THE race towards a low-carbon economy is about to speed up – a lot. By 2020, if all goes to plan, more than a quarter of the UK’s electricity supply will come from offshore generators exploiting wind, wave and tidal power. Vast investment in new ideas and technologies will be needed if these machines are to perform in sites that are farther offshore, in deeper water or in more ferocious currents than ever before.
This will not be the first time that UK waters have been used as an engineering laboratory. Last century, the North Sea oil industry had to develop new techniques to extract oil and gas from the seabed in ever-deeper waters. The effort required more money than the amount NASA spent putting humans on the moon.
The potential dangers of global warming mean that a similar cycle of innovation and investment is needed again, this time to generate energy without producing carbon dioxide. The offshore exodus will help the UK government meet its commitments to reduce national emissions of CO2 by 34 per cent of their 1990 levels by 2020, and by 80 per cent by 2050.
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The most mature technology in the race offshore is wind power, and already ambitious plans are in place to put it into practice. In January, , which owns the seabed around the UK, auctioned off the rights to exploit wind power over thousands of square kilometres of open sea, mostly in the North Sea. In the next 10 years, these areas should become home to 6000 turbines capable of generating around 30 gigawatts of power – enough to supply a quarter of the UK’s electricity needs.
This is one of the largest civil engineering projects on the planet. It comes with a price tag to match: a hefty £75 billion, according to Benj Sykes, a geologist at the , a government-funded organisation charged with catalysing a low-carbon economy. “That’s equivalent to building eight Channel Tunnels in the next 10 years,” he says. Sykes’s job is to identify technologies that will smooth the path to offshore renewables and to find ways around bottlenecks that prevent rapid adoption.
“This is one of the planet’s largest engineering projects and has a price tag to match”
Perhaps the biggest initial challenge is to make the whole project profitable enough to attract big finance. To do that needs new thinking on a range of technologies and procedures to cut costs, Sykes says.
For example, there is the problem of siting turbines on the seabed cheaply and efficiently. To sit in waters up to 60 metres deep, offshore wind turbines will have to be gigantic: from base to blade tip they will stand 220 metres tall, higher than the iconic London skyscraper nicknamed the Gherkin. The foundations of these monsters must be built to exacting standards while remaining cheap and easy to install.
If the UK is going to hit its CO2 targets, the rate at which turbines are being deployed needs to increase from the present one turbine every 11 days to more than two a day. “In deeper water, turbine deployment is significantly more difficult,” says Sykes. “It’s a huge challenge to achieve that rate of construction.”
The Carbon Trust recently held a competition to find new ways of attaching turbines to the sea floor. The trust is funding seven of the winning ideas, which range from undersea tripods to structures that, although buoyant, are kept in place by moorings on the seabed.
Improvements are also needed in the way turbines are installed. Conventionally, they have been carried out to sea in pieces and put together in situ. The base of each mast has to be attached to a pile that extends into the seabed, after which the turbine and rotor are assembled at the top.
All this requires ocean-going barges with pile-driving equipment and heavy lifting cranes. Such craft are in seriously short supply, and demand for them means that the cost of building wind farms is soaring.
Sykes is looking at new ways to deploy turbines more quickly without all this gear. One idea is a “self-deploying” turbine that stands on a tripod and attaches to the seabed via huge anchors that work like suction cups. The whole structure is constructed on land, towed out to sea on a barge and simply lowered into place.
“A self-deploying turbine could attach to the seabed with anchors that work like suction cups”
There are other ways to cut costs, says Sykes. One goal is to find cheaper, easier ways for maintenance engineers to access turbines even in rough seas, a feat sometimes achieved by winching someone down from a helicopter. “That’s not how anybody is going to be doing it in the North Sea,” he says.
Another area where Sykes thinks there is potential for savings is in minimising the effect of wind shadow, where the wake of one turbine reduces the output of generators downwind. There is also scope for making the systems that transmit electricity to shore more efficient.
Wall of water
Taken together, all these savings could cut costs by 20 per cent, says Sykes. That could amount to ÂŁ14 billion, creating a potential profit margin for investors that should attract the big boys.
Wind turbines aren’t the only way to harvest energy offshore. In the depths of Strangford Narrows, at the entrance to Strangford Lough in Northern Ireland, sits , the world’s first commercial-scale facility producing energy from tidal flows. Its two turbines are each turned by giant rotors 16 metres in diameter, and each is capable of generating 600 kilowatts. The turbines sit at either end of a horizontal crossbeam, which is supported on a vertical shaft pinned to the sea floor (see illustration). When the turbines need maintenance, the crossbeam can be raised to bring them out of the water.
Although its mode of action is similar to that of a wind turbine, the stresses on SeaGen are significantly greater. “The tidal race is equivalent to a fast-moving wall of water seven storeys high, coming at you at 2 metres per second,” says Peter Fraenkel, technical director of Marine Current Turbines, the company that built SeaGen. This exerts well over 100 tonnes on the rotor blades with the tide running at full pelt. “It is truly the problem of finding an immovable object to withstand an irresistible force,” he says. If carbon fibre, the material the blades are made from, had not been invented, it’s likely that SeaGen would not exist.
SeaGen has been delivering full power since December 2008, and Fraenkel now has his eye on the future. He says there is no point in making the rotors much bigger because of diminishing returns in the amount of power generated. “The maximum size is about 24 metres,” he says. So instead of making the turbines bigger, he hopes to build arrays of optimally sized turbines.
That opportunity is likely to come sooner rather than later. Two weeks ago, The Crown Estate announced that Marine Current Turbines had been awarded the chance to generate up to 100 megawatts – that’s eighty times as much power as SeaGen can produce. The announcement covers the sea around the Orkney Islands and the strongly tidal waters of the Pentland Firth between Orkney and the Scottish mainland. It also includes opportunities for two other would-be tidal-stream companies and five wave-power companies.
Wave power is not as well advanced as wind and tidal energy, but the rate of development is set to increase, says Peter Madigan of , a London-based association representing the renewables industry.
One reason wave power has been held back is a lack of facilities to enable prototypes and demonstration machines to be easily tested. However, that picture has changed in recent years with the development of sites such as the in Orkney, the world’s first facility for full-scale testing. Cornwall is about to get , effectively a plug-and-play socket on the sea floor for wave-power companies to try out new ideas.
“Cornwall is to get Wave Hub, a plug-and-play socket on the sea floor for trying out new ideas”
None of these projects is worry-free. Environmentalists have expressed fears that SeaGen’s huge rotors would shred any seals unlucky enough to get drawn into their slipstream, though so far these have proved unfounded. And the threat wind farms pose to migrating birds is well documented.
Despite these concerns, the offshore energy revolution is under way and is likely to be generating significant power, jobs and income in the not too distant future. How much we in the UK will pay for that revolution and the electricity it yields will depend largely on the ingenuity of inventors and the innovations they come up with.
Read more: Oceanology: Farther, deeper, faster
