[RE-wrenches] losses to competing angles in single strings

[Peter Parrish]

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
peter.parrish at calsolareng.com  
Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885


 

  _____  

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] 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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