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Applications: Balloons Make Unusual, Low-Cost Solar Collectors

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Anne L. Fischer, Senior Editor,

Concentrated solar systems are not attracting much new attention these days, but when the collectors are fabricated out of bonded thin films that look like a balloon, heads will turn. Cool Earth Solar of Livermore, Calif., is building a prototype solar plant with rows of these reflective 8-ft-diameter balloons secured on poles. The solar balloons look odd, for sure, but who can complain when each one can generate 1 kW of electricity?

Solar concentrators come in all shapes and sizes. These concentrators from Cool Earth Solar look like balloons.

Company founder Eric Cummings recognized that an effective energy solution had to be economical, massively scalable and readily deployable. Instead of developing a new solar technology and fitting materials into it, he decided to go with plastic thin film, which is manufactured in large quantities at low cost. Each Cool Earth Solar concentrator consists of about $2 of plastic, air, a tiny solar cell and a tiny amount of aluminum, according to Rob Lamkin, the company’s chief executive officer.

The way it works is that light goes through the side of the balloon that faces the sun. The light is reflected on an aluminum coating on the bottom and then concentrated onto solar cells in a receiver. According to Lamkin, this concentrated photovoltaic (PV) system generates the same amount of electricity as traditional flat panel PV systems “while using up to 300 to 400 times less solar cell material.” The sunlight that concentrates within the balloon generates heat as well as kilowatts, so a closed-loop water cooling system is installed.

The PV cell that sits inside the balloon can be a multijunction solar cell or a silicon-based cell – both readily available. Because the balloons are relatively small and modular, it’s not necessary to have the huge expanses of perfectly flat, sun-drenched land sought by most concentrated solar providers. To help angle the balloon to the sunlight, the amount of inflation can be regulated. Each module tracks the sun across the sky in two directions – from north to south and east to west.

Cool Earth Solar is currently building its prototype plant, which will produce between 100 and 200 kW, in Livermore. This winter, after completing that test system, the company intends to start building a 1.5-MW commercial solar power plant that will produce enough electricity to power 400 to 500 homes. That installation, which will be in Tracy, Calif., will sell electricity to a utility. Lamkin anticipates that, when installing “at scale” in a year or two, Cool Earth will be constructing solar power plants at $1 per watt of capacity.

Photonics Spectra
Jan 2009
Electromagnetic radiation detectable by the eye, ranging in wavelength from about 400 to 750 nm. In photonic applications light can be considered to cover the nonvisible portion of the spectrum which includes the ultraviolet and the infrared.
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