Article: Party time!
Publisher: The Economist
Date: March 5th 2009
Technology today is all about efficiency, because efficient technology is cheaper. This is true, for example, for solar cells. Since they are very expensive, it is desirable for them to work at the maximum capacity. Therefore, to make them more efficient, sunlight is concentrated on smaller areas of a cell to convert the same amount of light a larger area of the cell would normally convert. Normally, the concentrating of light is done by mirrors that are steered by motors so that they focus sunlight directly onto the cell. Now, however, a company called Cool Earth Solar (based in California) has come up with a cheaper alternative to these mirrors: balloons coated with metal on one side (the other is transparent).
The balloons, approximately 2.5 meters in diameter, are the equivalent of the mirrors; the inner surface of the coated side of the balloons acts as a concave mirror that focuses sunlight directly onto the solar cells. Since a balloon concentrates sunlight up to 400 times, the solar panels have to be immersed in water. Different methods of steering the balloons are being tested currently; the curve of ‘concave mirror’ can be adjusted by changes in air pressure in the balloon. Though the balloons only have a working life of about a year, they are much, much cheaper than actual mirrors. The kilogram of plastic from which the balloons are made costs about $2. The balloons cost $1 per watt of generating capacity to install. The result would be that the electricity generated by the solar cells could then be sold to California’s power grid for 11 cents a kilowatt-hour. Cool Earth plans to open a 1-megawatt facility to put this hypothesis to test. If it works, solar power plants will soon be looking a lot more festive.
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