In reality, shading 50 percent of one module will reduce the output of that string by about 13 percent. This loss will usually occur early in the morning or late in the afternoon when partial shade is most prevalent. Shading at solar noon will result in a negative ROI even when MLPE are used.
Many whitepapers regarding this topic in the European Photovoltaic Solar Energy Conference (EU PVSEC) library have been reviewed by industry experts and none support the Christmas tree effect when modules with bypass diodes are tested. In fact, shading studies fall short of discussing and testing different shading effects on different module technologies. A particular paper in this library entitled “Performance Measurement and Monitoring of Shadow Effects on PV Systems4” concluded that shading had less of an effect on thin film than crystalline solar modules.
2. MLPE have lower O&M and installation costs than string inverters.
Since every installation is different, this is a highly subjective claim and one that requires the installer to perform a cost comparison. Some manufacturers suggest that the estimated 20-year maintenance and replacement cost for a 7 kW string inverter system is $5,1925 while the same size micro inverter system, using 30 inverters, only costs $739. However, this information does not indicate if the $739 was for one inverter replacement or for all 30, or how the $5,192 string inverter replacement cost was derived (that figure is highly dependent upon inverter manufacturer).
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Optimzing PV Systems eFeature | July 2014
OPTIMIZING PV SYSTEMS - PART 1: INVERTERS