Connect and disconnect panels under load - Does it matter?

[cortijo]

I have just installed 6 panels in parallel.

It says on the leads that I should not connect or disconnect the panels when there is sun on them.

To comply with this I have placed a blanket over the panels before connecting or disconnecting them.

Is this really necessary?

It makes the job a lot more difficult.

[Naptown]

Yes unless you like very large sparks and destroying the connectors.
Another way to disconnect is to pull the fuses on the combiner or shut off the circuit breakers on the combiner.
Let me guess you don't have one. I hope you have 2 panels or less.

[Mike90250]

DC Arc welding. The connectors are not designed to make/break while powered. They (any connector pair being mated/demated) will likely be destroyed, such is the power of DC.

Just kill the charge controller or open the breaker. Don't try to pull the fuse out, if it's powered up, it willl arc weld too!

[Murby]

How about we rephrase this question.

If you have the proper disconnect switch or proper relay to handle the DC voltage and current, is there any harm in regularly breaking the connection between the PV array and an inverter or charge controller?

[SunEagle]

How about we rephrase this question.

If you have the proper disconnect switch or proper relay to handle the DC voltage and current, is there any harm in regularly breaking the connection between the PV array and an inverter or charge controller?

Unless you have a very large "air break" or "arc chute" you will create a big spark that will break down the equipment when you disconnect a DC load under power. That spark could be hot enough to weld metal together which IMO is not a good thing to have.

[Mike90250]

How about we rephrase this question.

If you have the proper disconnect switch or proper relay to handle the DC voltage and current, is there any harm in regularly breaking the connection between the PV array and an inverter or charge controller?

A proper, good device, rated for the DC voltage and amps in the system, will be fine, within the Mfg's specs. The PV panels and charge controller won't care a bit, it will seem as if the sun went behind a large cloud.

[bcroe]

The problem of breaking current flow becomes much more difficult with higher DC voltages. DC
disconnect switches get much larger than AC disconnects for the same current. Still the number
of operating cycles will be limited.

Covering panels won't fully shut them down, just the light hitting the back side will generate full
voltage at much reduced current. PV panels could be shut down with a properly rated transistor
(or bank of) that momentarily shorts out each panel, then the switch may be opened without
much voltage. This method might be used to "throttle" PV if needed. Bruce Roe

[Murby]

A proper, good device, rated for the DC voltage and amps in the system, will be fine, within the Mfg's specs. The PV panels and charge controller won't care a bit, it will seem as if the sun went behind a large cloud.

That's good to know but I wonder about the cloud analogy.. when a cloud moves in, or even if a human throws a blanket over a panel, the reduction in output is slow and measured in milliseconds or even as long as seconds.. whereas, when a switch is opened, the output goes to zero instantly.

Apparently, as far as the controller or the PV panels are concerned, it doesn't make any difference either way as you say.. That's good to know and solves my problem in the lithium battery thread.

Thanks again, you're advice is much appreciated... You folks are really helpful and it makes me wonder why everyone considering solar doesn't come to this place first.

[ButchDeal]

You should know that though most grid tie inverters come with DC disconnects that are properly rated, they almost all recommend shutting down before flipping the DC disconnect. There is arcing when under load that can pit the contacts. They are generally code required safety devices and not meant for daily use.

[Murby]

You should know that though most grid tie inverters come with DC disconnects that are properly rated, they almost all recommend shutting down before flipping the DC disconnect. There is arcing when under load that can pit the contacts. They are generally code required safety devices and not meant for daily use.

Yup.. we always turn off the AC breaker before turning off the DC switch...

I don't think it matters which order we turn them on however....

[NukeEngineer]

You should know that though most grid tie inverters come with DC disconnects that are properly rated, they almost all recommend shutting down before flipping the DC disconnect. There is arcing when under load that can pit the contacts. They are generally code required safety devices and not meant for daily use.

It also depends on how often you plan on operating the switch.

Standard circuit breakers in a residential panel are not rated for use as a "switch". Using it as a switch, thus making/breaking the circuit under load daily, causes it to fail prematurely. A breaker suitable to be used multiple times a day as a switch will be labeled SWD to indicate it is suitable for "switching duty".

The safety switches on the inverters might be good for single-digit operations under load, then will be too charred to continue functioning safely.

Here's the kinda arc you're dealing with: https://youtu.be/8kJen_E0HVU