Wiring Solar Array in Parallel with 4 Gauge?? HELP

[Stoveman]

Hello all,

I’ve scoured the net looking for a simple answer and can’t find it anywhere. I really really appreciate any help you can provide. I’m getting desperate here.

I have an 800w solar panel array. I plan to wire in parallel at 12 volts (20.4 Max). The amperage , if wired in parallel, is 40 amps. I need to run the cable about 15 to 20 feet from the SOLAR panels to the CHARGE CONTROLLER.

I’ve used some calculators online and found that I need to run 4 gauge wire from the panels to the controller to reduce voltage drop to 3%.

This is fine, but I can’t find any mc4 connectors that will fit 4AWG wire. Am I missing something?

Also it appears I would be hard pressed to find a charge controller that fits with 4 gauge wire as well.

Is there a secret I’m missing? I’ve spent hours looking for this answer.

If it’s not possible to run 4 gauge, I will wire them in series/parallel so that I get 24v at 20 amps . I’ve already bought my 4 to 1 connectors, so I’d rather avoid this.

Thanks in advance!!!

[Doktari]

What about dividing the panels into two groups. I would simply install two runs of standard 10 gauge PV wire that fits in MC4 connectors.
What charge controller are you using for 800 watts? It’s 67 amps to the batteries so you can get by with a 60 amp Controller. Panels seldom produce their rated power in real world conditions.

[Stoveman]

Thanks for the quick response. I am definitely looking at purchasing a 60 amp charge controller. When you say two groups, what do you mean? Do you mean to run four 10 gauge wires instead of two to the charge controller? And then use Y connectors to combine them before connecting to the charge controller?

Thanks again!

Also I saw that a couple people used homemade combiner boxes to change wire gauge. Maybe that’s an option?

[BeNimble]

What you are missing is there is no problem to run fat wires almost all the way, then thin them up at the destination to fit connections. Can just use few strands in connectors, or better to splice in smaller wire for a foot or so.

Connecting them in series for higher voltage is generally better, particularly for a bus rooftop.

[Stoveman]

Originally Posted by BeNimble

What you are missing is there is no problem to run fat wires almost all the way, then thin them up at the destination to fit connections. Can just use few strands in connectors, or better to splice in smaller wire for a foot or so.

Connecting them in series for higher voltage is generally better, particularly for a bus rooftop.

Thank you! That is totally logical. So I could trim down the diameter of the fat wire?

Why would you recommend series ? Just curious. The reason I do not want to wire them 100% series is that if one panel fails or is shaded, all panels will not function. If I do series & parallel, the same applies except the two - two panel strings function independently.

If I can run then in full parallel I won’t have to worry about individual panel performance effecting others. However, wiring it is much more expensive and complex

[Doktari]

Yes run 4 wires (standard 10 gauge PV wire) into a combiner box is the trick way to do it. Then you have breakers which make it very convenient to install and to maintain.
MidNite Solar Inc. Renewable Energy System Electrical Components and E-Panels

[BeNimble]

Shading can be a problem with series connections, but a bus is not parked in the shade if you want solar power.. The problem with connecting them in parallel is similar, the one with more output is pulled down by the one with less, they must have identical voltage output. I'm surprised this topic has not come up much here, it is a big deal for sailboats..but they have masts that create shade.

The ideal is to have a MPPT controller on each one in parallel that produces identical voltage output. I created a circuit board that does this can be connected right at the 12v panel and produces 24vdc output, so ALL panels produces exactly 24vdc output, and then use smaller wires. A bus has a lot of roof realestate unlike a boat, so just add more panels is the usual approach and don't worry about it.

[jofred99]

Wouldn't it be simpler to run the panels in series and use an MPPT charge controller in the inside of the bus? This way you would only have two wires entering the bus at nominal 48v, eliminate the combiner box and the charge controller will handle the battery charge at 12v.


This should allow the wiring to stay at 10 ga. and only have about 1.42 volts drop.

[dzl_]

Originally Posted by Stoveman

Hello all,

I’ve scoured the net looking for a simple answer and can’t find it anywhere. I really really appreciate any help you can provide. I’m getting desperate here.

I have an 800w solar panel array. I plan to wire in parallel at 12 volts (20.4 Max). The amperage , if wired in parallel, is 40 amps. I need to run the cable about 15 to 20 feet from the SOLAR panels to the CHARGE CONTROLLER.

I’ve used some calculators online and found that I need to run 4 gauge wire from the panels to the controller to reduce voltage drop to 3%.

This is fine, but I can’t find any mc4 connectors that will fit 4AWG wire. Am I missing something?

Also it appears I would be hard pressed to find a charge controller that fits with 4 gauge wire as well.

Is there a secret I’m missing? I’ve spent hours looking for this answer.

If it’s not possible to run 4 gauge, I will wire them in series/parallel so that I get 24v at 20 amps . I’ve already bought my 4 to 1 connectors, so I’d rather avoid this.

Thanks in advance!!!

Part of your problem is you appear to be using "12V" in your calculations which is not accurate. Use whatever number is stated as the Vmp of the panels (probably about 17-19V) Make this change and I suspect the math will at least allow 6 AWG if your distance is 30ft round trip.



But as others have mentioned, series parallel combination is a good idea for a number of reasons, If it were me I would consider 2S4P or maybe 4S2P (assuming you have 8 x 100W panels)


Also bear in mind, bypass diodes which all modern panels have, partially mitigates the devastating effect of partial shade on series connected panels. These diodes allow current from unshaded panels to flow around shaded sections of a panel (sections are usually half panels for small panels or thirds or sixths for large panels.

[Iceni John]

Just bear in mind that the greater the voltage stepdown that a MPPT charge controller needs to handle, the greater its inefficiency (and heat buildup: heat kills electronics). My two Morningstar TS-MPPT-60 have efficiencies in the high-90s percent when halving voltage, but it drops a lot when asked to reduce voltage more than that. That's one of several reasons I have all four panels in each of my two arrays wired in parallel, with each 255W panel fused with a 12A AGC fuse in two small combiner boxes on the roof, then 4AWG cables bring each array's combined 34 amps at 30 volts down to its CC's 50A breaker. (Essentially I have two entirely separate systems running in parallel, including two separate banks of batteries - aircraft designers call it redundancy!)

John

[dzl_]

Originally Posted by Iceni John

Just bear in mind that the greater the voltage stepdown that a MPPT charge controller needs to handle, the greater its inefficiency and heat buildup

John

I agree with you theoretically, as I understand it, somewhere in the ballpark of an array voltage of roughly 3x battery bank voltage is what many charge controller manufacturers recommend as optimal.

But I think its important to clarify that what is being referred to here:

Originally Posted by Iceni John

I think its worth noting/qualifying what you are referring to when you say: "My two Morningstar TS-MPPT-60 have efficiencies in the high-90s percent when halving voltage, but it drops a lot when asked to reduce voltage more than that."

Is only a difference of a few percent. Not worth ignoring, but also probably worth clarifying what is meant by "drops a lot".

For your controller at max output, we are only talking about a max difference of 3.5% between an array voltage of 13V (~96.4%) and 100V (~92.8%), 66V is ~94.1% efficient. (this is based on a 12.8v battery bank)

https://imgur.com/a/iXpq0Xr

Certainly a factor to consider if you are trying to optimize for efficiency, but just one factor of many that all have trade-offs. At least that is my 2c