308 watts from a 270 panel???? HUH?

[NEOH]

That is what I wanted to know.. I get the clipping part and I see it often.. But watching a 270 watt panel generate over 300 watts was a bit confusing.

I am willing to bet it was a combination of Cloud Effect, and your shiny slide and cooler air.
Yes, more Sun = more watts output.
The combined effects could have increased the watts by 15%.
300 watts = 270 watts x 1.15

The Cloud Effect is random, but the reflection from the shiny slide should happen every day ( when the sun is at the correct angle seasonally )

The 270 Watt STC Rating occurs at a specific amount of insolation & temperature, it NOT a panel maximum watts output rating.

That is why the output watts rating of your PV Panel varies, as shown below ...
270 Watts = STC
201 Watts = NOTC

That is a huge variance.

The Panel Voltage and the Panel Amps will vary with insolation and temperature.
Generally the power output will be lower than 270 Watts, but sometimes, it will be higher - ain't no big deal.

[max2k]

I am willing to bet it was a combination of Cloud Effect, and your shiny slide and cooler air.
Yes, more Sun = more watts output.
The combined effects could have increased the watts by 15%.
300 watts = 270 watts x 1.15

The Cloud Effect is random, but the reflection from the shiny slide should happen every day ( when the sun is at the correct angle seasonally )

The 270 Watt STC Rating occurs at a specific amount of insolation & temperature, it NOT a panel maximum watts output rating.

That is why the output watts rating of your PV Panel varies, as shown below ...
270 Watts = STC
201 Watts = NOTC

That is a huge variance.

The Panel Voltage and the Panel Amps will vary with insolation and temperature.
Generally the power output will be lower than 270 Watts, but sometimes, it will be higher - ain't no big deal.

not sure inverter string readings can be trusted when it is clipping. To state panels were 15% over STC I think OP needs to ensure inverter is within its rated power first otherwise there's probability this was simply 'measurement' error.

[Murby]

not sure inverter string readings can be trusted when it is clipping. To state panels were 15% over STC I think OP needs to ensure inverter is within its rated power first otherwise there's probability this was simply 'measurement' error.

I have 7.56 kW of panels hooked to a 6 kW inverter with 3mppt strings of 8, 8 and 12.. When the sun is shining anytime between around 10:30 and 4pm, my inverter output will be around 6050 watts and the DC array output will be at 6200 to 6300 watts (as is read through the inverter's interface software)

[max2k]

I have 7.56 kW of panels hooked to a 6 kW inverter with 3mppt strings of 8, 8 and 12.. When the sun is shining anytime between around 10:30 and 4pm, my inverter output will be around 6050 watts and the DC array output will be at 6200 to 6300 watts (as is read through the inverter's interface software)

if you're really after scientific proof you can disconnect 8 panel string (A or B) to get it back within power rating and then compare remaining 8 panel string vs 12 panel one as it won't be clipping even at full sun.

[Murby]

if you're really after scientific proof you can disconnect 8 panel string (A or B) to get it back within power rating and then compare remaining 8 panel string vs 12 panel one as it won't be clipping even at full sun.

What other kind of proof is there?
That's a really good idea.. I think I'll try that after I build up a bank for a while.. If I want to disconnect a string, I think I need to shut down the AC first so there's no load right? Then disconnect, then wait for the 5 minutes (seems like an hour) for the inverter to boot back up...
Or can I just turn off the integrated DC disconnect under load?

[NEOH]

not sure inverter string readings can be trusted when it is clipping. To state panels were 15% over STC I think OP needs to ensure inverter is within its rated power first otherwise there's probability this was simply 'measurement' error.

So WHY can't the inverter properly measure the DC Volts & DC Amps when the Buck Inverter is running at 9.99 Amps vs the Max Power Point?
The."9.99 Amps" I-V Point and "Max Power" I-V Point are just two different points on the same I-V Power Curve.
How does two different POINTS on the I-V Curve, all of sudden prevent proper measurement of the Volts & Amps reading?

[NEOH]

What other kind of proof is there?
That's a really good idea.. I think I'll try that after I build up a bank for a while.. If I want to disconnect a string, I think I need to shut down the AC first so there's no load right? Then disconnect, then wait for the 5 minutes (seems like an hour) for the inverter to boot back up...
Or can I just turn off the integrated DC disconnect under load?

I shut down AC side first, because it is "self-extinguishing" 120 times a second.
I shut down the DC side when there is no current flowing.

[max2k]

What other kind of proof is there?
That's a really good idea.. I think I'll try that after I build up a bank for a while.. If I want to disconnect a string, I think I need to shut down the AC first so there's no load right? Then disconnect, then wait for the 5 minutes (seems like an hour) for the inverter to boot back up...
Or can I just turn off the integrated DC disconnect under load?

what bank? Panels or batteries? I thought you don't have batteries / CC yet. In any case you need to make sure you have 0 current flowing through DC part before trying to disconnect anything there to avoid arch damage.

for grid tie system without batteries this is simply accomplished by turning off AC disconnect. You can leave DC disconnect ON as it is further down in the circuit. Please note strings will still be energized and their connector will have hundreds of volts DC at any irradiation level. If you have RSS, engaging it at this moment would cut off string voltages.

IIRC with AC disco off I was able to disconnect my string connector from my SB 3.8 inverter with no arching whatsoever even with DC disco ON. I was doing this tens of times one day trying to measure string Voc throughout the day.

[sensij]

This is a string inverter, the DC side will be a live 400+ V in the middle of the day, even with the inverter shutdown and disconnected. If you want to take string A offline in the middle of the day, please do it with extreme caution. A safer choice would be to just disconnect it overnight (when the forecast is for a relatively clear day), and accept the loss of 28% of production for the day in the name of science.

Edit: Using the rapid shutdown, if equipped, is a good idea, but I think this may be a ground mount that didn't require it

[Murby]

what bank? Panels or batteries? I thought you don't have batteries / CC yet. In any case you need to make sure you have 0 current flowing through DC part before trying to disconnect anything there to avoid arch damage.

for grid tie system without batteries this is simply accomplished by turning off AC disconnect. You can leave DC disconnect ON as it is further down in the circuit. Please note strings will still be energized and their connector will have hundreds of volts DC at any irradiation level. If you have RSS, engaging it at this moment would cut off string voltages.

IIRC with AC disco off I was able to disconnect my string connector from my SB 3.8 inverter with no arching whatsoever even with DC disco ON. I was doing this tens of times one day trying to measure string Voc throughout the day.

My "bank" is the utility company... The number of kWh they owe me..