Solar Install question

[VAHillbilly]

I am planning to install two 160 watt panels on the roof of a Class C RV. I would like to make the installation where I can add another 160 watt panel if needed in the future. The wiring will be in parallel down to a MPPT controller. I anticipate about a 20' run of wire from the roof to the controller and then probably less than 3' to the batteries (two 6 volt GC).

I am thinking I should use #6 marine wire from the roof to controller and the same to the batteries. The panels will have what I think is #12 wires to MC4 connectors.

My question is what type connectors or small junction box should I use from the panel pigtails to the #6 wire? Also what type fusing and disconnect switches should I use. Frankly any recommendations for a properly designed system to handle 320 to 480 watts of PV output would be greatly appreciated.

Any recommendations even specific brands, part numbers etc. would be most helpful. I am a bit of a neophyte on this but when I see factory mounted systems using 12 gauge wire and low end controllers I know there has to be a better way.

[pianotuna]

One of the members here had a poly and a mono from the same company with about the same wattage. When ever a cloud passed the sun the mono output dropped to nearly zero. The poly did much better.

red31 wrote:
Is there actual evidence of this?

The only difference I'm aware of is high temperature performance.

Cheap poly have a lower Vmp which yields a higher I which can be a benefit with PWM.

pianotuna wrote:
Not in low light.

[VAHillbilly]

Thanks everyone for your comments. After reading these replies and other reading I am leaning now connect the two 160 watt panels in series. I am somewhat limited in space to install the controller. I have been looking at the Morningstar Prostar 40A mppt model. Running the string calculator the converter should easily handle the two panels and will have the ability if I decide to add a third 160 watt panel with all three connected in series. It will fit the available space better than the Tristar 45A mppt unit. I think the Prostar mppt unit is relatively new.

Does anyone have any experience with the Prostar mppt units or any comments about using it for my application.

[red31]

Is there actual evidence of this?

The only difference I'm aware of is high temperature performance.

Cheap poly have a lower Vmp which yields a higher I which can be a benefit with PWM.

pianotuna wrote:
Not in low light.

[Almot]

Ed_Gee wrote:
My quality items were designed for my 320W system with potential for expansion to one more 160W parallel panel,

... and 500W array in series would have expansion room for another 500W - which is probably more than the roof space would allow. On the same #10 cable.

Ed_Gee wrote:
iPads are also made in China.

Comparing 40-year old tech company with a solar e-commerce hub is informative indeed. They don't disclose who and where designs and manufactures their quality items, btw.

Agreed with Westend - it's easy to make your own J-box, for cheap. Just don't see much reason going parallel with MPPT.

[pianotuna]

Not in low light.

Ed_Gee wrote:
Mono panels are superior to poly panels ... certainly more efficient.

[westend]

I would suggest to use MC4 cable from the modules to a combiner box. You can make your own or buy a bus box from any number of retailers. You won't need fuses or breakers inside this box because you only have one string of modules. Parallel the MC4 cables inside the box. Run your wire to the controller with an interrupter in that wire. I use a 25 amp manual circuit breaker but any switch rated to the total solar amperage will work. I'd say about 50% of RV installers do this and it is worthwhile for the couple of dollars it costs. You can cut power to the controller easily if you need to work with 12V wiring or the batteries.

I'd suggest to look at the price of 4 ga welding cable vs the #6 marine wire. I think they are similar in price and #4 will have less voltage drop.
You will also need a fuse or circuit breaker on the battery side with the controller's charge wire. I used a MEGA style fuse on the battery terminal stud, it bolts on. If you use a bolt on fuse, there is no need to buy a fuse holder.

[Ed_Gee]

Mono panels are superior to poly panels ... certainly more efficient. My quality items were designed for my 320W system with potential for expansion to one more 160W parallel panel, per my specifications. I'd also point out that iPads are also made in China.

[Almot]

Ed_Gee wrote:
I have two top of the line 160W panels ( Grape Solar ) feeding a Blue Sky Solar Boost 3000i charge controller, ( Solar Boost 3000i ) with 8 AWG wire. The system works just fine at maximum efficiency and I have room to add one more 160W panel with this controller. I run my panels in parallel to a custom refrigerator vent combiner box made by AM Solar,

Don't know what is "top of the line" these days when most panels are coming from the same village with so many farms appearing and disappearing every month that it's hard to keep a track record. On a brief glance, those are mono panels, not poly.

There are different ways to skin the cat, as usual.

Blue Sky 3000i is on the cheaper side of MPPT, low 50V input limit, can't use more than 2*12V in series or more than one 24V panel. Hence, parallel wiring, combiner box and thicker cable. Could've used PWM in this scenario as well.

OTH, MPPT with 150V input would allow up to 4*24V in series, and with 45A model it can be 2 panels up to 260-280W each, and still same #10 cable and no combiner box. 24V panels from 220W to 260W are practically same size.

[Ed_Gee]

VAHillbilly wrote:
I am planning to install two 160 watt panels on the roof of a Class C RV. I would like to make the installation where I can add another 160 watt panel if needed in the future. The wiring will be in parallel down to a MPPT controller. I anticipate about a 20' run of wire from the roof to the controller and then probably less than 3' to the batteries (two 6 volt GC).

I am thinking I should use #6 marine wire from the roof to controller and the same to the batteries. The panels will have what I think is #12 wires to MC4 connectors.

My question is what type connectors or small junction box should I use from the panel pigtails to the #6 wire? Also what type fusing and disconnect switches should I use. Frankly any recommendations for a properly designed system to handle 320 to 480 watts of PV output would be greatly appreciated.

Any recommendations even specific brands, part numbers etc. would be most helpful. I am a bit of a neophyte on this but when I see factory mounted systems using 12 gauge wire and low end controllers I know there has to be a better way.

You seem to be planning an identical system to what I already have on my motorhome. I have two top of the line 160W panels ( Grape Solar ) feeding a Blue Sky Solar Boost 3000i charge controller, ( Solar Boost 3000i ) with 8 AWG wire. The system works just fine at maximum efficiency and I have room to add one more 160W panel with this controller. I run my panels in parallel to a custom refrigerator vent combiner box made by AM Solar, ( Combiner Box ). No fuses needed between the solar panels and the charge controller, despite what you made have read here previously ... but a fuse or breaker is recommended between the controller and the batteries. I used this model: Blue Sea 30A breaker

[KCFDCapt]

http://www.amsolar.com/

[Almot]

One - or the only? 😉 - good thing about MPPT is that you can wire panels of any voltage in series, be it 12V or 24V panels. I don't know why using MPPT for 2 parallel 12V panels.

any recommendations for a properly designed system to handle 320 to 480 watts of PV output would be greatly appreciated.

Arrays over 400W normally call for 24V panels. So, there it goes:

#1: Get 2*200W or 2*240W panels, 24V nominal voltage each. Wire them in series with MC4 extension cable #10.. No junction box is necessary, in this case.

#2: No fuses before controller if using 2*240W in series, but you might add either switch or fuse as a disconnect in accessible location near controller - not really necessary as you can always undo one MC4 connector on the roof. But you do need fuse(s) or breakers after controller.

#3: Use 35-45A MPPT controller - Tristar MPPT 45 maybe. I am very happy with Rogue 30, 2*245W, but Rogue is not available anymore. 30A is on the small-ish side for 2*240, but it should work.

#4: (or should I say, #1?) - read The List of completed Solar Projects

[KD4UPL]

You are supposed to have a fuse in series with each panel wired in parallel. This is normally done with a "combiner box". These can contain fuses or breakers. MidNite solar, Outback, and others make combiner boxes.
#6 wire should be plenty from the combiner box to the charge controller. It should also be fine from the controller to the batteries. You will need a fuse or breaker in the positive wire near where it connects to the battery. 60 amp would be appropriate for the #6 wire.
It's not necessary to have a fuse or breaker between the combiner box and the charge controller but it makes it nice for servicing. If you don't have one you have to turn off the combiner breakers to kill the input to the charge controller.