Company making the solar balloons: Cool Earth Solar of Livermore, California
'Cool Earth’s insight was that if you coat only one half of a balloon, leaving the other transparent, the inner surface of the coated half will act as a concave mirror. Put a solar cell at the focus of that mirror and you have an inexpensive solar-energy collector.
Cool Earth’s balloons are rather larger than traditional party balloons, having a diameter of about 2½ metres (eight feet), but otherwise they look quite similar. The solar cell aside, they are ridiculously cheap: the kilogram of plastic from which each balloon is made costs about $2. The cell, the cost of which is a more closely guarded secret, is 15-20cm across and is water-cooled. That is necessary because the balloon concentrates sunlight up to 400 times, and without this cooling the cell would quickly burn out.
The result, according to Rob Lamkin, Cool Earth’s boss, is a device that costs $1 per watt of generating capacity to install. That is about the same as a large coal-fired power station. Of course, balloons do not last as long as conventional power stations (each is estimated to have a working life of about a year). But the fuel (sunlight) is free. When all the sums are done, Mr Lamkin reckons his company will be able to sell electricity to California’s grid for 11 cents a kilowatt-hour, the state’s target price for renewable energy, while still turning a tidy profit.
That belief will soon be put to the test. Cool Earth plans to open a 1-megawatt facility this summer. If it works, more will follow...'
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