WASHINGTON — Scouring the Earth for new sources of clean, renewable energy, scientists and engineers are exploring some unusual nooks and crannies.
Kites, waves, tides, ocean currents, geysers, garbage, cow manure, old utility poles, algae and bacteria are being enlisted in the effort to lower the world's reliance on climate-warming coal and oil.
Researchers are even trying artificial photosynthesis, producing electricity by imitating the way that green plants exploit the sun's energy.
Most of these ideas may never make economic or technological sense. It's always possible, however, that a daffy-sounding scheme could turn out to be the next Google, GPS, Facebook or similar breakthrough.
Many exotic proposals would be expensive, at least at first, and of uncertain reliability. They mostly depend on government subsidies, and probably the continued high price of oil, to make them competitive with the old standbys.
Here are some of the innovative ideas that researchers — and venture capitalists hoping for profit — are working on:
People have always been amazed at the enormous power of waves, especially those pounding the U.S. coastlines. Now they're trying to harness some of that wasted energy to generate electricity.
The European Wave Energy Centre (www.wave-energy-centre.org), based in Lisbon, Portugal, lists 63 such projects with catchy names such as Wave Dragon, WaveRoller, Manchester Bobber, Poseidon's Organ and many others.
Some use floating devices that bob up and down with the waves. Others try to capture energy from the surf along beaches. A ``wave swing'' hanging below the sea's surface generates electricity from the rising and falling pressure of waves passing overhead.
The up-and-down or back-and-forth motion of these experimental devices produces energy to drive electrical generators, provided that they can be scaled up to work at high volume and reasonable cost.
"No design has yet emerged to be the winner,'' said Chang Mei, an ocean engineering expert at the Massachusetts Institute of Technology in Cambridge.
One pilot project is the Pelamis Wave Energy Converter, based on the Orkney Islands north of Scotland. Pelamis resembles a huge snake made up of four 40-meter (about 130-foot) steel tubes, linked end to end, riding on the sea surface. Waves make the segments flex against each other, driving hydraulic rams that, in turn, drive electric generators. By next year, said the operator, Pelamis Wave Power Ltd. (www.pelamiswave.com), it hopes to supply the power that 10 percent of Orkney's 20,000 inhabitants need.
Another Scottish company, AWS Ocean Energy (www.awsocean.com), with backing from Shell, the big oil company, plans to deploy a small demonstration of its underwater Archimedes Wave Swing off the stormy coast of Scotland next year. It hopes to produce commercial power by 2011.
Suitable tidal currents are scarcer but more dependable than waves, Mei said.
An ambitious scheme being developed at Florida Atlantic University in Boca Raton would anchor a fleet of turbines to the seafloor under the Gulf Stream 13 to 15 miles off the east coast of Florida.
The vast, untapped power of the Gulf Stream would spin the turbines as it flows north at a steady 5 mph. Underwater cables would carry electricity to shore. A prototype turbine is being tested in a laboratory before it goes into the water next year, assuming that questions about the environment and the safety of fish are settled.
"Florida is the best location in the world to develop ocean current energy,'' said Susan Skemp, the executive director of Florida Atlantic's Center for Ocean Energy Technology, the project's sponsor. When fully deployed, she said, the Gulf Stream could produce as much electricity as four to eight nuclear power plants, enough to serve up to 5 million homes.
The United Kingdom is weighing a plan to place a 10-mile-long ``barrage,'' a sort of dam, across the Severn Estuary between Wales and southwest England. The rise and fall of the estuary's 48-foot tides would spin turbines, like a hydroelectric dam, but it would work both ways, as the tide roared in and out.
The $29 billion tidal-power scheme is being fought on economic and environmental grounds, and its fate is uncertain. A similar, smaller barrage has been producing energy in France for 40 years.
A company called Tidal Sails wants to string a line of underwater "sails'' — like a capsized sailboat — across a tidal stream to capture energy from the current.
Nova Scotia operates a tidal power plant in the Bay of Fundy. An experimental set of small underwater turbines is producing power in New York City's East River.
Wind turbines have become a common sight in the United States and Europe, but researchers are exploring novel sources of wind power.
A German company, Beluga Shipping (www.Beluga-Group.com), hooked a 520-square-foot kite to a freighter to help tug it 12,000 miles across the Atlantic last winter. The kite saved 20 percent of the fuel that's usually used in the crossing, the company said. The "Beluga SkySails'' will be installed on two larger ships in the future.
A California company, Makani Power (www.makanipower.com), received a $10 million grant from Google to construct a system of extremely high-flying kites to exploit the fact that winds are much stronger and steadier thousands of feet above the ground. Earthbound wind turbines reach only up to 300 feet.
"The average wind energy at high altitudes appears to be more than 10 times greater than at a well-sited terrestrial wind turbine,'' a statement from Makani says. "In addition, high-altitude wind is a highly dependable resource.''
A major problem with solar power is how to store the sun's energy at night or on cloudy days. All sorts of schemes have been attempted, from big batteries to tanks of hot oil to blocks of hot concrete
Now Daniel Nocera, a chemist at MIT, has found to way to imitate nature's solution: using plants to turn sunlight into water and carbohydrates, which then can be turned into energy.
"There's a lesson to be learned from nature,'' Nocera says in an online video (http://newsoffice.techtv.mit.edu/file/1243). Leaves on plants "store energy all the time" using photosynthesis.
Nocera's invention uses solar power to split water into hydrogen and oxygen more cheaply and easily than ever before. The chemicals are stored in fuel cells, which generate electricity when it's needed.
"You can do it in a glass of water at . . . room temperature,'' Nocera says in the video.
The process "at least opens a door for the large-scale deployment of solar, because we have an easy way . . . to store that energy," he says.
James Barber, a biochemist at Imperial College, London, praised Nocera's work. "A perfect solution to the energy problem is to mimic the natural system which has served us so well,'' Barber wrote in an e-mail. "Nocera has taken one big step towards this dream.''
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