A full scale tidal array in Scottish waters is drawing closer to reality for Glasgow-based renewable energy company Nautricity.
Consent has been given by Marine Scotland for the deployment of the first Contra Rotating Marine Turbine device, otherwise known as CoRMaT, in the Irish Sea, south of Machrihanish, Argyll. The device has been developed by Nautricity and has gone through a process of upscaling as it is taken through its various levels of testing.
Unique Tidal Technology
The first commercial scale CoRMaT device has been built over the last 18 months. It has a rotor span of 10 metres which is significantly larger than early test models. The device is more compact and lighter than the more conventional tidal devices and so the deployment and engineering costs are lower making it a cost-effective method of harnessing tidal energy.
The company has had the benefit of a £250,000 Smart Scotland grant from Scottish Enterprise and has also developed and patented its unique HydroBuoy station keeping technology. This is a tethered based mooring system to help keep the CoRMaT devices steady in strong currents.
With the shape of the wing of an aircraft, the buoy combines displacement buoyancy with hydrodynamic lift to vary mooring tension proportionally, according to the strength of tidal speeds.
The CoRMaT devices are held in tension by a subsurface float and can be deployed in a range of water depths of up to several hundred meters deep. The contra-rotating rotors are closely spaced and due to the fact that they move in opposite directions, they remain steady in the face of strong tidal flows. The result is that each device “flies” from a simple tensioned mooring. The devices can then maintain optimum alignment into the tidal flow and will vary their direction for maximum energy capture.
Work Will Start Soon
Nautricity is the fourth company to be granted full permission to deploy tidal devices in Scottish waters. Approval has also been given by Argyll and Bute Council for the construction of an onshore substation to provide a connection to the national grid.
The work on the substation is expected to start late in 2014 and the devices should be deployed in the water in early 2015.
It was only recently announced by the company that it was on track to become the first tidal energy developer to produce commercially viable electricity.
The testing of the full-scale device in real-life conditions is an important step forward and should play a vital role in proceeding to full commercial deployment. The data gathered from this stage is expected to cover much of the potential problem areas.
The Word From the Nautricity CEO
Cameron Johnstone is the co-founder and CEO of Nautricity and believes that the company could have a multi-megawatt array in place sometime after 2016.
“Once we have demonstrated the technology here and shown that it can provide affordable electricity, we will then build out to multi-megawatt arrays at home and overseas. In order to be able to compete abroad in the future, it’s essential that we have a robust, indigenous market from which to launch our international business development,”
“We believe we are doing all of the right things in developing lower cost, next-generation technology, through our progressive testing program and gathering the data to ensure that we are taking to market a product that works and can compete with other forms of energy generation.”
“Receiving full consent for this project is a great vote of confidence in our technology and our site development capabilities”.
When the turbines are deployed they are completely submerged and not visible from the shore. They will have no measurable adverse impact on the marine environment.
How the CoRMaT Works
The following is an explanation from Nautricity of how the CoRMaT works and why it is a more efficient method of harnessing tidal energy.
The CoRMaT second generation tidal turbine is innovative and proven technology employing two closely spaced contra rotating rotors, driving a contra rotating electrical generator. The first rotor has three blades rotating in a clockwise direction while the second rotor, located directly behind the first, has four blades rotating in an anti-clockwise direction.
This doubles the relative rotational speed compared with a single rotor turbine, allowing the turbine to directly drive a flooded, permanent magnet, contra-rotating generator, without a gearbox. The flooded generator is cooled passively by the water, eliminating parasitic energy losses associated with gearbox driven water tight active oil based gearbox-generator cooling systems and power absorbing shaft seals.
The magnetic field acts across the rotor and rotating-stator sections of the generator as a “differential”, equally splitting the torque between the two rotors. Reactive torque acting on the supporting structure is eliminated allowing the system to be moored rather than rigidly attached to the seabed.
This enables the turbine to be deployed in water depths from 8m – 500m. Buoyancy chambers at the front and rear sections of the nacelle are tuned to achieve neutral buoyancy. The turbine is connected to a tensioned mooring at a point in the water column where the flow velocity is greatest and surface wave action minimized. Tidal flow induced drag forces ensure that the turbine remains perpendicular to the flow at all states of the tidal diamond, resulting in maximum energy capture.