[RE-wrenches] voltage drop from online data?

[Darryl Thayer]

Phil 
The voltage measured at the inverter is the inverter determined voltage, not necessaryly Vmp-Vdrop The inverter can select the operating Vmp correctly or incorrectly, the shading or module mismatch will have a great effect on this voltage.  I have always found the measured to be below the theretical voltage.  
Darryl


--- On Tue, 3/17/09, Phil Schneider <phil at CEsolar.com> wrote:

> From: Phil Schneider <phil at CEsolar.com>
> Subject: [RE-wrenches] voltage drop from online data?
> To: "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
> Date: Tuesday, March 17, 2009, 12:02 PM
> 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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