Tidal kite powers up in Northern Ireland

Mon, 18 November 2013

A kite systems that ‘flies’ underwater is now generating electric power in the waters of Strangford Lough in Northern Ireland.

Called Deep Green, this innovative generating system has been designed to harness the power available in relatively low speed currents which could significantly widen the harnessing of tidal power for electricity production.

The Deep Green unit installed in Strangford Lough is a 1:4 scale version of a full size system. One of the main advantages of this system over other technologies is that no tower is required on which to install the generators and the Deep Green unit is simply moored to the sea bed, making installation quick and easy. The mooring wire or tether is attached to the ‘kite’ unit by means of a bridle and a swivel and this tether also incorporates the electric cable to takes the power to a central collection point and then to the shore.

The kite unit is inherently buoyant and comprises a wing-shaped top section that provides both the buoyancy and the lift. Below this is suspended the turbine rotor which is housed in a nozzle to increase the thrust. This rotor is directly connected to the generator so no gearbox is required and behind and below this is the rudder that controls the movement of the unit.

By means of the rudder the kite unit is made to track over a predetermined path limited by the scope of the tether. By following this underwater path to and fro in a sort of figure of eight motion the kite unit can move at over ten times the speed of the actual steady water flow and it is this increase in the water flow speed passing through the turbine that gives Deep Green its increased efficiency.

Minesto, the company behind this new system is claiming several advantages for their Deep Green kite system. The robust anchorage system does away with the need to install a permanent tower and low maintenance costs are claimed because only the attachment and detachment of the kite is done offshore with the remaining maintenance done on the unit when it is brought ashore. There is virtually no visual or environmental impact as the kite unit is always at least 20m under the surface of the sea which also keeps it below the waves. The full size kite unit will weight less that 7 tonnes and a unit of this size will produce around 500kW. It can operate in currents of less than 2.5m per second.

Four sizes of Deep Green have been developed, with the largest producing 850kW from an 11 tonne unit operating in water depth of between 90m and 120m in currents of between 1.4 and 2.2m per second. The smallest of these units is designed to produce 120kW in depths up to 65m.

“Our technology is indeed very different from other marine power plants, said Anders Jansson, CEO of Minesto. “It has been a long fight to get to the point where we are but when you have what we have it is worth it. This is a breakthrough for the entire renewables energy industry. We will produce renewable electricity with high reliability at a cost which will be competitive with or even lower than conventional energy sources.”

Minesto is owned by a consortium including Saab and several venture capital companies.

Further information:

By Dag Pike


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