Low and inconsistent solar voltage on mppt solar charge controller

mr-solar

New Member
Joined
May 25, 2022
Messages
3
Hello everybody,

I have problems with my little off-grid solar system. It has two S-ENERGY SM-255PA8 panels connected in series to a Epever 3210N MPPT charge controller and a 12V 70Ah AGM battery is being used. Load connects to a 500W inverter. The solar panels are used, I cannot tell how old they are.

The panels have the following ratings: Pmax = 225W; Voc = 36.6V; Isc = 8.25A; Vmpp = 29.7V; Impp = 7.6A.

Although they are connected in series and in unobstructed, pure sunlight, the charge controller displays a solar voltage of around 16V and the power goes to a maximum of around 100W (a load of around 250W was connected). The first time i connected the system, I once got around 250W at 36V with two panels in series, then it dropped quickly to the 16V with a complete cut off between that shortly. If only one panel is connected to the charge controller, there is no solar power at all, the solar voltage sits at around 13V, 0A current.

I measured open circuit voltage and short circuit current of both panels, which almost matched the ratings on the datasheet on the panels (just a little bit below). Open circuit voltage and short circuit current while connected in series also matched expectations. I tested all bypass diodes on each panel, which were all fine. So the panels seem okay to me.

So i thought it might be a faulty charge controller: i tried different charge controllers (PWM and MPPT, but of the same brand), which all gave the same result. Lately i tried another but brand new single solar panel on my charge controller and it showed, that the charge controller was okay, because it matched the Vmpp of that solar panel with around 36V and could deliver much more power while the solar voltage was always consistent.

Does somebody have an idea, what could be wrong in this system? I am guessing that I am dealing with faulty panels here, but I have no clue what exactly could be wrong with them. Maybe someone can give me some advice on this.
 
Last edited:

GLC

Solar Addict
Joined
Aug 26, 2020
Messages
773
Location
Texas
Hello everybody,

I have problems with my little off-grid solar system. It has two S-ENERGY SM-255PA8 panels connected in series to a Epever 3210N MPPT charge controller and a 12V 70Ah AGM battery is being used. Load connects to a 500W inverter. The solar panels are used, I cannot tell how old they are.

The panels have the following ratings: Pmax = 225W; Voc = 36.6V; Isc = 8.25A; Vmpp = 29.7V; Impp = 7.6A.

Although they are connected in series and in unobstructed, pure sunlight, the charge controller displays a solar voltage of around 16V and the power goes to a maximum of around 100W (a load of around 250W was connected). The first time i connected the system, I once got around 250W at 36V with two panels in series, then it dropped quickly to the 16V with a complete cut off between that shortly. If only one panel is connected to the charge controller, there is no solar power at all. The voltage then sits at around 13V, 0A current.

I measured open circuit voltage and short circuit current of both panels, which almost matched the ratings on the datasheet on the panels (just a little bit below). Open circuit voltage and short circuit current while connected in series also matched expectations. I tested all bypass diodes on each panel, which were all fine. So the panels seem okay to me.

So i thought it might be a faulty charge controller: i tried different charge controllers (PWM and MPPT, but of the same brand), which all gave the same result. Lately i tried another but brand new single solar panel on my charge controller and it showed, that the charge controller was okay, because it matched the Vmpp of that solar panel with around 36V and could deliver much more power while the solar voltage was always consistent.

Does somebody have an idea, what could be wrong in this system? I am guessing that I am dealing with faulty panels here, but I have no clue what exactly could be wrong with them. Maybe someone can give me some advice on this.
So to clarify:
You checked your panels individually and the voltage was as rated on the panels, correct?
You disconnected your panels and added one panel at a time but they both showed "0" on the controller as far as power?
With panels disconnected, controller showed 13, which is your battery voltage.
You connected a new panel and it showed watts/voltage/amps that matched the new panel?
Your unit 3210n is a 30 amp, 390 watt max solar controller at 12 volts. You are trying to push 450 watts through it, correct?
Have you tried to verify with a clamp meter to verify volts and amps before and after your charge controller to see if it matches?
(Wires coming from your solar panels while it is hooked up to your solar collector)
 

mr-solar

New Member
Joined
May 25, 2022
Messages
3
Thank you for your quick answer. That's all correct. I am only able to get solar power when both panels are connected in series. One panel at the time will lead to 0W solar power, no matter the load connected. I verified voltage and amperage manually. I have no idea, why one panel alone would not work at all. Regarding the 390W limit, I thought this is just the maximum power the charge controller can charge the battery with. Only 390W power can be used, even if more power would be available.
 

GLC

Solar Addict
Joined
Aug 26, 2020
Messages
773
Location
Texas
Thank you for your quick answer. That's all correct. I am only able to get solar power when both panels are connected in series. One panel at the time will lead to 0W solar power, no matter the load connected. I verified voltage and amperage manually. I have no idea, why one panel alone would not work at all. Regarding the 390W limit, I thought this is just the maximum power the charge controller can charge the battery with. Only 390W power can be used, even if more power would be available.
Yes, you can over panel up to, on this model, up to 1.5 x the suggested max. to 585 watts. I do this my self on my setups. But, If you go over the 585 watts or 30 amps or 90 volts, you will fry the controller. As longs as your batteries are not full of charge, it does not even need a load connected to it like an inverter to register solar gain. All you need is batteries, controller and panels. So if your batteries are not full, even a single panel will register solar gain. Since the new panel worked, I say your old panels may be toast. Just verify that your controller is hooked to the battery first and then the panels. If not it may not read correctly.
 
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