Tidal Generation Limited

Tidal Generation Limited (TGL), formed in Bristol in 2005 and since December 2009 a wholly owned subsidiary of Rolls-Royce, has developed a 500 kW tidal stream test turbine, which was installed and connected to the UK national grid in September 2010. As with all other test turbines at the Orkney site, TGL’s unit is connected via a single meter point at its test bay to the EMEC substation.

The TGL 500 kW turbine consists of a three-bladed, upstream pitch controlled rotor with a relatively standard drive train and power electronics. The turbine unit itself is buoyant to allow it to be retrieved to shore for maintenance within a single slack water period, i.e. 30 minutes. The device operates in depths of between 35 meters and 100 meters and has a foundation that TGL describes as a lightweight steel tripod, installed using patented fast drilling techniques.

Ease of deployment and retrieval enables all maintenance to be carried out onshore, significantly reducing the need for costly marine operations, while allowing a spare machine to continue generating, says TGL. The one-off demonstrator turbine was built at the Rolls-Royce Marine facility in Dunfermline, on the eastern side of Scotland.
“Our strategy was to build a 500 kW demonstrator at EMEC. It is now generating power at around the 400 kW level at present. We expect to operate at full power as time moves on with various tests and, once certain criteria have been met, we will build a 1 MW version later this year,” said a spokesman for TGL.

“We are ahead of the pack in some respects in terms of generating electricity. We think the market space is interesting but it depends on a lot of factors as to how we take the business forward. We don’t yet know what our final value proposition will be, but we do not plan on developing tidal power arrays ourselves – we will be an equipment supplier to array developers.”
Scotrenewables 250 kW prototype.


In July 2010, Orkney-based Scotrenewables, founded in 2002, appointed world-renowned Belfast shipbuilder Harland and Wolff to manufacture a 250 kW prototype floating tidal turbine, the SR250. The 30-metre long device’s two 8-metre diameter rotors deliver a very competitive power to weight ratio, says Scotrenewables. The prototype is being manufactured in Belfast, Northern Ireland, and is scheduled to be deployed at the EMEC test facility in March 2011.

By concentrating not only on conversion technology but – more importantly – on making its tidal turbine easy to install and maintain, Scotrenewables has joined a small group of developers, says Harland and Wolff.

“Our input was to assist their engineers in developing the design to make it production friendly. This makes it cheaper to manufacture and enhances quality,” says Harland and Wolff engineering manager Fred Black.

Scotrenewables aims to develop a full-scale 1 MW prototype. The one-fifth scale, 250 kW model, will maximize Scotrenewables’ chances of success in commercially developing its tidal turbine, as a 1 MW prototype was too big a leap, says Trevor Walls, lead electrical engineer.

OpenHydro tidal turbine
In May 2008, Irish company Open Hydro became the first tidal energy company to complete the connection of a tidal turbine to the UK’s national grid.
The 250 kW Open-Centre Turbine, which was installed at the EMEC site off Orkney in 2006, underwent 18 months of testing prior to connection to the grid.


The Open-Centre Turbine is a large underwater turbine resembling a jet engine affixed to the sea floor. The device is designed to be mounted onto the seabed at a depth that prevents the device from interfering with shipping and leaves no part of the structure visible from the surface.

The single 250 kW turbine is powerful enough to supply electricity to 100 homes but it paves the way for a significant tidal power development in the Channel Islands off the northern French coast.
Open Hydro plans to deploy 1 MW Open-Centre turbines and aims to be in a position to build an array of the devices off Alderney, where the local renewable developer Alderney Renewable Energy holds the right to export power both to France and the UK, where the company secured the right to supply 2000 MW of capacity into the UK’s national grid in 2010.

In March 2010, Open Hydro was awarded exclusive rights by the UK’s Crown Estate to develop a 200 MW tidal energy farm at Cantick Head in the Pentland Firth and Orkney Waters. Open Hydro and SSE Renewable have formed a joint venture called Cantick Head Tidal Development Limited to develop the site.
Atlantis Resources’ AK1000 turbine
Also installed at the EMEC site in Orkney is Atlantis Resources’ AK1000, which it describes as the largest and most powerful tidal power turbine ever built. AK series tidal turbines are commercial-scale horizontal axis turbines designed for open ocean deployments in harsh environments.

AK turbines feature a unique twin rotor set with fixed pitch blades, which eliminates the requirement for subsea nacelle rotation to improve operational reliability.
Dispatching 1 MW at a water velocity of 2.65 meters per second, the AK1000 turbine has an 18-meter diameter rotor, weighs around 1300 tonnes and has a height of 22.5 meters.

The AK1000 nacelle is fabricated by Soil Marine Dynamics in Newcastle, England, while the gravity base structure and system assembly is completed by Isleburn Engineering of Inver gordon on Scotland’s northeast coast.
Steel for the turbines is provided by Corus’ Scunthorpe facility. Soil Marine Dynamics and Isleburn Engineering are yet to be in a position to mass produce the AK1000, said Atlantis. But Atlantis is actively exploring the possibility of manufacturing the AK1000 turbine in-house.

“Going from a single, one-off build to a commercial unit that is part of a factory system will bring a lot of cost savings. Production engineering will drive the cost down,” a spokesman for Atlantis told Power Engineering International. Atlantis has developed a range of tidal stream turbines and is yet to ascertain the optimum size for mass production.

“The AK1000 is fully scaleable, but the problem with scale is that it has to fit the resource available. You can’t just make a 5 MW tidal turbine with 35-metre diameter rotors, because it won’t fit the available resource. Unlike a wind turbine, tidal stream turbines have to be specifically designed for the seabed surface resource available.”

MeyGen project
The AK1000 turbine has been earmarked for deployment in the Pentland Firth by MeyGen, a joint venture between International Power, Morgan Stanley and Atlantis. A 400 MW tidal array is also planned for the Inner Sound between the Island of Stroma and the mainland of Caithness.

The project will be built in six phases by 2020, the first consisting of 15 MW. MeyGen is seeking planning consent in the first half of 2012, with the first turbines entering the water either in 2012 or 2013.
The EMEC projects will be supported by a purpose-built service and supply base at Lyness on the island of Hoy, which is expected to be operational this March.
FenderCare Marine Solutions, which is installing the facility, says the base will offer essential marine services including deployment and mooring of wave and tidal devices and operational through-life support, as well as specialist fendering and sub-sea tooling requirements.

While several test turbines are connected to national grids around the world, no commercial turbines – i.e. sold at a profit – are yet in operation. That is set to change if the pace of development in the Scottish islands of Orkney continues apace.