'Saudi Arabia of renewable energy' off Scotland's coast

IT HAS been described as the "greatest untapped source of energy Scotland has ever had", capable of generating enough electricity for every home and business in the country several times over.

But while the Pentland Firth has been too deep and too dangerous to exploit, the race is now on to develop machines that will harness this "underwater hurricane" and fundamentally change Scotland.

Not only could it provide endless supplies of electricity for Scotland and beyond, but spare energy could be used to convert rubbish into environmentally friendly biofuel for cars, trains and airplanes, slashing greenhouse gas emissions and ridding the country of landfill sites.

In August, the world's largest tidal-current generator will be installed on Northern Ireland's Strangford Lough and, next year, ScottishPower will start testing an underwater turbine in the Pentland Firth itself.

ScottishPower believes its system could generate up to a gigawatt (GW) of electricity - equivalent to all of Scotland's wind farms put together, or the power produced by the Hunterston B nuclear power station.

But Professor Stephen Salter, who wrote an energy review for the SNP extolling the potential of the Pentland Firth, believes the actual amount of energy could be as high as ten to 20GW. He was turned down by the previous Scottish Executive for funding to investigate the potential of installing a tidal machine at depths previously considered out of reach, but believes the SNP government could be more receptive.

He said: "If we could do this, we could get twice the electricity Scotland uses at peak demand - it's absolutely enormous. The Pentland Firth is the Saudi Arabia of marine energy. But, if you are in London, energy from the Pentland Firth is a long way away and there's no cable to get it to your voters."

Prof Salter, of Edinburgh University, has developed a form of cylindrical turbine which he believes would be able to go deeper than ever before, where the Pentland Firth's most powerful currents are found.

The water in the fastest- moving channels is about 70 metres deep. His machines operate down to 50m, while seabed-based turbines could be used in the bottom 20m.

The Firth would generate energy in four regular tidal pulses a day, often generating large amounts of power in the middle of the night. Fuel cells or large industrial batteries could be used to store spare electricity, but Prof Salter said it could be used for a process which can turn waste into gas or liquid fuel.

Martin Wright, managing director of Marine Current Technologies, said the Pentland Firth was the "Mount Everest" for the industry. He added: "There's no doubt it is a stupendously energetic area and the technology will have to be appropriate.

"The big prize is the very fast-moving water in 60m to 70m of water. You are putting units in the equivalent of an underwater hurricane there.

"It's all a question of will. I think we could have done this in half the time if the only challenges were technical."

What was needed, Mr Wright said, was a strong statement of commitment from the Executive to developing at least half a GW of energy from the Firth, which would attract major global engineering companies.

Duncan McLaren, of Friends of the Earth Scotland, backed the potential of the Firth, but cautioned against fast-tracking energy schemes without assessing their environmental impact or adequate consultation.

Grasping the Thistle, a book co-authored by Mike Russell, now Scotland's environment minister, hailed the Pentland Firth as "the greatest untapped source of energy Scotland has ever had".

Asked how seriously the Scottish Executive viewed the potential of the Pentland Firth, Jim Mather, the energy minister, said its strategy "will have renewable energy at its heart".

Questions of power and the Pentland Firth...

How powerful is the Pentland Firth?

The flow of water from the Atlantic to the North Sea and back again can reach speeds of up to 12 knots.

About 2.5 million cubic metres of water - 1,000 Olympic pools - will pass through a line drawn across the Firth every second at peak times. According to Professor Stephen Salter, this could generate up to 10 to 20 gigawatts of power. Hunterston and Torness nuclear power stations can produce up to 2.5GW.

How can we harness this energy?

ScottishPower and Bristol-based firm Marine Current Technology (MCT) have developed underwater turbines which work in a similar way to wind turbines. Prof Salter has designed a spinning cylindrical turbine which he believes will be able to capture the energy of the Pentland Firth. Seabed-based turbines could be used with his system.

Where would the power go?

Bigger cables than currently exist would be needed to take power down the east coast to Aberdeen, Scotland's central belt, northern England and possibly London.

The capacity of proposed upgraded Beauly to Denny power line, currently being considered by a public inquiry, will already be used by wind farms in the pipeline.

How could we use the excess power?

Electricity can be stored in large industrial batteries or used to split water, H2O, into hydrogen and oxygen. Hydrogen can be used in fuel cells to power vehicles or turned back into electricity when needed.

It could be used to pump upwards into hydro-electric reservoirs, which can provide electricity at short notice to cope with sudden peaks in demand.

A cryogenic process can turn almost any waste into gas or "super-clean diesel" for vehicles and aircraft.