Invited Paper IPF-TuM1
The Prospects for Low-Cost Photovoltaic Electricity

Tuesday, October 16, 2007, 8:00 am, Room 602/603

In the last decade the photovoltaic (PV) industry has grown at an annual rate of about 35%. While PV modules made in the 1960s sold for hundreds of dollars per Watt, prices are now in the range of $3-$4 per Watt, and this corresponds to levelized electricity costs of about 20-25 cents/kWh for large commercial systems. Silicon technology has dominated the industry since its inception and about 91% of all solar cells sold in 2006 were based on crystalline silicon. However, there are a number of other technologies under development involving materials such as amorphous silicon, microcrystalline silicon, cadmium telluride, copper-indium-gallium-diselenide, gallium arsenide (and related compounds), dye-sensitized titanium oxide, nanocomposite materials and organic molecules and polymers. The U.S. Department of Energy has set a goal of attaining levelized electricity costs of 6 to 8 cents/kWh for commercial PV systems as part of the Solar America Initiative, and this will require not only a reduction in the cost of the PV modules, but also in the cost of inverters, support structures, wiring and installation. Continued improvements in solar cell conversion efficiency will help to reduce costs. While the efficiency of crystalline silicon PV modules is generally in the range of 12 to 15% today, the module conversion efficiency should increase to about 17 to 20% by 2015. In the laboratory efficiencies as high as 24.7% have been demonstrated for single crystal silicon solar cells. The efficiencies associated with other PV technologies also continues to improve, and thin film copper-indium-gallium-diselenide solar cells have been fabricated with conversion efficiencies as high as 19.5% in the laboratory. Efficiencies as high as 40.7% have been demonstrated for a triple-junction cell operating under concentrated sunlight. There are also a number of new potentially disruptive PV technologies that could lead to significantly higher efficiencies in the next few decades, and new types of solar cells may be developed using novel multijunction structures, intermediate-band semiconductors, multiple-carrier generation, collection of hot carriers, etc. that could lead to conversion efficiencies in excess of 50%. If the growth rate of the last several years continues, then PV module prices could fall below $1 per Watt by 2030, and PV could be supply about 10% of the world's electricity in the 2030-2035 timeframe.