Choosing SPD

[melbaylon]

I've watched videos and read articles but I'm still clueless on how to definitively choose the proper SPD for my solar setup.

What I understand so far is that I need to connect/parallel the DC SPD to the PV cables going into my SCC. I'm not sure what SPD to use though. I mostly see 500Vdc and 1000Vdc online.

 

[timselectric]

Just choose a voltage that is higher than your pv OCV, with temperature compensation.

 

[MichaelK]

Take a look at Midnight Solar's units. Those are the SPDs I use. Here is a wiring diagram they provide. They make both AC and DC versions.

 

[timselectric]

Take a look at Midnight Solar's units. Those are the SPDs I use. Here is a wiring diagram they provide. They make both AC and DC versions.
View attachment 88649

Those are fine, as long as your PV voltage will never get to 300v.
My VOC is 451v, and with temperature compensation 488v.

 

[melbaylon]

Those are fine, as long as your PV voltage will never get to 300v.
My VOC is 451v, and with temperature compensation 488v.

I see the max Voc of my SCC is 160V. Can you give me an explanation why the 500V and 1000V models will work just fine? I really want to understand it better. ?

 

[timselectric]

The voltage rating is the voltage of when it kicks on and absorbs the energy. You don't want a rating that is at or lower than your output. Or, it will absorb all of your wanted production.

 

[melbaylon]

The voltage rating is the voltage of when it kicks on and absorbs the energy. You don't want a rating that is at or lower than your output. Or, it will absorb all of your wanted production.

I see. Thanks! That really makes sense.

 

[melbaylon]

I see the max Voc of my SCC is 160V. Can you give me an explanation why the 500V and 1000V models will work just fine? I really want to understand it better. ?

Just additional clarification: following that 500V and 1000V will work just fine for my 160Voc SCC, in my case, it is better to go for the 500V, right? I mean 'cause it's relatively closer to my SCC's max Voc. Similar logic with circuit breakers.

 

[meetyg]

The voltage rating is the voltage of when it kicks on and absorbs the energy. You don't want a rating that is at or lower than your output. Or, it will absorb all of your wanted production.

But if the SPD exceeds the SCC voltage alot, will it still protect the SCC ?
I mean up to 500v into a 160v SCC will surely fry it...

 

[timselectric]

Just additional clarification: following that 500V and 1000V will work just fine for my 160Voc SCC, in my case, it is better to go for the 500V, right? I mean 'cause it's relatively closer to my SCC's max Voc. Similar logic with circuit breakers.

But if the SPD exceeds the SCC voltage alot, will it still protect the SCC ?
I mean up to 500v into a 160v SCC will surely fry it...

The goal is to be above expected normal voltage, plus a cushion for fluctuations. But, a lightning strike is going to exceed any of these arrestors. Keeping the arrestors voltage closer to your expected normal voltage, protects your system from other surges.
Like if a tree falls on power lines, and this voltage is somehow imposed into your system. Or if a roof leak manages to bridge a connection between the AC and DC systems, in your home.
For 160v system, it's safer to use a 300v arrestor.

 

[OzSolar]

Midnite does a great job of explaining their SPD's.

And the manual. https://www.midnitesolar.com/pdfs/SPD_Installation_Manual.pdf

 

[cdsolar]

I am confused. The image above from Midnight Solar shows the SPD on the PV side connected to two different positive PV busbars, probably because of two arrays? I though you were supposed to connect the SPD to both positive and negative. I probably misunderstand something.

 

[KITROBASKIN]

Surge Protection Device negative goes directly to ground wire. The more direct to ground, the better, right?
Midnite Solar provides written and visual instructions.