Promising though they are, conventional solar panels have some serious drawbacks. Because their semiconductor layers are sandwiched between panes of glass in a thick frame, they're heavy and bulky. They're relatively expensive to make and install, and their weight and rigidity limit them mostly to rooftops. These limitations create an opening for PV materials that are lighter, thinner, and cheaper. And they're coming. Known as thin-film solar cells, they take advantage of new manufacturing techniques that can deposit extremely thin layers of photosensitive materials on glass, metal, or plastic substrates. And some are made of non-silicon materials like cadmium telluride (CdTe) and copper indium gallium selenide (CIGS, pronounced "sigs") that appear to have potentially big advantages in cost and performance. Silicon inks, meanwhile, are being developed that appear to combine the strengths of silicon and thin film.
Today's thin films produce less electricity per unit area, with efficiency in the 12% to 15% range. But because they contain far less semiconducting material, they're cheaper to make and so much lighter and more flexible that they cut down on installation costs while opening up new real estate on walls and elsewhere. As the price of thin film drops relative to the wages of installers, its installation cost advantage over traditional solar panels will loom ever larger. From about 11% in 2007, thin film's market share is expected to soar going forward. As for which kind of thin film grabs the biggest share of this growth, that's where it gets interesting. Each producer has its own recipe, and right now they all sound revolutionary. Here's a brief look at three of the early leaders:
First Solar (headquartered in Arizona) turns cadmium telluride into a frameless laminate that it sells to utilities for large-scale installations. A proprietary production process enabled it to deliver PV in quantity for an industry-best $1.19 per watt in early 2008. Utilities are impressed, and they are buying whatever First Solar can make, which is quite a bit. In the quarter that ended in December of 2007, its sales nearly quadrupled, year over year, to $200 million. And its stock price gave a taste of what's in store for the best solar cell makers when the next leg of the bull market gets going: From a low of $24 in late 2006, it soared in one gorgeous arc to $280 before being caught in the early-2008 market downdraft and falling back to $200.
United Solar Ovonics
United Solar Ovonics (Michigan) uses "plasma-enhanced chemical vapor deposition" to lay down half-micron-thick layers of amorphous silicon, which, unlike traditional crystalline silicon, produces electricity even in overcast conditions. The laminates come in 18-foot-long rolls. "They're extremely lightweight and are backed with adhesive and a release paper," says United Solar chairman Subhendu Guha. "You can ship it to site, remove the paper and bond it to the roof. We have a big advantage in cost of installation." United Solar doubled its production capacity in 2007, to 58 megawatts, and plans to double that again in 2008.
Nanosolar (Silicon Valley) had the industry buzzing in late 2007 with a CIGS "nano-ink" that costs far less than traditional solar cells while operating at efficiencies close to that of silicon. If Nanosolar's process lives up to its billing, the possibilities are endless: The ink can be sprayed onto foil, plastic, or glass or incorporated into cement and other building materials, conceivably turning the entire exterior of a house or office building into a solar generator. Venture capitalists have showered the company with enough cash to build one of the world's largest PV factories, capable of producing 430 megawatts of solar cells a year, and as of early 2008, its first year's production run was pre-sold to European installers.
As thin film encroaches on crystalline silicon's turf, the war of words is heating up. ....read more