And they're full of energy. The National Renewable Energy Laboratory says the oceans are the world's largest solar energy collector and energy storage system.
For instance, "on an average day, 23 million square miles of tropical seas absorb an amount of solar radiation equal in heat content to about 250 billion barrels of oil," the lab says.
Add tidal and wave power, and that's perhaps why researchers, scientists and entrepreneurs are redoubling efforts to tap the resource and plug its clean energy into the grid.
Wave & tidal power get financing
Wave and tidal power have received most of the recent ocean power buzz. The U.S. Department of Energy in May 2011 handed out $4.7 million to companies involved in wave energy development off the coast of Oregon, according to the Portland Business Journal. Oregon Wave Energy Trust contributed another $496,000 in matching money.
Extracting the aforementioned solar energy via ocean thermal energy conversion also shows potential. Ocean thermal systems use warmer water at the surface and colder water from about a half mile down to generate energy. This works so long as the temperature difference is no less than 36 degrees F.
"An OTEC system can produce a significant amount of power," NREL says, estimating the overall potential to be about 10,000 gigawatts. A gigawatt is a billion watts.
Like a lot of renewable energy concepts, this one has its technological hurdles. The greatest is of course financial viability. Can it be done cost-effectively?
Some companies have taken on the challenge.
The Ocean Energy Council, based in West Palm Beach, Florida, says new designs for ocean thermal energy conversion remain mostly experimental. The council reports those that have been built have been small -- one near Japan that can generate 100 kilowatts and another off the coast of Hawaii, producing 50 kilowatts.
"A full scale OTEC would cost many millions of dollars, and it would be very difficult to build," the council says.
Ocean thermal makes gains
Ted Johnson, who worked with Lockheed Corp.'s on development of the floating ocean thermal pilot plant off the coast of Hawaii, says rising oil prices and technological advances have made the systems "increasingly attractive" to some countries.
"The technology exists to make ocean thermal energy a reality," he says in a statement.
His company, Lancaster, Pa.-based OTE Corp., is currently peddling the technology, along with accompanying water desalination and sea-water cooling.
A system was successfully created in 1929, when French engineer George Claude designed and built a 22-kilowatt on the Cuban coast. "He took the warm surface water and put it into an evaporator," reports the Ocean Energy Council. "The pressure was lowered which caused the water to vaporize. It was forced through a turbine and it produced 22 kilowatts of electricity. Cold water was piped up from lower ocean depths to cool the vaporized water so the cycle could begin again."
But storms kept breaking the pipe used to collect cold water from deep water, and the project was abandoned.
Ocean power & Dr. Pepper
I'm fascinated with the prospect of realizing energy from the sea. I lived third grade and many summers before that with my grandmother, spending nearly all of my free time on the beach, in the water or trying to get onto it in a skiff. I don't recall that it mattered how cold it was.
The power of the ocean amazed me back then. I recall holing up with my little sister during a storm at the highest point of the black shale beach under some driftwood. I wanted to see how far the waves would crash. They cascaded 50 to 60 feet and just over us. Grandma found me after a good four hours. Her expression was a mixture of profound relief and barely concealed anger. Turned out the whole town of Port Lions, Alaska was looking for us, so we got hot Dr. Pepper at the cafe.
Not every storm delivers hot Dr. Pepper. Irene ravaged thousands of miles of coastline, expelling its massive energy. If just some of that was captured, bottled and reapplied, we'd be giving power away.
The search continues
But the search for clean energy isn't simple. The ultimate solution to cheap renewable power eludes us for the most part.
Yet, ingenuity and mankind's desire to find solutions may ferret out a solution.
In many ways we're just like Daniel Defoe's "Robinson Crusoe," stuck on an uncharted island surrounded by blue seas with everything we need to survive. In Crusoe's case, it took many years for him to successfully figure out how to use all the resources he was given.
Maybe we just need a couple more years.
Art: Cover of the first edition "Robinson Crusoe."