VOC in Off-Grid Systems

[HighDesertOffgrid]

I'm not sure whether this belongs in beginners or advanced. How's that for a spectrum?
My question being: Is there a reasonable expectation that panels in an off-grid application are ever in a VOC situation with an MPPT charger?

 

[jasonhc73]

Every morning before production off-grid produce Voltage, but no amps. That is VOC.

Don't try to max out the VMP value of the panel to the limit of the MPPT, the VOC will be way over the limit of the MPPT.

 

[HighDesertOffgrid]

Every morning before production off-grid produce Voltage, but no amps. That is VOC.

Don't try to max out the VMP value of the panel to the limit of the MPPT, the VOC will be way over the limit of the MPPT.

Thanks for the response. My system has always started charging long before VOC is reached, thus pulling down the voltage. Do I just have awesome charge controllers?

 

[Bud Martin]

Did you measure the DC Voltage on the PV input of the charge controller real early in the morning to see what it shows before the SCC goes into charging mode?

 

[HighDesertOffgrid]

Did you measure the DC Voltage on the PV input of the charge controller real early in the morning to see what it shows before the SCC goes into charging mode?

I have sat with a cup of coffee and watched the charge controllers as the sun rose. (Yeah, I don't have a life). Pre-dawn, the charge controllers begin to react at around 12V above system voltage. Even at 0.1 amps they begin to draw down the PV voltage.?‍

 

[jasonhc73]

This is what mine do every morning:

All the voltage shown before 7:30 is zero amps. The MPPT attempts to put a load, ie draw a current, and the Volts drop to zero, so it tries that half a dozen times then goes into standby for about 15 minutes, then starts over for the day.




Here is the complete day of the voltage:

I notice at the end of the day, it does the same thing again as at the start of the day.

 

[HighDesertOffgrid]

This is what mine do every morning:

All the voltage shown before 7:30 is zero amps. The MPPT attempts to put a load, ie draw a current, and the Volts drop to zero, so it tries that half a dozen times then goes into standby for about 15 minutes, then starts over for the day.


View attachment 114637

Here is the complete day of the voltage:

I notice at the end of they day, it does the same thing again as the start of the day.

View attachment 114640

Interesting. What brand is your MPPT?

 

[Bud Martin]

So at around 7:15AM, the PV input is about 170V?
What is the Voc of the PV string?

 

[HighDesertOffgrid]

That voltage graph seems to show that charge controller acting opposite of what I would expect from an MPPT. It's hard to tell the two controllers apart but the beginning of the charge cycle looks like it's trying to pull a large load after 3-5 minutes and shutting down, instead of gently increasing the load to maximize the power point. Is it a 48v system?