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Putting the spotlight on solar power

Posted: 17 Mar 2010 ?? ?Print Version ?Bookmark and Share

Keywords:solar power? photovoltaic? solar cell?

One of the details it pays attention to is the phenomenon of light-induced degradation. When a solar module is installed, there is an initial drop in power. This drop might be as small as 2 percent or as great as 8 percent. SolarWorld offsets this drop in its module testing; that is, to ensure a 100W module, it will produce a 102W module. It also uses what is called plus-sorting. Across the industry, one of the problems of installation is a mismatched lot of modules, where the wattage from one module to the next might vary by 3 percent. Such variation degrades power output. SolarWorld keeps the variations minimal to avoid degradation.

SolFocus concentrator PV panels
[Photo courtesy SolFocus]

SolFocus uses solar concentrator technology in which a silvered glass parabolic mirror focuses incoming light onto a secondary mirror; from there the light is directed onto the 1cm? cell. The multi-junction cell, long used in space, has a germanium substrate with overlying layers. SolFocus cells achieve a concentration of 650xthat is, a flat, non-concentrated area 650x the size of the cell would receive the same amount of sunlight as the SolFocus cell.

The applications for the SolFocus technology are entirely in small and large power-field applications. It is not suitable for individual rooftop installations, but appropriate for powering towns or cities. The modules (groups of 20 mirror units) move on two axes in order to keep the mirrors aimed directly at the sun.

The technology is suitable for regions with low cloud cover and lots of sundeserts, semi-deserts and some high-altitude locations. SolFocus has important installations in Portugal, Spain, Hawaii and California. Within its environmental limits, the technology is highly productive: the current cell efficiency is between 38 percent and 40 percent. The theoretical upper limit for multi-junction cells is about 70 percent, compared to about 26 percent for silicon cells. Multi-junction cells also are able to maintain their efficiency at high temperatures, while silicon cells produce about 15 percent less at 30C and as much as 30 percent less at 45C.

SolFocus outsources all of its manufacturing, a great deal of which is already done in Asia. What makes outsourcing feasible is that assembly mostly involves glass and aluminium, much like automobile companies, but unlike other solar manufacturers. These qualities also make its manufacturing very scalable. It could double its current 50MW capacity within five months if needed. It is also the only concentrator solar company to have achieved IEC 62108 certification for quality and reliability [at the time of this writing].

- Tom Adams
Consultant, Sonoscan Inc.

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