Cool Earth Is Scaling Up Solar Energy Generation

Imagine a 1-megawatt solar power plant that has nothing to do with vast swaths of PV panels or mirrored troughs in a barren desert environment that require new transmission lines to population centers. Instead, picture a rolling, grassy field populated with 500 vertical poles that each hold two 8-foot-wide balloons. While cows graze among the poles, the large recyclable plastic balloons, each with a mirrored inside surface, truss and concentrated solar cell, follow the sun’s transit thanks to a small electric motor. A utility substation is nearby.

While balloons deployed across the land collecting solar energy is indeed a happy image, CEO Rob Lamkin would argue that the true serendipity of the startup firm’s technology has a more important source. “Enough solar hits the earth in an hour to power the world for a year. But flat panel PV installed is US $8 to $9 a watt, whereas our prototype is US $1/watt,” he says.

By using cheap, abundant thin film plastic as its primary technology component, Cool Earth has avoided the problem of being able to manufacture the PV required to generate enough solar energy to meet demand and reduce carbon. “The size of the energy problem is in TERA-watts and right now, there are less than 10 gigawatts of PV installed. China puts in that much coal-fired generation in a few weeks,” Lamkin says. “We need to ramp solar up to be doing gigawatts, or we are going to lose. A lot of people have figured out that we don’t make near enough PV. We would have to install 10 gigawatts of PV every four days until 2030 to get to carbon neutrality.”



The balloon-concentrator cell collector is the brainchild of Dr. Eric Cummings, an award-winning graduate of Caltech and principal investigator at Sandia National Labs. At a 2003 Department of Energy meeting of leading scientists and Nobel Peace Prize winners, Cummings was shocked to realize that even the best scientific minds seemed unable to find solutions to the unprecedented, urgent energy crisis. Most of their solutions were either not economically feasible using current technology or required a scientific leap that simply hadn’t yet occurred.

Cummings gave himself a mission to devise a solution to the global energy crisis that incorporated existing technologies or commonly used materials. After tinkering with ideas for months, Cummings decided to reverse his approach: Instead of devising a solar technology and fitting materials into it, he would calculate what materials could scale up enormously and create a technology to fit them. “I realized we couldn’t use rare elements. In fact, the materials had to be among the most abundant in nature or industry,” he said.

His answer: Plastic thin film was the only material with a great enough supply to solve the energy dilemma head-on. “If you used all of the plastic produced in a year to make just our solar collector balloons, they would generate 3 terawatts of energy, which is the Earth’s total demand,” Lamkin notes.

The idea of inflated concentrators arose quickly from Cummings’ determination that only a two-dimensional concentrator of thin film plastic would provide enough concentration of solar rays onto the solar cell.

By the end of the summer of 2005, having decided he could not manufacture the balloons, Cummings bought a bunch of 18-cent, 18-inch-diameter party balloons. Inflating them to different diameters, he traced their shadows on the wall, and digitized and ran them through mathematical analysis to trace the trajectories of the sun’s rays along the inner concavity of the balloons.

At this point, Cummings discovered that bonding a clear and reflective half together at the balloon’s equator created a far more efficient concentrator than he had expected. As a final touch, he added a batten (a rigid ring) around the balloon’s hemisphere that almost doubled the concentrator’s reflecting power and focus.

The plastic PV thin film mirror is Cool Earth’s main patent, the breakthrough, says Lamkin. “The plastic thin film makes a perfect curved mirror, which is very expensive to do with other materials,” he says. “When optics guys see it, they usually say, `Someone must have already done that! Why didn’t I think of it?'”

The first utility-connected Cool Earth project is scheduled to go online during the first half of 2009, a 1.5-MW plant on 12 to 13 acres near Tracy, CA. It is being financed with the firm’s US $21 million in Series A financing. The off-taker “probably will be a northern California utility,” says Lamkin.

Finding future sites will be easier than for other solar power plants, he says, because, at an installed cost of US $1 per watt and thus lower project ROI, “it doesn’t have to have maximum insolation [rate of delivery of solar radiation per unit of horizontal surface]” and the type of site it seeks is typically close to transmission.

One of the downsides to the technology is that the balloons cannot be placed on rooftops because the technology was designed to be utility-scale, not residential.

In addition, a Cool Earth plant must be manned to maintain the active flow of air and water among the balloons to ensure maximum power production and cooling. The circulation of air and water is fully automated, with micro-controllers monitoring individual balloon air pressure and the closed-loop circulation of 1 gallon of water flow per minute. But if a balloon is taking too much air because it has a leak, a signal light will go on, and maintenance personnel must patch it.

“When you add it all up, we will have a lot of O&M [operations and maintenance] items running. For 10 MW, 70 acres, we would expect to have 7 or 8 people working that plant,” says Lamkin. He adds that the number of air and water pumps they install has not been determined and will depend on location, such as in the desert, where they might need a shorter water line, or what kind of deals they get on air pumps.

The balloon films are rated to last 5 years outdoors, but Cool Earth says it will replace them every year.

Paul Wormser, director of engineering at Sharp Solar and co-founder of Konarka Technologies who also worked on commercializing solar technologies from University of Massachusetts labs, wonders if the plant O&M could prove to be Cool Earth’s undoing.

Acknowledging that he has only read about, not seen or tested, Cool Earth’s technology, he said, “even if you have a genuine technological breakthrough, very few startups succeed because they don’t have all of the things needed to make it happen. It’s not enough to have a high-efficiency cell, new lens, or inflatable collector. You have to be able to deliver kilowatt hours. The reality is that no one will know if they have properly estimated maintenance costs until they’ve done a few systems.”

Wormser also cited a “looming shortage” of the solar concentrator cells Cool Earth collectors use, which Lamkin disputes. “We’re not seeing a shortage of solar concentrator cells, and analysts are telling us there will be a surplus in the near term,” Lamkin says, adding that Cool Earth is talking to both Emcor and Spectralab, but not making any deals until it completes the development of its special PV receiver.

Marsha Johnston is a freelance writer based in California specializing in renewable energies, conservation and sustainable development.

For a detailed conversation with Rob Lamkin, CEO of Cool Earth Solar, listen to the November 6th edition of the Inside Renewable Energy podcast.

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