Lightning: Disconnecting the PV automatically beforehand

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Phil Gavin asked Oct 23, '19

Lightning: Disconnecting the PV automatically beforehand

I am in a lightning prone area.

I already use surge arrestors, ferrite beads, lightning protection and sound earthing techniques.

However, in my anecdotal experience, unplugging the family PC has always been better that relying on surge protection during a thunderstorm.

So following that reasoning, what I want to do is automatically create a physical break in the wiring between my panels and the MPPT's during a storm and at night.

I figure a lot of the thunderstorms are at night, and when they are during the day it gets pretty dark too. I am not making power anyway, so why expose the electronics to the risk.

What I want to do is monitor my incoming PV voltage, and if it drops lower than "X" volts, I want it to disconnect my panels ( both + &- legs), and as the voltage picks up in the morning or after the storm I want it to reconnect again.

There are several ways to achieve this, but none are particularly inexpensive. I have 6 arrays and things add up quick.

I may even consider some form of AC islanding from the grid during a storm, but I haven't given that much thought yet.

I can achieve this for about 65 USD/ array using DC MCB's and reclosers triggered by a 15 dollar DC UV/OV relay.

I'd like to hear if anyone has gone down this route before, or if anyone has any other "Keep it simple" ideas on how to achieve this.

It just seems to me that there should already something out there, off the shelf, that does this.

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Answer 1 · 2019-10-23T04:56:28Z

kai answered · Oct 23, 2019 at 04:56 AM

I did consider something similar. A relay would certainly interrupt induced currents (won't protect against a direct strike for obvious reasons). Consider the likelihood and magnitude of induced currents - disconnecting phone lines etc made sense because you potentially have hundreds of meters+ of electrically exposed wiring. Depending on your PV configuration, your exposure may be significantly smaller.

I do like your thinking around using the PV output as a proxy for detecting an "unneeded exposure" window.

Not entirely sold on the benefit - cost angle, but you want to pursue this I don't see a technical obstacle.

edit: if the PV output voltage is relatively high, you may run into regulatory issues around electrical rules depending on your location. In either case, care should increase with voltage level.

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Phil Gavin commented · Oct 23, 2019 at 10:15 AM

"disconnecting phone lines etc made sense because you potentially have hundreds of meters+ of electrically exposed wiring."

Just as a matter of interest, the CAT6 cabling that comes into the installation is isolated with fibre optic between two media converters for this very reason.

"Not entirely sold on the benefit - cost angle".

I suppose that depends on the cost, hence putting the question out there.

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