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50 HZ / 60 HZ STRING-INVERTER TEST
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PHOTON Lab has been carrying out inverter tests successfully since 2007, informing PHOTON readers whether or not a device is up snuff. The lab assigns grades ranging from A++ to E, which correspond to an overall efficiency defined by PHOTON.
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Since the beginning of 2007, PHOTON Lab has employed its own inverter test methodology, and regularly published results from those tests. To make these results easier to comprehend, the editorial staff, drawing its inspiration from school report cards, launched a grading system with its own testing certificates: the grades range from A to E. The highest grade (»A«) has three different levels: an A grade, an A+ or an A++. This was deemed necessary since one of the devices tested performed so much better than its competitors that it required a more subtle gradation. An E grade is as- signed to an inverter with an efficiency so poor that it‘s essentially not worth the money paid for it – put simply, so much of the produced solar electricity is either converted into heat or unabsorbed that the resulting loss in feed-in tariffs is so high that it exceeds the device‘s cost. In this sense, devices like these are too expensive to even give away.
To assign a grade, we first need to determine the efficiency to which the grade refers. Both peak efficiency and European efficiency aren‘t well-suited for this purpose. This is why PHOTON has decided to define its own efficiency value, the explanatory value of which will far exceed conventional efficiency data. Furthermore, the goal of this grading system is to enable better comparisons of individual devices. The grades provided in the survey can essentially be associated with the devices‘ overall utility, which is often difficult to determine from the pro- duct datasheets provided by manufacturers, as many of them omit important information on operating parameters.
Currently, above all, technical data from manufacturers often omits information on the efficiency‘s dependence on input voltage. Also, it‘s uncommon to find data on an inverter‘s suggested MPP operating point. And information on the influence of input current limitation on the operating point, and the relation between temperature and conversion efficiency, is often nowhere to be found. To give readers of our inverter test an immediate sense of a device‘s value, we assign a single grade for an efficiency determined by PHOTON to each inverter that takes into account all of the above-mentioned factors. No other individual scores have an influence on the grade. The parameters reflected in the grade are reviewed on an annual basis and are be discussed with manufacturers in advance.
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