Analysts predict that the future solar landscape will be painted with thin-film solar cells rather than the big, bulky aluminum-framed photovoltaic (PV) panels of yesterday. Thin is in for many reasons, not the least of which is that thin-film PV cells can be fabricated from materials other than solar-grade crystalline silicon (c-Si), which has been in short supply.
Amorphous silicon (a-Si) and silicon-free designs are the subjects of “Thin-Film Photovoltaics: 2008 and Beyond,” a July 2008 report from NanoMarkets, an industry analysis firm based in Glen Allen, Va. Today, a-Si is the largest segment of the thin-film market, but silicon-free designs that are garnering attention include copper indium gallium diselenide (CIGS), cadmium telluride (CdTe) and gallium arsenide (GaAs).
Amorphous silicon (a-Si) has dominated the thin-film PV market for some time; however, its dominance will begin to erode as CIS/CIGS and CdTe see gains in use.
The report compares manufacturing costs, efficiency, and advantages and disadvantages of each material. As a result of shortages, crystalline silicon is currently the most expensive, but future costs are difficult to predict because of unknowns in the supply. Currently a-Si and CdTe are the lowest in cost and have the most potential, according to NanoMarkets. CIGS may eventually be the lowest in cost (possibly dropping as low as $1 per watt) and has an estimated efficiency of 14 percent in the field, but it has failed to take off as previously expected. Gallium arsenide has been tested at 35 percent efficiency, but its cost and manufacturing challenges are serious disadvantages. It seems likely that GaAs will be confined mostly to niche applications.
What could go wrong
The thin-film photovoltaics market does look bright, with analysts at NanoMarkets forecasting that the industry will produce the equivalent of 26 GW by 2015 and will generate more than $20 billion in revenue in that time period. According to the report, however, several variables could vastly change the picture. The silicon supply could ramp up with attractive pricing, the high cost of fossil fuels could drop, the “fad” of clean technology could fade, and government subsidies could dissolve as the PV industry takes off. Then there’s the question of the supply for some of the newer materials, such as the tellurium used in CdTe and the indium used in CIGS. And finally, the reality is that clean technology really isn’t all that clean to manufacture – cadmium, for example, is highly toxic – so rigorous hazardous materials practices have to be put into place, especially for this market to maintain its image as being environmentally correct.
The report also looks at innovative technologies – for example, nanosilicon inks. Sunnyvale, Calif.-based Innovalight Inc. is currently the only company developing silicon inks specifically for solar and expects to release products in 2009. If the technology works and is accepted, other businesses are likely to follow suit.
Then there is the sliver solar cell being developed at Australian National University in Canberra, which could improve the light-trapping properties and efficiency of solar cells. Origin Energy, an Australian utility company, is investing in this research by constructing a $20 million manufacturing plant in Adelaide, South Australia. Designed to generate 5 MW initially, the utility plans to expand to 25 MW of production if the technology proves to be mass-producible.
Overall, thin film is not lacking any attention these days. With lower costs and increased conversion efficiencies approaching those of traditional silicon, forecasters at NanoMarkets expect the market to remain strong, with the variables keeping the industry on its toes.