Water Kites

Seriously cool development from the Swedish firm Minesto (part of Saab).

A completely new concept of underwater wave energy using a simple 7 ton kite turbine design has been developed by Minesto; which is a spinoff from the Swedish military and aircraft design firm Saab. The Deep Green underwater turbine captures the power of the ocean just like a kite in wind. The system could generate 18 terawatthours of energy annually, enough to provide nearly 4 million British households with reliably green electricity every year. UK households now use about a third of what average US households use in energy.

There is a video and picture at the link. This looks very promising.