news digest ♦ Solar
platforms are severely limited by the lack of long endurance power sources. To date, these systems must rely on on-shore power, batteries or solar power supplied by an above water platform. Attempts to use photovoltaics have had limited success, primarily due to the lack of penetrating sunlight and the use of solar cells optimized more towards the unimpeded terrestrial solar spectrum.
“The use of autonomous systems to provide situational awareness and long-term environment monitoring underwater is increasing,” says Phillip Jenkins, head, NRL Imagers and Detectors Section. “Although water absorbs sunlight, the technical challenge is to develop a solar cell that can efficiently convert these underwater photons to electricity.”
Even though the absolute intensity of solar radiation is lower underwater, the spectral content is narrow and thus lends itself to high conversion efficiency if the solar cell is well matched to the wavelength range. Previous attempts to operate solar cells underwater have focused on crystalline silicon solar cells and more recently, amorphous silicon cells.
Unlike silicon cells, high-quality GaInP cells are well suited for underwater operation. GaInP cells have high quantum efficiency in wavelengths in the visible light region, (between 400 and 700 nm) and exhibit an intrinsically low dark current. Both properties are critical for high efficiency in lowlight conditions.
The filtered spectrum of the sun underwater is biased toward the blue/green portion of the spectrum and thus higher bandgap cells such as GaInP perform much better than conventional silicon cells, notes Jenkins.
Preliminary results at a maximum depth of 9.1 m reveal output to be 7 W/m2 of solar cells, sufficient to demonstrate there is useful solar power to be harvested at depths commonly found in near shore littoral zones.
Calyxo boosts CdTe solar capacity to 85 MW
The German firm expects to own the largest cadmium telluride solar module facility in Europe by the end of 2012
Calyxo is investing in a second production line with a capacity of 60 MW at its home facility in Bitterfeld, Wolfen.
The firm currently operates a 25 MWp production line with over 150 employees at the manufacturing plant in Germany and will ramp the total capacity at the end of 2012 to 85 MW.
The capital for the expansion will be provided by a bank loan and cash contributions from the technology inventor Solar Fields, LLC, who took over ownership of Calyxo in February 2011 from its former partner Q-Cells SE. Solar Fields invented the technology while a resident at the University of Toledo Incubation Centre.
“Based on recent good results in production 142
www.compoundsemiconductor.net July 2012
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