Harnessing energy from the ocean

Humans have long depended on the sea as a source of food and a means of travel. But the world's oceans offer another essential resource: energy. And Scotland's Orkney Islands boast optimal conditions for harnessing the power of currents and tides.

"We've got the tides of the North Sea meeting the tides of the Atlantic Ocean, and as they are filtered through these very narrow channels between the islands, the currents pick up - and that's why we've got the best tidal resource in the world," says James Murray, an engineer with Scotrenewables, a company that's developing marine energy technology.

Ocean waves can also be formidable - averaging 2 to 3 meters (6.5 to almost 10 feet) but swelling to 18 meters in stormy weather. The challenge is to convert that power into electricity.

"To build a piece of machinery that's capable of withstanding that is a big ask," says Neil Kermode, director of the European Marine Energy Center (EMEC), a non-profit research laboratory on Orkney. "You have to design equipment that's flexible enough to react to the waves, yet durable enough to survive them."

Putting technology to the test

Companies from around the world have taken up the challenge, and each year they bring prototypes to EMEC for testing in real sea conditions.

Scotrenewables is trying out a turbine that looks like a yellow submarine (pictured at top). The 35-meter-long device was built at the Harland and Wolff shipyards in Belfast, best known as the birthplace of the ill-fated Titanic.

"Hopefully we'll have better luck than the Titanic," Murray jokes.

Dubbed the SR250, the turbine is far easier to install than devices that sit on the ocean floor. Installing those requires a special boat and crane, which cost more than 200,000 euros ($220,000) a day.

"Because the turbine is floating, we can use much smaller vessels to tow the floating turbine onto site," Murray explains. "Retractable rotors are lowered, the brakes released and the turbines can be generating within the space of about half an hour, so it's quite a different approach."

A problem for marine life?

Murray says the floating device is also unlikely to pose problems for fish and marine mammals, a view shared by marine biologist Gareth Davies.

"Whales, dolphins, seals and fish have been shown to react to persistent and loud sources of noise," he says, "but the level of noise that supertankers generate is far, far greater than any of the noise that comes from renewable energy devices."

A native of Orkney, Davies adds that existing energy sources are a bigger threat to wildlife - with oil spills fouling the water, coal and gas polluting the air, and excess carbon dioxide in the atmosphere causing the oceans to acidify.

The flipside, however, is certainly possible: that creatures in the ocean will cause problems for marine energy devices.

Sea lions are big, heavy animals, and they love to lounge on buoys, boats - anything that floats. "There's a lot of engineering and design going into how you might shape a turbine or coat it with Teflon so that a sea lion can't hang out on it," says Sarah Henkel, a scientist Oregon State University on the US west coast. "Having a sea lion sitting on your turbine would definitely affect the performance of the device!"

Other marine mammals could become tangled in lines that hold turbines in place. But Henkel thinks collisions are unlikely. Birds that crash into land-based wind turbines may be flying 80 kilometers an hour, but ocean creatures move much more slowly.

Costly business

That leaves one other concern for proponents of marine energy - cost. Until the industry agrees on a few top technologies, there are no economies of scale. John Breslin is general manager of SmartBay Ireland, another center for marine energy development.

"It took 25 years to develop the modern wind turbine," Breslin points out. Marine energy is in a phase of consolidation, he explains. "We have lots of different types of devices that harness power in different ways. We're going to see some people drop out, and over the next five to 10 years a few will emerge - and that's when this industry will really take off."

In the meantime, prices for conventional energy sources - oil, natural gas and coal - are down, reducing demand. Still, EMEC Director Neil Kemode thinks climate change will eventually compel the world to draw clean, renewable power from the sea.

"We can't just keep burning our way through one cubic mile of fossilized swamp goo every year," he says. "We know there is energy in the water out there, and we're a lot closer to it than when we started."

"We have done that piece of alchemy - of turning sea water into electricity," Kemode says. "We can make this work."

He adds that researchers at EMEC have found a way to create a storable source of power - hydrogen - from sea water, using marine energy. Now they're looking for funds to run a cable from Orkney to the Scottish mainland so they can share the islands' bounty with more people.