British sea power is making a comeback as the island nation seeks to once again rule the waves.
 | Picture Gallery (click on the image to start)A Pelamis wave power generator during sea trials. See how wave and tidal power can be won (Photo: Pelamis Wave Power) |
A new kind of armada is headed for British shores. And while certainly not as menacing as a fleet of Spanish galleons, the sight of dozens of 150-meter floating metallic tubes, known as Pelamis, may still be enough to startle an unassuming fisherman passing by. But if developers have their way, there could be dozens of these devices bobbing off the coasts of England, Scotland, and Portugal as early as next year.
Pelamis represent the next generation of renewable energy technology. A Pelamis tube converts wave power into electricity. Wave motion pushes hydraulic rams into a generator, which, in turn, pressurizes oil that is used to drive a turbine. Developers hope hundreds of these devices will eventually make up the world’s first wave farms, the biggest attempt so far to tap this unexploited source of energy.
The World Energy Council Survey of Resources 2007 suggests that currently economically exploitable wave power varies from between 140 and 750 Terawatt hours (TWh). If potential improvements are realized, annual output could rise to 2,000 TWh, more than 10 percent of the total electricity generated worldwide in 2005. A 30 Megawatt (MW) Pelamis wave energy farm would only occupy a square kilometer of ocean, but provide enough electricity for 20,000 homes.
Taming the sea
The Orkneys, an archipelago of storm-buffeted islands off the northern tip of Scotland, is home to the European Marine Energy Centre (EMEC), where Pelamis and numerous other prototype devices are pioneered and tested in the choppy waters where the Atlantic Ocean and North Sea meet. Even though there are already around 70 different wave power developers and 42 tidal power developers worldwide, EMEC managing director Neil Kermode insists the industry is still young.
“If I draw a parallel with aviation, we are closer to the Wright Brothers than Airbus,” says Kermode. “If you ask me about generating capacity, it is like asking the Wright Brothers about carrying capacity.” Others are less cautious. Sustainable Energy Ireland, for example, estimates that wave energy could supply 75 percent of Ireland’s electricity requirements, while the London-based Carbon Trust argues that marine resources could generate 20 percent of the UK’s energy.
Promising sites for wave power generation can be found around the world. France, Portugal, and Norway are especially interesting in Europe. Australia, New Zealand, South Africa, and parts of South America are of interest in the southern hemisphere.
Wave power devices range from those like Pelamis that float on the surface and “ride” the waves to seabed-mounted “oscillators” that extract energy from wave surges. Variability of wave size, frequency, and direction are challenges, as the devices must be able to both exploit commonly occurring low-power waves and withstand extreme high-power waves. Permanent exposure to salt water also puts the system under stress from corrosion.
Using the tide’s power
As for tidal power, jagged coastlines, narrow channels, and archipelagoes are prime sites. Harnessing the power created by strong tidal currents and ranges happens in two ways: through tidal barrages that exploit the cyclic rise and fall of the sea and work just like hydroelectric dams, and through turbines and other devices that are freestanding in the flowing tidal currents.
Barrages like the 240 MW La Rance plant on France’s Atlantic coast benefit from a very predictable flow of water. Large upfront costs, however, require massive government and private sector investment. Long construction times and fear of environmental impacts are additional obstacles.
Exploiting tidal currents with turbines that standing in the water current like wind turbines on land is less capital-intensive and quicker to deploy. Experimental projects are up and running in the UK, Norway, Italy, and New York’s East River.
Power to the people
With wave and tidal energy being harvested in the open sea, getting the power to markets is another challenge. EMEC director Kermode estimates that, at current prices, coal based electricity costs 3 to 5 Euro cents per kWh, while marine power costs 17 to 21 cents. Another problem is that the best tidal and wave energy resources are often located far from large population centers, which means high long-distance transmission costs.
“With oil, it is clearly worth bringing energy from one side of the globe to the other,” says Kermode. “Whether that is the case with wave and tidal power, we don’t know.”
The advantages of marine energy could make it a viable source of power, especially in the long-term. Sea power is abundant, predictable, and has a relatively light environmental impact.
The seas surrounding Britain have always been a source of political and military security for the country. With new technology and fresh money, those same waters could serve as a renewable source of energy security, too.
editor: James Tulloch
publishing date: November 20, 2007
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