Silicon vs. CIGS: With solar energy, the issue is material

What should solar panels be made of? Silicon has history on its side, but the future may lie in CIGS.

Silicon or CIGS. In the solar world, them's fightin' words.

The booming solar industry is in the midst of an argument over which material will become dominant in the future for harvesting sunlight and turning it into electricity. Solar panels made from crystalline silicon currently account for more than 90 percent of the solar infrastructure today.

Unfortunately, silicon panels remain relatively expensive to make. Without subsidies, it's still cheaper to get electricity from the grid. A two-year shortage of polysilicon, which may not ease until 2008, has severely limited growth and sales.

Panels that harvest energy with CIGS (copper indium gallium selenide) cost far less to make and install, say backers. The material can be sprayed onto foil, plastic or glass or incorporated into cement and other building materials. Conceivably, the entire exterior of a house or building could become a solar generator.

CIGS also doesn't degrade in sunlight like other thin-film technologies.

"The smartest investors are going short on silicon and long on thin film, especially CIGS," said Martin Roscheisen, CEO of Nanosolar, a start-up that has received $100 million in venture funds to build a plant capable of producing 430 megawatts-worth of CIGS panels.

Silicon solar panels

"The semiconductor is 100 times thinner. We combine low-cost materials with low-cost processes. The expenses on silicon are extremely high."

A huge vote of confidence in CIGS came earlier this year when Shell, one of the largest solar companies in the world, sold its silicon solar business to focus on developing CIGS.

So if CIGS is so good, why isn't there more of it out there? Mind share.

Silicon has become one of the most studied materials ever discovered, and advances in reducing processing time and manufacturing that were discovered in the semiconductor world rebound directly to silicon solar-cell manufacturers. Other alternatives--, photovoltaic dyes--have failed to undercut it in functionality and cost.

"Silicon has a reliability record which is unmatched by any other material," said T.J. Rodgers, CEO of Cypress Semiconductor, which is the primary stockholder in the fast-growing silicon panel maker SunPower.

"They could rename the company NanoDollar, because that's all they are going to be left with after we get done kicking their butt," Rodgers said referring to Nanosolar.

"The smartest investors are going short on silicon and long on thin film, especially CIGS."
--Martin Roscheisen, CEO of Nanosolar

He's got a point. Back in the early 1990s, CIGS was emerging as an alternative to silicon, but the declining price of silicon snuffed out the movement.

"The three most studied materials in history are steel, cement and silicon, so they have a leg up on us there," acknowledged B.J. Stanberry, CEO of CIGS developer HelioVolt. "I'd say you're a fool if you predicted the imminent death of silicon. But their inability to deliver is creating an opportunity for thin film, and CIGS will have a significant portion of the market within 10 years."

With demand cranking up to an all-time high for solar technology, the two types of panels will likely co-exist for years--especially considering the miniscule role solar plays now in generating electricity, according to various estimates, and that demand is expected to double by 2025. Solar accounts for less than 0.10 percent of the current total.

Nonetheless, growing momentum for one technology among researchers, equipment makers and, ultimately, customers could pave the way for one to become dominant over the other.

Similar debates weighing promise against pragmatism have occurred in chipmaking. Gallium, indium and germanium have also been used to produce superfast semiconductors, but the higher costs associated with these materials have kept them toward the margins in the market.

Silicon hits and misses

Silicon, even its adherents admit, is not ideal. Theoretically, silicon is capable of converting 29 percent of the sunlight that strikes it into electricity, according to Dick Swanson, a former Stanford professor who founded SunPower.

"That imagines a cell that is perfect in every possible way. That would be without any energy losses or leaks other than those demanded by the physics of silicon," Swanson said. "The practical limit, most say it is around 25 percent to 26 percent."

SunPower already sells panels that convert an average of 20 percent of the sunlight into electricity and will come out later this year with panels that . The high efficiency is due to the design of the company's panels. SunPower puts the electrical contacts at the back (or bottom) of the panel to increase surface area. The silicon also sits atop a reflective layer: Photos that would otherwise pass through the panel entirely are bounced back into it and effectively recycled.

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