How do you turn plastic into energy? By coating it with a thin layer of aluminum, doubling the layers to form an inflatable "balloon," and inflating it into an efficient shape for capturing and concentrating solar energy.

Source: Cool Earth Solar

The promise of using the free, abundant solar energy that falls on the earth every day to meet our energy needs is familiar to everyone; after all, enough solar energy falls on the earth in just one hour to meet the whole world's demand for an entire year. Almost as familiar is the conventional litany of obstacles that stand in the way of this achievement: conventional photovoltaic cells are expensive, and satisfying global energy demands will require impractically large amounts of silicon. Livermore-based Cool Earth Solar has a different vision of how large-scale solar energy can be made widely available and affordable.

GreenMomentum recently had the opportunity to speak with Rob Lamkin, Cool Earth's CEO, about the company's technology. Recounting the story of the company's origins, he says, "we didn't set out to form a solar company." Instead they asked, "knowing the size of the global energy problem, how do we do something to address that?" Solar energy is the "best and biggest resource to address our huge energy problem," compared to resources like coal, wind, and tidal power. Having decided a solar company was the way to go, they determined that what they had was fundamentally "a materials problem, because solar is a big resource but it's very dispersed when it hits the earth, so how much surface of the earth do we need to cover to get the number of TWh we need?" As it turns out, the amount is something comparable to the size of Great Plains of the U.S.; hence the question arises of what materials exist in sufficient quantities to cover this land mass. For better or for worse, one material we have in great abundance is thin-film plastic, of which we make five billion pounds per year.

How do you turn plastic into energy? By coating it with a thin layer of aluminum, doubling the layers to form an inflatable "balloon," and inflating it into an efficient shape for capturing and concentrating solar energy. Cool Earth's technology is designed to make the most of the available sunlight by using lenses and reflectors to concentrate the light on small arrays of high-efficiency solar cells, thus effectively reducing the area of solar cells needed to generate a given amount of energy by a factor of 300 or 400 compared to flat-panel photovoltaic systems. The solar receiver is at the heart of this unique design; as Lamkin notes, "all the other companies have a single-element piece of solar cell material, about 1 square centimeter, at the heart of their target that they're focusing all the light on; our target's 6-7 inches in diameter."

Cool Earth drastically reduces the amount of material needed to produce this energy by making their concentrators out of thin plastic film, rather than using the rigid constructions of aluminum and glass that conventional solar concentrators use. These light structures require less energy than the heavy rigid concentrators to track the sun's progress, as well as being more resistant to high winds (they can survive winds up to 125mph, and function in winds up to 40mph), which can be hazardous to rigid solar arrays.

Concerns have been raised about the environmental impact of the use of plastic in their equipment, to which Lamkin answers, "it depends on what you do with the plastic. If your goal is carbon sequestration, then the best answer is to leave all that oil in the earth." If the oil is removed, he notes, it can be combusted (which is the worst environmental choice), or another use can be found for it such as making plastic (which sequesters the carbon). If that plastic is then used to make solar energy and eventually recycled, the environmental benefits of putting it to use arguably outweigh the notional problems of extracting the oil in the first place.

Cool Earth's system is designed to be highly scalable, as it circumvents the problem of scarcity of solar-cell materials and minimizes the amount of additional materials needed to construct the concentrators. The extremely flexible design of the metallized-film concentrators also means that Cool Earth's plants can be installed in a variety of terrain types, rather than requiring large expanses of very flat land like conventional photovoltaic arrays.

The result of these cost savings is a much lower price per watt than other solar systems. The cost of materials adds up to around 20 cents per watt, or even less, because of the low quantities of material. The two most expensive pieces of their power plants will be the inverters and the solar-cell receivers, which together add up to about 2/3 of the plant's total cost. Cool Earth estimates that when they begin deploying 10-30 MW plants in a year or so, their price point will be around $1 dollar per watt installed, as compared to the $7-$8 per watt of a conventional system. This brings their price close to the price of natural gas (though it's still more expensive than coal), meaning that little to no subsidization is required, which removes some of the political obstacles that stand in the way of introducing large-scale renewable energy.

The company's technology team was assembled by Eric Cummings, who now serves as the company president and CTO. The team members were a group of friends from Cal Tech, coming from a diverse group of disciplines including mechanical engineering, aeronautics, and computer science. The technology team was later complemented by a business team. As Lamkin puts it, "since what we set out to do is solar energy, and build solar power plants, and to sell the electricity, you need both the technology and the strong base from which to build the plants, and then you need the team that can develop the plants and sell the electricity. I think that's what makes Cool Earth unique, that we have both parts, and both parts are very strong." Summer 2006 was when their thin-film idea came into shape and patents were filed; the company was formed in February of 2007, in summer 2007 was a $1 million angel-investor fundraising round, and in February 2008 was a $21 million Series A investment round. They've since filed six patents, and a few more are in the pipeline; Lamkin predicts that "I think we'll be producing patents for quite some time," since every subsystem generates new intellectual property.

The company is currently prototyping its third-generation technology, which will be deployed in the field in the fall, with the first pilot power plant scheduled for construction at the end of the year. There is currently no fixed target for the pilot plant's capacity; it is intended primarily as a proof of concept, so the capacity will ultimately depend on the performance tolerances of the manufactured components and field installations, which will affect how many components need to be deployed to demonstrate the desired functionality. The expected range of capacity is somewhere between 0.25 and 1 MW.