Turning the tide: Aquamarine's Oyster is among the type of wave technology equipment that is gradually attracting commercial interest As an island, Britain is blessed with vast potential amounts of marine energy. But putting complex metal machines into the waters that surround our shores and getting them to work efficiently and reliably is proving to be no easy task.
That’s not to say that progress isn’t being made. From initial tests to the first forays into commercial deployment, the sector is taking important steps forward. But there are still challenges to overcome.
Marine Current Turbines (MCT) is arguably the furthest along the path of proving its tidal turbine prototype. Its progress has not only demonstrated the potential of the technology in harsh marine conditions but has also helped to build confidence in the sector. In 2003, MCT installed one of the world’s first offshore tidal turbines – Seaflow – near Lynmouth, Devon.
This was followed by the installation of the first commercial-scale turbine, the SeaGen rated at 1.2MW, which began exporting electricity to the grid from Strangford Lough in Northern Ireland in 2008.
Matthew Reed, director of engineering at MCT, says: “We have learnt a huge amount right across our broad scope of work with SeaGen, which covers assembly, installation, commissioning, operation and maintenance.
“The SeaGen device has delivered a rich seam of knowledge and confidence, due in part to the number of operating hours since installation. This has enabled observation of long-term effects and collection of a vast amount of performance data which is used to validate design tools and models and provide the basis for optimisation of future turbines.”
MCT observed that when the tide flowed in a particular direction the rotor was in the wake of the cross-beam, causing an impulsive load on the blades that contributed to fatigue loading on the machine. This led to a refinement of the cross-beam design to minimise fatigue.
Scottish Power Renewables is also making waves in the marine sector and has been working with Austrian company Andritz Hydro Hammerfest to test the 1MW HS1000 tidal device at the European Marine Energy Centre in Orkney. Barry Carruthers, senior marine engineer at Scottish Power Renewables, says: “The technology works, but the proof of the pudding is putting them in place and seeing them work for a number of years.”
He says that, while a lot of the technology used in tidal turbines, such as the drivetrain, is similar to that tried and tested in wind turbines, it should never just be a ‘copy and paste’ scenario. There will always be the need for innovation and improvements because of the harsh marine conditions in which the devices are deployed.
Carruthers says: “One of the improvements recently made is the ability to turn the turbine blades around to catch the downstream as well as the upstream tides. The next generation of turbine will also have yaw to better capture the changing tide and will have larger rotor blades for increased energy generation.”
A smaller company, Tidal Energy Ltd (TEL), has been developing designs for many years but is still to test its commercial-scale prototype at sea. It will be installing its device known as DeltaStream in Ramsey Sound, Pembrokeshire this summer. The device has features that TEL hopes will increase efficiency and reduce installation and maintenance costs, and give it an edge over other designs. A triangular steel main base frame with ‘rock feet’ secures the device to the seabed and provides a gravity foundation for three nacelles. An independent horizontal-axis water turbine generator in each nacelle is supported on a tower at the apexes of the triangular main base.
But proving the worth of a single commercial-scale prototype is only the first stage. Trade body Renewable UK says: “To unlock investment from finance houses we need to demonstrate the devices’ reliability, and experience of installation and operation and maintenance of arrays of devices.”
Scottish Power Renewables plans to install 10 HS1000 turbines for a commercial-scale array demonstration by 2016 in the Sound of Islay, off the west coast of Scotland. Carruthers explains that even bigger plans lie ahead: “It’s a very good early-stage project but it is only a demonstration; 10MW is not the scale that we want to do this on in the long term. This is just the next stage – we’ve done 1MW, let’s do 10, then we’ll do 100 after that.”
MCT is also set to get its first demonstrator arrays in the water by 2016, starting off the Skerries, North Wales, using the SeaGen 2MW turbine. Reed says: “All of the necessary consents and grid are in place ready to go, subject to financing the project.”
For many companies, funding is the biggest obstacle standing in the way of achieving a commercial-scale array demonstration. TEL plans to move to a commercial demonstration at St David’s Head, a couple of miles north of its test site at Ramsey Sound, by 2017-18. It has already agreed a lease with the Crown Estate for the demonstration array but it needs to find a significant amount of money before it can achieve this goal.
Managing director Martin Murphy says: “In ball-park figures, to capitalise the investment that’s needed for St David’s Head, we’re talking about a requirement of £50 million – and that’s beyond the reach of our current shareholder.” TEL hopes that the investment will come following successful tests of its commercial prototype.
Dee Nunn, wave and tidal manager at Renewable UK, offers encouragement: “Large industrial players can now see the potential of marine turbines and are starting to get their feet wet with the sector.”
One such company is Siemens. Following the successful work done by MCT, Siemens acquired the firm from Rolls-Royce in 2012. Reed says the benefits of this takeover have been manifold. It has provided continuity of funding, which has seen the firm double its workforce and relocate to Bristol and Bath Science Park.
MCT has also acquired a manufacturing facility in Bristol and gained access to a wealth of expertise from Siemens employees in areas from production engineering to cost reduction, computational fluid dynamics, power conditioning, gearbox and substation design, and grid infrastructure.
Reed says one of the greatest benefits has simply been the credence gained from being associated with the big company: “With the Siemens name behind MCT, it adds significant credibility in the marketplace with important potential customers such as major utility companies,” he says.
“Without Siemens’ support it was challenging to engage with the utilities on significant projects – who would underwrite the technology? Who would provide warranties? Would MCT still be in existence after the devices were installed?”
Field of dream: artist's impression of an underwater Atlantis AR1500 turbine farm
This year has seen further cases of big business entering the field. Perhaps the most significant has been Lockheed Martin commencing a contract with Atlantis to optimise the design of its AR1500 1.5MW tidal turbine, one of the biggest single-rotor turbines ever to be built.
Atlantis chief executive Tim Cornelius says improvements have been made to previous designs: “We’ve made some significant advancements in how to physically control the turbine to maximise yield, and adaptations in respect to redundancy. We’re moving to double and triple redundancy on all critical systems that exist in the turbine. That’s because we’re aiming for a five- or six-year servicing interval. They will be submerged for that time so the redundancy systems become incredibly important.”
The AR1500 will initially support the MeyGen project in Scotland’s Pentland Firth and will also be deployed in Canada’s Bay of Fundy. Once completed, MeyGen – the world’s largest array tidal-stream project under development – is expected to deliver up to 398MW and contribute to Scotland’s 100% renewable energy target by 2020.
Financial support has not just come from big business. The government has also invested a great deal, following the publication of impressive statistics about the marine sector’s potential to help meet renewables targets and boost the economy. According to the Department of Energy and Climate Change, wave and tidal-stream energy has the potential to meet up to 20% of the UK’s electricity demand, representing 30-50GW installed capacity.
The department says: “Between 200 and 300MW of generation capacity may be able to be deployed by 2020, and, at the higher end of the range, up to 27GW by 2050.” The Carbon Trust has estimated that the UK could create 68,000 jobs in the sector.
This has prompted a range of policies, subsidies and funding schemes from the government to support the sector’s growth and investor confidence. In 2012 the government announced the Marine Energy Array Demonstrator capital grant scheme. It has since offered up £20 million to support two pre-commercial projects – £10 million went to fund MCT’s array demonstration in Wales.
But Nunn from Renewable UK stresses that state aid rules mean that government funding can only cover up to 25% of costs, adding: “Additional funds can be covered by technology developers with backing from industrials with big balance sheets, but this would involve taking on substantial risk and in the current economic climate the full investment is proving hard to come by.”
To attract additional investment, the government is to subsidise the industry with the allocation of five renewable obligation certificates per MWh for wave and tidal developments. It has also agreed to a £305/MWh strike price under the contract for difference.
TEL’s managing director Martin Murphy says: “The subsidy regime under the electricity market reform legislation sets the scene, but there is still a long-term uncertainty associated with it beyond the end of this decade.”
The government is also under pressure to help the industry solve other issues, such as the demand for extra grid capacity in resource-rich areas and the need to invest in the research and development of technology for energy storage.
While there are still obstacles on the road to commercialisation, important milestones are being reached. With big businesses beginning to get involved and the first array demonstrations due in the next few years, the marine industry is showing signs of progress.
Murphy says: “The confidence is there within the industry that we can do it – we’ve just got to prove that we can.”
Waves of encouragement
PE speaks to Martin McAdam, chief executive of Aquamarine Power, to find out about progress being made with its second-generation wave-energy machine, the Oyster 800.
What obstacles have you encountered during the Oyster 800 sea trials?
The surf zone is a turbulent, highly oxygenated and corrosive environment. That, combined with the mechanical loading of the waves every 10 seconds or so, results in extreme conditions. We have had extensive failures on wet-mate connectors for the control and instrumentation system and failures due to loosening fasteners, caused by a combination of corrosion and mechanical vibration. We have also had valves and other equipment fail due a combination of loading and cycle frequency.
You are now on your second-generation design of Oyster 800. What have you done to counter these problems?
The biggest challenge has been to design a machine that can survive and thrive in storms. Oyster is unique because when the waves get bigger it ducks down and allows the huge energy in the storm waves to cascade over the top. This self-limiting characteristic, which reduces the loading on the structure, is essential to its survivability.
What is the next step for the project?
Oyster 800 has survived through three winters and major storms and its structure has proven to be very reliable in all wave conditions. Our ability to produce power has been less reliable; improving this is our goal for the next couple of years. We also intend to build a completely new machine, the Oyster 801. It will utilise all the learning on Oyster 800 but with a few improvements including fabricating the machine from composite materials, which have good fatigue characteristics and don’t have the same corrosion challenge.
Have you had any commercial interest in your project?
We have a number of companies, including Scottish and Southern Energy (SSE), which are interested in deploying the Oyster technology commercially. We have been granted consent for a 40MW site off the west coast of Lewis and are developing a 200MW site with SSE in Orkney. We also have considerable interest from utilities in other countries including Ireland, Spain, Chile and the US.