Largest Tidal Stream System Installed

Marine Current Turbines, has successfully completed the first installation phase of the 1.2MW SeaGen Tidal System, previous post, the world’s largest grid-connected tidal stream system, into the fast-flowing waters of Strangford Narrows off the coast of Northern Ireland.

A crane barge safely positioned the 1000 ton structure onto the seabed in the early hours of Wednesday morning, 2 April, and released its four moorings on 3 April. SeaGen’s location is roughly 1km south of the ferry route between Strangford and Portaferry, approximately 400m from the shoreline.

When fully operational later in the summer, its 16m diameter, twin rotors, one shown above, will operate for up to 18-20 hours per day to produce enough clean, green electricity, equivalent to that used by a 1000 homes, four times greater than any other tidal stream project so far built.

“SeaGen is a hugely exciting project, as well as an historic achievement for both Marine Current Turbines and for renewables in the UK and Ireland. Tidal energy has the great advantage of being predictable and no other system can harness the power of the tidal currents in the way this one can. We take great pride and see enormous potential in the technology and hope it will eventually make a significant contribution to the future energy needs of the British Isles, Ireland and beyond.”

-- Martin Wright, Managing Director of Marine Current Turbines

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SeaGen had its final assembly at a dockyard in Belfast. Here it was winched onto a crane barge and then transported to Strangford Narrows on Sunday, 30 March.

The quadropod section that sits on the seabed will now be pin piled. Each of the four pins that secure SeaGen will be drilled to a depth of around nine meters. The installation work is scheduled to take up to 14 days.

SeaGen will enter commercial operation after a commissioning phase of around 12 weeks and supply electricity to the local grid. ESB Independent Energy, the retail subsidiary of ESB, Ireland’s national electricity company, has signed a Power Purchase Agreement with MCT.

SeaGen is based on MCT’s experience with its predecessor, the 300kW Seaflow system installed off Lynmouth Devon in May 2003 and still thriving in open sea conditions.

The technology being deployed by MCT, known as “Seagen” consists of twin axial flow rotors of 15m to 20m in diameter (the size depending on local site conditions), each driving a generator via a gearbox much like a hydro-electric turbine or a wind turbine. These turbines have a patented feature by which the rotor blades can be pitched through 180^o in order to allow them to operate in bi-direction flows – that is on both the ebb and the flood tides. The twin power units of each system are mounted on wing-like extensions either side of a tubular steel monopile some 3m in diameter and the complete wing with its power units can be raised above sea level to permit safe and reliable maintenance.

The device is almost entirely submerged, and so has little visual impact, and it creates no noise audible to humans.

Environmental impact studies, carried out by independent consultants, suggest that the technology is most unlikely to pose a threat to fish or marine mammals, or the marine environment in which they live. SeaGen's rotors rotate comparatively slowly at around 10 to 15 rotations per minute, where as a ship's propeller by comparison typically runs 10 times as fast - and moreover Seagen’s rotors stay in one place whereas some ships move much faster than sea creatures can swim. The risk of harming marine wild-life is thought to be extremely small bearing in mind that virtually all marine creatures that choose to swim in areas with strong currents have excellent perceptive powers and agility, giving them the ability to successfully avoid collisions with static or slow-moving underwater obstructions.

MCT takes its responsibilities to the environment seriously. It has established a £2million program to closely monitor the environmental impact of SeaGen, involving scientists from the Queen’s University Belfast (QUB) and from the Sea Mammal Research Unit at St Andrew’s University (SMRU). The program includes the presence of a Marine Mammal Observer on SeaGen at all times during the commissioning phase, when SeaGen will only operate during daylight hours, to observe how the Lough’s marine life interacts with the structure. There is also a sonar system monitoring seal movements, operated by SMRU, which has been partly paid for by the Npower juice fund.

The next project is for a 10.5MW tidal energy farm off the coast of the Welsh island of Anglesey in a fast flowing patch of 25 meter deep open sea known as The Skerries. The project will consist of seven 1.5MW SeaGen turbines, each likely to stand approximately 9 meters above sea level. Studies are now underway and will last throughout 2008, with a consent application likely to be submitted in mid 2009. Construction and commissioning timescales will be subject to the length of the planning process, but it is anticipated this could take place between 2011 and 2012.

MCT and BC Tidal Energy Corporation plans to install at least three 1.2 MW turbines in Vancouver’s Campbell River by 2009, subject to gaining the necessary consents. It is estimated that the tidal energy potential in British Columbia is in the region of 4000MW, making it one of the best areas for tidal energy anywhere in the world

MCT has also signed an agreement with Canada’s Maritime Tidal Energy Corporation to harness the huge tidal currents of the Bay of Fundy in Nova Scotia, Canada. At mid-tide, the flow in Minas Channel north in the Bay of Fundy equals the combined flow of all the rivers and streams on Earth.

Another milestone for renewable energy. Although tidal and current energy are not the biggest sources of renewable energy, they can contribute a significant and very worthwhile amount of power to some areas of the world. Places around Scotland and Ireland, the Bay of Fundy and the west coast of Canada could supply massive amounts of power.

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Comments

[Cyril R.]

They should put tubercles on the leading edge of the blades.

[Rip]

There's nothing like putting "rubber on the road"! There's no dearth of clever ideas for alternative energy, but far too few ever see the operational prototype stage. It is herein the operational/mechanical bugs get worked out and the financial promises are documented or discounted with real data.

[Chandranshu Pandya]

This news is indeed very much welcome.I am sure in the years to come, this technology is bound to grow fast.A lot will depend on the condition of the equipment operating under the sea but being slow moving turbines, the operations and maintenance may not pose any problems.
Close monitoring and reporting will provide interesting results for all future developments.
I wish the enterprise the very best of luck for the Seagen programme.

[Richard]

I am surprised at the use of horizontal rotors. I understand the preference for horizontal axis in wind applications due to low energy density and need for fast operation. Water use would seem to favor low speed high torque devices like a vertical axis rotor. The fact that a "patented" mechanism is required to reverse the blades when the tide changes further argues for a vertical axis turbine which turns regardless of flow direction. Better solutions would appear to be like those at www.windside.com or at www.quietrevolution.co.uk. Either of those designs would be simpler and work particularly well in low speed high torque applications. But I trust better minds than I have studied the needs and have a good product. I wish them well.

[technofossil]

Richard: I am surprised at the use of horizontal rotors.

I believe the issue is the cost/swept-area. As with wind turbines, the energy that can be extracted is roughly proportional to the circular area of the rotor, or the square of the rotor diameter. The 20m diameter rotor would theoretically be able to capture 25x that of a 4 meter diameter turbine.

As with large wind turbines, doubling the size increases extractable power by a factor of 4. The issue then becomes, how large can they be made before reaching the strength limits of the materials and foundation, or perhaps depth of water.

[Angus]

What they should be looking at now is putting Wind turbines on top of the mounting pillars using the same grid connections. Wind turbines are already proven technology and could further increase profits while keeping the footprint on the environment about the same. About one Wind turbine for every half kilometre sounds about right. The increase in electricity generated may be small but as with all renewables, every bit is profit once maintenance and capital costs are calculated in and using the same grid connection and mounting column reduces these cost by a large amount.

[Bob Wallace]

Not sure, but I suspect that tidal mills will be located in places where the wind is not as steady as it is further off shore.

Sticking a large wind turbine on top of one of these tidal towers would mean that the entire rig would have to be upsized, both structure and transmission cable.

[Richard]

Carl, thank you for the explanation. Seems like the engineers who study it generally come back to horizontal designs as the best solution. I still feel an attraction to vertical axis devices. I probably should just get over it.

[Richard]

Angus - I do have a follow-up on your idea. The issues presented by Bob about rig structure might be resolved by using the design located here http://www.speakerfactory.net/wind.htm.
As you page down note that he has a floating mount for a water location. This could be attached to the underwater unit and the power grid connected very cheaply.

[Will]

A few years ago I asked MCT about siting wind turbines on top of their structures. They informed me that while they had a patent for such doubling up, most of the locations where there are good tidal streams are not locations where there are good steady winds. So, they said, it would rarely be economically viable to make use of that patent.

[Max Reid]

Wonderful achievement. This small company has been working to many years to achive this.

Meanwhile windmills have gone upto 6 MW range, but they are typically very large.

With just 16 meters, if this marine turbine gets 1.2 MW and that too working for 16-18 hours / day will make it very economical.

I hope they get more support and eventual commercialization.

[Bob Wallace]

"most of the locations where there are good tidal streams are not locations where there are good steady winds"

That's certainly my observation along the California coast from several years of sailing in and out of harbors.

When one most needs a good steady wind, fighting an oncoming tidal stream, one instead generally gets poor, confused winds caused by onshore hills and structures.

If you want good sailing, go out a few miles and turn right or left. That's where the good, steady wind lives.

[David Matos]

For river applications, and for poor areas, where pumping water is needed as well, cylinder/ piston may work better and probably with more efficiency.
I am an Angolan, southern Africa.
I have a design for a submersed water pump for river flows working only with the river flow.
We can fabricate simple machines in Angola, and cylinder/pistons assembly is easy.
Two cylinders, one with 1 meter diameter and the other 0.2 m/diameter. Pistons are in the same shaft. Area ratio is of 25 X. Pressure ratio of 25X.
The bigger cylinder has a diffuser of a diameter of 1.5 meter in both ends and is open on both sides.
When we submerse it in the river flow, the water flows in and pushes the piston. On the other end of the cylinder the water flows out in the direction of the river flow.
It is a shrouded cylinder with a diffuser and two half diffusers, like impellers to move the system around.
The piston pushes the second piston, in a closed cylinder (0,2m/d) and pressures water. The inlets and outlets of this double side cylinder have retention valves to control aspiration and discharged of the cylinder.
The cylinders rotate on its axis, enabling continuous cycles.
It is a water pump that uses only the river water flow.
Please I need to find the pressure on both cylinders, if the river flows at 1 m/s, and power calculations if the pressure water works on micro hydro turbine to produce electric energy. Any one can help?

Thank you
David Matos

[Linear Actuators]

Very useful information for me, thanks for posting.

[oilfield equipment]

wow this is so amazing. what technology can do today.

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