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. www.offshorevaluation.org/
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. http://environmentalresearchweb.org/blog/2010/11/barrage-sinks.html
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 www.minesto.com
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 www.verderg.com.
The above is based in part on the end of year Annual Supplement to Renew: www.natta-renew.org