108 November 2009
Ask the Editors Whether it’s about fi nancing, technology, or individual components: <strong>PHOTON</strong>’s editorial staff answer question about every aspect of PV in its editorial offi ce hours. Radioactive modules? ? Since ruthenium is used as a dye in pigment-based solar cells, can you give me conclusive proof that, even if the material undergoes extreme stress due to module breaking, disintegrating, or splintering, no radioactivity will be released into the environment? Jan Teckelmann, by email ! Pigment-based solar cells use a red compound containing the metal ruthenium (Ru) to absorb a specifi c portion of the sunlight’s wavelength. »Naturally occurring isotopes of ruthenium are not radioactive,« explains Nils Metzler-Nolte, who holds the chair of Inorganic Chemistry at the Ruhr University in Bochum, Germany, »so normal pigment-based solar cells containing ru- When does it pay to buy thin-film panels? ? I’ve heard that thin fi lm modules are, on average, one-third cheaper than polycrystalline modules, but also only produce half the power. Is that true? Klaus Wäring, by e-mail ! There is really no generic answer to this question, since local irradiation conditions must be taken into consideration. According to <strong>PHOTON</strong>’s module price comparison, the average price for thin-fi lm modules was roughly 20 percent less than the price for polycrystalline modules at the beginning of July. At the beginning of October, the difference was around 15 percent. Correspondingly, the effi ciency of thin-fi lm modules is generally lower than that of polycrystalline modules, which have effi ciencies of around 14 percent. The effi ciency of cadmium telluride (CdTe) and copper-indium-diselenide (CIS) modules is around 10 percent, compared to 7 to 8 percent for amorphous microcrystalline silicon modules. Panels using amorphous microcrystalline modules would produce 33 to 50 percent less power per m2 of module Not a source of radiation: pigment-based solar cells using red dye containing ruthenium thenium compounds cannot discharge radioactive ruthenium.« Fuel elements from nuclear reactors do contain small amounts of radioactive ruthenium iso- An array consisting of crystalline silicon modules (left), and one with thin-fi lm modules (right). Whereas the power yield per nominal W is quite similar for both technologies, thin-fi lm panels’ output per m2 of module surface is much lower. surface space than crystalline modules. But a panel’s effi ciency does not really tell you how much power you will get per rated W. Nominal output is measured under standard test conditions (STC), topes, but that doesn’t mean the element itself is always radioactive. Metzler-Nolte says there’s no greater risk of toxicity with these compounds than with alternative dyes that don’t contain metal. As a general rule, if a dye module containing ruthenium breaks, you should handle the debris with care – but that’s true of all solar modules. Apart from that, ruthenium is indispensable in pigment-based solar cells for technical reasons. »There’s currently no substitute dye that works as well, but we’re still working on it,« says Henning Brandt, a researcher at the Fraunhofer Institute for Solar Energy Systems. djs, ste which is 1,000 W of irradiation per m 2 . Thus this measurement only takes one possible set of conditions into account. It fails to demonstrate whether the panel’s performance differs under other solar conditions. The results of <strong>PHOTON</strong>’s fi rst fi eld test showed that CIS and CdTe modules surpassed their crystalline competitors when solar irradiation was between 45 and 80 percent of STC. Above or below STC, polycrystalline modules perform better. Nonethelsee, depending on how prevalent certain solar conditions are at a given location, thin-fi lm modules can actually certainly outperform polycrystalline modules. According to <strong>PHOTON</strong>’s test, a polycrystalline and a monocrystalline module came in fi rst and second place in terms of power production for measurements taken throughout 2008. They were followed by a thin-fi lm panel, manufactured by First Solar Inc., which came in third. nw November 2009 109 Roberto Mettifogo / photon-pictures.com Greatcell Solar SA Our editorial offi ce hours is a service for subscribers. Do you have questions about an article, or general questions about PV? Our experts can be reached every friday between 9 and 12 by phone at 415/509-5296. Please have your customer number available (it’s located on the magazine address label). We will answer any questions per email, letter, or fax upon receipt – include the keyword editorial offi ce hours Industry Industry Registry Classifieds Job Opportunities Ask As the Editors Internships Education Education Educatio Educatio & Training Events Statistics Test Lab
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