Low voltage from rooftop solar panel - looking to confirm diagnosis

danwrona · July 30

We've been having issues charging the battery from the original rooftop solar panel. My tentative diagnosis is a bad panel, but I'm looking for any alternate possibilities before we replace it. Specs, testing to date, and other details below:

Original 100W rooftop solar panel
Weize 12V 100Ah AGM battery
All tests below were done mid summer, mid-day in full sun facing south
Screenshot of Victron status below

The Victron app indicates that the charger is off; the error message identifies the reason as the solar not delivering >5V more than the battery. The solar voltage usually reads between 13-15 in the app (typically ~13.7), and I don't remember a time when it was greater.

Through reading other posts, I realized I should also test the panel itself to rule out wiring and other hardware issues. Voltage at the quick-connects at the solar panel matched what I was seeing in the app (~13.7). This leads me to believe the panel is the problem.

In desperation, I cleaned the panel to determine the impact of dirt/grime, but it only increased by .5-.75V to 14.23V, as shown in the screenshot below.

Additional context:
Last year, the panel peeled up off the roof at the top and bottom, so we had a local service center reseal the edges. While they did a crap job, it didn't seem to change performance.
We burned up the original 64Ah battery over the past two seasons. I assumed this was due to newbie user error, but this may be an alternate explanation.

Are there any other issues we should consider/test before replacing the panel?

Thanks for your help!

Image: https://us.v-cdn.net/5021717/uploads/editor/7u/7ps8qjvivkua.png

pthomas745 · July 31

Show us your history page and battery settings pages. If the settings are still set for lead acid charging, the Victron is seeing a fully charged lead acid battery. "13.6" is also the basic voltage you will see when a lead acid battery is being charged by any source.

Shw us the History and Settings pages.

danwrona · July 31

Thanks! See below.

I selected the AGM Spiral cell preset when installing. The history shows the past 4 days, but voltage range is comparable (with no charge) over the past 3 weeks since installing.

Image: https://us.v-cdn.net/5021717/uploads/editor/k1/mnwn0ow3vna3.jpeg

Image: https://us.v-cdn.net/5021717/uploads/editor/rs/rqbyhriwb78l.jpg

over

pthomas745 · July 31

I'm really sorry, I saw the "Weize" battery, but my brain skipped over the "AGM" part!

Your battery voltages appear to be completely charged for a lead acid battery. Has the trailer been sitting with the switch off? Or on shore power? Every one of the battery numbers (status, min/max, etc) show a completely charged battery. The "charging is off" on the app because the battery does not need charging, according to the history.

What happens with the trailer running something like the fan or the fridge? Letting it run for a while, and see if the solar kicks in?

danwrona · July 31

No problem on the AGM part.

Yes, the battery is mostly charged. I put it on a charger before installing, and we've only camped with shore power since I'm not confident in the solar. That makes sense that it won't charge a full battery - I wasn't thinking about that angle, thank you.

I accidentally left the battery disconnect switch on a few days ago, which may be responsible for the drop from '2 days ago' to 'yesterday' in the screenshot. All equipment was powered off, so that would have been all due to parasitic draw. I could try leaving something on to draw it down further to see if solar would kick in.

That said, my logic says that may not make a difference. If I remember correctly, the minimum battery voltage is ~12.2 before it needs to be recharged. If the controller requires >5V greater, the solar panel would need to be providing at least 17.2V. If the panel itself (tested at quick-connects on the roof) isn't putting out more than 14.4-15.6 under optimal conditions, it doesn't seem like it will ever reach the voltage needed.

Am I missing anything in my logic or assumptions?

ckjs · July 31

danwrona said:

. If I remember correctly, the minimum battery voltage is ~12.2 before it needs to be recharged. If the controller requires >5V greater, the solar panel would need to be providing at least 17.2V. If the panel itself (tested at quick-connects on the roof) isn't putting out more than 14.4-15.6 under optimal conditions, it doesn't seem like it will ever reach the voltage needed.

Am I missing anything in my logic or assumptions?

Nope; the panel is the problem. It should be generating a higher voltage in the sun. That’s independent of the battery’s state of charge. Perhaps it was damaged when it was re-secured to the roof.

pthomas745 · July 31

I've never really understood what Victron means by "5 volts". That 12.2 reading, according to many "lead acid state of charge" charts, would practically have to use 40 amp hours from a 80 amp hour battery before solar charging would begin. That situation is not what I have ever experienced with my solar panels.

Try it yourself. Run the fan for a few hours, with the trailer in the sun. See when or if the solar panels actually start recharging the battery.

AnOldUR · July 31

That 5V difference is between the solar panel output and the battery. I believe it uses the open circuit voltage (Voc), not the maximum power voltage (Vmp). The mppt monitors the Voc before any current is flowing, so there's no voltage drop. That rating is usually above 20V, so the 5V difference is not unrealistic even with a lithium battery and low light. Once the load is applied the voltage drops, but it's programmed to not shut down until there's a 1V difference.

Image: https://us.v-cdn.net/5021717/uploads/editor/jd/msspblgb4ess.jpg

Marceline · July 31

If your AGM is fully charged (or close to it) the solar controller isn't going to send any current to the battery. Try running your battery down a bit and then do your testing.

Jfrei · August 1

Sorry Dan I don't understand when you said:

"Through reading other posts, I realized I should also test the panel itself to rule out wiring and other hardware issues. Voltage at the quick-connects at the solar panel matched what I was seeing in the app (~13.7). This leads me to believe the panel is the problem."

Are you saying the issue is that at the panel you should be reading a higher voltage?

I'm asking b/c I'm dealing w/ solar issues too and looking for answers.

I will add if you are having problems with your solar get to nuCamp right away. We're 2 weeks past our 1 year warranty and they will not do anything about ours.

AnOldUR · August 2

Jfrei said:

Are you saying the issue is that at the panel you should be reading a higher voltage?

Voltage from a solar panel should be higher than the battery rating. A typical voltage will be over 20V's when in sunlight and not connected to a controller. Have you checked the voltage coming from the panel?

Howdy, Stranger!

Quick Links

Categories

Low voltage from rooftop solar panel - looking to confirm diagnosis

Comments