The British city of Bristol is arguably the spiritual home of marine energy. Tim Probert visits two companies at differing stages of development: Marine Current Turbines, recently acquired by Siemens and Offshore Wave Energy, a start-up struggling to raise finance, to find out how marine energy will be brought to market. This article first appeared in the October 2012 issue of Materials World magazine.
Bristol knows all about the power of tides. The huge tidal range of the River Avon has always presented it with a problem.
Before the construction in 1809 of a floating harbour that allowed vessels to stay afloat without being affected by the changing tides, ships anchored in Bristol would rest on the river bed and be subject to immense pressure as the water in the river ebbed and flowed from the sea.
This often caused considerable damage to the timbers and as a result Bristol-built ships became renowned for their sturdy craftsmanship, leading to the famous phrase ‘shipshape and Bristol fashion’. While much of Bristol’s maritime infrastructure has since been regenerated as shops and eateries, Bristol continues to harness the power of the tides.
Marine Current Turbines (MCT) is the poster child of the UK’s burgeoning tidal power industry. The company was founded in 1999 to develop Dr. Peter Fraenkel’s ideas for harnessing tidal stream currents to generate electricity via submerged power generating turbines.
Fraenkel, the now-retired former technical director of MCT, is seen as the ‘Godfather’ of marine energy in Bristol. Most of the city’s tidal and wave power companies can trace their lineage back to Fraenkel and IT Power, a renewable energy consultancy of which he was a founding partner. Fraenkel dates his involvement with tidal power to the 1970s when he installed a turbine in the Nile River.
In 1994, Fraenkel installed a small tidal power generating unit in Loch Linnhe in Scotland to prove the concept of harvesting tidal streams and this led to Sea Flow, the world’s first offshore tidal turbine, which was installed in Lynmouth, Devon by MCT in 2003. Satisfied with the results from this non-grid connected, 300 kW system, the conceptual principles were applied to SeaGen, a 1.2 MW grid-connected system installed in Northern Ireland’s Strangford Lough in 2008.
SeaGen can be loosely described as a wind turbine in water, with the blades driven by marine currents. The turbine is fixed on a pile and twin, 16m diameter rotors rotate with the tidal flow, pitching through 180 degrees to track direction and speed. The primary advantage of tidal power is that generation is predictable in the tidal cycle.
The Strangford Lough demonstration unit has been hailed as a success – it regularly generates 20 MWh daily and has achieved a capacity factor of over 60 per cent, twice that of wind power – and was an overarching factor in the decision taken by Siemens to invest in MCT in 2010, later taking 100 per cent ownership in March 2012.
Andrew Tyler, formerly chief operating officer of the Ministry of Defence’s Equipment and Support organisation, joined MCT as CEO in 2010. Tyler has been charged with turning SeaGen into a commercial product and the lessons learned from Strangford Lough will now be applied to SeaGen-S2MW, a 2 MW rated machine with 20-metre diameter rotors, which MCT is developing to be an “industrial product” by the end of 2013, he says.
Engineering lessons learned
The primary engineering lesson learned from Strangford Lough, says Tyler, is the persistent challenge of turbulence-induced vibration. “We are harvesting a highly turbulent flow field and that turbulence is translated by the tidal device’s mechanics into the structure: the powertrain, the gearbox, stresses placed on the blades and so on.
“We can engineer this out but it manifests itself in lots of different ways. SeaGen has been of incredible benefit because so many of these problems emerge after years, not months, following installation.”
Subject to a force of over 100 tonnes, SeaGen’s rotor blades have suffered a number of fatigue cracks and even a break, forcing a redesign. Other factors included the reliability of the powertrain, i.e. gearboxes and slip rings. SeaGen uses a small, planetary wheel gearbox from Czech manufacturer Wikov and at one stage some pins sheared. The gearbox continued to work but the associated overhaul took several months.
The biggest differences between the turbine at Strangford Lough and SeaGen II are an upgrade of the powertrains from 600 kW to 1 MW and a cost-engineered structure. Tyler notes that Strangford Lough was significantly over-engineered, which is the right thing to do for a prototype if not always cost-effective for industrial products.
The design will undergo testing next year, initially onshore at a number of sites. A Bristol site will be used to test system level equipment and blades, while powertrain testing will be conducted at the National Renewable Energy Centre’s dedicated tidal turbine test facility in Newcastle.
MCT plans to build two arrays in the UK with SeaGen-S2MW: the Kyle Rhea 8 MW project sited in a strait between the Isle of Skye and the Scottish mainland, and the 10 MW Skerries array off the north-west coast of Anglesey. Both are due online by the end of 2015 and MCT is currently seeking utility partners to invest in the projects.
Costs and support mechanisms
The prospect of being eligible for five Renewable Obligation Certificates (ROCs) – equivalent to £210/MWh at current values – is not yet sufficient, so MCT is also seeking funds from the Department of Energy and Climate Change’s (DECC) £20 million Marine Energy Array Demonstration Fund, the Scottish Government’s £18 million Marine Renewables Commercialisation Fund, as well as the Renewable Energy Infrastructure Fund.
“It is a lot of support but we are right at the top of the cost curve, and we are under no illusions that our follow-on projects won’t require government capital support,” says Tyler. “Hopefully we will start to eat the ROCs, and we know receiving five ROCs is not sustainable. Anybody who thinks we are going to be in an Electricity Market Reform regime getting the long-term equivalent of five ROCs is on the wrong planet.”
So the onus is on MCT to bring down costs rapidly to be a commercial prospect. Tyler puts theprovisional capital cost from a SeaGen-S2MW tidal turbine at £5 million per megawatt installed in a 10 MW array. “If one was to take a 35% capacity factor, we are just north of £200/MWh,” he says. This compares to offshore wind, which has a similar capacity factor, at around £140-150/MWh.
MCT’s objective is to be cost-competitive with offshore wind by 2020. While SeaGen has a major competitive advantage in having two powertrains on one turbine foundation, to arrive at even £200/MWh will require a great deal of cost reduction, admits Tyler. “There will be natural economies of scale in areas of fabrication and integration of system to leverage the supply chain and the ability to enter into partnerships, buying steel in bulk and so on. And as with offshore wind, the turbines will be uprated and we have a roadmap of uprating potential to put larger powertrains and blades on the same foundations.”
Despite being a wholly-owned subsidiary of Siemens, Tyler says MCT will resist the temptation to use in-house, proprietary components. “You don’t arrive at a cost-competitive business if you gift yourself with self-sourced supplies, as there would be no competitive tension and that’s the road to rack and ruin. We are a stand-alone business within Siemens and we are charged with delivering the most cost-effective product. They won’t just give us equipment for free.”
The best way to drive down costs, of course, is to make more turbines. MCT sees enough potential business in the UK and France to keep it busy for the next 20 years, but it believes there is a big opportunity in the Bay of Fundy in the Canadian province of Nova Scotia and to a lesser extent Asia-Pacific.
A major drawback of constructing tidal as opposed to wind turbines, however, is a heightened requirement for site-specific engineering. As the gap between the seabed and the sea surface changes, tidal turbines need to be installed at different heights, requiring differently-sized foundations.
Moreover, the extreme tidal range of the Bay of Fundy would require an entirely separate concept, says Tyler. “We are not going to use different powertrains, blades, power processing or control systems, but the powertrain may not, as SeaGen does, move up and down on a crossbeam. We are looking at alternative structures to suspend the systems in the water.”
Tyler envisages MCT developing a small range of products suited to different classes of site. MCT expects to be producing 50 tidal turbines a year within the next decade, although it has no current plans to build a manufacturing facility. “We are going to have an integration facility to bring the powertrains together in Bristol but the fabrication and assembly of the marine structure has been put out to tender.”
Wave power: Struggling to gain traction
While MCT is reasonably close to commerciality, other marine energy firms are struggling to build a demonstration unit. In stark contrast to MCT’s headquarters at the striking, glass- and timber-fronted Bristol and Bath Science Park, Offshore Wave Energy Limited (OWEL) is an essentially part-time operation, run from home offices.
The company was founded by Professor John Kemp, who built and tested models of a wave energy converter in his bath, and its major shareholder and technical consultant is IT Power. Highlighting the somewhat incestuous nature of the marine energy industry in Bristol, IT Power’s principal engineer is Jeremy Thake, who was MCT’s chief engineer before leaving to found Tidal Generation Limited, now owned by Rolls-Royce.
OWEL is developing a floating wave energy converter to compress air and drive a turbine. Waves enter through a duct, creating a seal to trap pockets of air. As the waves move along the duct the pockets of air are compressed and pushed through in pulses to drive a unidirectional turbine.
OWEL’s chief technical officer Ned Minns says the device has a 25-year design life, with an initial capacity factor of 31%, rising to 32% and then steadily to 35% over the next five years. Minns has a target efficiency of 30% for wave-to-air power conversion which, combined with 80% for air-to-electrical power conversion, would provide a wave-to-wire efficiency of 25%.
Minns says wave power production is smoother and more consistent than wind or solar, but seasonal variations apply as winter conditions offer higher wave heights than in summer. There are also daily variations, meaning that a “stable sea state” lasts for on average three hours.
The torque of the generator can be tuned for a typical stable sea state, for example a wave cycle of 7.5 seconds and a height of 4m, to control the impedance of the turbine, while the water ballast can be adjusted to change the moment of inertia and therefore the pitch. The device is anchored.
OWEL is currently designing a demonstration prototype and aims to install it at the grid-connected Wave Hub test centre 10 miles off the Cornish town of Hayle next summer. The prototype will be a single duct, 45m long, 350 kW device made of steel. The aim is to build a triple duct, 70 m long, 2 MW unit built by 2016, with commercial deployment from 2018. Eventually, says Minns, OWEL’s device would be made of cheaper concrete, making them look not dissimilar to Mulberry harbours used by the Allied Forces during the Normandy landings.
Yet OWEL is struggling to raise funds to build even the prototype and is yet to sign a contract to lease a berth at Wave Hub. Chris Rich, OWEL’s Head of Finance and Investor Relations, says the cost will be at least £10 million and while it has a £5 million grant from the Technology Strategy Board it needs to be pari passu with the private sector.
Passing through the Valley of Death
“We are at the Valley of Death,” says Rich. “We’d hope to be specifying and tendering the steel panels in the autumn and commence fabrication in the winter, but to be in that position we need £5 million to get the prototype built and fund overheads and working capital until the end of 2015.
“We are now in the market looking for equity investment, but the current financial climate is grim. Venture capital has dried up, partly because they are short of money and partly because of their experience with marine technologies to date.
“Investors in 2005/6 were promised a fantastic return within a few years, but the companies are still at the prototype stage. Prior to being bought out by Siemens, MCT had spent £70 million. It’s more capital-intensive than people first thought.”
Rich is confident that once the demonstrator is in place, OWEL will succeed. “The investor market says ‘Get this prototype working and we want to buy you’,” he says. “The likes of Alstom, Siemens and ABB have said ‘Get this prototype in the water throughout the winter at a capacity factor the right side of 30% and come back to us’.”
Rich, who works for OWEL as a sideline to his management consultancy business, say once commercial-scale wave power happens it will happen fast due to the relatively easy installation of floating devices. “We expect wave power to be a cheaper option from 2020 onwards; we are aiming for £150/MWh.
“Our business plan does not include ROCs, as we won’t have arrays of them installed water by 2017, but at commercial-scale deployment scale, we believe we have a financially-viable product equivalent to 3 ROCs.”
Rich speculates it will be Aquamarine Power, whose major shareholders include ABB and utility SSE, will be the first wave power company to earn ROCs with its array of three, 800 kW ‘Oyster’ machines off Orkney by the end of 2013. AWS Ocean Energy, which is 40%-owned by Alstom, may be next with its 2.5 MW doughnut-shaped machine.
The Carbon Trust estimates wave and tidal energy has the potential to power 11% of the UK’s current energy needs by 2050, as well as to create 26,000 new jobs and bring £3 billion pounds a year to the UK economy. If these somewhat ambitious figures are to be proven, the marine energy industry must hope that both the private and public sectors give it their full support.