Performance of Large Outback system [RE-wrenches]

[Bill Brooks]

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Darryl, Matt, and Doug,

Where are your irradiance measurements? How do any of your output readings
have any meaning without an irradiance measurement? Do any of you own a
Daystar meter or do you have a spare module that you can get a Isc
measurement from? Carl brings an important point about temperature, but it
is a much lower order effect than irradiance. No power measurement should
even be written down without a corresponding irradiance measurement.

Forgive me for bringing up my pet peeve again, but I recently came from an
installation of one of the most knowledgeable installers in the state. The
array wasn't working well so they suggested removing the 3 C-40 charge
controllers and installing 3 MX-60 charge controllers in their place (a very
expensive proposition as you all know).

The problem had nothing to do with the C-40s. A quick check of the string
currents showed a 3:1 differential from the best string to the worst string.
As it turned out with further inspection (with a $21K Daystar curve tracer
that I don't expect anyone to own), that every single string had failed
modules. The array will be replaced, but the sad thing is that this "very
knowledgeable" installer could not tell that the array was a total mess and
suggested a fix that did absolutely no good.

My plans are to design an advance PV Design, Installation, and
Troubleshooting course. Is there any interest from current installers? I've
been working with grid-connected systems for over 16 years now, and I'm
learning new things every single day.

Understand that I am not trying to be patronizing about this--I'm just
trying to get installers to do things properly so that they can be confident
with the results of any measurements they make on their systems. Please go
back and send some information on performance that is related to irradiance
and temperature.  I'm sure everyone on the list is interested in informative
results.

Bill.

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