It is perhaps important to distinguish between wave energy and tidal energy. Waves form as winds blow over the surface of the sea, with the size of the waves dependent on the wind speed, duration, the distance of water over which the wind blows (known as the ‘fetch’), the bathymetry of the sea floor (which can focus or disperse the energy of the waves) and currents. The movement of the water carries kinetic energy which can be harnessed by wave energy devices. The best wave energy resources are found in areas where strong winds travel over long distances. With regard to Europe, that means the western European seaboard of the Atlantic Ocean. Wave energy devices are situated in deeper waters because the energy decreases closer to shore due to friction with the seabed.
Wello Penguin at EMEC wave test site Billia Croo (Image: Mike Brookes-Roper, courtesy of EMEC)
Tidal streams on the other hand are created by the constantly changing gravitational pull of the moon and sun on the world’s oceans. Tides never stop and so tidal stream devices capture the kinetic energy generated by the tides moving back and forth in tidal areas. These can be predicted with complete accuracy, in accordance with the relative positions of the sun and moon and this makes tidal energy an invaluable resource. The highest tidal ranges are generated by spring tides (nothing to do with the season by the way) when the sun, moon and earth are in line, exerting a greater gravitational pull. The neap tides are the lowest tidal ranges which occur when the positions of the sun, moon and earth describe a right angle. This creates a split gravitational pull which reduces the volume. Tidal stream resources are generally largest in areas where a good tidal range exists, and where the speed of the currents are amplified by the funnelling effect of the local coastline and seabed, for example, in narrow straits and inlets, around headlands, and for example through the many islands that make up the archipelago of Orkney.
EMEC provides wave and tidal energy developers with scale and full-scale testing facilities. The test centre operates according to full test laboratory standards (ISO17025) and ISO/IEC 17020 accreditation meaning that EMEC can provide independently-verified performance assessments and Environmental Technology Verification (EMEC-ETV). The facility employs a technical team that provides a range of services which can be customised to suit individual clients. Each team member is highly experienced in marine renewable energy, enabling EMEC to adapt and integrate quickly, providing skills such as test centre design, hardware testing, deployment methodologies and procedures, operational management, health and safety and consenting. Data collection and research methodologies are two other highly valuable services on offer at EMEC. The facility is also currently involved with Marine Scotland to streamline the consenting process and is at the forefront of moves to develop international standards for marine energy as well as working with other organisations abroad to stimulate the development of a global marine renewable energy sector.
Deployment of EMEC test support buoy at scale wave site (Image: Mike Brookes-Roper, courtesy of EMEC)
The facility itself consists of 14 grid-connected test berths (6 wave, 8 tidal) and 2 non-grid connected scale test sites. More marine energy devices have been deployed there over the years than any other single marine energy facility in the world, brought to EMEC by developers all over the globe. globe. EMEC’s grid-connected wave test site is located at Billia Croo outside Stromness on the western edge of Orkney. It experiences one of the highest wave energy potentials in Europe, with an average significant wave height of 2-3 metres. However, it can also reach extremes of up to 17 metres (the highest wave recorded by the facility so far). Five cabled test berths are located at Billia Croo, approximately 2 kilometres offshore and 0.5 kilometres apart. Four of the berths are in waters up to 50 metres deep with another in water 70 metres deep. Another berth is located closer to shore for shallow water projects.
Five sub-sea cables link these berths with the EMEC substation which has been designed to minimise visual impact and houses the main switchgear, backup generator and communications room. The cables feed the electricity generated by the wave energy converters directly into the national grid.
Armoured sub-sea cables (Image: EMEC)
Two waverider buoys measure wave height, period and direction while a purpose-built weather station provides real-time met data which is fed into a SCADA (Supervisory, Control and Data Acquisition) system providing live data feeds on the marine and met conditions. These are available to view on EMEC’s website.
The berths are monitored by CCTV located at EMEC’s observation point at Black Craig. This was originally a coastguard lookout station but it has since been converted to house powerful cameras that are controlled remotely from EMEC’s data centre.
Aerial view of Fall of Warness test site (Image: Aquatera)
EMEC’s grid-connected tidal test site is located at the Fall of Warness, just west of the island of Eday. It lies in a narrow channel between Westray Firth and Stronsay Firth which has high velocity marine currents that reach almost 4 metres per second (7.8 knots) at spring tides. These flow in from the North Atlantic but increase in speed as they are funnelled through Orkney’s northern islands. There are eight tidal test berths here, located at depths ranging from 12 metres to 50 metres, within an area 2 kilometres wide and approximately 4 kilometres long. A series of 11 kilovolt sub-sea cables extend from the middle of the tidal stream to the substation at Caldale on Eday which controls the supply from each tidal device and the connection to the national grid. These cables also contain fibre-optics which allow developers to communicate with the devices and transmit monitoring information back to the data centre. The electricity is converted from 11 kilovolts to 33 kilovolts at an adjacent Scottish and Southern Energy (SSE) transformer. There is another purpose-built weather station at this site, which, like that at Billia Croo, provides real-time met data fed back to the EMEC data centre.
Alongside these grid-connected test berths, EMEC also operates two scale test sites where smaller scale devices can obtain real sea experience in less challenging conditions. These are located at Scapa Flow and Shapinsay Sound and provide a more flexible sea space that helps developers to close the gap between tank testing and larger scale demonstration at the grid-connected sites.
Concentric wave spike at FloWave, Edinburgh (Image: FloWave)
EMEC works closely with FloWave Ocean Energy Research Facility at the University of Edinburgh. The two organisations share their expertise in ocean and laboratory testing with FloWave replicating the wave and tidal conditions at EMEC in their test tank.
FloWave was established in 2014 with a 25 metre circular test tank in a dedicated building on the edge of the university’s King’s Buildings campus in Edinburgh. It is the only facility in the world to combine both waves and tides in its modelling and is designed for cutting-edge academic research into wave and tidal current interactions. It can therefore help developers to ensure that their projects perform ‘right first time’. It enables them to ‘derisk’ new designs and refine their performance before they start building a full-scale prototype. For those developers who already have prototypes up and running, FloWave provides an opportunity to run model-scale tests on revised designs incorporating ‘lessons learned’ from devices actually in the water.
“Testing full-scale ocean energy technologies at sea can be an expensive and risky business” says FloWave Chief Executive Officer Stuart Brown. “The closer you can replicate real ocean conditions in the laboratory, the better you can refine your prototype and validate how it might perform – before testing part-scale or full-scale devices at sea. To date, test tanks have only been able to generate waves or tidal flows – but anyone who has been to Orkney will know, Scotland’s oceans are much more complex and usually combine both. At FloWave our unique facility gives us the ability to create both waves and tidal currents at the same time.”
Brown adds that the process is similar to the way an airliner would be tested in a wind tunnel during development and so it is a real first for the ocean energy sector in that developers now have a clear pathway from the computer to the laboratory to EMEC and then back to FloWave again. EMEC is providing FloWave with a wealth of data, gathered over the years by ‘Waverider’ buoys, radar and acoustic Doppler current profilers (ADCPs), which FloWave is using to develop accurate models which replicate, as closely as possible, the complex sea states encountered in Orkney. The work is being led by research engineer Sam Draycott, who is in his third year of a four year industrial doctorate in offshore renewable energy at FloWave.
“Developing a marine energy technology is not a linear process” says EMEC Managing Director Neil Kermode. “You may start in a test tank before you bring an idea to sea, and then once you find out what works and what doesn’t, you end up back in the laboratory. At EMEC we have spent a lot of time recording wave and tidal data and are focussed on measuring the things that are important to developers. Our interest is in monitoring the conditions at a site, so that developers can use that data to aid their design process, and we can then validate the performance and potential power production of their technology.”
EMEC is purpose- built for sea trials, but working offshore can be expensive which is why it makes sense to utilise the capabilities of FloWave in order to develop representative EMEC conditions in the test tank. Sharing this date will enable EMEC to accelerate learning from lab to sea and back again, thereby enabling the UK to stay at the forefront of the industry as it matures.
Alstom 1 MW turbine at Hatson Quay (Image: Alstom)
More marine energy devices have been tested at EMEC than at any other single site in the world. The facility has so far hosted 16 wave and tidal energy clients (with a total of 25 marine energy devices) spanning 9 countries. The facility is well known for providing test and demonstration facilities to technology developers, but 12 years of front-line testing in the sector has enabled a range of wider projects and collaborations, generating cross-sectoral innovation and knowledge sharing.
With more than 1000 marine energy activities, including device deployments, grid connections, cable laying, data collection and on-going monitoring, EMEC is pushing its infrastructure and experience to the max to ensure maximum benefit is derived for the marine renewables industry.
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