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 <p...@cesolar.com> wrote: > From: Phil Schneider <p...@cesolar.com> > Subject: [RE-wrenches] voltage drop from online data? > To: "RE-wrenches" <re-wrenches@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 > > > _______________________________________________ > List sponsored by Home Power magazine > > List Address: RE-wrenches@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 _______________________________________________ List sponsored by Home Power magazine List Address: RE-wrenches@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
