Acceptable spread in panel performance

[bob-n]

Please correct me if I'm wrong.

The measured output per panel varies with location but is not patterned.
There is no shading.
The array puts out roughly the expected amount of power.

I just looked at the data sheets from a few optimizers and NONE give monitoring accuracy specifications. It is easy to measure voltage accurately and hard to measure current accurately. Measuring current consumes energy, so to get the efficiency high and cost low, they might have compromised measurement accuracy.

Is it possible that the optimizers are just really inaccurate at monitoring power, and you're simply seeing +/-15% optimizer calibration differences? I know that sounds like a lot, but it's within spec because there is no spec.

The ultimate test would be to swap optimizer locations. See if the high reading stays with the panel or stays with the optimizer. That requires disconnecting MC4 connectors, which requires either dexterity with little pointy things or a special tool. It also means FIRST shutting turning off the AC disconnect and THEN turning off the DC disconnect on the inverter, before you disconnect a panel or an optimizer. A string of panels produces a large voltage. If you do it wrong, it can cause a serious arc - with DAMAGE, INJURY, AND POSSIBLY DEATH.

As Bruce mentioned, another good test would be to measure the current coming out of each panel, not the current coming out of the optimizer. Be sure that you're not shading a part of the array when you measure. That test requires a clamp-on DC ammmeter, but doesn't require disconnecting anything and doesn't require shutting down the array. Not every clamp-on ammeter measures DC amps. For example, Klein sells three similar models. The $80 model doesn't measure DC amps but the $130 model does.

https://www.amazon.com/Resistance-Continuity-Klein-Tools-CL900/dp/B019CY4FB4

[PugPower]

Using the SolarEdge dashboard layout tab you can do a daily playback of your panels performance and see if some panels are experiencing shading. Based on the data you posted it appears that four of your panels are producing similar higher results and the remaining ten panels are producing similar lower results. It's possible you have some shading maybe early in the morning or late in the day that is affecting the ten panels with lower output.

[brymeow]

We just got a new solar system installed on a flat roof in Arizona, the system consists of 14 Sun Power 327W panels installed in two rows of 7 on a fixed rack, with SolarEdge optimizers and one SolarEdge SE7600H inverter. The system produces the output expected for our environment of around 30 kWh/day, however we have noticed marked differences in individual panel performance. Three panels are running up to 18% below the calculated average for all 14 panels and the spread between the highest and lowest producing panel is 33%. There is no shading on the panels, the three that are lower in production are not located on the outer edge, and the panels are all clean.

We contacted the installer to get information about the normally observed spread in panel output, however we did not get an answer other than to be content that the expected daily output is achieved.

Any insight what spread to expect would be appreciated.

Hi, i'm planning to install solar panels on my garage top flat room (re-roofing with 1-2 degree pitch, hot mop/torch down roof). What kinda mount did your solar company use? Were you worried about potential leak?

[Jon Fisher]

Thank you for the additional input. J.P.M was right, I eered with regard to the date I took the panel reading, should have said 06/25/2020. I appreciate the warning reading potential life threatening hazards when taking measurements directly at the panel level. As the system has only recently been installed we are working with the installer to have him assess why a few panels are apparently showing subpar performance. Following bob-n's input I am also contacting SolarEdge to see what they can say about optimizer specifications The ideas of taking direct measurements at the panel and swapping optimizers to see whether the observed lower performance moves with them are next steps. Again, thanks for the input, will provide an update once we learn more.

Regarding brymeow's question, I am familiar with two different systems. On a foam roof, the contractor located the trusses, cut out the foam all the way down to the plywood to screw the small stand footing all the way down into trusses and then refoamed the location and coated the foam. The other system used on a flat garage roof with an EPDM roof membrane, here a non penetrating solar ballast system was used. No leaks were experienced and the panels held up well even after storms with high wind velocity.