CLEANTECH: Solar Alley

By Published On: September 26, 2008

Row upon row of huge plastic balloons containing palm-sized solar cells may help solve the global energy crisis. At least one company hopes so. Cool Earth Solar, based in Livermore, developed what it says are readily expandable concentrated photovoltaic units at a fraction of the cost of photovoltaic panels and other renewable resources. The technology, developed and patented by two-year-old Cool Earth, involves eight-foot parabolic-shaped balloons filled with air. The bottom half of the unit is painted black and covered by a thin layer of aluminum, which reflects and concentrates the light towards a solar cell sitting in the center at the top of the balloon. The top of the bubble is covered by a plastic film. The capacity of each 20-pound bubble unit is expected to be 1 kW. Rob Lamkin, Cool Earth chief executive officer, believes that solar balloon farms could replace polluting coal plants. “We are not doing one roof at a time,” he said. “Resolution of the global energy crisis needs to be equally large.” The solar balloons are tied to small towers that look like tall fence posts with steel cables. The devices work best in winds 40 miles per or lower. If reinforced, the generating bubbles can stand winds up to 120 mph but that requires more material, which drives the price up. The unit’s per-watt cost of installed capacity is estimated at $1 compared to the $4-$5/watt of rooftop photovoltaics, according to the solar industry. “It is not magic or technology, just engineering,” said Lamkin. The price difference is because the overall system uses far less expensive materials, and ones that are more available than those used in other solar power systems, according to Earth Solar. For example, the amount of aluminum in one can of Pepsi is about the amount of metal used in 750 concentrated solar bubbles, said Tony Chen, Cool Earth’s senior business developer. On top of that, the solar cells are not dependent on silicon but can also use triple junction cells. These cells were developed decades ago to power satellites. “One layer captures the light energy from the infrared band, another layer captures the energy from visible light, and the third layer captures the energy from the ultraviolet band,” said Chen. They are usually composed of elements such as germanium and gallium arsenide. They are ten times more expensive but far more efficient. “The multijunction cell allows the entire system to save 50 times in [terms of the] cost of solar cells,” Chen said. The life of all the materials used to manufacture the sun powered bubbles, except the plastic covering, is estimated to be 30 years. The plastic film will be replaced annually, although it is said to have a three to five year life. These solar units also take up less land than photovoltaic panels, according to the company. Installing 10 MW worth of these units would cover 80 acres, according to Lamkin. The average projects are expected to be 10-30 MW and built close to existing transmission lines. In contrast, a proposed concentrated solar plant by Oakland-based BrightSource is estimated to take up 3,400 acres for 400 MW. Because of the solar balloon technology’s low cost, Cool Earth is confident that it will land deals with public and private utilities in the state. The only issues from its perspective are how fast they produce the solar units, as well as possible visual impact concerns. The company systems qualify for the federal production tax credit, but would not qualify for the California Solar Initiative rebate because of their size. Cool Solar has yet to build a solar generating facility. It expects to launch its first one by the end of this year in Livermore. The 250kW facility is expected to occupy two acres.

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