Solar plan for Parallel

[salubrious]

Hi,

Just after some solar connection advice pls. I'm adding 3 x 510W panels to my boat and planning on putting them in parallel into a Victron 250/85 MPPT. I have done the calculations etc on the victron site. This MPPT will handle them in series if I want to change later.

Anyway, one panel is fine on 6mm cable. If I wire them in parallel and then feed one wire back to the the MPPT I will need to run much larger cable. So, my question is, can I run each panel on 6mm cable and bring them back to a Solar Pos and Neg Buss in the electrical locker right next the the MPPT. Each Panel would terminate on the buss and then the Buss would have a short run of thicker cable to the MPPT.

The Short Circuit current is 12.42A so the total current load max will be 38 Amp max.

Does that work / stupid / correct or some other option?

Thanks
jeff

 

[PaulRainbow]

Without doing any calcs on the current, yes, you can run the cables to busbars. Cables from the busbars to the MPPT don't need to be massive, just rated for the max amps, as they will be so short voltage drop doesn't come into it.

 

[salubrious]

Great, thanks.

Follow up. Instead of a 20amp fuse for each panel, why can't I put a 20amp DC MCB for each panel?

Thanks
Jeff

 

[lustyd]

If the panels are permanently wired as you describe and there's no chance the wires would have anything else connected then you don't need fuses on the panel side of the MPPT, just a switch to disconnect panels for maintenance purposes. You do need a fuse on the battery side.

 

[VicS]

If the panels are permanently wired as you describe and there's no chance the wires would have anything else connected then you don't need fuses on the panel side of the MPPT, just a switch to disconnect panels for maintenance purposes. You do need a fuse on the battery side.

With multiple panels in parallel each panel should be separately fused if the total short circuit current for the whole array exceeds the maximum recommended fuse value for the individual panels.

This is to guard against the consequences of a short circuit occurring within one of the panels.

I'd regard circuit breakers as a bit of an overkill .

 

[lustyd]

This is to guard against the consequences of a short circuit occurring within one of the panels.

Surely the diodes cause a "short circuit" any time there's shading, what does the fuse protect against?

Edit - just googled and it's to stop the components like diodes from blowing which are rated to the array max.

 

[noelex]

If you wire the three panels in parallel you do need a fuse (or often better a circuit breaker) on each solar panel output. This is to stop the internal wires inside the solar panel from overheating and possibly starting a fire in the event of a fault condition. The maximium fuse size will be listed in the specifications for the panels (maximum series fuse rating). Wiring to a busbar is fine. The link below is worth reading:

How/When to Fuse a Solar Panel Array

It is also worth considering using three smaller solar controllers (one per panel) instead of one larger controller. This will result in a higher solar yield and provide some redundancy in the event of a controller failing. Often this is only a little more expensive. Sometimes it can less expensive, in addition to being better, a nice combination.

Finally, if you have a 12v house system then the controller you propose is too small. If you have a 24v house system it is fine. The input current from the panels is OK, but the output current is not with a 12v house bank. MPPT controllers are always limited by their output current.

 

[VicS]

. The link below is worth reading:

How/When to Fuse a Solar Panel Array

Yes, that is the link I would have posted if anyone had challenged my post.
.

 

[noelex]

A point I should have made is if using a fuse be careful to check the voltage rating. Marine fuse holders or the fuses themselves often have a voltage rating too low for this application.