Up through the times lots of cool engineering projects have been initiated to harness wind or waves, even to pull energy from the mixing of river water with salty sea water, or harness the temperature deltas between the ocean surface and the water at 20 metres depth, but rarely they scale up to commercial operations.

SkySails is one example I can think of. Apparently a small investment and installation on just about any existing cargo ship, and the shipping company may in average save some 5-6% of the fuel costs by utilizing high-attitude winds, without compromising on the shipping time. (Of course it is possible to save 100% of the fuel costs by using such systems if one is willing to increase the shipping time slightly and decrease the delivery time predictability). From what I understand, the investment would be paid down within a year or two from the saved fuel costs.

The company was founded in 2001, the first pilots started in 2007 ... and what has happened since? Not much, except for layoffs.

Wikipedia has more information about other projects utilizing high winds at High-altitude wind power and Kite rig.