Here is an idea for generating energy from the oceans. The interface where rivers dump into the oceans releases tons of potential energy everyday. The potential is due to the dissoved mineral concentration gradient between fresh and salt water.

The simpliest way to harness this potential is a low tech power cycle. Place a membrane between the two waters. Osmosis will cause the fresh way to flow into the salt water. Uses an osmotic pressure cycle to run a piston.

If we want to get a little higher tech, the ion concentration is also a renewable chemical potential that can generate low voltage. If we tie this low voltage into the voltage needed to make hydrogen from water, we make hydrogen generation from water a little cheaper.

If we combine the two application into a three parallel chamber device; fresh water in the middle and salt water on the ends, we use the voltage apsect to make hydrogen and oxygen from the fresh water. Since the osmotic chamber wants the center water to leave the fresh water chamber, shouldn't the generation of oxygen and hydrogen (osmotic water is leaving as gas into the salt chamber) be a way to take advantage of the osmotic potential?

The overall goal is to use some of the solar induced fusion potential within the hydrogen of water vapor, i.e., evaporation, to clouds, to rain, to fresh water to salt water, to help generate hydrogen.

may be it is easier to extract energy from waves

here's a much more powerful way, it seems:

http://www.wired.com/wired/archive/13.06/craven.html

While I grant you that both methods would be very cost-intensive to establish infrastructure, the "cold-water" method appears more efficient in terms of potential power output.

-ss

The biggest advantage of the salt water-fresh water gradient is that it is useful anywhere on the earth, hot or cold. All one needs is a river and an ocean. I agree about the infrastructure being expensive. Utilization here in the states would animate so many rational and irrational special interests that the added cost and time delay would probably kill it dead in the water, i.e., best interests of the majority being sacrificed to appease the irrational needs of those with too much time on their hand. The technology might be useful in second and third world coastal countries where poor people would be grateful for self sufficient electricity.

Like trillions of rubber bands.