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Shedding new light on solar power

Posted: 23 Feb 2010     Print Version  Bookmark and Share

Keywords:Solar power  cell  technologies 

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% or as great as 8%. SolarWorld offsets this drop in its module testing; that is, to ensure a 100W module, it will produce a 102-watt 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%. Such variation degrades power output. SolarWorld keeps the variations minimal to avoid degradation.

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 1cm2 cell. The multi-junction cell, long used in space, has a germanium substrate with overlying layers. SolFocus cells achieve a concentration of 650 times— that is, a flat, non-concentrated area 650 times 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 sun— deserts, 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% and 40%. The theoretical upper limit for multi-junction cells is about 70%, compared to about 26% for silicon cells. Multi-junction cells also are able to maintain their efficiency at high temperatures, while silicon cells produce about 15% less at 30°C and as much as 30% less at 45°C.

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].

Figure 3

Figure 3: SolFocus concentrator photovoltaic (CPV) panels. [Photo courtesy SolFocus].

Tom Adams also writes the Process Control column on EE Times India.

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