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Tag Archives: wave power

Going offshore (part 1)

Offshore wind energy is booming, with for once the UK in the lead, having installed over 1000 Megawatts (MW) of offshore wind farm generation capacity. Denmark is second in the league table, with 640MW in place, followed by the Netherlands at 250MMW and Sweden at 164MW. But several other EU countries are moving ahead. Belgium, Finland and Ireland all have working offshore projects, while Germany has started up its first large offshore project – it wants 10,000 MW by 2020. France has announced 10 zones for offshore projects off its Atlantic and Mediterranean coasts – it wants to have 6,000MW in place by 2020. However the UK seems likely to stay in the lead – it aims to install up to 40,000MW by around 2020, maybe more.

That’s not to say there have not been problems. Costs have risen, in part because of the increased cost of materials like steel, which in turns reflects the increased costs of conventional energy. And there have been teething problems with some of the designs. A minor fault in the design of the transitional piece which connects the tower to the monopile foundations of the newer machines has been detected, which has resulted in movement of a few centimetres in a number of turbines. Fortunately it is not thought that there is any safety risk or threat to service or output and it’s evidently planned to deal with the as part of the usual rolling programmes of operation and maintenance, with any repairs that are necessary being carried out turbine by turbine, so that there should be no impact on the operation of the rest of the wind farm. The fault evidently does not effect earlier offshore designs.

Clearly issues like this will have to be taken into account in the design of new much larger 10MW machines now being developed. However, one of the newer designs, the 10MW SWAY floating turbine being developed in Norway, won’t face quite the same problem – it’s actually designed to tilt by 5–8 degrees in the wind.

Outside the EU, in 2009 China installed a 3MW offshore turbine, the first unit of a 100MW project. And, after nearly 10 years of sometimes heated debate, the Cape project off Nantucket Sound in New England has at last got the go ahead. It will be the USA’s first offshore wind farm – with 130 turbines. But many others are being considered, including floating versions for use in deeper water. For example, researchers at the Worcester Polytechnic Institute (WPI) have a $300,000 grant from the US National Science Foundations for a three-year on floating wind turbine platforms.

The EU is of course well advanced in this field – with for example the Norwegian Sway device mentioned above, Statoil Hydro’s Hywind and the UK’s 10MW Nova project. There is also the novel floating Poseidon wave and wind platform system being developed in Denmark – a 10MW version is now planned.

But a report released by the US Dept of Energy in 2008, says the 28 US states that have coastlines consume about 80% of all the electricity the US produces, so maybe they’ll have an incentive to push ahead too.

As in the EU, the idea of an offshore supergrid to link up offshore wind projects has also been mooted in the US. Researchers from the University of Delaware and Stony Brook University say that linking Atlantic Coast offshore wind parks with high-voltage direct current (HVDC) cables under the ocean would substantially smooth out the fluctuations. As a fix for intermittency, they say “transmission is far more economically effective than utility-scale electric storage”.

http://www.pnas.org/content/early/2010/03/29/0909075107.full.pdf+html

Currently there are proposals for five offshore wind farms from Delaware to Massachusetts. As plans stand, each would have separate underwater transmission cables linked into the nearest state electric grid. But the report suggest a single, federal offshore Atlantic Transmission Grid would be a better bet. Co-author Brian Colle said: “A north-south transmission geometry fits nicely with the storm track that shifts northward or southward along the U.S. East Coast on a weekly or seasonal time scale. Because then at any one time a high or low pressure system is likely to be producing wind (and thus power) somewhere along the coast.”

http://solveclimate.com/

Offshore wind isn’t the only offshore option. The use of wave energy and tidal streams is also moving ahead around the world, with once again the EU, and the UK especially, in the lead. For example 1,200 MW of wave and tidal current turbine project have just be given the go ahead in Scotland. But US company Ocean Power Technologies (OPT) has been making progress winning contracts for its Power Buoy wave device including one from the Australian government.

Tidal current turbine projects are also developing around the world, for example Ireland’s Open Hydro has linked with Nova Scotia Power to deploy a 1MW tidal turbine in the Bay of Fundy. And the UK’s Marie Current Turbine Ltd is to install a 1.2MW Seagen there too. Meanwhile, South Korea is pushing ahead with a range of ambitious tidal projects, over 2,000MW in all, while businessgreen.com has reported that Israeli marine renewables company SDE Energy recently completed construction of a 1MW wave power plant in China. The $700,000 plant consists of a floating buoy attached to a breakwater. It’s been installed near the city of Dong Ping in Guangzhou province. SDE is also reportedly in the final stages of negotiations over other projects to be built near Zhanjiang City and in the province of Hainan. SDE has talked in terms of ultimately having 10GW of wave energy systems along the Chinese coastline.

It looks like offshore renewables could really become a significant new option.
The big advantage of going offshore is that there is less visual impact. The energy potential is also large – wind speed are usually higher and less variable, and for tidal flow systems, there is a lot more energy in moving water than in moving air. But there may be some environmental impacts (e.g. on fish and sea mammals), something that the device developers are very keen to avoid by careful location and a sensitive design.

However, it is argued that relatively slowly rotating free-standing tidal rotors, or wave energy buoys or platforms, should not present many hazards, while it seems that offshore wind turbine foundations can provide a substrate for a range of sea-life to exploit. As with on-land wind turbines, birds can be at risk of collision with moving wind turbine blades, but observations have suggested that sea birds avoid offshore wind turbines.

Even so, environmental and wildlife impact issues need attention, for example in terms of influencing the choice of location and layout. Overall, a precautionary approach has been adopted: developers have to submit detailed Environmental Impact Statements and there is much research on specific impacts.

http://www.cefas.co.uk/publications/files/windfarm-guidance.pdf

But most of the problems seem to be during the installation process (e.g. noise impacts when driving piles for wind-turbine foundations and disruption during cable laying). Once installed, there seem to be fewer problems, other than possibly sea-bed sediment movements, although navigation hazards have led to some debates.

http://www.offshorewindfarms.co.uk/Pages/COWRIE/

  • A new UK report co-ordinated by the Public Interest Research Group puts the total practical UK resource for offshore wind, wave and tidal power as 2131TWh p.a. (six times current UK electricity use: www.offshorevaluation.org). I’ll be looking at that in a subsequent blog.
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Wave and tidal power – which will win?

Wave power and tidal current turbine technology, if successfully developed, could supply the UK with about 20% the electricity it needs and possibly much more. The UK has one of the world’s best resources, but there are also significant potentials elsewhere. For example it has been claimed that the US could generate 10% of its electricity from wave and tidal schemes.

Wave power was the initial leader – the UK launched a R&D programme in the 1970, with some scale model devices being tested in open water. However we then lost a couple of decades following the withdrawl of government funding for most of the work in 1982 and for the remainder in 1994. Work on Tidal power was also halted – the emphasis at that time being on large tidal barrages across estuaries. Now however, all three options, wave, tidal-current turbines and tidal barrages, are back on the agenda, with the UK still being in the lead, just.

Tidal current turbines seem to have the edge in many ways. Whereas with wave energy you are trying to extract energy from a chaotic interface between water and air with multiple energy vectors, with tidal flows, a few metres under the sources, you have nice laminar flow and a more stable environment. And whereas with barrages you are in effect blocking an entire estuary, with freestanding tidal turbines you are only intercepting parts of the flow, so the environmental impact is much lower.

It’s perhaps not surprising then that there are reputedly 150 or so tidal projects at various scales under tests around the UK. Most are small lab tests but some full-scale systems are now in place – notably the 1.2 MW Seagen tidal turbine in Strangford Loch, Northern Ireland. That has now been signed up to received Renewable Obligation Certificates for the power it feeds the grid. A 10 MW tidal farm is now planned off Anglesey. Next in line is the novel “Open Hydro” open-centred turbine device, the Pulse Tidal oscillating hydrofoil system, the “Lunar Energy” ducted rotor device and Neptune’s vertical-axis “Proteus” ducted rotor.

There are many others under test – for example TidalStream Ltd reports that their unique tidal-turbine platform design – Triton – has successfully undergone validation testing at the deep-water test basin at Ifremer in Brittany, France. Meanwhile Swanturbine’s Cygnet device is being be assembled at Swanturbine’s facilities in South Wales ready for deployment at the European Marine Energy Centre Tidal Test Site (EMEC) in Orkney. A 1.8 MW full-scale machine is under development. And ScotRenewables, located on the Orkney Islands, has raised £6.2 m to build a working prototype of its floating tidal turbine. An 8-metre long prototype will, it’s hoped, go into the water at the EMEC in 2010. Commercial versions would weigh 250 tonnes, and have generation capacity of 1.2 MW.

There are many more projects emerging elsewhere in the world, such as Clean Current’s ducted rotor and Verdant Power’s propeller units, as well as some novel ideas like Indigo Pearl Marine’s open centre “Mer” Vertical Axis Turbine tidal device, while Atlantis, who had already developed a ducted rotor system, have just announced details of a new double-rotor propeller unit, with contra-rotating blades.

But wave energy is not out of the race. The leader is the UK developed Pelamis wave snake system – a 2.2 MW version of which was installed in Portugal. There have however been minor hitches with this system as you’d expect with any new technology – and money for new projects is tight. But new ideas for wave energy are emerging. Cornish wave power developer Orecon has won a contact to install three of its 1.5&nnbsp;MW wave devices off Portugal. Meanwhile a 350 KW version of Aquamarine’s Oyster sea bed mounted “hinged flap” inshore system has been under test in the UK. Next will be a 2 MW demonstration unit, to be expanded if all goes well to 10 MW in 2012. Cardiff-based Tidal Energy Ltd meanwhile is about to test its DeltaStream wave device.

A clever new idea is the 500 kW Wave Treader (developed by Aberdeen-based Green Ocean Energy), which is a new wave unit designed to be attached to an offshore wind-turbine tower, adding to its energy output while sharing the infrastructure costs of cabling and foundations. And Web Engineering in Wiltshire have developed and patented a Sea Wave Energy Accumulator Barge, a novel variation to the “overtopping” reservoir wave-energy concept, but fixed to the sea bed, unlike the floating Danish “Wave Dragon” system.

Progress is also being made on the novel Danish Waveplane concept, which has a series of slots, in three rows, with the higher waves reaching the top row of slots, the rest going into the lower ones. The captured water is let tangentially into a horizontal pipe in such a way as to create a spinning vortex of water, which drives a turbine.

Even so it’s certainly not always straight forward to develop new ideas. For example, the UK’s Trident Energy has been deploying its novel linear motor based wave device for testing off the Suffolk coast at Southwold, but its 20 kW demonstration device sank when being taken out to sea.

Moreover, while small wave and tidal systems may be interesting, there is still inevitably a major focus on large tidal barrages, if nothing else because of their scale-like 11-mile long 8.6 GW barrage proposed for the Severn estuary. A new round of consultation on that and its rivals is planned and interest is still being shown in smaller barrages elsewhere in the UK, including the Mersey, Solway Firth, the Wash and the Humber.

The UK maybe at the forefront in tidal power and also wave power but the potential elsewhere is also large – especially for tidal. For example, Tidal Today’s second annual Tidal Summit held in London in November was told that South Korea’s theoretical tidal resource was up 1000 GW, and they have some ambitious projects underway or planned, including nearly 2 GW of tidal range projects and 100 MW of tidal current turbines.

That’s not to say that wave power is out of the running – there are many projects underway around the world, including a range of tethered buoy systems, and in the UK work is in now underway on the £42 m Wave Hub project 10 miles off the coast of North Cornwall. The seabed “socket” can take up to four devices at any one time for field testing, without the need for them to build additional grid links. That could speed up the development wave power.

For updates on these and other renewable energy projects, visit www.natta-renew.org.

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