Minesto’s underwater kite could harness tidal energy

Unlike wind kite energy generating concepts, a concept of underwater wave energy which uses a simple 7 ton kite turbine design has been developed by Minesto. Minesto’s innovation “underwater kites” originates from the wind department at Saab Group (the aircraft and military Saab, not the automaker), who started development in 2003. The concept was more suited for water currents than winds, and since the concept was beyond the Saab Group’s core business, Minesto was formed in 2007. “Minesto” means tide and dragon in Greek.

Originally Saab was working on a kite design for a wind turbine, but found that the concept would actually work better in water, which is 832 times denser than air. The new technology could contribute to a substantial increase of power from the tides with its ability to produce energy from areas where other technologies are less efficient. The main reason for this is the extended site areas available when looking at sites with a current velocity of 1.2-2.2m/s and depths between 60-120 meters. If mounted in UK shores, the system could generate 18 TW-h of energy per year, and that is enough to provide approximately 4 million UK households with reliably green electricity every year.

The principle of the technology can be explained as a two stage process. The first stage increases the relative flow speed entering a turbine. When the tide hits the wing it creates a lift force, since the kite is mounted to the ocean bed with a tether and is controlled by a rudder, the kite can be taken in the desired trajectory. The method increases the flow velocity into the turbine with 10 times the current speed. The second stage uses a conventional plant to convert kinetic energy into electrical power. The net result is increased power from a smaller package. This makes the Deep Green concept very suitable to harness power from slow moving waters. And no gearboxes are needed.

According to the people from Minesto, each megawatt-worth of kites would weigh 14 tons, so it would seem that each 7 ton kite is a 500KW unit. According to CEO Anders Jansson’s estimate, these could probably produce power for somewhere between $0.09 cents and $0.20 cents per kwh.

The Carbon Trust based in the UK gave early development support. Minesto’s Deep Green is now funded in part by the UK and Swedish governments, and has nearly $3 million in additional capital from parent company Saab Group, Midroc New Technology, Verdane Capital and Encubator. So far a scale 1:10 prototype of the Deep Green has been built, and a scale 1:4 prototype will be ready in the waters outside the coast of Northern Ireland in 2011.

With its simple and cost effective design, this could be the tidal generating power of the future. However, there are some aspects of it which need to be considered. The technology can’t be good for marine life near them. The flow of the water currents which are essential for the climate and life could be affected if we overuse the technology. There are also questions related maintenance and re-installation of broken turbines. It is a nice idea which needs a lot of tweaking. Let’s hope they’ll use some of the funding to find the solutions to the mentioned and other potential problems, instead spending all on prototype construction.