I have been looking at a couple of my friend’s combiner box installations and have noticed that there is no standard in the components used and it seems that the installers just use what they have on hand or can get hold of at the time.

So, the question is, how would you size your combiner box components (I.e. Fuses, SPD’s and Isolator MCB’s)?

Thinking out loud, and ignoring inverter specs (I.e. Max PV Input, MPPT Input Range and PV input current) for the sake of this discussion, would it be correct to start by looking at the Solar Panel specs (I.e. Operating Voltage (Vmp) and Open Circuit Voltage (Voc) as well as the Operating Current (Imp) and the Short Circuit current (Isc))?.

As an example, looking at the Canadian 545w panel specs (see picture) you have the following Solar Panel specs:

·         Vmp = 41.5v

·         VoC = 49.4v

·         Imp=13.14A

·         Isc = 13.95A

Ignoring possible future expansions, would it be correct to say that for a single string (no paralleling) of say 10 panels in series ( 494Voc   /  13.95A Isc ),  I could use a 15A or 20A solar fuse on each line (Positive & negative) and a 500V/15A Isolator as well as a 500v SPD?

Then if I wanted to double the number of strings (parallel 2 strings so the specs would be ( 494Voc   /  27.9A Isc), I would change these slightly and use a 30A solar fuse on each line (Positive & negative) and a 500V/40A Isolator as well as a 500v SPD.

Would the above work and I suppose getting back to the original question, is there a correct way to size your components based on each installation (What would the correct specs be and how would one calculate what components to use)?

Any insights would be appreciated.

Thanks

Edited November 16, 20232 yr by Marcodp

2 hours ago, Marcodp said:

I have been looking at a couple of my friend’s combiner box installations and have noticed that there is no standard in the components used and it seems that the installers just use what they have on hand or can get hold of at the time.

So, the question is, how would you size your combiner box components (I.e. Fuses, SPD’s and Isolator MCB’s)?

Thinking out loud, and ignoring inverter specs (I.e. Max PV Input, MPPT Input Range and PV input current) for the sake of this discussion, would it be correct to start by looking at the Solar Panel specs (I.e. Operating Voltage (Vmp) and Open Circuit Voltage (Voc) as well as the Operating Current (Imp) and the Short Circuit current (Isc))?.

As an example, looking at the Canadian 545w panel specs (see picture) you have the following Solar Panel specs:

·         Vmp = 41.5v

·         VoC = 49.4v

·         Imp=13.14A

·         Isc = 13.95A

Ignoring possible future expansions, would it be correct to say that for a single string (no paralleling) of say 10 panels in series ( 494Voc   /  13.95A Isc ),  I could use a 15A or 20A solar fuse on each line (Positive & negative) and a 500V/15A Isolator as well as a 500v SPD?

Then if I wanted to double the number of strings (parallel 2 strings so the specs would be ( 494Voc   /  27.9A Isc), I would change these slightly and use a 30A solar fuse on each line (Positive & negative) and a 500V/40A Isolator as well as a 500v SPD.

Would the above work and I suppose getting back to the original question, is there a correct way to size your components based on each installation (What would the correct specs be and how would one calculate what components to use)?

Any insights would be appreciated.

Thanks

There are 2 factors that is going to influence the Voc(Stc) and Isc(Stc) that is on the data sheet, temperature and solar radiation. When designing solar arrays the temprature characteristics bottom right should also be considered. The Voc at 0°C will not be 494v for the 10 panel string but rather 494 x (25x 0.26%)=526v then the 500v Isolator should rather be 600v dc rating or even better 1000vdc. Isc at 0°C would then be 14.12A Fuse rating should be Isc x 1.56 and then select closest standard dc fuse size. 2nd factor is if irradiance would exceed 1000wm² that could happen due to cloud edge. Use max series fuse rating on data sheet if in doubt. The installation site will determine temp factors.

Edited November 16, 20232 yr by TaliaB