On Monday, June 22, Xunlight Corporation announced the successful installation of its first 25-megawatt wide-web, roll-to-roll photovoltaic (PV) manufacturing module. The 25-megawatt rating is, as far as I can tell, the amount of energy generated by the thin film produced by the module in a year. If someone can enlighten me on this, though, please speak up.
It’s a press release, so it reads like a translation from a Japanese computer manual, but the essence is that the module spits out mile-long sheets of silicon solar-enhanced flexible stainless steel sheets three feet wide that can be laid on roofs or placed on the sides of buildings to generate solar energy.
The module itself is a series of interconnected vacuum deposition chambers, 200 feet long, which use a plasma-enhanced chemical vapor deposition (PECVD) process to bond thin-film silicon to the stainless sheets.
Say that again? Okay, plasma is an ionized gas (in this case, probably silane and oxygen) that, via the application of electricity, resolves itself into a solid state as silicon dioxide. This is deposited (possibly via “sputtering") on to the steel as a uniform substrate, or layer. Roll-to-roll simply refers to the fact that a roll of stainless steel goes in one end of the machine, and a roll of solar-collecting silicon/steel – plus a few other interesting ingredients - comes out the other, at a rate of 720 square feet per hour.
This particular piece of equipment is reportedly Xunlight’s first, and is aimed at commercializing its thin film process. Installed at the company’s Toledo, Ohio plant, the module is the first step toward mass production, and Xunlight (which designed and built the module) plans to add three more by the end of 2010, upping the company’s production capacity to 100 megawatts. Xunlight says the equipment will redefine the solar energy industry by lowering production costs.
Thin-film solar is cheaper than conventional solar panels, because less silicon is used. It is also, unfortunately, less efficient in terms of capturing sunlight and converting it to energy. Xunlight says its thin film has a maximum of 9.2-percent initial efficiency, expected to stabilize at about 7.8 percent. A similarly-sized solar panel achieves about 22 percent efficiency. Rated in watts, Xunlight’s panel achieves 330, while the same-sized solar panel is 740 watts. However, Xunlight has achieved added efficiencies by creating triple junction cells; that is, they use three different materials, each aimed at capturing a different portion of the solar spectrum. This is something no solar panel can do.
Thin film manufacturers argue that the way efficiency is currently measured is the real drawback to thin film's advance in the solar industry. This efficiency is based on peak power, or the maximum amount of electricity that a panel can produce under ideal conditions, and is often noted as kWp (kilowatt hours, kW, at peak, or p). Solar panels “peak” in the morning (just like people after that first cup of java), but energy production declines as the panels heat up (been there, done that). Thin films, stable at higher temperatures, run the race like turtles – slow and steady all day long.
Thin films also produce electricity on partly cloudy days, or in smoggy conditions, which solar panels don’t. Of course, thin films, with their thin and less-than perfectly uniform surfaces, also tend to degrade faster in the presence of light and air, even when the surface is sealed, so their “lifetime” (rated at 25 years for solar panels) is somewhat less than solar panels.
Nonetheless, thin films, and companies like Xunlight, are starting to make serious inroads into what was formerly a silicone cell-dominated solar industry, and driving down production costs (and, hopefully, consumer costs) through mass manufacturing can only help spur the industry to new heights.
Image courtesy of Xunlight
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