Panel over voltage

[Roo]

Can any expert here answer this question, this issue has hit me twice on my off grid system.

One of my panels, all 340w 9a is currently putting out 40.5v; it's now 5.00pm and cloudy. Usually they all max out at 28v at midday with sun. My system is 24v.

As you would realize with this over voltage my charge controller shuts down the system rendering it useless. I can't believe that it's producing 40v at this time of day and cloudy. At about 2.00pm it was giving 42v. Both the charge controller and my multimeter agree on the numbers.

What could possibly do this? I'm stumped for an answer.

(I have another panel with the same behavior - got round the problem with a dc step down. Resolved the voltage issue but lost same amps, so not happy with the result. But I need to know why?)

 

[upnorthandpersonal]

Your battery is full, your charge controllers disconnects the solar panels (essentially open circuits them) and what you're seeing is Voc of the solar panel. Check your charge controller and solar panel manuals for Voc, or maximum open circuit voltage or something along those lines. You always want to make sure your MPPT can handle Voc (not just Vmpp, max. power point, since Voc is higher). Also keep in mind that Voc specified in the solar panel manual is usually specified at 25C. Voc can be significantly higher when temperatures drop.

 

[offgriddle]

Your battery is full, your charge controllers disconnects the solar panels (essentially open circuits them) and what you're seeing is Voc of the solar panel. Check your charge controller and solar panel manuals for Voc, or maximum open circuit voltage or something along those lines. You always want to make sure your MPPT can handle Voc (not just Vmpp, max. power point, since Voc is higher). Also keep in mind that Voc specified in the solar panel manual is usually specified at 25C. Voc can be significantly higher when temperatures drop.

Excellent information thank you as well!

 

[RCinFLA]

If hot Voc is 40.5v and they max out at 28v while charging, I would say you likely have a PWM charge controller.

Same answer as above to question, but I will add you are wasting potential PV power with the higher voltage panels using PWM controller. With a MPPT charge controller you will get near same panel current at about 36v on panels. About 25%-30% more power while charging. With MPPT voltage drop should yield about 20% more charge current to battery.

 

[Roo]

I'll try to make this a little more clear. This is a very strange phenomena.

24v batteries, MPPT charge controller. VOC panel shutdown is at 29.9v as per battery manufacturer specs.

It is 7.00 am in the morning, batteries are at 50%. It's been raining overnight so very cloudy. It is winter. SCC is shutting down the panels as there is over charge. Volt meter reads 40.5v coming from the panels, SCC agrees with this value.

I cannot find any logic to this scenario.

 

[gnubie]

What make / model of SCC?

 

[Roo]

What make / model of SCC?

Epever AN series 40amp.

 

[Dzl]

Do you have a link to the panels or a picture of the stickr on the back or datasheet?

 

[nosys70]

Winter=cold
Cloudy=diffuse light with high reflection

All the best condition to have high voltage on panels
Usually SCC are able to deal with very high voltage.
So either you choose the wrong panel type of the wrong SCC.