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.

View Images 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."