Although VOC measurements using the ambient air temperature in the area are interesting. Perhaps a more thorough diagnosis is in order. As a first step I recommend getting array ISC, VOC, MODULE temperature, and solar irradiance. There is equipment available to make these tests easy, or if you are on a budget, it can be done with multiple pieces of less expensive equipment. Based on the findings, you can take the next step and use a curve tracer. A visual inspection and perhaps thermal imaging and the use of UV lights can also be used to look for damaged, dirty or defective modules. Pieter Huebner Project Manager Off Grid Enterprises ________________________________ From: RE-wrenches <[email protected]> on behalf of Dave Tedeyan via RE-wrenches <[email protected]> Sent: Tuesday, February 10, 2026 2:06 PM To: RE-wrenches <[email protected]> Cc: Dave Tedeyan <[email protected]> Subject: [RE-wrenches] Q.PEAK DUO BLK-G6+ underproduction
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 -- [https://ci3.googleusercontent.com/mail-sig/AIorK4zoZ4JdaR79CFcLmy74s-VRVaVovMEuRmw5pzk3XBT09h8ZNlFbMgJ4yHW2Uxf91_2codJGB4DALADN] 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
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