THE TIDE RUSHES IN…CLOSE TO THE CASTLE OF MEY

At Bohemianmojo we make no bones at all about our intense dislike of wind turbines. From our viewpoint they’re noisy, ugly, expensive, bird-killing eyesores. We’ve also pointed out the disastrous environmental legacy that solar panels are going to leave behind when they have to be recycled.

Tidal energy has always been our preferred sustainable option for power, especially for islands and coastal nations of course. So we’re going to look at the latest developments in tidal generation on the British Isles where things are growing apace at the exciting Meygen Project in Scotland. 

The Pentland Firth in the North of Scotland is a rugged, romantic and hugely dangerous stretch of water lying between the shores of Caithness and the Orkney Islands. It is not a place for the faint hearted and even those prodigious seamen the Vikings were in awe of this firth.

No surprise really as the North Atlantic rips and tears through this sound at speeds of 11 miles per hour and natural bowls on the sea floor create several terrifying, boat-drowning maelstroms.  The most famous of these is at the northern point of the little island of Stroma. It’s a whirlpool called The Swelkie – Norse for ‘The Swallower’ - which the Vikings believed was created by the mill wheels of a sea witch, grinding salt to keep the ocean saline.

Scottish Nationalist politicians earmarked the Pentland Firth as a potential source of tide power back in 2006 with First Minister Alex Salmond proclaiming it could be ‘the Saudi Arabia of tidal power.’ Then in 2013 Oxford academic Dr Thomas Adcock declared it was ‘the best site for tidal stream power in the world.’

It was only a matter of time before big players like Morgan Stanley, Rolls Royce and General Electric were attracted to the Firth and in 2010 the MeyGen consortium was founded named after the iconic Castle of Mey, on the mainland shore, and a shortened form of ‘generation.’ They won licences to develop a three and a half mile grid to the east of Stroma.

The scene was set and since then it has grown into the largest tidal stream project in Europe and as I write they are preparing to add the world’s largest single tidal stream turbine to their existing set-up of two, smaller, AR 1500 turbines. 

At first glance the tidal version looks very similar to a wind turbine but these are far sturdier, heavier pieces of kit designed to be bolted onto the seabed and weather the storms of the Atlantic. The new AR2000 turbine, built by Simec Atlantis Energy, is a massive mechanism weighing 150 tons, which will stand proud of the seabed at twenty five metres in with twenty metre rotor arms which will spin between six and fourteen times a minute.

The aim is to have an array of 400 turbines within the inner sound of the Pentland Firth generating an almost completely sustainable 398 megawatts of power. But the ultimate ambition is to create a £6.1bn industry employing 19,500 people engaged in the construction and export of tidal stream turbine technology around the UK and the world.

At this point perhaps some definitions and descriptions might be in order. Essentially tidal energy comes in two forms (wave power is a different concept.)  It can be harnessed by impounding the sea. This can be achieved either through the construction of a barrage across an estuary or large inlet, or by building a lagoon in coastal shallows. Both rely on turbines built into the sluices that allow the tide to fill and empty the pound of water behind the wall of the barrage or lagoon.

The other is the tidal stream where turbines are attached to the floor of the sea in arrays to capture the power of the ebbing and flowing ocean. Depending on the geography and geology of the location the turbines can be lined up in straight ‘fence’ formation or spread in a complex array that minimises turbulence and ensures turbines to the front of the array are not stealing flow from those behind. In some situations, for instance the Severn Estuary, proposed tidal flow arrays would be exposed at low tide on the rocky ‘grounds’ that cover large areas of the estuary.

The Pentland Firth will establish the cost per unit of power although this can’t yet be compared to a barrage or a lagoon because none has been built despite proposals to build a prototype lagoon off Swansea and a relatively short barrage in Morecambe Bay. Essentially successive governments spent their ‘green’ budgets on wind turbines and there was nothing left in the kitty for a lagoon.

We like the idea of lagoons because they come with some substantial   advantages for the environment, as the wall itself will provide habitat for birds and marine mammals such as seals. Inside the wall of the lagoon the impounded water provides space for recreation such as sailing and canoeing and also for aquaculture, with oyster and mussel beds and ‘fields’ of samphire.

Realistically however the construction costs of a lagoon and therefore the cost per unit of power, are likely to be a lot higher than for a tidal flow project. This crucial equation serves to focus industry attention, at least for now, on the Pentland Firth. It leads the way in tidal power and represents one of dozens of sites around the UK where the same or similar arrays could be constructed. 

There’s one other hurdle to overcome, as the Pentland Firth is the setting for of fantastic sea life with orca and Minke whales moving through the sound on passage. There are migrating Leatherback turtles too. Hopefully these important sea creatures will be able to adjust to the relatively slow turn of the turbine propeller and avoid harm unlike the thousands of birds killed by wind turbines around the UK every year.

Whichever way you look at it the advantages of tidal stream turbines outweigh those of the ubiquitous wind turbine. First and most obvious is the regularity of supply with the tide rising and falling twice a day as sure as the moon circles round the Earth.

Wind, well it’s wind, and strong as it can be on occasion it doesn’t blow on demand, not with anywhere near the metronomic precision of the tide and certainly not with such enormous kinetic energy.

And to be honest, all things being equal, I would much prefer my green, sustainable energy to be generated where it doesn’t ruin my view of the landscape or make me suffer from tinnitus.  Bohemianmojo will be watching the progress of the Meygen project enthusiastically as it harnesses natural forces so powerful they create the Viking-scaring Swelkie!

Next time we’ll be giving readers the latest updates in the progress of hydrogen power and the search for the tantalizing ‘hydrogen economy.’

Previously in Bohemianmojo:

Harvest the Tide

Smoke in the Mirrors