Cool Earth Solar eyes rural power with balloons

Cool Earth Solar has one of those radical green-tech ideas that may actually make a real commercial impact.

In the next two weeks, the company plans to start testing a prototype solar plant built around rows of reflective balloons hung on poles. The solar balloons, which are eight feet in diameter, look something like a tube for sledding or laying around the pool, but each one can generate 1 kilowatt of electricity.

An early version of Cool Earth Solar's solar concentrator without the 'receiver' that holds the solar cell.

(Credit: Cool Earth Solar)

It's a design that combines cheap building materials, notably plastics, with expensive high-efficiency solar cells. Light goes through the side of the balloon facing the sun, is reflected on an aluminum coating on the bottom, and is concentrated onto solar cells in a "receiver."

The method can concentrate light between 300 and 400 times. To keep heat under control, the balloons have an automated water-cooling system.

The test installation for Cool Earth Solar, which was founded in 2006, will be small--on the order of a few dozen suspended balloons, according to a company representative. That's so that the company can make changes to the second version of its concentrating solar balloon.

Following that test system, which will generate about 100 or 200 kilowatts of electricity when done, the company intends to start building a 1.5-megawatt commercial solar power plant this winter, said CEO Rob Lamkin. One and half megawatts is enough power to supply about 400 or 500 U.S. homes. That installation, expected to be constructed in Tracy, Calif., will sell electricity to a utility.

Following that, Cool Earth Solar hopes to ramp up quickly, Lamkin said. It is planning another test facility, sized at 10 megawatts, for next summer, he said.

Unlike the rest
Cool Earth Solar's design is nothing like most concentrating photovoltaic (CPV) systems, which concentrate sunlight onto solar cells to make electricity.

Typically, concentrating solar devices use lenses and mirrors to direct and focus light to squeeze more electricity from high-end cells. The lenses, as well as the mounting and cooling systems, add significantly to the cost.

Cool Earth Solar's device, too, concentrates light onto expensive solar cells. But using materials like aluminum-coated plastic--the same sort of thing you'd find in a Power Bar wrapper--means the company can make electricity at $1 per watt, a few dollars per watt cheaper than other companies, Lamkin said.

Early version of Cool Earth Solar's concentrators mounted on poles.

(Credit: Cool Earth Solar)

He said that Cool Earth Solar will be able to sell electricity to utilities at the low end of what solar power plant providers project, which is in the range of 10 cents to 14 cents per kilowatt-hour.

Equally significant to cost is the flexibility that the balloons allow in terms of location.

Concentrating photovoltaic systems demand the right sun conditions, making them suitable only for certain areas like the southwest United States. That has set off a race among solar technology companies to find and get approvals for appropriate land. But Lamkin said that Cool Earth Solar is looking at a far broader set of possible locations where land is not as much in demand.

"It turns out, land is not an issue for us," he said. "What's exciting is because we are modular, we don't need to find super flat land in the lower Mojave desert. We're happy to be in farm land in rural California that no other solar companies are going after."

Cool Earth Solar raised $21 million in funding earlier this year. Lamkin said the company doesn't intend to raise more money in the coming year.

[cvye]

what happens when the wind kicks up?

[mlamonica]

The company says the balloons can withstand 125 mph winds.

[Manhattan2]

This company is on the right track. We have the optimal solution and it will be up to the next president and congress to make it happen at the scale that will be required to make a difference. Solar Transfer is the only solution that makes sense. Our researchers and engineers have that as our first requirement for any of our solutions. It has to make sense, be useful, and make a difference in some way. The answer is coming. George Bush didn't want to hear the solution, Hopefully our next president will be open to the power to reason. Cool Earth should contact the designers at Solar Transfer.

[Joe Real]

There is too much wasted space that sunlight is not captured from the total area occupied by the system. This is not a problem if the cost of land is very cheap, like in desert areas. In residential areas where land is at a premium, this is not a very efficient design to maximize power from a given area.

[Manhattan2]

Mr Real, at 10 percent efficiency with a 50% land mass saturation how many square miles do you need to power the US consumptions of energy electricity for manufacturing, transportation, food distribution. That's all energy. How much space? Solar Transfer is the solution. These guys are on to something. Something we have been talking about for a decade now at the Manhattan 2 Project. We have not released our Energy Manifesto yet. So the answers are still kept within the group. When the right people contact us at [e-mail] the system will be put in place.

[Joe Real]

Manhattan2, if you look at how they arranged the ballons, they are like wasting 75% space. If the individual ballons are 10% efficient, then their overall efficiency is just 2.5%.

The best terrestrial plants in the world are a lot better than that. In my previous stint as a researcher helping various scientists with crop simulation and modeling, some plants can be pushed to 5% overall efficiency if all biomass produced are accounted for.

This technology is not a wise use of prime land, and only the low grade lands are good enough for this, because it is the cost per watt that counts. Unfortunately those lands are far from urban centers where power is to be used, and so this would require tremendous infrastructure to obtain transfer and redistribute power from the waste lands unto the urban centers.