http://www.good.is/post/deep-green-kite-based-tidal-power/

The Swedish start-up Minesto is working on a new kind of
underwater turbine, called "Deep Green." Here's how it works: You tether this
kite-like apparatus to the ocean floor, at a depth of anywhere from 60 to 150
meters. Then, as a tide or current pushes against the kite, it moves from side
to side because its wings create a lift force. As it moves, water flows through
a turbine in the kite. And because it's moving, the velocity of the flow of
water through the turbine can be 10 times the surrounding stream flow, according
to Minesto.