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INDUSTRY I CPV


in efficiency at the system level. CPV’s competitiveness has also increased through improvements in the efficiency of triple- junction cells, which are getting cheaper and cheaper. Today they only account for a low-double-digit percentage of the system cost – in the past it was up to 20 percent. According to Hartsoch, the lower costs stem from increased competition: “The market was dominated by one or two guys for a long time. Now there is a lot of pressure.” Cell shipments have also gone up, which leads to lower production costs through economies of scale, and there is the promise of far larger orders.


Shifting landscapes


How CPV is installed is also changing. Up until now, quite a few of the CPV projects have been focused on generating electricity for very local consumption. For example, Sol Focus recently completed a 1 MW installation for a pistachio farmer in California’s central valley that provides 70 percent of the power for his processing facilities. But from now on, deployments for utilities will account for a higher and higher proportion of CPV system shipments.


These deployments initially targeted the sunny parts of Europe, such as Greece and Spain, where developers could exploit very attractive feed-in tariffs. But those great incentives have now been withdrawn, and the South-West US is the new hotbed for CPV. “If we look at 2011 and 2012, probably about half our market will be the US; maybe a quarter Europe, the Middle-East and Africa; and a quarter the rest of the world,” says Hartsoch.


Lerchenmüller offers several reasons why California, in particular, is a very attractive place for deploying CPV systems: a strong


demand for summer, daytime electricity due to widespread use of air-conditioning; incredibly sunny sites that are 100 miles or so from areas with a very high population density; and a day- time premium on electricity. Although there are no feed-in tariffs in operation, CPV installations are able to apply for investment tax credits (ITC).


Hartsoch believes that CPV deployments in California have the potential to generate electricity at a cost of 11 or 12 cents per kWhr, even without incentives. And Lerchenmüller agrees, saying that he expects Soitec’s near-term projects to produce electricity at a cost of 12-15 cents per kWhr, a figure that should fall to 10- 12 cents per kWhr without the ITC in three-to-four-years’ time. “That, for me, is really grid parity on a power plant level,” says Lerchenmüller. “Below 10 cents is clearly another hurdle.”


The case for CPV is so strong in the sunny climes of California that it has helped SolFocus to win two or three contracts against two of the biggest names in the PV sector: The trailblazer of CdTe-on-glass panels, First Solar; and SunPower, a massive player in the silicon sector with annual sales of a more than a billion dollars. SolFocus won the contracts, says Hartsoch, because although it had slightly higher capital costs, its system would generate 20 to 30 percent more energy.


She believes that within a few years, CPV systems will be able to start making a stronger impact in ‘rest-of-the-world’ areas where there are no incentives. In many of these regions, energy prices are currently unpredictable, and a switch to CPV could quash these fluctuations. In addition, this form of power generation could bring electricity to regions that are currently without this


Soitec and SolFocus: Adopting different approaches


The CPV system manufacturers Soitec and SolFocus have adopted different approaches to focusing sunlight onto triple-junction cells: the former uses a single lens, while the latter employs reflecting mirrors.


Soitec prides itself on the simplicity and robustness of its module. Its top part consists of a glass sheet, which underneath it has a 70 mm-thick silicone film that is embossed and includes the Fresnel lens. The bottom section also features a sheet of glass, which is the foundation for mounting metal heat distributors and the III-V cell.


Engineers at the European outfit have extensively tested silicone for its stability under UV radiation. “We started with just normal UV bulbs, and we didn’t see anything,” says Hansjörg Lerchenmüller, Senior VP of the Customer Group of the Solar Energy Business Unit at Soitec. So they added more lamps, but were still


unable to detect any changes to the silicone. “So we then went down the brute force method and found a guy with a UV laser, and saw the first signs of degradation at UV doses equivalent to something like 3000 years.”


The modules that Soitec makes operate at concentrations of 500 suns. This factor could be increased to 800 or even 1000, but higher concentration requires the addition of a secondary focusing element.


According to Lerchenmüller, it is not clear whether savings resulting from using less semiconductor material outweigh the combination of the additional cost of a secondary optical element; reductions in overall efficiency that stem from additional reflections; increased risk to reliability; and lower manufacturing yields that result from a more complex production process. Modules made by Soitec use just one


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Fresnel lens made from silicone to focus the sun’s rays onto triple-junction cells.


With SolFocus’ reflector-based systems, which currently operate at 650 suns, the case for going to higher concentrations is much stronger. Regardless of the focusing technology, increases in concentration pay the penalty of a reduction in the acceptance angle of the incoming light.


However, according to SolFocus, the acceptance angle for its reflective system – which is over 1° for today’s modules – is two to four times higher than that for most Fresnel-based equivalents.


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