[RE-wrenches] voltage drop from online data?

[Joel Davidson]

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" <phil at CEsolar.com>
To: "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
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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