Too much Panel for the SCC?

[OurVentures]

I have a Class A motorohome that has too much on the roof and as such I am really limited to panels that are less that 35 inches across. I am also trying to build on a budget, so looking at panels from SanTan. The two that they have are a 185 watt panel (vmp 36.4 and imp 5.1) and a 230 watt panel (vmp 41 and imp 5.61 amp)
For Black Friday I got what I think was a good deal on 2 Victron Smart MPPT 100/30.
More important info:
I have four 6V golf cart Lead acid batteries in 2s2p. each are 235 ah, so a total of 470 ah with 50% usable to 235 ah at 12v.
The motorhome has a Magnum set up with a Magnum 2012 inverter charger with auto gen start and the RC50 contoller.
I plan on using these panels mainly in the summer in the northern US and maybe in the Southwest US in the winter.

So my question, is can I use two of each of the above panels in parallel?
I THINK the max output of the solar controller is 14.4v x 30 amps = 430 watts.
Two of the 230 watt panels is 460 MAX which likely is slightly over paneled and fine
Two of the 185 watt panels is only 370 watts and under paneled. Do to the space limitation I do not want to underpanel at all.
Three of the 185 panels is 555 watts and likely way over paneled.

Any other narrow 200 to 250 watt panels out there that are cheap?

 

[sunshine_eggo]

So my question, is can I use two of each of the above panels in parallel?
I THINK the max output of the solar controller is 14.4v x 30 amps = 430 watts.
Two of the 230 watt panels is 460 MAX which likely is slightly over paneled and fine
Two of the 185 watt panels is only 370 watts and under paneled. Do to the space limitation I do not want to underpanel at all.
Three of the 185 panels is 555 watts and likely way over paneled.

Any other narrow 200 to 250 watt panels out there that are cheap?

Panels in parallel must have similar Vmp. The 185W and 230W would be okay together, but each would pay about 10% power penalty.

2S 200W would pair nicely in parallel with 1S 230W

Victron often recommends up to 30% over-paneling due to the lack of regular availability of that last 30%.

Victron controllers can be over-paneled to whatever level is allowed by your array assuming you don't exceed the 100Voc limit in any conditions (you can only run all panels listed 1S, never 2S) AND never exceed the PV input current limit:

https://www.victronenergy.com/upload/documents/Datasheet-SmartSolar-charge-controller-MPPT-100-30-&-100-50-EN.pdf

which is 35A for that unit. So using theoretical numbers on an imaginary maximum over-paneled array:

60Vmp * 32A (35A Isc) = 1920W

Actually, now that I look at the specs, the 200W panels are about 60Vmp and 10.2A Isc, so you could do a 3S3P array of those panels for 1800W on each MPPT. Obviously, you'd lose out on a lot of that peak power, but you'd pump 30A most almost all day.

You can safely go:
3P on the 200W panels
6P on the 185W panels
5P on the 230W panels.

2S 200W + 1S 230W in parallel with each other twice, so 2S2P 200W + 2P 230W

Hopefully, that gives you the tools you need to maximize your configuration options.

 

[OurVentures]

Panels in parallel must have similar Vmp. The 185W and 230W would be okay together, but each would pay about 10% power penalty.

2S 200W would pair nicely in parallel with 1S 230W

Victron often recommends up to 30% over-paneling due to the lack of regular availability of that last 30%.

Victron controllers can be over-paneled to whatever level is allowed by your array assuming you don't exceed the 100Voc limit in any conditions (you can only run all panels listed 1S, never 2S) AND never exceed the PV input current limit:

https://www.victronenergy.com/upload/documents/Datasheet-SmartSolar-charge-controller-MPPT-100-30-&-100-50-EN.pdf

which is 35A for that unit. So using theoretical numbers on an imaginary maximum over-paneled array:

60Vmp * 32A (35A Isc) = 1920W

Actually, now that I look at the specs, the 200W panels are about 60Vmp and 10.2A Isc, so you could do a 3S3P array of those panels for 1800W on each MPPT. Obviously, you'd lose out on a lot of that peak power, but you'd pump 30A most almost all day.

You can safely go:
3P on the 200W panels
6P on the 185W panels
5P on the 230W panels.

2S 200W + 1S 230W in parallel with each other twice, so 2S2P 200W + 2P 230W

Hopefully, that gives you the tools you need to maximize your configuration options.

Thanks! this was super informative.

I was planning on either getting up to 6 230 watt panels or 6 185 watt panels.

So, If I do 4p for the 230's I get volts at the 41v and the amps are 5.61*4 = 22.5
And 5p is the same 41v and 28.1 amps

Is 28.1 amps too close to the limit?

For me the best would be 4 panels in parallel in the front of the rv and a 4 panel array in the back.

This would get me theoretically the 430 watts total per array or 860 watts.

Using the average of 5 hours of sun per day in the US that should net about 4300 watts or 358 amp hours?

 

[OurVentures]

My Next question is about wire gauge.. If I have wires going the 30 feet from the back of the RV, and then down 11 feet, that is max run of about 41 feet. Add in a bit of wiggle room and crossing from the other corner and we are at 45 feet. at 30 amps being pushed, doesn't that mean it needs to be pretty big wire? like 4 AWG?

 

[sunshine_eggo]

Is 28.1 amps too close to the limit?

Not at all. It a protection limit, i.e., if you wire the array backwards, it will protect itself as long as panel Isc doesn't exceed 35A. If you DON'T wire it up backwards, you can technically go higher.

For me the best would be 4 panels in parallel in the front of the rv and a 4 panel array in the back.

This would get me theoretically the 430 watts total per array or 860 watts.

Using the average of 5 hours of sun per day in the US that should net about 4300 watts or 358 amp hours?

No. It will actually be higher. Each array will be 920W if you're talking 4P on each MPPT. Your output will be clipped:



The 5 hr calculation would be correct if you actually only had 860W total array. Since you have 1840W total, you'll be getting full 860W for about 7 hours per day from 8:30am to 3:30pm...PLUS whatever the array produces on both sides of those times.

Northern latitudes and flat panels will perform notably worse in the winter - typically about 40% of summer performance, so your 4.3kWh will be closer to correct in winter, but probably a little optimisitic.

My Next question is about wire gauge.. If I have wires going the 30 feet from the back of the RV, and then down 11 feet, that is max run of about 41 feet. Add in a bit of wiggle room and crossing from the other corner and we are at 45 feet. at 30 amps being pushed, doesn't that mean it needs to be pretty big wire? like 4 AWG?

Nope.

41V @ 23A, 10awg, 41ft:

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

4.59% voltage drop.

 

[Rocketman]

on my MotorHome I used 200w panels- they fit well. I added a second array w/the Victron 100/30 - it has 600w of panels on it now (originally had400). In good sun it is often clipped. It will only deliver 30amps - that’s about 440watts.

Fit the panels on the roof- you may want/need one more Solar Charge Controller.

You could go up one size of wire to 8awg. The voltage drop will be lower - 2.89% but it costs more.

 

[OurVentures]

Not at all. It a protection limit, i.e., if you wire the array backwards, it will protect itself as long as panel Isc doesn't exceed 35A. If you DON'T wire it up backwards, you can technically go higher.



No. It will actually be higher. Each array will be 920W if you're talking 4P on each MPPT. Your output will be clipped:

Would it be better to do 2s2p with 4 panels? This gets me 82v and 11.2 amps which would allow better flow through the wires.

this drops the Voltage drop from 4.59% drop to 1.2% drop for 10 AWG for the same 4 panels, while still staying within the SCC limits using the calculator you showed. And a 60 foot run (extreme) would still be below 2%.

Nope.

41V @ 23A, 10awg, 41ft:

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

4.59% voltage drop.

 

[sunshine_eggo]

Would it be better to do 2s2p with 4 panels? This gets me 82v and 11.2 amps which would allow better flow through the wires.

this drops the Voltage drop from 4.59% drop to 1.2% drop for 10 AWG for the same 4 panels, while still staying within the SCC limits using the calculator you showed. And a 60 foot run (extreme) would still be below 2%.

Nope.

Voc is what matters, and you're at 90Voc. You'd break 100V around freezing.

You don't get to count losses. Maximum voltage is at 0A. At 0A voltage loses are 0V.

 

[OurVentures]

How would the number change if I exchanged the Victron SCC from the 100/30's I have to two 100/50's

I can still use the same 2s2p settings for the 230 watt panels (82v and 11.2 amps)

BUT I will output to the batteries ~600 watts per controller vs ~420 watts per controller which is close to 42% more energy going in optimally, but with sun being what it is it would be somewhat less?

 

[sunshine_eggo]

How would the number change if I exchanged the Victron SCC from the 100/30's I have to two 100/50's

You would simply be able to deliver 50A of charging vs. 30A - about 725W.

I can still use the same 2s2p settings for the 230 watt panels (82v and 11.2 amps)

I'm sorry, but you're not listening. You must use VOC. I actually misread the voltage from the image from the 185W panels. The 230W panels are 48.7V, so 2S would be at 97.4V. You'd exceed 100V at about 20°C/68°F.

From above:

Victron controllers can be over-paneled to whatever level is allowed by your array assuming you don't exceed the 100Voc limit in any conditions (you can only run all panels listed 1S, never 2S) AND never exceed the PV input current limit:

You can safely go:
3P on the 200W panels
6P on the 185W panels
5P on the 230W panels.

The ONLY way you can do 2S with ANY of those panels on a 100V controller are 1) if it's NEVER below 77°F or 2) you go with a 150V MPPT.

 

[OurVentures]

You would simply be able to deliver 50A of charging vs. 30A - about 725W.

I'm sorry, but you're not listening. You must use VOC. I actually misread the voltage from the image from the 185W panels. The 230W panels are 48.7V, so 2S would be at 97.4V. You'd exceed 100V at about 20°C/68°F.

From above:

The ONLY way you can do 2S with ANY of those panels on a 100V controller are 1) if it's NEVER below 77°F or 2) you go with a 150V MPPT.

I follow now. Thanks for your patience.
I am learning so much but it's a bit overwhelming

My current (yeah, bad pun) thought is:
Front of the motorhome gets 4p set up as one array, 2 panels each side going to one 100/50. This can use 10 AWG. This is about a 2.8% drop
Rear of the motorhome has a much further run, so I would be limited to 3p set up using 10 AWG again and this is about a 3.5% drop.

All of the important values should now be in harmony
4p and 3p VOC is still below 50v (check)
Both runs are under 4% loss (check)
Not having to run 45' of 8 AWG (check)
Actually listening to sunshine_eggo (check)

 

[sunshine_eggo]

My current (yeah, bad pun) thought is:
Front of the motorhome gets 4p set up as one array, 2 panels each side going to one 100/50. This can use 10 AWG. This is about a 2.8% drop

Yes.

Rear of the motorhome has a much further run, so I would be limited to 3p set up using 10 AWG again and this is about a 3.5% drop.

IMHO, I would accept > 4% voltage drop provided I'm well within the wire current rating. You'll never have more than 24A on 30A rated 10awg, so I'd strongly consider 4P here as well.

All of the important values should now be in harmony
4p and 3p VOC is still below 50v (check)
Both runs are under 4% loss (check)
Not having to run 45' of 8 AWG (check)

Confirmed, but again, I would rather compromise on the 4% loss by adding 33% more PV at 4P and staying within wiring current limit.

Actually listening to sunshine_eggo (check)

LOL

 

[OurVentures]

Confirmed, but again, I would rather compromise on the 4% loss by adding 33% more PV at 4P and staying within wiring current limit.



LOL

Would that be too much heat in the wires due to the smaller size?

 

[sunshine_eggo]

Would that be too much heat in the wires due to the smaller size?

No. The heating of the wire depends on both the current and the voltage drop. Longer wire actually dissipates more heat because of more surface area, but you lose power due to the voltage drop.

When selecting wire:

1) start with the rated current of the wire; 10awg can typically handle 30A
2) Increase size as needed to attain acceptable voltage drop.