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Pv overvioltage . Does anyone know why my panels are creating more voltage than the rated voltage on panel. It is causing my string inverter to shut

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alan.com

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Pv overvioltage . Does anyone know why my panels are creating more voltage than the rated voltage on panel. It is causing my string inverter to shut down.
I have 12 panels rated 48 volts and inverter has max 600volts . Sometimes it goes up to 650volts and inverter shuts down. Is there a way of presenting this from happening without removing a panel.
 
Yeah, all it takes is for each panel to go over it's VOC by 2volts on a cold day for you to reach the 600V limit.

That's too close for comfort.
Depending on your inverter you could likely split it into 6 parallel and 6 series to mitigate the problem.
 
No. Panels do go over their voltage depending on temperature.

What is your panels rated VOC?

You probably need to remove 2. ASAP, before it kills your string inverter.
 
alan.com said:
Is there a way of presenting this from happening without removing a panel.
Click to expand...
No. You probably need to remove two panels.

Voc of a PV panel is temperature dependent. As temperature falls, Voc goes up. This temperature - voltage relationship is listed on the panel's spec sheet.

Good string design accounts for the string's voltage at the lowest expected temperature in your location.
 
Andrewr05 said:
Yeah, all it takes is for each panel to go over it's VOC by 2volts on a cold day for you to reach the 600V limit.

That's too close for comfort.
Depending on your inverter you could likely split it into 6 parallel and 6 series to mitigate the problem.
Click to expand...
Can't do that. The amps will be too high
 
alan.com said:
The temperature at present is 18 Celcius.
Click to expand...
That will increase voltage by ~ 2% - 3.5% over the STC Voc.

Your string is already 12 x 48.7 V = 584.4 V. Add 2% - 3.5% to that and you are at 596 - 605 V.

And the colder it gets the more the voltage goes up. Need to to remove at least one panel from the string. And possibly two to allow for extra cold temperatures.
 
wattmatters said:
No. You probably need to remove two panels.

Voc of a PV panel is temperature dependent. As temperature falls, Voc goes up. This temperature - voltage relationship is listed on the panel's spec sheet.

Good string design accounts for the string's voltage at the lowest expected temperature in your location.
Click to expand...
Would DC optimisers prevent this happening. Temperature is 18 Celcius and this and Vic is 48.7
 
wattmatters said:
That will increase voltage by ~ 2% - 3.5% over the STC Voc.

Your string is already 12 x 48.7 V = 584.4 V. Add 2% - 3.5% to that and you are at 596 - 605 V.

And the colder it gets the more the voltage goes up. Need to to remove at least one panel from the string. And possibly two to allow for extra cold temperatures.
Click to expand...
The string inverter keeps voltage input from string at around 500-540 and works fine 99.9% of the time, I don't want loose a panel. Would DC optimisers prevent this from happening. It normally happens when sun comes out from dark clouds
 
alan.com said:
Can't do that. The amps will be too high
Click to expand...
Amps / current is pulled down (drawn} by the controller. It's not forced into the controller the way volts are.

Volts was the much more important number for you to consider.

If the panels are able to produce more current than the controller is capable of then it would clip the extra.

Basically it is wasted but not harmful. (unless you reverse the the polarity accidentally)

More current than the controller is rated for is called over paneling and is done on purpose to keep production up during cloudy days.

The voltage maximum should never have been exceeded and there already may be damage to the unit . Switch the pv off and remove at least one panel, possibly two.

Then do the calculations or simplfy by staying 20% under the controllers V max. This way cold and cloud edge effect won't fry anything.

Napkin math says your panels can prob put out 55v during certain conditions which rounded down is 10 panels. 11 if it doesn't get too cold.
 
alan.com said:
This happens when sun comes out from behind clouds sometimes.
Click to expand...
On the West coast of Scotland so conditions are similar, your panels cool down when its cloudy then the clouds clear and until the panels heat up the voltage is high. Worst after a cold night with a cloudy morning and then the sun pops out and you get a voltage spike. Voltage kills Inverters, too high amps are less of an issue as the Inverter pulls amps so will stick to its upper limit so you will just lose output not kill the inverter.

After a night followed by clouds the panels will be lower than 18C until the sun comes out.

Best you give the full specs for the panels and for the inverter so a solution can be proposed.
 
Last edited:
alan.com said:
Would DC optimisers prevent this happening. Temperature is 18 Celcius and this and Vic is 48.7
Click to expand...
Not in all cases. As long as power is being taken, the panel should stay in operating range. But, if the inverter is not taking power, the voltage rises, and there is nothing the mppt can do (power backs up at the panel, voltage rises, mppt passes that to its output, and inverter ...).
 
The inverter is 12 amps
KnobCountry said:
Amps / current is pulled down (drawn} by the controller. It's not forced into the controller the way volts are.

Volts was the much more important number for you to consider.

If the panels are able to produce more current than the controller is capable of then it would clip the extra.

Basically it is wasted but not harmful. (unless you reverse the the polarity accidentally)

More current than the controller is rated for is called over paneling and is done on purpose to keep production up during cloudy days.

The voltage maximum should never have been exceeded and there already may be damage to the unit . Switch the pv off and remove at least one panel, possibly two.

Then do the calculations or simplfy by staying 20% under the controllers V max. This way cold and cloud edge effect won't fry anything.

Napkin math says your panels can prob put out 55v during certain conditions which rounded down is 10 panels. 11 if it doesn't get too cold.
Click to expand...
The inverter is rated for 12 amps max DC current and isc pv absolute max is 15 amps.
The solar panels are rated at 6.9 amps. Would 2 strings work out so I don't loose a panel or am I pushing it
 
alan.com said:
I don't want loose a panel. Would DC optimisers prevent this from happening. It normally happens when sun comes out from dark clouds
Click to expand...
The edge of cloud affect. Panels cool down then they get a blast of full sun.

Who is to say you cant put two of those panels on a separate controller? I'm adding 3 more strings with controllers to my 24v system in a few days. It will add about 2500w (840w per string)

As they say, just keep stacking.
 
sunsurfer said:
The edge of cloud affect. Panels cool down then they get a blast of full sun.

Who is to say you cant put two of those panels on a separate controller? I'm adding 3 more strings with controllers to my 24v system in a few days. It will add about 2500w (840w per string)

As they say, just keep stacking.
Click to expand...
Panels are so cheap now it's hard to resist more stacking
 
alan.com said:
The string inverter keeps voltage input from string at around 500-540 and works fine 99.9% of the time
Click to expand...
The problem is the 0.1% of the time can seriously damage your inverter. Never exceed the inverter/MPPT Voc rating. Good units will have some protection, but there is only so much they can do.
 
Will say it again in this thread: Best to think of PV voltage like a high cliff. One step too far, even for a portion of a second, and you're unlikely to be able to repeat that faulty step. Physics and Darwin take over.
 
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