In principle, two strings with different orientations should not be wired in parallel into the same inverter. However, when the mismatch is minor (15 degrees in pitch or 15 degrees in azimuth) there is practically no degradation. Fronius circulated a white paper for a while that argued that their inverters did maximum power point tracking on the string with the greatest irradiance and therefore did an optimum mppt job on the string with the greatest "available power". This part of the argument makes sense. What I have never been clear about is how close to "optimum" this arrangement is (optimum being two separate monitors one for each string).
Fronius appears to be backing away from this white paper, as I was told about six months ago from a member of their tech support staff that they recommended two separate inverters. - Peter Peter T. Parrish, Ph.D., President California Solar Engineering, Inc. 820 Cynthia Ave., Los Angeles, CA 90065 CA Lic. 854779, NABCEP Cert. 031806-26 [email protected] Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885 _____ From: [email protected] [mailto:[email protected]] On Behalf Of Nick Vida Sent: Wednesday, September 09, 2009 6:38 PM To: wrenches Subject: [RE-wrenches] losses to competing angles in single strings hello wrenches. I was wondering if any of you have any data on what the losses would be if you had your string split with 2 different angles, but at the same azimuth. For instance, string of 11 with 8 facing 180 south at 30 degrees, and 3 facing south 180 at 45 degrees. I have heard that the voltages and currents would differ and the IV curve would be inefficient as a string, but I don't know how much of a loss would be expected. thanks in advance, and hopefully I didn't miss anything in the archives. thanks, nick
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