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Renew your energy: January 2011 Archives


For moment the EU leads the offshore wind field, with nearly 3GW in place, 1.3GW off the UK coast. The world's largest offshore wind farm is currently the UK's 300MW array at Thanet, in the North Sea. But the 500MW Greater Gabard project 23km off Suffolk is coming along and the 1GW London Array in the outer Thames estuary will top that, and many more are planned off the UK and also elsewhere, for example France is now looking for 30 sites for 3GW of offshore wind and wants 6GW by 2020. Overall, nearly 20GW has now been consented in EU waters. The longer term EU potential is put at maybe 150 GW, or much more, given newly emerging deep-water technology, allowing for location much further out in the North Sea and elsewhere, for example, off the coast of France, Spain and Portugal.

Although some projects are now emerging off New England, the US has been slow to develop offshore wind projects, in part since, unlike the UK and some other EU countries, it doesn't have shallow water off its (east) coast. But deep-water technology solves that problem and, as in the EU, opens up a very large resource.

Deepwater Wind, a company based in Providence, Rhode Island, has drawn up plans for what could be the largest wind farm in U.S. waters – a 1GW Deepwater Wind Energy Center with 200 turbines off New England, which would cost $4–5bn. It would use 5MW turbines mounted on four legged platforms 18 to 27 miles off the Rhode Island coast at a depth of 52 meters: more than twice that of conventional steel 'monopole' wind turbine platforms.

As water depth increases, the diameter of monopoles must increase exponentially, making them uneconomical in water deeper than about 20 meters. By using a four-legged design, the company says they will be able to work in depths that were previously prohibitively expensive. And being far out to sea there should be fewer problems with objections over visual intrusion- a major issue so far in New England. More: www.dwwind.com

The basic deep-water technology, involving structures with multiple legs, was originally developed for oil and gas platforms and a version has already been used for some deep-water offshore wind turbines in the EU e.g. the Beatrice 2 x 5MW turbine project off Scotland. So-called 'tension leg' technology, with typically four semi-submersible piles tethered to the sea-bed, has been used. The 2.3 MW Dutch Blue H turbine, tested off Italy, used this concept. And in Portugal, EDP is developing a 2 MW WindFloat with three legs, while in France Nénuphar, Technip, and EDF are developing a novel Vertiwind device, with vertical axis wind turbine mounted on three legs. After work on a prototype, they hope to test a full scale 2MW device at sea in 2013.

If you want to go even further out and into deeper water then you need fully floating systems, like Norways Sway and HyWind, which, it's claimed, can operate in depths of between 120 and 700 metres. See my earlier blog.

Sway is about to start testing a scale prototype of its proposed 5MW floating turbine off the coast of Norway at site near Hordaland. The Sway turbine can tilt by 5–8 degrees from the vertical.

Although, a 2.3 MW version of HyWind has already been tested,10km off Norway, in general fully floating device technology is relatively undeveloped. But hopefully not for long. In addition to the work mentioned above, 19 partners from 8 EU countries, under the direction of the Fraunhofer IWES, have entered the conception phase for HiPRwind, the largest publicly funded research project for the development of enabling technology for deep-water offshore wind, with €11 m contributed to the €20 m 5-year project by the European Commission.

That's in parallel with the EU's £3m DeepWind Vertical axis Darrieus ('egg beater') type floating 10MW wind turbine project led by RISO in Denmark, Spain's 50MW floating wind project 30km offshore in depths up to 100m, and the UK's novel V-shaped vertical axis 10MWAerogenator X, developed out of the ETI's Nova project.

China is also developing offshore wind technology. Its first offshore wind farm, a 102 MW array near Shanghai, is being followed by others Construction of a 1GW offshore wind farm in Bohai Bay, around three hours from Beijing, is expected to be complete by 2020. The Government has invested €1.6bn in the project, which is being managed by the state-owned China National Offshore Oil Corporation.

However, they are not currently looking far out to sea. As I reported in a previous Blog, they are looking at what they see as less risky and more commercially viable near-shore options: http://environmentalresearchweb.org/blog/2010/12/offshore-wind-costs.html.

In particular, with a potential 100 to 200GW being available in extensive tidal flats, the emphasis in China in the short term is on intertidal projects. There should be at least 10GW of installation by 2020 in Jiangsu province. A 30MW pilot project is under construction there and a 300-MW may follow, using 3.6MW turbines and a novel five pile support structure to cope with the tidal flat's muddy seafloors and shifting sandbars.

www.technologyreview.com/energy/24978/?mod=related

It's hard to know if deep-sea wind will prosper. If they can be developed successfully, floating wind turbines can be towed out to be located on station, and so can avoid some of the large deployment costs associated with drilling piles into the sea bed, and they can also be brought back to harbour for maintenance, avoiding the difficulty and cost of getting access at sea. But there are significant extra costs with longer undersea grid links. However, if and when a full North sea supergrid network is established, then some of these costs would be shared with other projects, and the system as a whole would earn more income by being able to transfer power between the UK and the other EU countries involved with the supergrid: see http://environmentalresearchweb.org/blog/2010/12/the-north-sea-supergrid.html.

District heating networks, using gas, waste heat from power stations or heat from biomass combustion, to heat houses and other buildings collectively, are common across much of continental Europe, especially in the North. There are also some large solar-fed heat grids and many heat stores. There are even some inter-seasonal heat stores, which help to deal with variable supplies over the year, and variable demand for heat, e.g. during winter evenings. See my earlier blog.

More district heating projects are proposed. For example, 'Heat Plan Denmark' a study financed by the Danish District Heating Association, argues that District heating is the key technology for implementing a CO2 neutral Danish heating sector in a cost effective way. They claim that the Danish heating sector can be CO2 neutral by 2030 by upgrading and expanding the existing system, with, for example, heat pumps being used to upgrade the heat energy currently supplied and more heat stores being added. At present much of the system still uses gas as the main energy input, but they look to the use of more renewables, and more efficient waste-to-energy Combined Heat and Power (CHP) plants with flue-gas condensation. So the emphasis will shift increasingly to using large-scale solar heating, biomass /biogas CHP, geothermal energy and excess wind energy – and more heat storage.

Overall, they see district heating moving up from 46% to 70% of the market share, and suggest that the remaining heat market can be covered by domestic-scale heat pumps and wood pellet boilers in combination with individual solar heating. However, they claim that district heating combined with CHP plants and larger scale renewable energy is more cost effective than domestic-scale solutions based on more investments in the building envelope and/or in individual renewable energy solutions. More at www.danskfjernvarme.dk.

A similar conclusion emerged from a study of district heating in Copenhagen, which has the world's largest heat network, currently fed mostly by 10 CHP plants with a total of 2 GW of heat capacity. About 45% of the fuel is from renewable sources (biomass/wastes), and that proportion is planned to expand. In addition to using geothermal heat, they are testing a demonstration solar plant to deliver solar heat to the district heating system, with a heat pump being used to raise the temperature of the water from the solar panels, or a linked heat storage tank, before the heat is delivered to the district heating network.

By contrast, we have a long way to go in the UK. Heat accounts for about 44% of UK energy consumption, mostly for heating homes and providing hot water, using individual domestic boilers – 84% of UK homes are heated by gas. This may change as and when the Renewable Heat Incentive (RHI) and the Zero Carbon Houses programmes kick in and domestic-scale solar, biomass micro-CHP and so on are taken up. But what about the larger scale and all of the waste heat from power stations?

The UK's total demand for heat is about 800 TWh p.a., about the same as that released by all power generation/industrial processes as waste. So far, with gas being relatively cheap, Combined Heat and Power, which can reclaim much of this waste, has not lifted off very significantly in the UK, a few biomass-fired plants aside. Neither has district heating or heat storage. But with gas prices rising and concerns about emissions growing, heat reclamation and storage ideas are now being explored-borrowing from what's happening elsewhere in the EU. For example, the Energy Technologies Institute is looking at waste heat collection and storage on a large scale. As they note 'It is technically possible to store very large quantities of heat energy below ground in geological structures such as saline aquifers or disused mines. The heat could even be accumulated through the summer to be used during the winter. Many of the potential heat sources and storage areas are close to centres of population and could be used to support large-scale district heating schemes.

And the recent DECC Microgeneration Strategy Consultation also looks at energy storage, and in particular at Underground Thermal Energy Storage (UTES). It includes a mini case-study of a UTES installation in Sweden, which paid back the additional installation cost (compared to an oil fired system) in under four years and continues to save money, energy and carbon year on year. It reported that, as well a tapping heat from power stations, this approach "can be particularly effective to create energy clusters where excess heat from buildings with a net cooling load can be utilised as a source of heat for others nearby with a net heating load to save carbon and reduce energy consumption".

However, DECC's focus seems to be on the smaller scale. It added: "Work is on-going between Sweden and the UK to use similar underground thermal energy storage techniques on a domestic scale." It commented that in the UK: "In the domestic sector there is scope to store hot water generated by renewable energy through the wider deployment of hot water cylinders." But, it said: "74% of the circa 1.5 million boilers fitted annually are 'combination' boilers, so the opportunity to future-proof homes for renewable-heating technologies, through the provision of hot water cylinders, is limited." And it noted that: "There are no plans to set mandatory requirements for the provision of hot water cylinders – there is a trade-off between the benefits of large water volumes needed to bank/smooth renewable-energy supplies and the higher standing losses from large volumes at elevated temperatures. There are also design issues to consider. Larger cylinders weigh more and take up more space and there is a greater risk of stratification. There may also be an increased threat of legionella from water storage facilities, unless the appropriate elimination steps are taken."

So, as seem to be the norm, we are taking it very slowly and cautiously, and focusing mainly (the ETI project apart) on the domestic scale. Ideas like large-scale solar district heating are still evidently heretical. Someone had better tell the citizens of Graz, a city in NE Austria, which has a District Heating network with 6.5 MW of solar thermal input.

The coalition government has talked a lot about decentralisation and supporting small-scale local projects. The preface to DECC's Microgeneration Strategy consultation says: 'There will be a role for small-scale electricity producers in homes, schools, offices and factories around the country to complement the substantial new investments needed in large-scale Carbon Capture and Storage, nuclear and renewable electricity such as offshore wind; a new supply of locally-produced power that spreads the risk and can help make us all more self-reliant. And there will be a step-change in the use of renewable micro-technologies such as heat pumps, as we tackle the single biggest cause of greenhouse gas emissions, the heating our homes.'

The deployment of micro-generation options like micro-wind and PV solar, has been left mainly to the small existing 'Clean Energy Payback' Feed-In Tariff scheme and, for housing, the ZeroCarbon Hub, an agency the government has commissioned to deal with the issue.

In theory, micro-gen will be picked up as and when building and construction companies get to grips with the governments requirement that all new build houses must be 'zero net carbon' by 2016.

However, there is still some uncertainty as to what that actually means. Under pressure for clarification, the Labour administration had indicated that, although the aim was for houses to generate all their own power, some power could still be imported, and the upshot seemed to be that new-build houses were only expected to have to cut emissions by 70%. But now an even more flexible approach seems to have emerged, with only 56%, being required. Evidently, 70% was seen as 'particularly challenging and may not be achievable in all cases,' according to the ZeroCarbon Hub. What that means in terms of how much of their net energy they must get from on-site renewables, still remains a little unclear. The Building regulations are also being 'rationalized', so it's all still rather muddy. See: www.guardian.co.uk/environment/georgemonbiot/2010/nov/26/zero-carbon-homes.

The same goes for the proposed Renewable Heat Incentive, now delayed until June. But, when it comes into force, it could stimulate solar heating, and the use of biomass and biogas in micro CHP units, plus heat pumps and even fuel cells, at the domestic level.

Although it's mainly aimed at remedial domestic energy efficiency projects, some micro-gen options may also eventually get some support from the Green Deal, which aims 'to radically overhaul the energy efficiency of homes and small businesses' by making energy efficiency affordable for all, whether people own or rent their property'. The details emerged in the Energy Bill in December. The scheme is expected to start in late 2012.

The Green Deal is basically a short-term credit system – money is loaned by participating commercial organisations for upgrades, but paid back continually through a charge on their energy bills. As DECC explains: 'The upfront finance will be attached to the building's energy meter. People can pay back over time with the repayments less than the savings on bills, meaning many benefit from day one. It will help save carbon, energy and money off fuel bills.'

DECC added that it's estimated that there are 14 million insulation measures like loft, cavity and solid wall to be carried out; and that the most energy-inefficient homes could save, on average, around £550 p.a. by installing insulation measures under the deal. When the occupier moves on, not only will a more efficient property be left to the next occupier, the charge will also be left behind.

According to Chris Huhne, the scheme could support 250,000 jobs over the next 20 years, from the projected £7 bn of Green Deal private-sector investment per year, assuming all 26 million households take up the Green Deal.

All the above schemes focus mainly on domestic-scale projects and upgrades. Larger community-scale energy supply projects are the focus other schemes like the Community Sustainable Energy Programme (CSEP) – an £8 m open grants programme, run by the Building Research Establishment as an award partner of the BIG Lottery Fund. The Feed-In Tariff also provides support for local community projects – up to 5 MW. And DECC has a 'Community Energy Online' information service.

However, overall, the government does not seem to see community-scale projects as very significant. The new revised National Policy Statement on Energy says: 'The government does not believe that decentralized and community energy systems are likely to lead to significant replacement of larger-scale infrastructure.'

This despite the fact that an earlier report by the Energy Saving Trust ('Power in Numbers') suggested that there were significant economies of scale: 'Little to no benefit is observed in progressing from individual action, i.e. single household, to the five household level, even after the implementation of additional policy support. It is only when action occurs at scales above 50 households, and ideally at or above the 500 household level, that significant carbon savings become available.'

Community-scale projects could, it says, economically meet 4.3% of total UK energy demands if householders were to act collectively. That's 13% of total annual UK household energy demands.

Community projects might get some support from the changes that are proposed in the governments new Localism Bill, which gives councils, communities and individuals a greater say in local planning decisions. But equally it might lead to opposition to the adoption of new technologies large and small ‐ some have seen it as a NIMBY's charter. The bill introduces new rules allowing for local referendums where local people, councillors and councils can instigate a vote on any local issue, including planning proposals; and new powers to allow communities to give planning approval to chosen sites on local land.

It makes sense to use local energy sources to meet local energy needs wherever possible, and there is a lot of enthusiasm for a more decentralised community-based approach, as well as for domestic scale projects. The latter may have it limits, but done properly it can make a useful contribution, not least in alerting householders to their energy use and associated lifestyle energy and eco-issues. Community-scale projects by contrast should also be able to make a much more significant contribution on the supply side, if given proper support. So far though that seems rather patchy. However, Housing Minister Grant Shapps announced recently that the government would look into developing a community energy fund to ensure that new homes built after 2016 are carbon neutral.

Neil Crumpton has outlined an ambitious bio-energy future, based on solar driven bio (algae) oil production, and the use of Carbon Capture and Storage (CCS) to achieve carbon-negative energy generation.

While he sees Concentrated Solar Power and wind power as major global energy solutions, he believes that combining desert-based algae production with CCS could become a global scale carbon-negative climate solution.

He sees Seawater Greenhouses or similar desert-based low-tech structures as potentially ideal for algae production in photo bio-reactors.

The 'Seawater Greenhouse' is a solar-driven technology which uses adapted greenhouses (low-cost polytunnels) to desalinate seawater in arid regions to provide suitable growing conditions for food – or energy crops like algae.

Seawater is evaporated by drawing the hot desert air through a wetted cardboard wall in one side of the greenhouse. The cooled humid air passes over the crops and condenses to provide water for the crops. The humid air is then expelled from the greenhouse and can be used to improve the growing conditions for nearby outdoor plants: www.seawatergreenhouse.com. Sunny locations near the sea would obviously help, but the cost of piping sea-water long distances inland may not be significant.

The 'Sahara Forest project' is a supercharged variant of this concept, which would link huge greenhouses, potentially for growing algae, with concentrated solar power (CSP), which uses mirrors to focus the Sun's rays and generate heat and electricity. The combination of these desert technologies would provide more energy for evaporation, pumping and algae production – and desalinated water for mirror cleaning, CSP cooling and algae production.

Further potential synergies could lead to higher bio-oil yields, says Crumpton. The thermo-chemical liquefaction and the trans-esterification of the algae 'soup' to produce bio-diesel could be achieved by heating some algae types to 300 °C under pressure for 30 minutes – just the job for CSP technology: www.futurity.org/earth-environment/pressure-cook-algae-to-make-better-biofuel/. Also, reject CSP heat could be used in power direct CO2 air-capture devices and the CO2 could be bubbled through the algae soup to enhance production.

Crumpton says that by 2040 bio-oil from such desert-based bio-energy systems, if proven, could be shipped to gas turbine or fuel cell/CCS gasification schemes in countries with more variable renewable energy resources (e.g. Europe), to provide reliable and carbon-negative daily grid back-up and strategic energy reserves.

By 2040, bio-oil importing countries could have extensive CCS infrastructure, deployed initially to abate gas and coal power stations and industry in the 2020s. A recent study of North Sea CCS deployment and storage potential estimated that there might be about 450 mt CO2 per year injection capability by 2050. Crumpton estimates that this could equate to a carbon-negative potential of up to 2 tonnes per UK resident per year. He sees coal and gas CO2 sequestration as paving the way for, and potentially being replaced by, CO2 sequestration from bio-energy gasification, including imported algae.

It sounds pretty ambitious, but many of the components are in place or under development. CSP technology is moving ahead rapidly. New CSP technology, such as the 'Mulk' curved aluminium sheet mirror system, may achieve significantly lower costs compared to conventional glass troughs, by reductions in system weight and other design and construction benefits: www.mulkre.com.

Several experimental Seawater Greenhouse projects have been tried and tested. Soon the world's first commercial Seawater greenhouse will be completed in Australia: www.seawatergreenhouse.com/australia.html.

Also algae production is picking up, for example Argentine company Oilfox has opened the country's first plant to make biodiesel from algae, which it claims can be grown using seawater. There have been reports that a Texan company, Petrosun, has developed an algae-to-biofuels facility using a series of saltwater ponds spanning 1,100 acres.

CCS in geological strata remains unproven at large scale, and is sometimes seen as undesirable if it simply facilitates unchecked fossil fuel use, but the carbon negative bio-oil application proposed by Crumpton might give CCS a new renewable direction. Trials are also underway to enhance algae production by bubbling captured carbon dioxide through the algae 'soup'. The Carbon Trust has launched a major algae R&D project funded by DECC.

Using deserts, algae and seawater would certainly avoid most of the land-use and biodiversity conflicts that have bedevilled biofuels so far, although there could still be conflicts with food growing that might otherwise be done in the seawater greenhouses.

Neil Crumpton has worked for Friends of the Earth and more recently the Bellona Foundation, which is a partner in the Sahara Forest project. He is currently a consultant to B9 Coal, which is a fuel cell/gasification CCS power-station project development company.


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