Underwater kites harness energy from predictable tidal currents

A new design could greatly increase the efficiency of tidal energy generation

Spotted: Tidal energy is a source of renewable power in which energy is harnessed from either the natural rise and fall of ocean tides or the movement of tidal or ocean currents. Although not yet widely used, tidal energy has a huge potential for future electricity generation. Unlike wind and solar energy, tidal streams and ocean currents are predictable and continuous. First-generation tidal technologies tend to require strong tidal flows in order to be commercially viable. However, a new approach could greatly expand the energy potential of tidal flows.

Startup Minesto has developed a ‘kite’ with a turbine that ‘flies’ underwater to generate electricity from predictable tidal streams and ocean currents. The device is attached to a tether and uses the hydrodynamic lift force created by the underwater current to move. An onboard control system autonomously steers the kite in a figure-of-eight trajectory. This motion pulls the turbine through the water at a water flow several times higher than the actual stream speed – and this faster speed generates more power.

The tether contains cables for communication and power and is connected to the seabed foundation by a connector that can be easily latched and unlatched for installation and recovery. Electricity generated is sent to the grid using a power cable within the tether.

Minesto claims that its use of a wing design and its underwater ‘flight’ makes this technology more efficient than other tidal energy technologies. On its website, the company explains that, “This means that when the kite multiplies the relative speed which the turbine is pushed through the water, the electricity produced by the generator is several times greater compared to if the turbine would be stationary. By adding this step of energy conversion, Minesto expands the global tidal and ocean currents’ extractable potential.”

Other recent renewable energy innovations that harness the flow of water include a floating platform that harvests energy from rivers and a new design that could allow wave energy to be harvested from the open ocean.

Written By: Lisa Magloff