It would be fairly easy to spot bypass diode issues or cell current imbalance issues with a hand-held IR imager on a decently sunny day. Maybe time to go on the roof and take a peek?
Roy Rakobitsch Windsine LLC 631-514-4166 On Tue, Feb 10, 2026, 18:25 Jay via RE-wrenches < [email protected]> wrote: > Looking at it from performance ie watts, how far off does it appear to be? > > Jay > > > > On Feb 10, 2026, at 2:07 PM, Dave Tedeyan via RE-wrenches < > [email protected]> wrote: > > > Hi All, > > I was just reviewing a site installed about 5 years ago and am finding it > is not doing nearly as well as I would have expected. Most of our sites > produce relatively close to our projections, but this one is pretty far > off. There are 3 strings of 12 Q.PEAK DUO BLK-G6+ modules. Two strings go > to a 7.7kw inverter and one string goes to a 3.8kw inverter - both of which > are the -41 series SMA inverters. There are Tigo TS4-R-F rapid shutdown > devices on all the modules. > > Vmp for 12 of these panels should be about 407V at STC. At 50C (which is > really hot for upstate NY), the Vmp should be around 380V. On a perfect > summer day, I am seeing Vmp of around 320V. On a perfect spring day > (cooler, with some power clipping, I am seeing Vmp of around 355V. And on a > perfect winter day (when there was no snow) Vmp is around 365V. All three > strings are pretty consistent with each other, so I don't think that there > are specific installation issues with any panels, unless we managed to > forget to wire in two panels in all three strings which is extremely > unlikely. > > So, I can only think of two things that might be at play here: > 1. Maybe these modules are just crap, and are not at all performing to > spec. > 2. Maybe the Tigo devices are causing issues. > > Has anyone out there experienced production issues like this? Everything > appears normal, it is on an open rooftop, and there are not things like > partial shading, weeds, bird poop, or other soiling affecting the modules. > I don't have another site with the same modules that also has good > monitoring data, but maybe some of you do! > > Thanks for the consideration! > Cheers, > Dave > -- > > Dave Tedeyan, P.E. > Owner | Sungineer Solar > p: he | him | his > a: 1653 Slaterville Rd. | Ithaca, NY 14850 > w: www.sungineersolar.com <http://www.sungineersolar.com/> > c: (607) 270-0370 > _______________________________________________ > List sponsored by Redwood Alliance > > Pay optional member dues here: http://re-wrenches.org > > List Address: [email protected] > > Change listserver email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > There are two list archives for searching. When one doesn't work, try the > other: > https://www.mail-archive.com/[email protected]/ > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > http://www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > http://www.members.re-wrenches.org > > _______________________________________________ > List sponsored by Redwood Alliance > > Pay optional member dues here: http://re-wrenches.org > > List Address: [email protected] > > Change listserver email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > There are two list archives for searching. When one doesn't work, try the > other: > https://www.mail-archive.com/[email protected]/ > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > http://www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > http://www.members.re-wrenches.org > >
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