In 2015, a £25m project was launched to install underwater “kite-turbines” in Holyhead Deep, off the coast of North Wales.
Swedish developer Minesto has built the turbines and plans to commission the project in stages, starting in 2017 with a 0.5 MW demonstration unit of their patented Deep Green ocean energy power plant.
Unlike airborne kites, which turn a generator on the ground, these underwater kite-turbines have a wing with a turbine attached directly to it.
The underwater current lifts the wing and the kite is steered in a figure-of-eight at several times the speed of the current.
The water flows over the turbine blades and turns them, producing electricity, which is then transmitted through to a cable to the kite-turbine’s tether on the seabed and from there to the grid onshore.
Most existing tidal technology is large, fixed and can operate only in currents that are faster than 2.5 meters per second.
Because the movement of Deep Green increases the speed at which currents flow over the turbine, it can operate at lower speeds than fixed installations, down to 1.2 meters per second.
Each turbine is rated at between 150 and 800 kW and can work submerged in depths of 15 meters to 300 meters.
Kite-turbines can also be up to 15 times lighter than fixed alternatives, at around 10 tonnes.
The locations for these generators have to be chosen so that they don’t interfere with shipping or other sea users.
Following the demonstrator project in 2017, the site will be gradually expanded to house 20 power plants producing 10 MW.
Minesto have also announced that they are looking to take the eventual size of the array to 80 MW.
The cost of energy from this technology could be around £1 million per installed MW at this point, although costs could decrease with scale.
The UK is in a unique position to harvest energy from tidal resource – it has around half the European tidal resource and 10-15% of global resource according to Minesto.
Tides are also very predictable, making this kind of technology very attractive if it can be deployed at scale because it uses renewable resource and its output can be predicted with a high degree of accuracy.