Two decades after the Exxon Valdez spilled 11 million gallons of crude oil into Alaska’s waters, the Prince William Sound, its fishermen, and its wildlife have still not fully recovered.

Led by China, the developing world is engaged in a flurry of dam construction, touting hydropower as renewable energy in an era of global warming. But critics point out that the human and environmental costs of dams remain high.

Even as they debut the next generation of hybrids and battery-powered cars, auto company executives are not confident that the American public will buy them.

A number of companies, including one headed by biologist and entrepreneur Craig Venter, are developing genetically engineered biofuels that they say will provide a greener alternative to oil. But some environmentalists are far from convinced.

The potential for electric vehicles has been talked about for decades. But a former Israeli software entrepreneur is developing a game-changing infrastructure that could finally make them feasible — a standardized network of charging stations where drivers can plug right in.

Despite daunting challenges, technology to harness the power of the waves and tides is now being deployed around the world from Portugal to South Korea to New York’s East River. These projects, just beginning to produce electricity, are on the cutting edge of renewable energy’s latest frontier: hydrodynamic power.

Any federal assistance package for U.S. automakers must require that they finally commit to retooling their industry to produce cleaner, more fuel-efficient cars.

You’ve heard the environmental horror stories: rivers running black, air unfit to breathe, two new coal-fired power plants a week. But thanks to a surging entrepreneurial spirit and new policies, China is fast becoming a leader in green innovation, from recycling to developing electric cars to harnessing the wind.

Until now, geothermal technology has only been used on a small scale to produce power. But with major new projects now underway, deep geothermal systems may soon begin making a significant contribution to the world’s energy needs.

After years of false starts and failures, the electric car may finally be poised to go big-time. With automakers from GM to Chrysler to Nissan preparing to roll out new plug-in hybrids or all-electric models, it looks like the transition from gasoline to electricity is now irreversible.

Congress has repeatedly failed to extend the tax credits for renewable energy, which expire at the end of this year. The gridlock is discouraging investment in renewables and jeopardizing major solar and wind projects throughout the country.

Texas billionaire T. Boone Pickens has always been one to think big. But his sweeping 10-year energy plan for America faces obstacles that may be insurmountable.

After years of optimistic predictions and false starts, it looks like solar's moment is here at last. Analysts say a pattern of rapid growth, technological breakthroughs, and falling production costs has put solar power on the brink of becoming the world's dominant electricity source.