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matt-bowler avatar image
matt-bowler asked

Surge Protection in Off Grid Solar System?

Hi,

I'm looking to install an off-grid solar system in a home, 6kw panels, 3 x Multiplus II 48/5000/70-50 230V (we must have tri-phase), MPPT RS 450/100 TR, Lynx Shunt and Distributor, Cerbo - 48 v battery system 20kwh storage.


My question is about surge protection, specifically from lightening. We live at the top of quite a big hill, and while the house has been here a few hundred years, and there are some big trees around, the lightening storms can be quite something so it seems likely that we will get hit at some point, what is recommended for surge protection (other than a MASSIVE earth rod!)?


Thanks in advance,

Matt.

offgridsolar
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4 Answers
Jons Collasius avatar image
Jons Collasius answered ·

You should and in many countrys thats mandatory, install a DC surge arrester on every mppt string like: https://www.phoenixcontact.com/en-pc/products/type2-surge-arrester-val-ms-600dc-pv-2v-2800642

Installation: panels -> surge arrester -> circuit breaker -> mppt
Grounding of the surge arresters with 16 mm² copper wire.

You should also look at AC surge arrester on every phase (L1, L2, L3) like: https://www.phoenixcontact.com/en-pc/products/lightning-surge-arrester-type1-2-val-ms-t1-t2-335-125-31-2800184

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jetlag avatar image
jetlag answered ·

In such a "problematic" or exposed location it would make sense to contact a company that is specialized in lightning protection because a complete external lightning protective system might be the best solution here.

The reason is, you have to distinguish between lightning protection of direct lightning strikes AND over voltage protection through induced peaks (often caused by lightning strikes in the surroundings). It is also very common, that the over voltage is incoming thorugh the grid, thats why a adequate SPD on the grid input is also mandatory. It can destroy your grid connected equipment independent if you have solar installed or not.

The SPDs on the MPPT input are most often only capable to protect an over voltage that is caused by a near field lightning strike, but no direct strike. For direct strikes you need to a overall aligned concept, it is not that easy like installing some SPDs here and there.

So you have to evaluate what is more expensive for you, - a lightning protection system or a defective solar system...

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ahtrimble avatar image
ahtrimble answered ·

Think "layers" of protection.

Starts with good/appropriate grounding, then surge protection, breakers, fuses between potential strike points and your equipment.

It's gonna take a lot of research on your part to do it right, but you will be the owner/operator and know your system.

A quality professional installer will do it right but it will cost you more money.

I would check with your insurance company as well. They may have requirements in order to honor a strike related claim. They may require listed equipment, a type of installer, etc. They may not cover DIY work.

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matt-bowler avatar image
matt-bowler answered ·

Thanks, @Jons Collasius. That is very helpful regarding the protections to include. This was exactly the kind of answer I was hoping for.

Thanks, @Jetlag. I completely agree, just a night after my post we had a strike nearby (I presume) which caused our the SPD on our input to trip. I have always taken the view that a direct strike is going to lead to contacting the insurance company no matter what. Perhaps I am now realising an unintended benefit of the work we have had done on the house: we just had the roof replaced and in order to meet anti-seismic regulations we had to have a huge ring of structural steel installed all around the top of the house. It seems to me that installing lightening rods on the two high points (chimmneys), and having them additionally connected to the installed steel reinforcement on the way to ground, will create something akin to a Faraday cage for the house. I may be wrong, but I mention it because even though your answer was not the one I was looking for it has given me food for thought and further investigation, so thank you.


Matt.

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