Deep Green is an underwater-surfing kite, tethered to the bottom of the sea and equipped with an electrical generator. The kite follows an 8-shaped trajectory, moving faster than the water current, and produces electricity from low velocity tidal and ocean currents. Long-term ocean trials have been conducted for several years off Northern Ireland, and have demonstrated that the technology is both functional and cost efficient.
”Deep Green has received a lot of attention. In 2014, Minesto won The WWL Orcelle Award. It is handed out by Ocean Exchange, an innovation directed organization looking to reward the best solutions to the world’s most pressing problems. The British magazine Power Technology recently ranked Deep Green as one of the six most promising new green power technologies”, says Anders Jansson, CEO at Minesto.
Not affected by weather or climate
”Harnessing the energy present in tidal and ocean currents is not a new idea. Tidal and ocean currents are energy dense, and streaming water has an energy content 800 times that of wind. They are predictable, reliable and continous, and available in every part of the world. So far, areas with strong tidal currents have been in focus – since they contain more energy”, says Anders Jansson.
”Conducting operations in areas with strong currents is problematic and costly, however. The power plants have to be large and heavy, and working conditions are difficult. Also, such waters are generally further away from settlements, since the currents make fishing and shipping dangerous. If electricity is produced in such areas, additional infrastructure is needed to bring the electricity to the consumers”, says Anders.
”Those conditions makes it difficult to reach cost efficiency – but our concept turns the tables. We develop an alternative technology, with low-cost, lightweight power plants, suited for deployment closer to the existing infrastructure. Deep Green also has an advantage in the fact that ocean currents are nearly constant and tidal currents almost totally predictable, making the technology unaffected by intermittent weather conditions”.
Low velocity currents
The Deep Green concept was invented in 2004 by Magnus Landberg, engineer at the aircraft manufacturer Saab. Deep Green consists of an underwater kite (a wing), which carries a turbine and a nacelle containing power take-off and control systems. A rudder, a servo and a control system steers the kite in a predetermined trajectory. A tether attaches the kite to a foundation on the seabed or a buoy at the surface.
Deep Green produces renewable electricity by a principle similar to how a kite flies in the wind. The wing generates a lift force when hit by the ocean current. The kite, tethered to the bottom of the sea, is steered by a rudder to move in the desired trajectory. This method makes water flow through the turbine at a speed ten times the water current speed. It is the same principle that applies when a sail boat is able to travel faster than the wind. The electricity is transported in a seafloor cable to a transformer station on the shore, where it is converted to the standard of the grid.
Power plants will be connected in arrays. The configuration may vary depending on i.e. the distance to the shore, the depth, and the seabed conditions, but a typical Deep Green array may consist of 100 devices supplying electricity for 33,000 households.
”We have the opportunity to get a head start and cover more than half the global tidal market. We offer the best technology available to harvest energy from ocean currents. Commercial operations will begin with the installation of a full scale power plant (DeepGreen 500) at Holyhead Deep off Northern Wales. The next step will be the installation of a 10MW marine energy array. Our technology is innovative, cost efficient and has impressing efficiency. The demand for renewable energy is on the rise, and we know that we have developed a concept that can make a real difference. When this is going to happen? Soon.” says Anders Jansson.
The article was published in February 2016.