Panel or Inverter Problem

[BobE]

I guess I'm the latest DIY Solar guy. Had a system installed in November 2019, went to submit a repair request to determine the contractor is already out of business.

The system is small, 16 325W Canadian Solar panels with Enphase microinverters. On install, there was about 10% difference in production between the high and low panels. That was acceptable. However, now there is a real outlier at 62%.

Attached below is data from a cloudless sunny day. First a good panel adjacent to, and then the problem panel. Can anyone definitely tell from the data if it's the panel or microinverters? I'm going to swap the inverters, the problem will either follow the inverter or stay with the panel. But wondered if this would be obvious to someone more knowledgeable than I am. Basically, the bad panel/inverter has a limit of about 170W.

This problem is not shading. There is obvious shading late in the day just before sunset.

Thanks!

 

[MisterSandals]

Hopefully you have a couple micro inverters on hand as replacements for a quick test/swap.

I have had a single micro inverter go bad after a little over a year so i would not be wildly surprised if that is your case. Solar panels do not have a very high failure rate where the voltage drops by 50% - if there is a problem, its usually a total loss with a electrical trace or cell connection getting broken.

But, your test of switching 2 micro inverters will definitely isolate the problem. If convenient I would probably check the connections for the bad unit first (unpower, disconnect, inspect, securely reconnect).

 

[BobE]

I also suspect the microinverters. Both panels ramp up, in perfect sync (time and solar radiation level) to 160-170W as the sun rises. Not sure what could establish an output "plateau" as observed in a solar panel, with no early indication. Several possibilities in the inverter......

 

[John Frum]

If you don't have a spare perhaps you can swap the inverter from a known good panel.
If the problem follows the inverter then its likely the inverter.
If not then its likely the panel.

 

[BobE]

That's exactly the plan. Won't happen till Sunday, then take a few days to collect the stats from the Enphase logging.

The more I think about this, the happier I am to be using a microinverter system. It makes troubleshooting so much easier. With a string system, there would be no per panel statistics to review. If there were enough panels combined in the statistics data, this problem might not even be detectable.

 

[Steve_S]

Assuming this is a fixed mounted system likely on a roof or rack of sort and you said this was installed in November !
You haven't mentioned where you are located. Go to this page, enter your country, state & city and it will tell you the optimal solar angles, also show you the amount of Sun Hours you should expect through the seasons and other related info. Everything hinges on how the panels are setup, the angles & directions as to how well they will take the sun and how much they will generate at any given point throughout the year.

If your in Canada or USA, November - February is most blah time period for solar generation usually...

Before climbing up on a roof or racking and fiddling with the enphase inverters... BTW you will NEED a tool to un-couple the MC4 connectors, doesn't take much to wreck them. It's better to look at the angles, installation and try to identify when your setup will generate the most and when they will generate the least, to start with. If the panels are installed in a bad position, furtling wit the inverters won't help you.

IF the contractor is out of business already, 4 months after the install... That's an eyebrow raiser & RED FLAG indeed. Fingers crossed for ya.

 

[Anson Guo]

Mr. Mr Steve_S suggestion upstairs is very good!

Supplement: The angle and orientation of the solar panel installation will affect the maximum output power of the solar panel. When installing the entire system, it is necessary to accurately calculate their data.

The conversion efficiency of the inverter depends on the input power of the solar panel. If you have doubts about solar energy, you can try to install (Edge Power) optimizer to improve and optimize solar output power. (This is not an advertisement, it is just a suggestion, provided that your capital budget is sufficient ~)

 

[svetz]

Can't wait to hear what you learn!
You might also be interest in this: Shade on your solar panel can void your warranty
(Probably not your case since you're using microinverters)

 

[Hedges]

However, now there is a real outlier at 62%.

Basically, the bad panel/inverter has a limit of about 170W.

This problem is not shading. There is obvious shading late in the day just before sunset.

Thanks!

I like to be a contrarian or devil's advocate, so here goes:

The ~1/3 reduction in power output just happens to be the amount of power produced by each section of diode-bypassed cells in a 325W Canadian Solar panel. So I'll put my money on a shorted diode. Check open-circuit voltage and see if that is also 2/3 of a good panel. (Any chance you can query the microinverter for voltage and current?)

This might be due to shading (causing current to go through the diode to get past shaded cells), and either faulty or poorly heatsinked diode. The guys promoting optimizers or inverters per panel claim to address the problem, which they attributed to manufacturers putting in cheap diodes. Solution is to buy expensive per-panel electronics? May not have solved anything in your case. Besides, it's heatsinking. Anybody can read a diode's data sheet, but it takes an engineer to get the diode to perform to spec. (and I are one)