There are some fascinating proposals for power generation using tethered kites and balloons, so why not investigate the equivalent of underwater kites for generating power? Why not indeed, because that is exactly what two independent teams of researchers are doing, one from Minesto, Sweden and the other from Worcester Polytechnic Institute, USA [Source: Discovery News].

Minesto Underwater Kite

Just as traditional kites use air currents to generate lift, underwater kites use water currents to generate hydrodynamic lift. The tethered motion of the underwater kite generates electricity as water flows through an attached ducted turbine.

Water currents tend to be much more reliable and predictable than air currents so the expectation is that using water currents to generate electricity should be a more dependable power source. Also, given that water is approximately 800 times denser than air, the underwater kites can be much more compact for a similar power output compared to airborne kites. On the downside, water tends to be a hostile environment for machinery (especially metals). Also water is a relatively good conductor, so extra precautions are necessary for transmitting electricity.