Solar Panels Vs Lightning!!

[aju11]

How to protect roof-top Solar Panels installation and connected system (battery and inverter) during thunder storm?

[Berni]

Insurance.

[Rerouter]

The panels: Possibly a nearby lightning rod, however be aware there is no guarantee the EMI from a strike wont cause damage to the surrounding. not to mention the kick from the cable can break bricks if you confine it too much.

The Batteries? If lead acid, then good luck hurting them, You can spot weld with jumper leads off a lead acid without hurting them much.

If lithium and you where pretty much topped off, then things get interesting. make sure you have fire proof matting between any flammable surface or object and the battery pack... this should be standard practice.

The inverter? depending on the technology it will likely have some kind of inductor on the input, and if well built may have a MOV or similar spark gap to case ground, now this likely wont save it, but it will reduce the damage elsewhere.

[HB9EVI]

I think the best advice one can give you is to consult the local regulations; in Europe there are tons of norms (DIN, EN, ISO aso.) with certifications concerning lightning protections and how what has to be done according to code.
Insurance alone is no help, since they can refuse you coverage in case you didn't follow the regulations and laws when installing.

[BradC]

How to protect roof-top Solar Panels installation and connected system (battery and inverter) during thunder storm?

Stand on your roof at the peak and hold a 1 iron in the air. Not even god can hit a 1 iron.

[Seekonk]

I was hit by lightning. Blew a hole in one panel. Kudos for cheap internal bypass diodes.  They shorted and saved the panels.  Took out a bunch of electronics. The only protection you can really do is against fire.

[mtdoc]

Nothing is likely to save them if it's a direct strike.  For nearby strikes, my 2 solar arrays have the frames grounded to a ground rod at the base of the array. This is not required by the NEC. The NEC does require PV panel grounding to run back to the common system ground - usually the homes ground rod.  So unfortunately this NEC required ground provides a path back to the electronics - inverter and charge controller (if battery based system).  Some of us have systems were the "back to the home ground" has mysteriously become disconnected after the AHJ inpection is signed off on....

[Berni]

Yep lightning protection is mostly about not starting a fire.

The laws and standards for how this is done vary drastically around the world. But even with the up to the hilt standards of having lightning rods all over the roof and wired to separate earth rods at points around the house you still are not fully protected. A strong direct hit into the rods will have the strike safely guided into the ground, but all your electronics are sitting next to a long conductor that suddenly has many thousands of amps run trough it with a ridiculously fast di/dt rise time. The strong magnetic field it creates around it can easily couple into any wiring running close to it and blow up things on the ends of those wires.

In fact a strong lightning strike can send so much current trough conductors that the magnetic effects push against the conductor so hard that it tears itself out of a wall.

However if such a strong hit strikes a house with no lightning rod the current will still seek a path to ground trough the house, causing it to arc over in various places to get there and this arcing can easily happen inside the wooden roof structure where it ignites a fire. Its also likely to find some electrical wiring as a convenient ground path and use that, blowing up everything along the path.

Here it is standard procedure to have PV arrays grounded by the metal frame. Its likely more for the case that if a panel was to short to the frame this could lead to the entire structure raising to high voltage (Remember arrays often have lots of series panels that can generate up to 100 to 1000V)

[mtdoc]

A high quality surge protector - such as those sold by Midnite Solar can provide a modicum of protection for electronics.

At about 2:18 on the first video there's some interesting testing done.

[Red Squirrel]

Need lightening arrestor on the positive, and then negative tied to ground, and the frame being grounded is good too.  Keep in mind that if lightning hits the solar cells directly and not the frame then simply grounding it is not enough as the electricity will travel through the positive to the equipment.  So the lightning arrestor is what ideally will block it by shunting it to ground.

Having a lightning rod nearby might help too I imagine, that way lightning is more likely to hit that instead.   

[james_s]

It's almost impossible to protect anything against a direct strike, thankfully direct lighting strikes to most structures are exceedingly rare. Sure it happens, but not often to you. It's a bit like driving, accidents happen many times each day, but the likelihood of one happening to any given person on a particular day is low enough that most of us don't spend a lot of time worrying about it.

[aju11]

Will the following add to the protection?

1. Covering the panels with a thick glass sheet

2. Covering panel with a wire net-as in the image and grounding the net

[james_s]

Probably not, and doing either of those things will significantly reduce the output.

[Berni]

Don't think it would help.

What i see on large arrays is that every few meters there is a bundle of sharp spikes (~30cm) that point in all directions. These spikes grab the charges out of the air to make it less charged and harder for lighting to propagate trough and if it does strike its likely to hit one of those spikes and get guided into the metal frame.

EDIT: Oh another way is how they tend to protect equipment mounted on roofs of large buildings(such as AC and ventilation equipment) is to put up metal grounded posts around it and then run a bare metal wire between all of them above the equipment. Any strike that does happen will hit the wire suspended above or the metal post rather than the equipment itself.

[Red Squirrel]

I was thinking that too, and it might just be what I do for my setup.  I have too many dissimilar metals in my setup as everything is typically only available in one material like when you want certain fasteners you get whatever is at the hardware store and they're not going to start stocking every metal.  For Unistrut it only came in galvanized, the bolts I used are stainless, and the panel frames are aluminum etc.  I tried to match it to prevent galvanic corrosion but was impossible to do due to what is available in what material.   So trying to ground that is quite difficult.  You can't just connect copper wire straight to it as it may even speed up galvanic corrosion by introducing yet another dissimilar metal.

Come to think of it,  wonder if putting in a large metal pole that is higher than the roof would work. Simple and can even avoid shadows if you plan it right. The top could have a bunch of spikes.   Only thing it would need to be fairly thick to handle the lightning.  How many amps is a typical lightning strike?  Or do you simply consider it sacrificial?  Ex: it will explode and send molten steel everywhere but your electronics will be ok?

[Berni]

The currents involved in lighting  are around 5 to 30kA , but above 100kA is possible in a strong strike.

Any long metal pole that would be strong enough to stand up this tall under its own support will be thick enough. to handle the current. While the current is extremely high it lasts only for a short moment and metal is very conductive so it would get warm at best. I think the magnetic effects on the pole could be more dangerous to it. If its just a simple hollow pole in the ground with no guide wires you can get it to flex quite a bit in the wind, a lightning strike could put a very sharp force transient on it, equivalent of hitting it with a hammer and under a stressed condition it could cause a place in the hollow tube to buckle in. Once it buckles it pretty much looses all strength and would likely fall over, potentially hitting something or someone. Lightning is more impressive when it hits trees as they are not very conductive and you get lots of I^2*R heating, all that heat quickly boils the water in the tree causing a steam explosion inside that often splits the tree right in half.

In experimental setups we are capable of creating magnetic fields strong enough to crush a solid metal coin into a ball using magnetism alone (google coin crushers). So id imagine a long pole like this could also have some significant magnetic forces with such a current.

There is no grantee it would save all your electronics, but the situation will be much better than if it hit your solar array directly. Also note that the ball of spikes on top will deter lightning from striking in the general area in the first place, so its helping even if it doesn't get struck.

[Miyuki]

Lightning surge arrester shall be installed between panels and electronics, and of course have fuses and safety switch
(Some) Panels can be fried but expensive stuff will survive

They are rated for 100kA pulses even bigger are available if needed

[TerraHertz]

Relevant: http://everist.org/NobLog/20160504_solar_panels_vs_emp.htm

When the transient E-field in free space near a lightning strike is high enough to drive current paths through the insulating clear plastic encapsulating the solar cells, and so fast risetime that the current paths pretty much ignore the conductive metal traces on the face of the cells, there is not much you can do.

The biggest fire and damage risk, is from panel section reverse protection diodes that get *partially* destroyed. If they become low resistances they end up dissipating all the power the panel can generate under full sunlight, and get very very hot. Setting fire to things hot.
The ones that go open circuit, or dead short, don't become 'solar heaters.'

[larrybl]

When working communications in the military (20+ years ago) We would set up a mobile microwave relay on hill tops. One method we used to protect against lightning was to install a cable strung over the communications equipment using 15 foot masts spread 20 - 25 feet apart with a grounding cable strung between them over the equipment and grounded at each end. Not sure if this is still being used, but I remember being on site in a tent during a T-storm and the site was hit. Everyone in the tent got shocked to a certain extent, and several surge arrestors were blown on the equipment. I think after this we would say "Install the Lightning Attractor" on later site installations.

[Doctorandus_P]

Big high antennas in the neighbourhood have been the default method for a long time.

You could ground the metal frames of all the panels, but lightning level induced currents are going to leak into your system.

There won't be much Sun during a thunderstorm. You could disconnect the cables from the solar panels to the Inverter. That would probably limit any damage to (a few) of the panels, but keep the relatively expensive inverter intact.

If the lightning current has nowhere to go (disconnected cables) but to the grounded frame, more than one damaged panel seems unlikely.