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Tag Archives: wave power

Whatever happened to wave power?

By Dave Elliott

‘The average rated capacity of wave energy devices over the past three years (2015-2017) was 70% lower than (in) the period between 2000 and 2014. In contrast tidal stream saw a 124% increase in the average rated capacity during the same period’. So says a report from Imperial College London and Strathclyde University, looking at what went wrong with the UK wave energy programme.


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EU Renewables round up

By Dave Elliott

Renewables are roaring ahead in Europe, with wind at over 140GW and PV surpassing 100GW. There have been some spectacular successes, with renewables briefly supplying 87% of German electricity at one point, and Portugal achieving similarly high contributions-something that’s a regular occurrence in Denmark. But progress may soon be slowed as  economic pressures mount and political reaction sets in with support schemes being withdrawn or constrained. For example, in Germany it’s all change as the government revises the Energiewende energy law with a slow down for wind and solar expansion, via annual capacity caps and reduced support levels. Portugal has also started to phase out its support for renewables, although not quite so aggressively as happened in Spain, or, for that matter, the UK. (more…)

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Innovation: new energy for the UK

By Dave Elliott

Technological innovation is exciting but risky: blue skies thinking can open up possibilities, but they also have to be tested against reality. It’s easy to get deceived by early hopeful predictions of potential success and allegedly ‘game changing’ developments. We are regularly hit by blasts of enthusiastic coverage of hi tech innovations in the energy field, but not all of it will prove to be viable (more…)

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Down on wave and tidal farms

By Dave Elliott

In my last post I looked at how solar farms were being constrained in the UK. But they are not alone. Marine renewables are also facing problems. Tragically, pioneering wave energy company Pelamis has gone into administration, after failing to secure development funding. And Siemens is to sell off Marine Current Turbines (MCT), the pioneering UK tidal company it look over in 2012, due to the slow pace of orders. Aquamarine Power, who have developed the Oyster inshore wave device, is also to “significantly downsize” its business. (more…)

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Energy return on energy invested

by Dave Elliott

There is inevitably some energy ‘embedded’ in energy generation systems, and it is useful to compare the energy needed to build and run plants relative to the useful energy out, but estimating ‘Energy Returns of Energy Invested’ (EROEIs) can be tricky. The ratios can range up to 200:1 or more, and down to single figures- very worryingly since then it is hardly worth running the plant.


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Wind power reliability

by Dave Elliott

Earlier this year (26/6/13) Daily Telegraph columnist Geoffrey Lean said that ‘it has become an article of popular faith that building wind farms also involves constructing fossil-fuelled power stations for back‑up when the weather is calm. As a result, some opponents go on to say, wind turbines do little or nothing to cut carbon dioxide emissions’.  But he reported that the National Grid says that, although between April 2011 and September 2012 wind produced some 23,700 gigawatt hours of electricity, only 22GWh of power from fossil fuels was needed to fill the gaps when the wind didn’t blow- under 0.1%. Moreover this standby burning of fossil fuels only reduced the emission saving from having wind on the grid by 0.081%. He commented ‘not surprisingly, given these figures, no new fossil‑fuel power station has been built to provide back‑up for wind farms, and none is in prospect’.


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UK marine renewables

By Dave Elliott

A report by RenewableUK says that electricity market reforms could act as a springboard for the growth of wave and tidal energy, or could undermine investor confidence in marine power at a crucial stage of the industry’s development. It also highlights challenges such as delays in getting grid connections for wave and tidal projects, and the high cost of transmission charges.

The report, Conquering Challenges, Generating Growth, lays out the progress made so far: 12 full-scale single devices with a capacity of 9 MW deployed in UK waters generating clean electricity – more than the rest of the world combined. It notes that commercialization of the tidal sector is just around the corner, with the deployment of the first arrays (multiple devices) beginning in 2014, and an expected increase to 100–200 MW of wave and tidal installed by 2020. Major engineering firms such as Siemens and Alstom are working with the UK and Scottish governments, universities and electricity companies to develop British marine power. The Crown Estate has awarded leases for more than 1.8 GW of capacity at nearly 40 sites in UK waters. The British Isles has 50% of the total European wave-energy resource and 25% of tidal-energy resource – these technologies could generate up to 20% of the UK’s electricity needs.


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New wave-energy technology

Wave energy is developing rapidly, but perhaps not quite so rapidly as tidal-current systems – in part since it’s harder to develop devices that can extract energy from the chaotic multi-vectored energy pattern that exists at the interface of the sea and the air, than from the smooth laminar tidal flows further down.

However, there are already some clear winners more or less fully developed, like the UK’s Pelamis wave snake, the near shore Oyster hinged wave flap and Wavegens oscillating water column (OWC) system. In addition, Australian company Oceanlinx has developed a variant of the OWC concept and there are many buoy type systems, like that developed by US company OPT. But there are also a host of less well known and sometimes novel ideas emerging and being tested. For example, Wave device developer Wello Oy is testing a 500 kW device at EMEC on the Orkneys. Called the Penguin, it is a floating asymmetric vessel which houses an eccentric rotating mass, mounted on a vertical shaft.

A perhaps simpler approach is to use wave motion to power hydraulic pistons, as with the Sea Dog pump developed by Independent Natural Resources Inc in the USA ( In the UK Ecotricity is backing a bicycle pump-like ‘Searaser’ piston device, which, similarly, pumps sea water to shore, possibly up into a reservoir on a hill, so that electricity can be generated via a turbine when required. They may test a prototype soon off Falmouth:

Floats or buoys of various designs are clearly still popular ways to extract energy from the rise and fall of the sea. Some systems, like Clearpowers Wavebob, can be tuned to match different wave frequencies. Perhaps less familiar is the CETO system, which has an array of submerged buoys tethered to seabed pump units. The buoys move in harmony with the passing waves, driving the pumps which pressurise water that is delivered ashore via a pipeline, to drive hydroelectric turbines. The high-pressure water can also be used to supply a reverse osmosis desalination plant, replacing electrically driven pumps usually required for such plants. More at:

Somewhat similar is Atmocean’s Wave Energy Sequestration Technology (WEST) system which consists basically of small buoys connected to one another over a stretch of ocean. They are planning to install 10 to 20 units 60 miles off the coast of New Jersey.

A more complex version has been developed by 40southenergy, with a part submerged unit, at a depth between 15 and 25 meters (depending on model type and site) called ‘Lower Member’, and one or more parts submerged at a depth between 1 and 12 meters (depending on sea state) called ‘Upper Members’. The relative motion between Upper Members and Lower Member is converted directly into electricity. A full scale 100 kW prototype, the D100t, has been in the water since Aug 2010.

The conventional OWC concept has also be revisited: Dresser-Rand working with Cranfield University have developed a variable radius turbine called HydroAir, which is said to be more efficient and flexible than the normal two-way Wells turbines used in OWC.

Some devices make use of fixed platforms, with wave energy absorbers underneath, like Buldra system developed by Fred Olsen. Australian company, AquaGen Technologies has come up with a SurgeDriv system, which has a series of floats linked with tension cabling via the seabed and then to a generator on a platform above the sea surface, thus keeping as much of the infrastructure out of the water as possible. The floats can be retracted below the surface to ride out storms. It has a 1.5kW demonstration system at the Lorne Pier in Victoria.

Portuguese company ‘Sea For Life’ has developed a ‘gravitational wave-energy absorber’, WEGA. It has an articulated suspended body, semi-submerged in the water attached to a mount structure via a rotary head, which allows it to adapt to the direction of the waves: so it oscillates in an elliptical orbit. Power is extracted via an hydraulic cylinder, which pushes high pressure fluid through an accumulator and a motor, to drive a generator. Multiple devices can be placed on a single mount structure. The hydraulic motor and electric generator are on top of the mount structure, which protects them from the elements and enables easy access for maintenance.

Fully submerged systems also have their attractions – they can follow the circular motion of the waves under the surface. US Air Force Academy researchers in Colorado Springs have demonstrated that submerged energy converters can harness up to 99% of the kinetic energy inherent in an ocean wave. Dr. Stefan Siegel has developed a fully submerged cyclodial wave-energy conversion device, with funding from the National Science Foundation.

Ideas for smoothing out the energy absorbed from waves are also being explored. For example, the floating Danish Waveplane has a series of slots designed to catch waves at different heights, the captured flows then being used to create a vortex to drive a turbine. In the UK, Ecotricity are backing the Snapper linear motor wave unit invented by Prof. Ed Spooner at Edinburgh University. It has magnetically tripped springs storing burst of energy. The project is being co-ordinated by Narec with an EC FP7 grant.

Finally, Danish company Floating Power Plant is developing a 10 MW commercial version of their Poseidan prototype hybrid wave/wind device. Poseidon is basically a floating, anchored, platform, which can accommodate both wave-energy converters and wind turbines. It is claimed that it can achieve an efficiency in transforming inherent wave energy to electricity of 35%, and should be able generate 28 GWh per year if located in the Portuguese part of the Atlantic Ocean. A 37 meter wide 25 metre long 350 tonne model was tested at the Vindeby wind park, off Lolland coast in 2008. The wave system is based on a hydraulic power take-off system, using a double function piston pump to transform the energy from the wave into water pressure that is then sent through a turbine, thus generating electricity.

The wave-energy field is clearly still is a state of creative flux, with many rival ideas under test – the above is just a sample. It will be interesting to see which pan out.

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Marine Renewables – end of year report

Offshore renewables have been doing well- notably offshore wind (see my Blogs earlier this year) now nearing 1.5G off the UK coast, but also tidal current turbine systems. MCT’s 1.2MW SeaGen has been earning ROC’s in Strangford Narrows, Northern Ireland. And dozens of other tidal current devices have been under test, some at full scale (1MW and above), including Neptunes ducted vertical-axis Proteus rotor system (in the Humber), and Open Hydro’s Open Centre turbine (in the Bay of Fundy) . Meanwhile, Pulse Tidal is looking to install a 1.2MW version of its novel twin hydrofoil device off Skye in Scotland, and Hammerfest Strom UK has developed a 1MW version of its turbine which is to be deployed in Scotland. The largest unit developed so far is Hydra Tidal’s 1.5MW multi-rotor tidal device, being tested off the Norwegian coast.

Wave energy had a somewhat less good year. Although the 600kW in-shore Oyster wave flap device has proved very successful, the leading wave device, the Pelamis segmented wave-snake, three units of which had been installed of Portugal in a 2.25MW tidal farm, had technical and financial problems. In addition, the giant 2.5MW Oceanlinx project Oscillating Water Column prototype fell foul of heavy weather just off the coast of Australia at Port Kembla, and was wrecked – much like the UKs 2MW Osprey, with which it shared some features- back in the 1980’s.

Waves are clearly harder to tame than tidal flows, with even novel designs sometimes not doing so well- Tridents 80 tonne 20kW linear motor prototype sank off East Anglia back in Sept 2009. And even what you would think was a robust design, Finavera’s prototype buoy system, sank off the Oregon coast just before its 6 week test period ended.

However, lessons are being learnt, with wave developers pressing on- the Mk 2 750kW Pelamis P 2 is being deployed at EMEC in Scotland with backing from E.ON, along with Oyster 2, an enlarged 2.5MW version of Oyster wave flap, and the Wave Hub undersea power socket off North Cornwall is now open for business. Wavegen is also moving ahead with its 4MW in-shore Siadar project off the Western Isles. And, as with tidal current turbines, new ideas are emerging all the time, like the clever Wave trader device that is attached to the bottom of the tower of an offshore wind turbine, and shares its grid link to shore. And elsewhere in the world, there’s Portugal’s WEGA ‘gravitational wave energy absorber’, and in the USA, Atmoceans WEST Wave Energy/Sequestration Technology, using buoys, and Florida Tech’s ‘wing wave’ system, using a sea-bed mounted flap.

We need all we can get of both wave and tidal of course, so there is no direct competition. Earlier this year The Crown Estate allocated Scottish sites for over 1.2 GW of wave and tidal current projects on an equal basis, and the UK governments new £22m Marine Renewable Proving Fund supports each type equally, as does Scotlands new £12m funding. Nevertheless, PIRC’s Offshore Valuation claims that, contrary to earlier assessments, the practical tidal current resource (now put at 33GW) is actually larger than the wave resource (18GW), so maybe the former will dominate in the UK.

Elsewhere it may be different: wave projects are moving ahead around the world- OPT are doing well, and there is talk of a 10GW wave programme in China. But South Korea seems to be focusing on tidal, as does Canada – e.g. in the Bay of Fundy. Basically it comes down to the physical resource, and, the tidal regime in both these places, as in the UK, is large. Canada and the USA are both supporting tidal projects on the NE east coast.

In Korea, although several tidal current projects are underway, the emphasis is on tidal range projects, and tidal barrages and lagoons did figure in some UK plans, notably for the Severn estuary e.g the 8.6GW Severn Tidal Barrage, despite it being opposed by all UK environmental groups. Smaller less invasive barrages concepts have also re-emerged for the Mersey and Solway Firth, although they have also attracted opposition. Moreover, the PIRC study put the UK tidal range resource at only 14GW- not insignificant, but smaller than wave and certainly less than for tidal currents. Tidal range was also seen as the most costly option.

Looking at all the options long term, the Department of Energy and Climate Change produced a 2050 Pathway report which had wave and tidal stream capacity running neck and neck in their maximum ‘Level 4’ programme- delivering 70 TWh and 69TWh p.a by 2050 respectively, with 58GW in all installed. However, DECC made clear this it felt this was very optimistic- the most that could be realistically conceived. Their lower level 3 programme only had 29 GW of wave and tidal stream (68 TWh) and level 2, only 11.5GW (25TWh). For comparison, tidal range was put at 1.7GW (3.4TWh) at level 2, 13 GW (6TWh) at Level 3 and 20 GW (40 TWh) and Level 4, by 2050- all much lower than wave or tidal stream . Perhaps then it wasn’t surprising that when the government finally published its long await review of tidal projects for the Severn estuary, tidal range was seen as unattractive, and not to be followed up at this point.
With that out the way, we might expect more progress on tidal current projects, although we can also expect problems and technical glitches. For example, Open Hydro’s 1 MW test project in Nova Scotia, installed in 2008, has had to be extracted a year ahead of schedule, after blade failure. And just before it was due to be tested at EMEC, faults were found in the blades of the 1MW Atlantis double rotor tidal turbine system. But they evidently were replaced and space has now been allocated for a 400MW project in the inner sound area of Pentland firth, bringing the total planned wave and tidal deployment there to 1.6 MW by 2020.

There are many other new ideas emerging. One of the most intriguing is the tidal kite- being developed by Swedish company Minesto. It’s an aerofoil wing, with a rotor and generator mounted on it, which is tethered to the sea-bed but free to move under the tidal flow. However it doesn’t just stay in one place, but moves rapidly in a figure of 8 glide pattern under the influence of the tether, a rudder and the lift forces created by the tidal flow. That means the rotor turns faster than if it was simply in the tidal flow- in fact, it’s claimed, up to10 times faster. Given that, unlike other tidal devices, it doesn’t need expensive foundations or towers, it ought be to be cheaper, and less invasive, and there should be many locations where it could extract power from relatively low tidal flow- thus, in effect, expanding the potential tidal resource. A prototype is to be tested off Northern Ireland

Perhaps even more exotic, one of the new concepts supported under the governments Seven Embryonic Technology Scheme, and then backed as a long term possibility in the DECC review of Severn Tidal options, is the Spectral Marine Energy Converter, SMEC, developed by VerdErg. It’s based on the venturi effect – creating a low pressure area via vanes mounted in the tidal flow, which can be used create higher flow rates in a secondary flow, to drive a turbine. This concept could be used in cross-estuary tidal fences and may offer a way to extract energy from tidal flows without having major environmental impacts. So a Severn barrage, of sorts, or a project elsewhere (e.g. on Solway Firth) may still be on the cards, although the idea can also be used at smaller scale, e.g. in shallow river locations

The above is based in part on the end of year Annual Supplement to Renew:

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Going offshore (part 2)

The UK offshore wind, wave and tidal power resource could supply about six times current levels of electricity demand, and even if we only exploited part of it, the UK could become a net exporter of power, according to the first comprehensive assessment, The Offshore Valuation produced by an informal collaboration of government and industry organisations co-ordinated by the Public Interest Research Centre (PIRC).

Drawing on published data, it puts the total practical offshore resource at 2131 TWh p/a from 531 Gigawatts (GW) of generating capacity, 406 GW of which would be wind capacity. England had 54% of the total practical resource (286.5 GW), Scotland 39% (206 GW) and Wales 7% (39.5 GW), with wind power dominating in each region.

PIRC point out that their scenarios “are neither predictive nor prescriptive” but calculate that, even if only 29% of the total resource was exploited, by 2050, the UK could have 169 GW of offshore capacity, supplying 610 TWh, equivalent to total electricity consumption by that time, making the UK a net electricity exporter.

Most of the supply capacity (116 GW) would be conventional sea-bed mounted offshore wind but there would also be 33 GW of floating wind turbines, further out to sea, plus 5 GW of wave, 9 GW of tidal stream and 6 GW of tidal-range projects. This would create 145,000 new jobs, provide the Treasury with £28 bn in tax receipts and reduce carbon emissions relative to 1990 levels by 30%.

Under a more ambitious scenario, utilizing 76% of the total practical resource, by 2050 there could be 406 GW of offshore capacity generating 1,610 TWh – about the same as total UK energy demand (not just the electricity demand) expected by then. That would involve an additional 212 GW of floating offshore wind capacity, while wave would rise to 14 GW, tidal stream to 21 GW and tidal range to 10 GW. The jobs total would rise to 324,000, most of these being for the floating wind turbines.

Some of the scenarios are clearly very ambitious. Even using just 13% of the total, to supply 50% of UK power would need a 34 GW mix of back-up/storage/interconnector links to balance variable supplies, and if higher percentages were used then more cross-channel interconnection would also be needed for exporting excess power – 85 GW for the 169 GW scenario and 321 GW for the 406 GW scenario.

So what would it cost? Using DECC figures, PIRC estimates that the 169 GW scenario would cost £443 bn but calculates that in 2050 it would earn £62 bn p.a in net electricity exports. The 406 GW scenario would cost £993 bn and earn £164 bn p.a. Most of the technologies cost £100–125/Mh initially but get cheaper (10% p.a “learning rates” are assumed), though wave and tidal range are more costly, at ~ £175/MWh.

Most of the technology exists or is under development, but floating offshore wind turbines are relatively novel and clearly play a major role in the more ambitious scenarios. As noted in my previous offshore wind blog entry, some floating systems are already under development but there may be limits to what can be obtained from them. The PIRC report states: “The technical limitations of current designs restrict floating wind to water depths of between 60m and 700m. There has also been some concern that it will not be possible to install floating wind beyond 100nm from the coast due to the time taken to get to and from the site.” Also “access for installation and maintenance may be limited”. Of course, the longer undersea grid links to land will cost more. Even so, the resource is huge. The PIRC puts it at 870 TWh/yr, with a further 660 TWh/yr available beyond 100 nm out. That compares to 180–240 TWh/yr for conventional fixed offshore wind, additional to current site allocations.

The resource for wave and tidal range (barrages/lagoons) is seen as much smaller, at 40 TWh/yr and 36 TWh/yr respectively but that for tidal streams is seen as more significant at 116 TWh/yr. This is larger than some previous estimates. The PIRC says: “Until recently the UK’s practical resource had been estimated to lie within the range 4–30 TWh/yr. However, academic research has since highlighted uncertainty in both the underlying methodology and the assumptions used to estimate this resource, which has had the impact of increasing this range to 4–110TWh/yr.” It notes that the “kinetic energy flux” method is widely used (e.g. by Black and Veatch) but Stephen Salter’s “bottom friction” and David MacKay’s “shallow wave” method both give a factor of 10–20 more. To navigate these uncertainties a “bottom-up” calculation was employed by the PIRC to get the technical resource and this was then reduced by 60% to provide an estimate of the practical resource. It was put at 33–200 TWh/yr, corresponding to a power density of 5 MW/k sq m and 30 MW/k sq m respectively. The average of this range – 116 TWh/yr – was used in the report.

The group behind the report, co-ordinated by the PIRC, included the UK, Scottish and Welsh governments, the ETI, the Crown Estate, E.ON, DONG, RWE Innogy, Mainstream Renewables, RES, Scottish and Southern Energy, Statoil, and Vestas. The government’s Climate Change Committee also provided some support.

Tim Helweg-Larsen, director of research at the PIRC, said: “To discover that we own a resource with the potential to return the UK to being a net power exporter, and on a sustainable basis, is genuinely exciting, and a wake-up call to those in a position to foster the further development of this industry.” But, to put the UK on a path that allows it to access its “substantial and valuable” resource, the PIRC said that Round 3 offshore wind grid connections would have to be made “super-grid compliant” to enable potential future electricity sales to Europe. The PIRC wants the government to take a leading role in the current EU super-grid negotiations, to ensure that the UK derives maximum value from its design and implementation. The domestic supply chain would also have to be developed to enable economic deployment at scale, while new financing structures would have to be created to support the scale and pace of the industrial growth required.

Peter Madigan, head of offshore renewables at trade association RenewableUK, said that “we have long been saying that the North Sea will become the Saudi Arabia of wind energy” and the results of this study “amply bear this out”.

As I discussed in my previous blog entry on this topic, environmental impacts must of course be considered. For example, offshore systems have the potential for significant effects on marine wildlife, including dolphins, porpoise, grey seals and wildfowl but a range of environmental studies have been completed or are in hand and so far no major problems seem to have emerged that cannot be limited with by sensible design, location or mitigation measures. So it does seem that the UK could be on to a winner.

Source: PIRC

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