Mass Production of Plastic Solar Cells
In a significant milestone in the deployment of flexible, printed photovoltaics, Konarka, a solar-cell startup based in Lowell, MA, has opened a commercial-scale factory, with the capacity to produce enough organic solar cells every year to generate one gigawatt of electricity, the equivalent of a large nuclear reactor.
Organic solar cells could cut the cost of solar power by making use of inexpensive organic polymers rather than the expensive crystalline silicon used in most solar cells. What’s more, the polymers can be processed using low-cost equipment such as ink-jet printers or coating equipment employed to make photographic film, which reduces both capital and manufacturing costs compared with conventional solar-cell manufacturing.
The company has produced its cells in a relatively small pilot plant with the capacity of creating about one megawatt of solar cells a year. The large gigawatt capacity of the plant was made possible by the fact that Konarka does not require specialized equipment to make its solar cells. Indeed, the factory and equipment were formerly owned by Polaroid and used to make film for medical imaging. With minor modifications, the same equipment can now be used to make solar cells. Richard Hess, Konarka’s president and CEO, says that the company’s ability to use existing equipment allows it to scale up production at one-tenth the cost compared with conventional technologies.
Unlike conventional solar cells, which are packaged in modules made of glass and aluminum and are rigid and heavy, Konarka’s solar cells are lightweight and flexible. This makes them attractive for portable applications. What’s more, they can be designed in a range of colors, which can make them easier to incorporate attractively into certain applications. One of the first products to use Konarka’s cells will be briefcases that can recharge laptops. Another company is testing Konarka’s solar cells for use in umbrellas for outdoor tables at restaurants. They could also be used in tents and awnings.
The solar cells are based on a design by Alan Heeger, a professor of physics at the University of California, Santa Barbara, who won the Nobel Prize in 2000 for his work helping to develop electrically conducting polymers. His solar-cell design included two main components: a polymer that releases electrons when exposed to sunlight, and carbon nanostructures called fullerenes, which escort those electrons away from the polymers and to an external electronic circuit, generating electricity. Konarka’s solar cells use similar polymers and fullerene-like nanostructures. These materials, as well as positive and negative electrodes made from metallic inks, can be spread over a sheet of plastic using printing and coating machines to make solar cells.
However, the technology has several drawbacks that will initially limit its applications. The solar cells only last a couple of years, unlike the decades that conventional solar cells last. What’s more, the solar cells are relatively inefficient. Conventional solar cells can easily convert 15 percent of the energy in sunlight into electricity; Konarka’s cells only convert 3 to 5 percent. As a result, they require much more area to generate electricity, so they’re not as attractive as ordinary solar cells for generating electricity on rooftops, where space is limited and the technology’s light weight and flexibility aren’t needed, says Dana Olson, a research scientist at the National Renewable Energy Laboratory, in Golden, CO.
At first, Konarka will focus on niche applications such as umbrellas and tents, while working to increase the efficiency of the solar cells to between 7 and 10 percent, at which point the company could compete in cost with conventional sources of electricity, Hess says.
The company plans to gradually ramp up production at its new factory, reaching full capacity in two to three years. Because the solar cells can be made transparent, Konarka is also developing a version of its solar cells that could be laminated to windows to generate electricity and serve as a window tinting.
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