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Tides of change: the Pentland Firth has been touted as the Saudi Arabia of tidal energy. Realisation of its potential could transform the industrial landscape of northern Scotland.

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Some places are inextricably linked to their industrial past. Coventry, for instance, will always be known as the home of the motor ear. Think of the South Wales valleys and it's coal mining that springs to mind. And Tyneside will be forever linked with shipbuilding.

The problem with a heavy dependence on one industry, though, is that when times change and markets evolve you can be left with joblessness and social deprivation. That's the cause of concern in Caithness, the remote county at the north-eastern tip of Scotland. This far-flung and sparsely populated region is home to the Dounreay nuclear facility, which provides one in three jobs in the area. But, with the decommissioning of Dounreay taking place over the next 20 years, there is a worry that many of the skilled engineering and technical jobs provided by the site will slowly migrate elsewhere.

Fortunately Caithness is blessed by nature. Off its coast, running in a channel between the mainland and the Orkney Islands a few miles to the north, lies the Pentland Firth. This violent stretch of water, with its chaotic overfalls, sea surges and big whirlpools, is seen as one of the best tidal resources on earth. Estimates of the energy potential in this few square kilometres range from 2GW to 8GW.

Now an organisation called the Pentland Alliance is aiming to harness that enormous potential, helping to move Caithness in the long run from a nuclear to a marine economy. "If you waved a magic wand and took Dounreay away, there would be a major impact on jobs in Caithness and on the local economy," says Gerry MeGill, director of the Pentland Alliance.

"We cannot transfer these skilled jobs into sectors like agriculture and fishing, there needs to be something else" He believes that Caithness must look to exploit its abundance of tidal resources and that the skills of nuclear engineers in areas such as materials testing could be transferred into this new sector.

The Pentland Alliance comprises the UK Atomic Energy Authority and engineering companies Amee and US-based CH2M Hill, all three of which are involved with the decommissioning of Dounreay. The alliance recently commissioned marine energy firm Tocardo to produce a report on the potential of the firth. The resulting pre-feasibility study provides what is described as a route map towards accelerated, large-scale tidal energy development in the region.

But the route to such ambitions is by no means straightforward. There is still a lack of detailed tidal resource information available on the Pentland Firth. The grid connection in Scotland is weak and requires big reinforcements, and the tidal energy industry is still in its infancy. But, despite these problems, the study concludes that the firth represents a major social and economic opportunity for Caithness which needs to be grabbed now.

"We are there to act as an enabler," says McGill. "What we want to do is create the level of interest where people who can make a difference--engineering firms, government and investors--can come together and get things moving. There is a real opportunity here." He says that Caithness is a wonderful place to live and many engineers employed at Dounreay have made their lives there. But there has to be long-term sustainable employment for them.

Indeed, the development of the Pentland Firth as a tidal resource is beginning to gain momentum, with academics starting to take a more scientific interest in the potential it offers. Professor Ian Bryden, who holds the chair in renewable energy at the University of Edinburgh, reckons that the firth probably accounts for at least half of Scotland's tidal potential, and possibly even as much as 70%. "What we've got here is a really energetic, compact resource. And that should give us hope for ultimate exploitation in the future," says Bryden.

But he says that any predictions, at present, are an educated guess. "I don't know the full potential of the Pentland Firth. And if at any time anybody tells you that they do, that's probably an indicator of their lack of understanding about this resource. What I can give is an idea of the present best thinking of the potential of this stretch of water."

Bryden says that marine experts need a better understanding of water flow and of other factors, such as the topography of the seabed. Some data has been gathered by lowering traditional acoustic doppler current profilers (ADCPs) from the surface. But Bryden says that the firth needs to be viewed as an enormous three-dimensional body of water, with a maelstrom of whirlpools and eddy flows across its width and depth. To have reasonable confidence about modelling the flow, a number of techniques must be used together.

Bryden suggests using surface radar measurements to produce a two-dimensional map of flow speeds in the upper boundary of the water. This could be combined with a much greater number of ADCP measurements, gathered over at least two full spring and neap tides.

'A frightening but not unmanageable volume of material would need to be produced," he says. "It's important that we have a better understanding of issues such as turbulence so that we can work out how it would affect the ultimate design of the devices in the water."

In the meantime, Bryden and his colleagues at the University of Edinburgh have produced a mathematical model based on predictions of a well-defined hypothetical stretch of water of roughly the same width and depth as the firth.

This work enables him to make a prediction of a maximum extraction energy flux of around 9GW, producing an average of about 1.7GW. "These are conservative underestimates,' he says. "When issues such as seabed friction are built in, we could be talking about figures four times higher."

Looking to the future, initial research into the types of tidal devices that might be used can be whittled down to four areas: horizontal axis turbines, vertical axis turbines, Venturi-based designs, and linear lift devices. Bryden says that he doesn't think that the energy conversion technology which will emerge will be particularly surprising or novel. The main engineering challenge, be says, will be around installation and maintenance.

"How do you hold the technology in place?" he wonders. "The Pentland Firth is some of the most violent water in the world and it will try to wash your technology away. So do we use big gravity bases, multiple piling or some kind of anchoring? These, in my mind, are the big engineering issues which the pioneers of tidal energy will encounter."

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Bryden has some experience of these types of problems. A couple of years ago he developed and built a half-size device called the SeaSnail, which was installed in 25m of water off the coast of the Orkney Islands. The device produced power, before being removed and the seabed returned to its original condition.

"I learnt more in the first five minutes of that device being in the water than I did in my entire previous career," he says. "I learnt about the dangers and the difficulties of handling such installations. I was working with some very experienced marine operations specialists but I soon realised that this is not an environment that you go into lightly. Fixing devices in deep water and exporting electricity remains a massive challenge."

Then there are the bureaucratic and political hurdles to overcome. "Despite the difficulties, there are no insurmountable engineering problems that tidal energy has to overcome" he says. "But there has to be a political will to see this through, even though the returns won't be immediate. Some small-scale funding in targeted areas is required to help remove some of the barriers we have discussed"

The next step in the development of the Pentland Firth is a series of stakeholder meetings and workshops including government, utilities and industry. Earlier this month a conference in Edinburgh on the potential of the firth attracted more than 200 delegates, including Scotland's first minister Alex Salmond. "We are starting to see some impetus going forward," says McGill from the Pentland Alliance. "It would be ideal to start seeing employment in the tidal sector going up as the Dounreay jobs curve starts to go down."
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Title Annotation:ENERGY
Author:Hibbert, Lee
Publication:Professional Engineering Magazine
Geographic Code:4EUUS
Date:Feb 27, 2008
Words:1366
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