Technology Assumptions and Issues

Thin film PV devices are very different from today's common PV devices made from crystalline silicon. Thin film s use 1/20 to 1/100 of the material needed for crystalline silicon PV, and appear to be amenable to more automated, less-expensive production. For a review of thin film PV see References 16-32. There are three thin films that hav e demonstrated good potential for large-scale PV: amorphous silicon (a-Si), copper indium diselenide (CIS), an d cadmium telluride (CdTe). Others are at somewhat earlier levels of maturity (film silicon and dye-sensitized cells) . The system in this document is a composite based on the three most mature thin films. It is generally believed that all thin films share similar characteristics: the potential for very low module cost (under $50/m 2 of module area) and reasonable module efficiencies (13%-15% or more), implying potential module costs well under $0.5/Wp. See References 22-32 and a cost analysis below for an in-depth discussion of thin film module manufacturing costs. Thus, this assessment is a projection of a 'best, future' grid-connected thin-film PV system such as might be used in the U.S. to produce daytime electricity, after the turn of the 21st century.

Thin film PV modules currently in production are based on amorphous silicon. Others, based on polycrystalline thi n films, are in pilot production. Substantial commercial interest exists in scaling-up production of thin films. As thi n films are produced in larger quantity, and as they achieve expected performance gains, they will become mor e economical for large-scale electrical utility uses and for large-scale non-utility off-grid uses in developing countries . Even though some thin film modules are now commercially available, their real commercial impact is only expecte d to be significant during the next three to ten years. Beyond that, their general use should occur in the 2005-2015 time frame, depending on investment levels for technology development and manufacture. The 'best future' grid-connected PV system described here requires that thin films continue to make the high-risk transition from lab-scale success t o commercial success throughout this same period. As such, the technical and financial risks remain substantial. These affect the uncertainty of the projections.

Although some thin film modules are commercially available, developmental work is ongoing and remains key to their success. Indeed, to meet the economic goals needed for large-scale use, much more technical development is needed Near term (3 to 10 years) commercial products will not be inexpensive enough to compete with conventional system s for volume U.S. utility-connected applications. Important technology development must be carried out to (1) transfe r very high thin film PV cell-level efficiencies (up to 18%) to larger-area modules, (2) to optimize processes an d manufacturing to achieve high yields, high rates, and excellent materials use, and (3) to assure long-term outdoo r reliability. Today's technology base suggests that (with adequate resources) all of these important goals can be achieved [16-32], but each will be challenging.

Funding by the government for technology development has been critical to the thin film technologies described here . Current Federal PV R&D funding is about $40M annually. Federal funding for thin films is about half this total ($20M/year). Without it, most people believe that thin film PV would not exist in the U.S. Since almost every P V company is presently losing money, they would not be likely to pursue advanced R&D without public investment. The U.S. Federal investment in thin film R&D is more than half of the total U.S. corporate investment in thin films . Continued government funding of thin film technology development is crucial, and were it to dissipate, none of th e projections in this characterization would likely be realized. Secondly, worldwide government spending is no w expanding in 'markets', and to some extent we assume that this trend will continue. However, we are not assuming that market subsidies will drive the future of PV, as research funding does. (At current system prices of $5-$10/Wp installed, $10 million per year of Federal spending would only buy 1-2 MW of PV. This kind of spending cannot drive dow n prices.) Instead, the current State and Federal market support is aimed at facilitating PV market entry, not pulling P V costs down a 'learning curve' at an accelerated rate. Future funding is uncertain, and major changes could occur i n either direction: critically enhanced or critically reduced PV budgets for technology development or marke t development. Either would change our picture about the future, but reductions in R&D investment would invalidate many of the conclusions of this assessment.

At some point (as PV costs drop), new forms of financing for U.S. and international markets must be developed fo r PV to become of global significance. We see hints of this future in the World Bank's Global Environment Facility (to fund CO2 reductions in developing nations). However, as PV becomes a more relevant participant in global markets , developing new financial tools will be critical. Without some stimulus, U.S. utilities (and those in developed countries) are unlikely to press for large-scale use of PV. This is true in the near term (due to high prices) and may even be tru e in the longer term, especially if commodity energy prices stay low. This utility inertia may occur because even at lower costs (under 60/kWh), PV will remain marginally attractive on a purely avoided energy cost' basis. (This is not t o discount large-scale use for peak shaving and other specialty markets.)

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