Phil,
What measurements do you get for:
Location
Date
Time
Weather (clear, hazy, cloudy, partly cloudy)
Irradiance
Ambient Temperature
System DC STC Power
Cell Temperature
DC Voltage (at what point?)
AC Power
Joel Davidson
----- Original Message -----
From: "Phil Schneider" <[email protected]>
To: "RE-wrenches" <[email protected]>
Sent: Tuesday, March 17, 2009 10:02 AM
Subject: [RE-wrenches] voltage drop from online data?
Wrenches,
I was looking at some of our web-based monitored systems this morning to
check in on some performance numbers, and this question came up.
I can see a measured DC array voltage on-line (as measured at the
inverter),
and I have cell temp information so I can calculate the theoretical
temp-adjusted Vmp (based on module nameplate). When I look at the
difference between theoretical and measured, it seems that this can
largely
be attributed to voltage drop in the DC wiring between array and inverter.
Am I missing other factors that would lead to this difference between
theoretical and measured? Power-point tracking errors, Vmp tolerance and
module mis-match, cell temp accuracy are a couple that come to mind. I
realize that field measurements at different points in the system would
give
me more information from a scientific standpoint, but in this age of
remote
monitoring I make sure we understand it's utility.
Phil Schneider
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