Warwick Bruce Chapman avatar image
Warwick Bruce Chapman asked

Matching SPD to MPPT

This is a question I have been discussing with colleagues and there seems no clear answer.

I have noted that most of the SPDs on the market are either Uc 600VDC, 1000VDC or 1500VDC. But our MPPTs are 150V MAX, 250V MAX or 450V MAX.

It seems thus, that a 600VDC SPD might protect something in the system against over voltage but that would not include the MPPT which would be exposed to over-voltage before the SPD had begun protecting (Uc).

Should we not be getting 145V, 245V and 445V SPDs manufactured which match the Victron products to properly protect MPPTs against over voltage? I have spoken to a manufacturer willing to do this but MOQ is 250 units which is a bit much for me to "test" the concept with.

Any insight would be valued.

MPPT SmartSolarmppt rsspd
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2 Answers
solarhack avatar image
solarhack answered ·


The industry trend appears to be going in the direction of higher voltage lower current MPPTs. This makes sense as the arrays can be simpler and are less affected by shade. Victron is also doing this with its latest MPPT (Smart Solar 250's and the Smartsolar MPPT RS).

There are few manufacturers that make lower voltage surge protectors and even though they re not the exact values above they should largely cater for Victron's MPPTs

Prosurge (200V Din rail and 100V PCB mount)

Citel (Din rail - 75V, 95V, 130V, 220V, 280V)

Citel (Din rail 450V)

I hope that helps

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Warwick Bruce Chapman avatar image Warwick Bruce Chapman commented ·

I am aware that there are these options available eg. 220V or 280V Citel and the like. My question is not whether there are 200V or 300V etc SPDs on the market.

The question is, if we were to develop a product like a 245V for use with 250V Victron MPPTs, would that be helpful? It seems to be this would help protect the MPPT from edge of cloud and the like as well as surges.

The challenge is we cannot test this without such SPDs being in existence. I will do some testing with 220V on a system that usually starts the morning in the 225V range and see what happens.

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solarhack avatar image solarhack Warwick Bruce Chapman commented ·
Cool, sorry didn't quite understand that
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jonaaal avatar image jonaaal Warwick Bruce Chapman commented ·

@Warwick Bruce Chapman Did you ever manage to test the concept with a 220V SPD?

I am in exatly the situation you describe with a 250/70 and panels with a Voc of 205V.

Interestingly, the new edition of BS7671 has requirements for SPDs on the DC side of a PV installation that requires them on the AC side.

712.443.101 and 443.4.1 if anyone has a copy to hand...

I look forward to hearing any developments.

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seb71 avatar image
seb71 answered ·

Mostly you want Up (voltage protection level) to be lower.

Uc (maximum continous operating voltage) must be slightly above your maximum PV array voltage (in normal conditions). So Uc should be something like 1.2 Voc, or slightly above that (here Voc is your maximum array Voc).

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Warwick Bruce Chapman avatar image Warwick Bruce Chapman commented ·
This is really the nub of the question. I'm asking about whether it is possible or practical to calibrate the SPD to match the maximum operation voltage of the MPPT eg. 245V on a 250V MPPT and whether that would serve to protect the MPPT from overvoltage eg. edge of cloud as well as surges.
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skydog avatar image skydog Warwick Bruce Chapman commented ·

@Warwick Bruce Chapman I know this is an old thread, but I'm having the same challenge. However, I have found a CITEL SPD supplier in the Czech Republic that supplies what we're looking for at reasonable prices. Check this link This particular SPD could be used on a 250/100MPPT as it has a Uc of 275V. There are others that you could search for to meet your specs.

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Warwick Bruce Chapman avatar image Warwick Bruce Chapman skydog commented ·
Yes, I am sure that will be fine. Over the years we've softened a little in our view on this question.

The regulations in South Africa (and most other places) required only Type 2 SPDs for PV. Type 2 protects against switching surges and indirect strikes only. Typically, PV systems see neither of those two, and the most likely damage will be caused by direct strikes which require a Type 1 & 2 SPD for a hope of protection.

We've installed well in excess of 1500 MPPTs and grid tie inverters and we have never seen a spend DC SPD module. AC SPDs, we replace all the time, but DC not. When there is damage, it is from a direct strike, and everything is fried including the SPD.

Most installers use the very commonly available 600VDC SPDs and nobody I am aware of has ever had an issue where the SPD engages but the MPPT is destroyed.

Its either nothing at all, or everything fried including the SPD.

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