5 of 5
Balloons that boost solar power
Balloons that boost solar power
Cool Earth Solar, Livermore, Calif.

Solar cells that generate electricity are all the rage, but what if you could boost their power dramatically by increasing the amount of sunlight that hits them? The startup Cool Earth uses air-filled balloons to focus the sun on a solar chip lodged within.

Founded: 2007

Technology: Traditional solar concentrators use expensive optical equipment to focus sunlight on a solar cell to increase the electricity produced. Tapping the power of air is the key to Cool Earth's solar balloon, which weighs 20 pounds and is made from $2 worth of thin-film plastic like that found in potato chip bags. Cool Earth's innovation - developed by Caltech scientists - is to use the air pressure inside the balloon to constantly change the shape of an aluminum-coated reflector to track the movement of the sun and focus its rays on a highly efficient solar cell. The concentrated sunlight boosts electricity generation 300 to 400 times. Because the balloons are suspended about ten feet off the ground, they don't interfere with wildlife and take up less land than other solar power plants.

Energy production/savings: One balloon produces one kilowatt. Two to three balloons could power a typical home.

Stage of development: A demonstration power plant is under construction; ground will be broken on a 1.5-megawatt power station in early 2009.

Reality check: The solar balloons - designed to withstand 125-mph winds - need to be replaced every year.

Last updated October 15 2008: 8:45 AM ET
More Galleries