[RE-wrenches] Odd Inverter Behavior

[August Goers]

Hi Wrenches -



I posted this original thread a ways back but we've now had the opportunity
to fix the problem...



What I had failed to mention in my original post (below) is that this is an
off grid Sunny Island based system. The Sunny Island wasn't properly setup
and thought that the battery bank was full so it was telling the Sunny Boy
to throttle back (I believe by adjusting the AC frequency). Anyway, we
reprogrammed the Sunny Island with the correct battery setup and the system
is now cranking. Once the battery bank is full and if the loads go down the
Sunny Boy will in turn crank down its output which is just what we want it
to do.



Thought I'd let you know - I guess that goes to show that I haven't done any
off grid work for a long time (since the late 90s)! -August



---------- Forwarded message ----------
From: *Darryl Thayer* <daryl_solar at yahoo.com>
Date: Thu, Feb 3, 2011 at 4:59 PM
Subject: Re: [RE-wrenches] Odd Inverter Behavior
To: RE-wrenches <re-wrenches at lists.re-wrenches.org>

I have seen that behavior almost.  if open cirucit is 330 then MPPT should
be about 264 which is to close to bottom of the window.  Last summer a sunny
boy in a similar situation of 8 modules in string was droping out on MPPT
tracking.  The inverter had additional module added and started to behave
correctly.  Sometimes the manufacture wants the sale and some inverters
might not be in spec, so becarful of string sizing calculators.

Another case the tracking algorithm was defective and the modules were
operated at to high a voltage above the Vmp voltage, I replaced the inverter
and problem fixed.


------------------------------

*From:* August Goers <august at luminalt.com>
*To:* RE-wrenches <re-wrenches at lists.re-wrenches.org>
*Sent:* Thu, February 3, 2011 6:01:11 PM
*Subject:* [RE-wrenches] Odd Inverter Behavior


Hi Wrenches -



We were called out today to check out an under performing system installed
by another contractor. This is an odd case.



The system has 24 Suntech 180s in three strings of 8 and a SMA Sunnyboy
4000us. Open circuit voltage for each string was about 330 Volts and we
verified that everything appeared to be wired in correctly. There is no DC
side grounding at all. Just a positive and negative coming down off the roof
for each string.



With all modules in direct light the inverter is only pumping out about 250
Watts steady state. We noticed that when we turn it off and on again that
the power went up to about 1500 Watts as it started tracking the max power
point. Then it slowly veers off course and settles out at about 250 Watts
and is running very close to the open circuit voltage of about 330 volts. I
would expect the MPP voltage to be closer to ~280 Volts. The inverter MPP
tracking range goes down to 250 Volts so I don't think that's the problem.



Anyone ever seen anything like this before? What might be causing the
inverter to get confused? The only thing I can think of is that something
fishy is going on with the lack of a DC side ground and that certainly needs
to be fixed anyway.



All thoughts welcome.



Best,



August








_______________________________________________
List sponsored by Home Power magazine

List Address: RE-wrenches at lists.re-wrenches.org

Options & settings:
http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org

List-Archive:
http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org

List rules & etiquette:
www.re-wrenches.org/etiquette.htm

Check out participant bios:
www.members.re-wrenches.org




-- 
August Goers


Luminalt Energy Corporation
1320 Potrero Avenue
San Francisco, CA 94110
O: 415.641.4000
M: 415.559.1525
august at luminalt.com
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20110701/35d073b5/attachment-0004.html>