Green Giants: World's biggest clean-energy projects

The Middle East is hardly known as the capital of clean energy, but Bahrain and the United Arab Emirates are trying to change that.

A few weeks ago, 100-foot-wide (30.5-metre) propellers began turning on the recently completed World Trade Center building, making Bahrain home to the world's first building-integrated wind turbine skyscraper. The building includes two sail-shaped towers that climb 54 floors above the beachfront site. Three small bridges link the towers, with a massive wind turbine hanging from each. The towers funnel the ocean winds into the turbines, which generate more than 10 per cent of the energy used by the building.

As climate change and renewable-energy policies level the playing field in the energy industry, alternative-energy companies are racing to assure investors, policymakers and the public that they can scale to meet the needs of energy-starved consumers. During the last few years, a clutch of clean energy projects have emerged on a scale never seen before. Forbes.com has identified the biggest and boldest projects among them.

We surveyed the clean energy landscape for new and recently completed projects in solar, wind, geothermal and wave energy that produced the most grid-connected electricity. Forbes.com also identified the green government initiative and green building project with the highest estimated dollar value. The results are different from what most people would expect.

Bahrain isn't the only desert blooming green this year. California's Mojave Desert is rapidly filling up with solar-thermal power plants, courtesy of Gov. Arnold Schwarzenegger. Solel Solar Systems, an Israeli solar-thermal company, recently agreed to supply Pacific Gas & Electric with 553 megawatts of solar thermal energy for 25 years, starting in 2009.

Like other companies, PG&E is racing to meet California's 20 per centrenewable energy requirement by 2010. As a result, Solel plans to string 1.2 million mirrors in large arrays over nine square miles of California's southeastern desert. The plant will use parabolic 1-metre-by-1.2-metremirrors developed by Solel to convert the sun's heat into steam that powers turbines.

Deserts aren't the only place being developed quite a few projects are taking place in the ocean.

Scotland boasts roughly 25 per centof the entire European Union's tidal power potential and 10 per centof its wave energy potential. In an effort to tap those resources, Scottish Power, a wave-energy company based in Scotland, plans to build the world's largest wave-energy farm off the coast of Orkney Island. If wave energy proves as profitable as many say, Scotland could produce more than 1,300 megawatts by 2020, enough to power a city the size of Seattle, according to some estimates.

Despite Scotland's ambitious foray into wave energy, the Orkney project is small change compared with what's happening off the coast on the opposite end of the island.

England is the windiest country in the European Union. Slightly smaller than Louisiana, the island nation is already hard-pressed for space, which wind farms need a whole heap of to make a difference. As a result, England has done what England has always done head to sea.

The London Array project plans to erect a constellation of more than 340 wind turbines in the outer Thames Estuary, roughly seven miles off the Kent Coast. When construction ends, London Array will be the world's largest offshore wind farm, generating more electricity than Denmark's Middelgrunden offshore wind farm, which is the largest offshore farm operational today.

Although London Array is hard to beat on the big scale, that's hardly enough to stop a Texas oil tycoon like T. Boone Pickens from trying. Nothing shows the continuity between Big Oil and Big Green quite like Pickens, the oilfield roughneck turned Texas oil tycoon who plans to build the world's largest wind power farm.

Pickens has invested heavily in a planned wind power farm that will stretch across four counties in the Texas panhandle near Amarillo. The farm's 2,700 wind turbines will be able to power 1 million homes when construction ends.