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:

Waves

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 Lisbon, Portugal-based European Wave Energy Centre (www.wave-energy-centre.org) lists 63 such projects with catchy names such as Wave Dragon, WaveRoller, Manchester Bobber and Poseidon's Organ.

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.

"No design has yet emerged to be the winner," said Chang Mei, an ocean engineering expert at the Massachusetts Institute of Technology.

Currents

Suitable ocean 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 are settled.

Tides

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 plan 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.

Wind

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.

An Alameda 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.

Artificial photosynthesis

A major problem with solar power is how to store the sun's energy at night or on cloudy days.

Now Daniel Nocera, a chemist at MIT, has found a way to imitate nature's solution: using plants to turn sunlight into water and carbohydrates, which then can be turned into energy.

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.

Call Robert S. Boyd, McClatchy Washington Bureau, (202) 383-6007.