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<div class=Section1>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt;color:black'>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.</span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt;color:black'> </span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt;color:black'>The question is: “How different can
the orientation be for the different sub-arrays?</span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt;color:black'> </span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt;color:black'>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.</span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt;color:black'> </span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt;color:black'>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.</span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt;color:black'> </span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt;color:black'>I am quoting a system as we speak, so my
inquiry is not hypothetical in nature. Any help would be appreciated.</span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt;color:black'> </span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt;color:black'>- Peter</span></font></p>
<div>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'>Peter T. Parrish, Ph.D., President<br>
California Solar Engineering, Inc.<br>
820 Cynthia Ave., Los Angeles, CA 90065<br>
Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885<br>
CA Lic. 854779, NABCEP Cert. 031806-26<br>
peter.parrish@calsolareng.com</span></font><font size=2 color=blue face=Arial><span
style='font-size:10.0pt;font-family:Arial;color:blue'> </span></font></p>
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