[RE-wrenches] Inverter with two strings of different orientation

[Peter Parrish]

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.parrish at calsolareng.com 

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