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Scottish Marine Renewable Energy: A New Wave of Development

At the end of August, the Scottish Government announced that five marine energy developers will benefit from a total of £7.9 million in funding to further develop testing of new wave and tidal prototypes in the seas around Scotland.

The second round of WATERS (Wave & Tidal Energy: Research, Development & Demonstration Support) funding has been released to 'enable Scottish developers and supply chain firms to capture an increased share of the growing international marine energy market,' which could be worth up to £4 billion for the Scottish economy by 2020.

So, what wave and tidal technologies will be funded by WATERS2?  What will the projects entail?  And what are the prospects for the future development of marine renewable energy technologies in the UK?

Albatern

Albatern's WaveNET technology, developed by the company's Chief Technology Officer, David Findlay, is made up of a number of modules that are attached together to form the WaveNET array.  Each module has a vertical buoyant 'riser' with a node attachment at its base.  The riser is 'surface piercing,' with most of its length submerged — and three link arms are attached to the node at the foot and rise at an angle to surface piercing floats. 

As David Campbell, CFO at Albatern, explains, the technology also features 'power take off units,' operating at each nodal connection of the riser to the link arms, and at each connection of the riser to the floats — giving a total of six for each module. 

"The node is a fully articulated joint, and all the joints are capable of extracting energy from waves passing by the module.  The wave energy results in a kinetic movement of the module.  This is captured through hydraulic rams on each power take off unit," says Campbell.

"The hydraulic pressure is rectified on the device and is formed in series between rams, creating high pressure and low pressure rings," he adds.

Within the array, generators are sited in the float assemblies on the surface, making them easy to access for inspection.  This also means that the generators can be 'sized' to account for the expected sea states and wave energies where the device will be installed.  Campbell explains that the generators themselves are 'marinised hydraulic motor/gensets' that create AC power that is 'rectified electrically' to produce DC — which is then taken off the device.  For grid connected systems and other AC systems, the DC is then inverted back to meet requirements either onshore or at the point of electrical use (e.g. an aquaculture farm). 

Under the auspices of the WATERS2 project, Albatern has been awarded a £617,000 grant towards a cost of designing and building the first WaveNET array, consisting of up to six modules of 7.5-kW or 45-kW rated capacity.  An initial module, based on the company's 'Squid 1 device,' will be followed by two more incorporating any necessary improvements identified in the first test phase.  A final tranche of three modules will then be constructed — again incorporating any improvements made following the 'lessons learnt' on the earlier modules. 

"The project will cover the deployment and performance measurement of the array and allow comparison with extensive theoretical modelling already carried out by Albatern," explains Campbell.

"In building the devices, opportunities to improve the design for efficiency of yield, deployment [or] maintenance, and also opportunities to bring down manufacturing costs will be sought.  Already, we can see cost saving from using cast parts where we need many standard components," he adds.

The WaveNET demonstrator will be deployed from late 2012 to late 2013 in a number of phases to measure output in a variety of configurations in different sea states.  Pilot sites in aquaculture farms and 'remote communities' will be developed during 2013 and 2014.  Campbell believes that 'a significant opportunity exists' for smaller scale devices in aquaculture globally and that smaller devices 'can also support remote island communities.'

Partner relationships are also being developed throughout 2012-13 to progress the development of grid scale devices based around nodes at 75 to 100 kW, building into arrays of up to 10 MW with 'devices in the water' from 2014 onwards.

AWS Ocean Energy

AWS has been awarded a £3.9 million grant towards the total £15.6 million cost of a project to design, build and launch its AWS-III Wave Energy Converter (WEC) at full scale.  A 1:9 scale model of the AWS III, a floating device with a rated power output of 2.5 MW, was tested in Loch Ness in 2010, with a full scale prototype planned for deployment at the European Marine Energy Centre in 2014.

According to AWS, the device consists of a 'multi-cell array' of flexible membrane absorbers which covert wave power to pneumatic power through the compression of air within each cell.  The cells are inter-connected, thus allowing interchange of air between cells in 'anti-phase.'  Turbine-generator sets are provided to convert the pneumatic power to electricity.

A 'typical' device is made up of an array of 12 cells, each measuring around 16 metres wide by 8 metres deep, arranged around a circular structure with overall diameter of 60m.  Such a device is capable of producing an average of 2.5 MW from a rough sea whilst having a structural steel weight of less than 1,300 tonnes.  The AWS-III will be 'slack moored' in water depths of around 100 metres using standard mooring spreads.

Nautricity

According to Cameron Johnstone, Chief Executive Officer at Nautricity, the 'development ethos' behind Nautricity’s CoRMaT technology was to deliver a tidal energy technology that 'could be held on station without the need for a big, heavy and expensive supporting structure' and produce a turbine that 'considerably reduced complexity' in its operations of capturing energy from the tidal flow and converting this to electricity.  The company also believed that efforts to reduce the weight and complexity of such systems would ultimately lower the costs associated with tidal energy power generation.

Johnstone explains that the technology is 'unique' in that it uses axial mounted contra-rotating rotors, with fixed pitched blades, to directly drive a contra-rotating, permanent magnet generator.

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"Since the generator is flooded, it is cooled naturally by the tidal flow passing over it.  The nacelle has buoyancy chambers at the front and rear so that the turbine is neutrally buoyant," he says.

The turbine is held on station via connection to a tensioned mooring line, which is secured to the seabed and held in tension by either a surface or sub surface float.  The turbine can be connected to the mooring riser at any point in the water column where the tidal flow has the highest velocity.

"This tensioned mooring approach enables the turbine to be deployed in any depth of water up to 500m deep," says Johnstone.

Funding from the WATERS2 programme will help to fund a commercial demonstration of the CoRMaT technology between now and early 2014, and enable it to be deployed at 'full commercial scale and generate electricity into the electricity supply network.'

"Following this, we would be looking to build this out in Scotland and elsewhere.  Markets of interest include North America [and] Asia - and South America is beginning to emerge," says Johnstone.

Oceanflow Energy

Oceanflow's 'Evopod' tidal technology is a semi-submerged floating body that is tethered to the seabed by a multi-line spread mooring system.  The surface piercing struts support a deeply submerged nacelle that houses the generator and power electronics in a watertight enclosure.  As Graeme Mackie, managing director of Oceanflow, explains, the turbine itself is a horizontal axis 'unducted' turbine, similar to that used in wind turbines 'only of a smaller diameter for the same power output due to the much higher density of water compared to air.'

The slow rotating turbine is coupled to a step-up gearbox that drives an induction generator.  The variable voltage and frequency AC output from the generator is conditioned to a constant 400V/50Hz output using Siemens power electronics configured by Optima Control Solutions.  Power is 'stepped up' to 3,000V for export to shore.

"The unit weathervanes about its mooring position so that it always faces into the tidal stream. The streamline support struts cause minimal wake interference into the downstream turbine," says Mackie.

"Power is exported to the seabed through a Focal slip ring coupled to a flexible umbilical cable, similar to the technology used on oil and gas floating production platforms," he adds.

Oceanflow Energy has already built and tested a 1.5 metre diameter mono-turbine Evopod at a site in Strangford Narrows and, with Scottish Enterprise WATERS1 support, is currently building a larger 4.5m diameter mono-turbine unit, which will be deployed in Sanda Sound near the Mull of Kintyre and connected to the grid later this year.  A twin turbine variant has been tested at model scale at Newcastle University and the WATERS2 funded project will involve deploying a version with twin 4.5 metre diameter turbines.

"The project will extend the knowledge gained through operation of the mono-turbine unit and will demonstrate the improved economics of mounting twin turbines off a single support platform," says Mackie.

According to Mackie, Oceanflow has taken a 'stages development' approach - moving up through the scale of the devices it has deployed as it builds up essential in-sea operating experience.  In this way, he believes that a small company like Oceanflow can avoid expensive failures and achieve progressive test milestones without expending vast sums of shareholders funds.

The company’s strategy is to build up operating experience with its 35-kW mono-turbine and 70-kW twin turbine Evopod units, deploying multiple units to gain understanding of operating small arrays, before progressing to a full scale 2-MW (2 x 1-MW) twin turbine unit by 2015. 

"The Sanda Sound development has demonstrated that such small units have application to community energy projects and provide invaluable knowledge of not just technical performance but also societal and environmental issues," says Mackie.

Scotrenewables Tidal Power

Scotrenewables has developed an innovative floating tidal energy converter, known as the Scotrenewables Tidal Turbine (SRTT).  The SRTT is a floating tidal stream turbine featuring two contra-rotating rotors that extract the kinetic energy of the tidal flow, which is converted to electricity though a power take-off system.  The main structure of the device is a cylindrical tube to which the horizontal axis rotors are attached via retractable legs.  The retractable rotor legs enable the SRTT to operate in two separate configurations — operational mode, with the rotors down to generate power, or transport/survivability mode, with rotors retracted to decrease draught — allowing the device to be towed into harbour for maintenance or reduce loads in heavy seas.

The concept employs a catenary-type mooring system with a single mechanical and electrical connection point. Once the turbine is connected to the mooring system it is free to passively orientate itself into the tide.

"As a floating concept this mooring arrangement allows the turbine to respond to the dynamic changes in current and wave conditions, rather than having to withstand them as fixed structures do," says John McGlynn, Business Development Manager at Scotrenewables Tidal Power.

"A further advantage of the concept is that the floating design of the system allows for the rotors to be placed in the most energetic part of the water column – near the surface and away from seabed induced turbulence," he adds.

The concept has been trialled at increasing scales in both laboratory and open ocean environments since its inception in 2002 and most recently demonstrated at 250 kW ‘full scale’ at the European Marine Energy Centre (EMEC) in Orkney.  McGlynn says that results from the 'SR250' test programme to date have been 'extremely encouraging' — with the turbine now undergoing longer term fully grid-connected tests — and have provided the company with the confidence to progress to demonstration of a ‘commercial scale’ turbine rated up to 2 MW.

"The 2-MW will be the first of a number of SRTT units installed in a commercial demonstrator array project of initial 10-MW capacity with eventual expansion to 30 MW," he adds.

The company's WATERS2 project will involve the design, construction and installation at EMEC of a commercial demonstrator SRTT rated up to 2 MW.  The SR2000 turbine will be the final stage in the development of the concept prior to commercial rollout.  The objective of the project is to build on the success of the SR250 project and to use the considerable learning and experience gained to deliver a commercially viable floating tidal turbine demonstrator suitable for array deployment.  Following preliminary EMEC testing the SR2000 will form the basis for a 10MW demonstrator array in Scottish waters.

"We are confident that even in the early stages, the technology can deliver a lower cost of energy than competitors’ long-term projections.  This is primarily due to the considerably lower installation and maintenance costs involved in the SRTP concept as well as low capital costs," says McGlynn.

Looking Ahead

According to McGlynn, the future prospects for the UK and global wave and tidal technologies sectors are very bright.

"The UK is the undisputed world leader in the development of marine energy technologies and will be the site of the first multi-MW commercial array projects.  Tidal energy offers the potential to provide a significant proportion of energy demand both in the UK and further afield," he says.

"A generally accepted figure for the UK is  from 5% to 6% — excluding tidal barrages.  Other countries with real potential include France, Canada, United States, Korea, Japan, Chile, Argentina & New Zealand among many others," he adds.

Crucially, McGlynn stresses that tidal power offers the potential to reduce dependence on imported fossil fuels and thereby contribute to security of energy supply.

"This, combined with the absolute predictability of tidal power are really the key advantages.  As well as being predictable, tidal power is also not as intermittent as other forms of renewable generation — a portfolio of sites located around the UK would deliver consistently into the grid," he says.

"The industry has experienced rapid and increasing levels of growth over the past two to three years to the point where we are now seeing the first array projects now take shape — we expect this activity to continue to intensify over the next two years," he adds.

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