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Photo of a ship erecting a wind turbine in the DanTysk offshore wind park.

A ship works to erect a wind turbine in the German North Sea at the DanTysk wind facility. Submarine cables are increasingly needed to transmit new offshore wind energy.

Photograph by Carsten Rehder, dpa/Corbis

Patrick J. Kiger

for National Geographic

Published August 18, 2014

In the German North Sea, 80 wind turbines now under construction will eventually generate enough power for some 400,000 homes. That power will travel via advanced cables buried along several miles of ocean floor, part of a growing move toward undersea transmission of electricity.

Submarine power cables have been around since the early 1800s. But for most of their history, such cables were used primarily to transmit electricity from conventional sources such as coal plants, either between countries or out to islands or oil platforms.

As recently as a decade ago, the submarine cable industry was in decline. That changed in the mid-2000s, as rising energy prices and concerns about climate change stimulated interest in developing offshore wind and more efficient transnational power grids.

The worldwide market for submarine electrical cables has surged over the past decade, according to industry observers, and is set to grow even more. A report published in November 2013 by Navigant Research, a Boulder, Colorado-based firm that tracks the energy industry, predicts that global sales of high-voltage submarine power cables will nearly triple over the next decade, from $1.9 billion in 2014 to more than $5.3 billion in 2023.

Bringing the Sea's Wind Energy to Shore

"I can tell you that there is a demand for submarine cables," said Walt Musial, principal engineer for the National Wind Technology Center, a program of the U.S. Department of Energy. "Offshore wind installations are growing in number—you're seeing development in the North Sea and the Asian markets, and there's a strong possibility the market will develop in the U.S. as well."

Per-Arne Osborg, a Norway-based research and development manager at cablemaker Nexans, also predicts continued growth, particularly in high voltage DC (HVDC) submarine lines that can transmit electricity for long distances with fewer losses than alternating current, or AC, lines. "Yes definitively, the renewable power has to be distributed and a grid capable of transporting the power will be needed," Osborg said in an email. (See related: "High Voltage DC Breakthrough Could Boost Renewable Energy.")

The $340 million submarine transmission cable being built for DanTysk, the wind farm in the German North Sea, will stretch nearly 99 miles (159 kilometers). The company building the line, Italian-based cablemaker Prysmian Group, also is a player in Western Link, an ambitious plan to link Scottish and English power grids with a $1.1 billion, 239-mile (385-kilometer) submarine cable under the Irish Sea. And Canada is moving ahead with construction of a $1.5 billion line that would allow Nova Scotia to import hydroelectric power from Labrador.

ALT
Specialists work on cable at a transformer station at the DanTysk wind farm. Underwater cable will also be needed to transmit electricity from the turbines.
Photograph by Carsten Rehder, dpa/Corbis

Forging such underwater connections will help nations use electricity more efficiently and take advantage of distant renewable sources, while also preserving green space on land, said Julian Pease, a U.S.-based Prysmian business manager for submarine cables.

"Scotland has more offshore wind farms to build, and that power is needed in the south of England," he said. "It would have been difficult to get government permits for the traditional method of using overhead lines, because it would have cut across a lot of picturesque countryside. This is an alternative solution, which reduces the environmental impact."

Pease said that wind power provides about 60 percent of the market for cables. In addition to long lines to shore, a wind farm with 200 turbines also might require as much as 125 miles (200 kilometers) of cable to link them all together.

Costs and Unknowns

Burying cables about 6.5 feet (2 meters) under the ocean floor, which involves the use of specially designed ships and robotic vehicles, does have some environmental impacts, according to a 2009 report by the Convention for the Protection of the Marine Environment of the North-East Atlantic. Cables can provide artificial habitats that attract animals and plants not normally found in an area, "but such change is not likely to be significant," the report said. But because of a lack of research, not as much is known about what, if any, effect of electromagnetic fields and heat generated by the cables might have on aquatic life, the report noted.

But proponents of submarine cables argue that improving energy efficiency on land and reducing emissions of greenhouse gases will tip the scale positively in the long run. One salient example is the 360-mile (580-kilometer) NorNed submarine cable, which allows Dutch consumers to draw on hydropower generated in Norway during daytime peak demand period, while Norwegians can draw power from Dutch coal-burning power plants when they need it. The increased efficiency produced by the linkage reduces carbon dioxide emissions by nearly 1.7 million tons per year, according to cablemaker ABB.

NorNed, which was completed in 2008, currently is the world's longest submarine power cable. But far bigger projects have been proposed. Perhaps the most ambitious is the 621-mile (1,000-kilometer) submarine cable that Iceland's state-owned electricity firm Landsvirkjun has proposed building to Great Britain, which would supply some of the island's abundant geothermal, hydro and wind energy to British consumers. British financier Edi Truell is exploring how to raise more than $6 billion needed to build the line, whose feasibility is still being studied.

In the United States, Google and other sponsors want to connect the mid-Atlantic region with a high-voltage submarine cable that would bring offshore wind power to New Jersey and other states in the region. But that offshore wind capacity doesn't exist yet: Projects such as the Atlantic City wind farm proposed by Fishermen's Energy have suffered regulatory and other delays, and the website for the Atlantic Wind Connection lists the cable's completion date as "TBD."

Google was willing to invest in the $5 billion Atlantic line, it said, because it made "good business sense" and because otherwise, each wind farm project would need to build its own transmission lines, causing delays and grid inefficiencies.

Prysmian's Pease said that advances in technology—in particular, the use of cross-linked polyethylene plastic to replace paper as an insulation material—have made cables easier and less expensive to manufacture, and improved their performance. While the plastic-insulated cables haven't yet caught up the conventional paper-insulated cables in their ability to handle high voltages, Pease predicted that they eventually could close most of the gap.

But several problems could impede the future growth of submarine cables, according to Navigant research director Bob Lockhart. Laying cables requires navigating through the often complex regulations that various countries impose upon their territorial waters, which can add years of delay to projects. There are relatively few consulting firms able to conduct surveys of the sea floor, another essential step, and the supply of specially equipped ships for cable-laying is similarly limited.

Even so, Lockhart foresees a bright future for submarine cables, as the demand for renewable energy increases. "What about a huge solar farm in North Africa that would transmit energy to Europe?" he said. "That would have to go underwater."

This story is part of a special series that explores energy issues. For more, visit The Great Energy Challenge.

6 comments
bill FORTUNE
bill FORTUNE

All this is not only expensive but also unnecessary!  Wind and solar farms are being constructed because of hype, hysteria and stupidity.  Small Modular Reactors using improved rods can be build in factories, placed underground and located close to where power is needed, thus eliminating the need for large transmission lines.  The excess heat energy can be used for district heating and cooling of large numbers of buildings such as schools and government buildings or even a small town.  Heating and cooling can be delivered easily for about 1 mile from the power plant by using heat pumps at the buildings.


W. Fortune  Industrial Consultants Inc

Alec Sevins
Alec Sevins

More junk in the oceans is what this amounts to. Visual blight on formerly smooth horizons is going to keep getting worse. I hope those cable casings don't erode over time and add to the "garbage patch." Almost everything Man does ends up blighting or interfering with nature's balance.

Andy Webb
Andy Webb

As far as I read the economics, wind power should be dead.  It isn't even viable on land, much less in the water.  Figuring out how to efficiently distribute power over distance, however, is very important if we want to use relatively green energy of any sort. 

Joe Ratley
Joe Ratley

As a VERY GREEN promoter of Green Energies I'm shocked by several of the premises of this article, disturbed by (A) the size of these undersea grids, and the "need" to send these energies such extreme distances, (B) why these lines need to be buried 2 meters under the sea floor and how this exponential cost raises low cost of wind energy, (C) in particular the example of Norway, who is very rich in cheap wind and hydro energy, should be part of a grid with the Dutch, and need to "sometimes" buy coal fired electricity from them. This "reason" for such an arrangement does not seem to benefit the Norwegians - the whole sell ice water to Eskimos scenario, (D) there is an almost total ignorance - and dismissal - of the huge, ubiquitous availability of ocean current and tidal electric generation. These waters move just as the wind and are available for electric generation, and (E) Why have these grids at all? It's obvious to me that this is a way for huge international corporate conglomerates can inject themselves, and their exorbitant "overhead" costs, into a worldwide embarrassment of riches, which is this reality - the availability of ocean current, tidal, wind, solar, geothermal, and biomass energies. OF COURSE WHEN I SEE ON NAT GEO'S BANNER PAGE THAT SHELL OIL IS YOUR TOP SPONSOR, IT ALL MAKES "sense". 

paul bedichek
paul bedichek

@bill FORTUNE  Small Modular  Reactors should be an excellent method for power production but: we don't have them now,we hope we will in 2022 with NuScale reactors.The other maker B&W is having problems,these reactors will not have the very high heat needed for process heat. To reach real benefits a giant industry of supply line would be needed ,hopefully that will emerge. Would you buy one in 2022 when in 2030 you could get a FHR reactor with higher heat? I really like Transatomic Power and Terrestrial Energy, the NRC is far too conservative.

Larry Hammond
Larry Hammond

@Andy Webb  really? Wind power should be dead? Yeah at 2.5 cents a KW (2013 installed), I can see why utilities wouldn't want to use it. Do some research.

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