I don't think this topic has been dealt with in this forum. Ocassionally we want to use a single inverter with two or more strings, each string being loaded by a single sub-array. A sub-array being defined as having a single uniform tilt angle and azimuth. All modules are identical. And each string/sub-array contains the same number of modules.
The question is: "How different can the orientation be for the different sub-arrays? Let me pose a concrete example: Xantrex GT5.0, two strings of BP Solar SX3190s. One string has an orientation of 15 deg tilt and 188 degrees azimuth; the other has 23 degrees tilt and 139 degrees azimuth. For reasons that are difficult to explain, none of the orientation angles can be changed, at least for the purposes of this discussion. To visualize what I am talking about: the tilts are fairly close (8 degrees) and the azimuths differ by about 45 degrees. How do I calculate the combined performance? How much power does one give up compared to using separate inverters for each sub-array/string? Are there rules of thumb as to what works and doesn't? Do conventional inverters have algorithms that can navigate the non-ideal I-V characteristic under load? I know there was a tech bulletin from Fronius a while ago: I read it but didn't come away with any definitive answer. I also had first hand knowledge with MPPT algorithm problems with the Fronius inverters during that time period, which caused me to discount the tech bulletin. I am quoting a system as we speak, so my inquiry is not hypothetical in nature. Any help would be appreciated. - Peter Peter T. Parrish, Ph.D., President California Solar Engineering, Inc. 820 Cynthia Ave., Los Angeles, CA 90065 Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885 CA Lic. 854779, NABCEP Cert. 031806-26 peter.parr...@calsolareng.com
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