Greentech Media

Concentrating solar: This technology uses mirrors to concentrate sunlight and direct it onto solar cells. These systems have the advantage of using smaller silicon cells and therefore less expensive silicon or other photovoltaic material. (Photovoltaic materials, such as silicon and germanium, convert sunlight into electricity.) In the silicon shortage, concentrating solar and thin-film have attracted increased interest and venture-capital funding. But the number of rooftop concentrating-solar installations lags far behind conventional solar installations. Aside from Solaria, examples of concentrating-solar photovoltaic startups include SolFocus, Energy Innovations, Prism Solar and Soliant Energy.

Thin-film solar: Instead of cutting solar wafers - the building blocks for solar panels - out of silicon pieces, thin-film companies coat plastic or other substrates with, literally, a thin film of silicon or other photovoltaic material. Some companies, such as HelioVolt, are using copper-indium-gallium-selenide, a technology that can match the efficiency of conventional solar panels while avoiding the use of expensive silicon. Other thin-film technologies include cadmium-telluride and amorphous silicon. All these technologies use little or no silicon, and companies claim thin-films could potentially deliver far lower cost than conventional solar. But the technology is more expensive today - with some technologies unable to convert sunlight as efficiently as traditional panels - and has historically been unable to reach the larger production numbers necessary to reach the theoretically lower costs.