a rich source of energy, while heat from the volcanic underground can power turbines.

Iceland currently has five large geo-thermal power plants that generate both heat and power. The largest, Svartsengi Power Station, supplies one of Iceland’s most popular attractions, the famed Blue Lagoon geothermal spa, with mineral-rich water heated to 98 to 102 degrees F.

Most Icelandic homes are warmed by underground heat, and residents have a hefty appetite for energy, even by Scandinavian standards: Each citizen consumes 51,000 kilowatt-hours (kWh) a year. That’s more than three times as much as the average Swede and eight to nine times as much as a Dane. Most power, however, is sold to large, energy-intensive companies that have moved to Iceland for its abundant supply of cheap energy.

Iceland’s power is controlled by Landsvirkjun, which is owned by the government. According to its calculations, only 20 percent of the country’s energy potential is utilized today. In other words, there is more than enough hydroelectric power and geothermal energy underground to go around — even across the sea. Consequently, energy could be

Iceland’s new export commodity.

The agreement with Britain is the first, but Landsvirkjun is hoping to lay more international cables, including one that would run 1,180 miles to Germany.

Finding the optimal route

The world’s first submarine cable was a telegraph cable laid along the floor of the English Channel in 1850 that linked France and England. In the following decades, telegraph cables connected the whole world. Those have long been replaced by fiber-optic cables that transfer data and phone calls; some 95 percent of all intercontinental communication now takes place via submarine cables (the rest is transmitted via satellites).

Power cables are now following a similar path, enabling the transfer of large amounts of energy between an evergrowing number of countries. Submarine cables already link Sweden and Finland and Norway and Denmark, and many new ones are coming online. Norway and Germany have agreed to establish a link that is expected to be ready in 2018.

The Icelandic cable is expected to supply Britain with as much power as a large nuclear plant — and the British are going to need it. Several of the country’s nuclear plants are so old that they must be phased out, and the North Sea’s oil and gas reserves are quickly being depleted. Although Britain is erecting dozens of new wind turbines, there is a danger that the country will suffer a power shortage in the foreseeable future, which is why it’s making energy agreements with nearby countries like Iceland.

Before a submarine cable can be laid out, engineers and geologists must find the most appropriate location by mapping the ocean floor. Using echo sounders, remote-controlled submarines and sonar, engineers examine the bottom of the sea for hurdles such as reefs or steep slopes. Seismic measurements also are essential, in order to inform technicians of how thick the seafloor sediments are and what lies beneath them.

Engineers must also collect information about existing cables, and where any shipwrecks or other obstacles are located. Although the cable doesn’t take up much space, the engineers will typically map out a path about a half-mile wide before the final location is decided. The precise route of the cable that will link Iceland and the United Kingdom hasn’t yet been determined, but it will probably run by the Shetland Islands and northern England. The ocean depth is relatively modest all the way — no deeper than 1,640 feet — but there may be difficult areas where the cable will need to be secured to steep slopes to keep it from sliding down, or where extra-strong armor will be needed to protect it from a particularly rough stretch of the ocean floor.

Submarine cables are laid by specially designed ships, whose limits will be tested by the Icelandic cable. The North Atlantic is notorious for its stormy weather. When the seas turn very rough, the ships won’t be able to lay the cable; if a vessel is caught in particularly violent weather, the crew may be forced to cut the cable. Work can resume once the weather calms down, but picking up where they left off will be no easy task.

Additionally, wherever the cable is cut, it must be joined to the next section with a connecting sleeve. These are the weakest points of the cable, so ideally there should be as few connections as possible. For this reason, the cable sections are becoming ever longer — lengths of cable running more than 12 miles between sleeves are not unusual.

On a good day, a cable ship can lay out about six miles of cable. The work requires expert seamanship, since the ship should maintain a steady pace — not too slow or too fast. A general rule of thumb calls for the cable to be rolled out at a speed 2 to 3 percent faster than that of the vessel, to compensate for the fact that the cable is unlikely to lie in a straight line along the ocean floor.

Minimizing energy loss

The power used in a typical household power outlet uses an alternating current: The movement of the electricity reverses direction 50 times per second. This type of current is appropriate when power is transferred over short distances, but when long distances are involved, power is usually transferred as a direct current. This will be the case for the power that will be cabled from Iceland to England. Energy loss is lower when the current moves in only one direction — some 3 percent for every 620 miles of cable. The Iceland-Britain cable should lose only 4 to 5 percent of its energy. The greatest energy loss occurs at transformer stations, where the current changes from direct to alternating at one end and vice versa at the other.

International energy exchange

In the infancy of electrical power, a single plant could supply an entire city. But as cities grew — and, accordingly, their demand for power — they became part of an expanding power grid; entire regions were soon linked by high-voltage lines.

Increasingly, those connections are being made between countries, across oceans as well as borders. Sharing energy confers great advantages: Countries with lots of wind turbines can export power on very windy days, generating income and reducing the importer’s use of coal-or gas-powered plants.

Some of this excess energy can even be stored for later use. For example, in Norway, energy is used to pump water up to elevated lakes. When the demand for power increases, the water from the lake is sent down through a hydroelectric power plant. Although some energy is lost in the process, about 80 percent can be retrieved and transferred to parts of Europe via cable. Thus, cables can link anything from nuclear plants to wind farms to tidal turbines. Energy that is stored and exchanged between countries enters the grid. Someday, solar systems in the Sahara may even join in, supplying Europe with power both from Icelandic volcanoes in the far north and from the vast desert near equatorial Africa.

Sturdy armor protects cable

The power cable that will link Iceland and Britain is a little larger than 4 and 1/2 inches in diameter; a 3-foot section weighs a little under 175 pounds.

The cable will be situated in the deep, salty water of the North Atlantic, at a pressure of up to 50 atmospheres. Thus, the cable will need to be protected by several layers of insulation and armor to keep it from being eroded by the salt as well as from the force of the pressure and any impediments on the seafloor. The life span of a submarine cable is 40-plus years.

Submarine power cables link Europe

Europe’s power-supply system is becoming ever more intricately linked, thanks not least to submarine cables.

Cables running along the seafloor connect the Netherlands to Norway, and the United Kingdom is linked via submarine cables to Ireland, France and the Netherlands. The Scandinavian countries have been exchanging power for many years, and more links are planned. Lithuania and Sweden will be connected in a few years, as will Norway and Germany and the United Kingdom and Norway. (The latter two nations have agreed to establish a submarine cable in 2020.)

In Iceland, the national power utility wants to lay more cables connecting to the rest of Europe, including one that would run 1,180 miles to Germany. Some of the future cables will also transfer power from wind farms.

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