Balloons, The New Green Power

Here's the ingenious part of the technology, developed by scientists at Caltech: Instead of using expensive optics to concentrate sunlight on the solar cell, Cool Earth manipulates the air pressure inside the balloon to change the shape of the mirrored surface so that it focuses the maximum amount of sunlight on the solar cell, boosting electricity generation 300 to 400 times.

By replacing expensive materials like steel with cheap-as-chips plastic and air, Cool Earth aims to dramatically lower the price of solar electricity. "We strongly believe it's all about cost," says Lamkin, "not how clever the technology is or if it is 1% more efficient." For instance, the amount of aluminum in a can of Coke would provide enough reflective material for 750 balloons, he notes.

The company, founded in 2007, has raised $21 million so far. It plans to build solar power stations in the 10-megawatt to 30-megawatt range. Two to six balloons will be suspended on wood poles and anchored with cables about 10 feet off the ground. That means the earth won't have to be graded, reducing the environmental impact of Cool Earth's power plants - a growing issue given that most solar thermal power stations will be built in the desert, home to a plethora of protected wildlife. The relatively compact size of Cool Earth's power stations also means they can be located close to existing transmission lines.

A prototype power plant is being built in a field across the street from Cool Earth's offices and Lamkin says a 1.5 megawatt plant will be constructed early next year in the Central Valley town of Tracy.