April 20, 2012

Alta Devices Solar Everywhere Vision for 2020

The basic form factor of solar modules hasn’t changed in decades – they remain heavy, rectangular, glass-covered entities that impose expensive handling and mounting requirements. What if we could abandon this form-factor limitation and open the door to entirely new ways to innovate on form factor? The ideal technology would be free of the confines of the traditional “rectangular, glass module” form factor. It would be thin and flexible and environ- mentally robust, opening up the door to innovation that will fundamentally eliminate costs, and not just reduce them. With solar available in wholly new forms, we can imagine a plethora of new ways to capture and use the sun’s energy. Flexible solar cells, with sufficiently high energy density, can be incorporated directly into roofing materials, including asphalt shingles standing seam metal and stretched membrane roofs. That eliminates all of the extra hardware and labor needed to mount and install the solar cells, directly reducing the fixed area costs. There’s a virtuous cycle that begins how solar performs best. Providing energy when high-energy-density solar cells near the point of consumption, thereby become “throw-away cheap. Instead of glass and metal modules, just have a plastic tarp covering solar cells.

Technology Review - Alta researchers have found ways to create rugged films that aren't prone to cracking. And not only do the thin films use little of the semiconductor material, but the valuable gallium arsenide substrate can be reused multiple times, helping to make the process affordable.

Research by Alta's founding scientists has also led to techniques for increasing the performance of the solar cells. Photovoltaics work because the photons they absorb boost the energy levels of electrons in the semiconductor, freeing them up to flow to metal contacts and create a current. But the roaming electrons can be wasted in various ways, such as in heat. In gallium arsenide, however, the freed electrons frequently recombine with positively charged "holes" to re-create photons and start the process over again. Work done by ­Yablonovitch and Atwater to explain this process has helped Alta design cells to take advantage of this "photon recycling," providing many chances to recapture photons and turn them into electricity.


Flexible power: Alta’s solar cells can be made into bendable sheets. In this sample, a series of solar cells are encapsulated in a roofing material. Credit: Gabriela Hasbun




Alta's efficiency record: its cells have converted 28.3 percent of sunlight into electricity, whereas the highest efficiency for a silicon solar cell is 25 percent, and commonly used thin-film solar materials don't exceed 20 percent. Yablonovitch suggests that Alta has a good chance of eventually breaking 30 percent efficiency and nearing the theoretical limit of 33.4 percent for cells of its type.

The high efficiency, combined with gallium arsenide's ability to perform at relatively high temperatures and in low light, means that the cells can produce two or three times more energy over a year than conventional silicon ones, says Norris. And that, of course, translates directly into lower prices for solar power. Norris says a "not unreasonable expectation" is that the gallium arsenide technology could yield a "levelized cost of energy" (a commonly used industry metric that includes the lifetime costs of building and operating a power plant) of seven cents per kilowatt-hour. At such a price, says Norris, solar would be competitive with fossil fuels, including natural gas; new gas plants generate electricity for around 10 cents per kilowatt-hour. And it would trounce today's solar power, which Norris says costs around 20 cents per kilowatt-hour to generate.


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