Photovoltaics (solar electric power) deployment has enjoyed greater than 30% growth per year in the United States and Europe. Nevertheless, PV still provides just a very small fraction of our electricity needs. US DOE projections toward 2050 bifurcate: some expect PV to remain with a very small share of just a few percent, while others see it playing a much larger role, 10% or greater. Many believe that the technology is currently at a "tipping point", where technology and energy economy drivers are being shaped that will determine the outcomes in the marketplace.

Within PV, crystalline silicon continues to dominate and has recently made impressive gains in both efficiency and cost reduction. Thin-film technologies, however, also continue to make sizable inroads into consumer markets. Leading thin film architectures for terrestrial PV applications include amorphous silicon, copper indium diselenide (and related derivatives), and cadmium telluride.

This session will explore technical difficulties, challenges and opportunities for each of these major solar technologies. For crystalline silicon, both areal volumetric material utility are critical -- particularly the latter, in the face of material shortages worldwide. For thin films, durability, robustness of material in existing processing conditions, and the development of novel conditions and processes are some of the topics of interest. As thin films emerge into a broader market space, inroads are limited by customer acceptance and reliability -- actual or perceived -- and ultimately, cost. Along these lines some " third-generation" structures are also interesting candidates, primarily in earlier stage technology development; these will be highlighted briefly.

Finally, there is a paradigm shift underway: toward the consideration of PV costs on an annual, averaged energy delivery basis, rather than the more traditional peak power capability ratings. Technology and market developments that address this new paradigm will be the likely winners.