Shell Renewables and Akzo Nobel in the Netherlands are jointly developing a low-cost process for mass-producing flexible solar cell panels. A special semiconductor coating is applied to rolls of flexible foil substrate on an almost continuous basis. The process is being developed in parallel by the Technical Universities of Delft and Eindhoven, Utrecht University, the Energy Research Centre of the Netherlands, NOVEM the Dutch agency for energy and the environment and the European Union. This technology promises to be ideal for roof and wall panel application.
Other PV technologies include cadmium telluride (CdTe) cells being developed in the USA (BP Solar) and Germany (Siemens). First Solar in the USA has developed a 100 MW CdTe coating facility and a 25 MW module fabrication plant. The process deposits CdTe on glass with a transparent conducting oxide. Modules of 0.75 m2 (8 ft2) will be produced by a plant commencing 2002. The efficiency is modest at 8% but, in compensation, the cost is low combined with the fact that it can be employed as roof and wall covering. The main disadvantage is that cadmium is a highly toxic metal.
The Boeing Corporation has developed a gallium arsenide thin film cell which can achieve high absorption rates. A single junction cell has realized 28.7% efficiency whilst a tandem two-junction cell has reached 33%.
Siemens has focused on a copper indium diselenide (CIS) cell with an efficiency of 9-11%.
An innovative technology has been developed by Daystar Inc. of Denver, Colorado. It employs 1 mm diameter filaments of polycrystalline copper indium gallium diselenide (CIGs) as a semiconductor deposited on stainless steel wires. Light is focused onto the wires by built-in elliptical lenses. The cost of materials is claimed to be one fifth that of silicon cells and peak efficiency is said to be 18% (www.daystartech.com/products.htm).
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