Edge of Cloud Effect.

verdigo

I just observed edge of cloud effect on my Classics display for the first time, at least in a big way. My 2320 watt array was putting out close to 2800 watts @ 51 amps. I still have another 1200 watts of PV to mount and am now wondering if my 80 amp DC ground fault breaker will hang in there in similar conditions.

I suppose I'll just wait and see.

BB.

You could program the Classic to limit output current to XX amps max. In general, an 80 amp breaker should pass 80 amps for several minutes--But it really does depend on the specifications.

Most US breakers are rated to run at 80% of rated value continuously, and at 100% of rated value will probably trip in minutes to hours.

I think Outback rates their breakers differently (i.e., a 63 amp breaker is rated to run a 60 amp circuit)--So need to know the details.

But one question... Does your Classic have the internal Arc-Fault detection/shutdown circuitry? If so, I don't think you need the DC Ground Fault Breaker setup (unless you want a handy way to turn off your solar array).

-Bill

OLDPCDUDE

Hi Guy's,

I would like to convey an explanation for the current surge that I think is more accurate.
First we should all be aware that every solar panel has a temperature coefficient.
I am using Sunpreme GBX340 which has a coefficient of Pmpp = 0.28%/ C
This is a very low number. SunPower is 0.3% and many of the other China models are very high ~0.4% to ~ 0.5% and I expect some don't specify their number because it is so high.
I have Solar Edge Optimizers on each panel so I can observe each panel's power every few minutes.

I see a power increase when:

Sun angle rises over Tree Shading Lower 4 panels at 12:30pm power is high and then declines in the next 3 minutes as the panels begin to heat up.
Water is flowed over Panel reducing temperature. Power increase is approximately 0.28% Power increase for each degree C drop
When I go from cloudy to Sunny condition abruptly.
When I cover a panel with card board long enough to lower its temp and then quickly remove it.

So in conclusion temperature of the panel plays a factor here.
A good test would be to use an Irradiance meter on a Sunny day versus a transition from clouds to Sun and see if it is wildly different. I suspect that is not.

If you can test individual Panel power
Another good test is get Laser Temp Reader and big piece of cardboard. On Sunny day where the panel is running over 100 C cover it with cardboard for 10 minutes and check its temp
then remove it abruptly validate the power increase based on the temp coef.

Some examples

Fahrenheit
Celsius
Delta C


75
23.9



105
40.6
16.7



0.28% * 16.7 = 4.67%
0.4% * 16.7 = 6.68%
0.5% * 16.7 = 8.35%

a poorly designed panel may heat up more
for example.


Fahrenheit
Celsius
Delta C


75
23.9



120
48.9
25.0



0.5% * 25C = 12.5% (This is a big number)

verdigo

BB. wrote: »

You could program the Classic to limit output current to XX amps max. In general, an 80 amp breaker should pass 80 amps for several minutes--But it really does depend on the specifications.

Most US breakers are rated to run at 80% of rated value continuously, and at 100% of rated value will probably trip in minutes to hours.

I think Outback rates their breakers differently (i.e., a 63 amp breaker is rated to run a 60 amp circuit)--So need to know the details.

But one question... Does your Classic have the internal Arc-Fault detection/shutdown circuitry? If so, I don't think you need the DC Ground Fault Breaker setup (unless you want a handy way to turn off your solar array).

-Bill

The Classic does have arc fault detection but according to what I have read NEC 2008 requires GFP on every PV array. This http://www.solar-electric.com/instal...ndc-gfp80.html is what I am using.

If you read the PDF under the detail section for the breaker "Ground Fault Protection Explained" it will do a better job explaining than I could.