How many series, how many parallel?

[kb0zke]

Looks like ten 100W solar panels on the roof is fairly common. If you have such an array, how are you wiring them? Would you do it any differently if you were to do it over again?

[richard5933]

We have four 100w panels on the roof, all laying flat, two along each side. The two on each side are wired in series, and the two pairs are wired parallel to each other.

The main reason I chose series/parallel is that it raises the voltage and helps eliminate voltage drop - it also allows a slightly smaller conductor.

Kind of a crap shoot which two panels were in series and which two were in parallel though. So, I put the two on each side in series assuming that the sun would usually be coming/going over our trailer in that way since most of the time we end up parked north/south on our favorite campgrounds.

[PaulBristol]

Ten 100 watt panels on an RV is not very common. That would be 1000 watts.

Fewer higher capacity panels are becoming common for arrays that large. Some install 300 watt or so panels. Bigger panels may not work well on a curved roof.

My 2025 Trade Wind has 600 watts on the roof. I think they are longer, flexible panels. Still investigating.

1000 watts of 20 volt panels could deliver 50 amps. That requires 8 AWG cable or larger.

Putting them in serial pairs would reduce current to 25 amps at 40 volts. 25 amps requires 10 AWG gauge cable or larger. A solar preinstall may have 10 AWG cable already threaded through the roof.

[SVTRIDE]

Originally Posted by richard5933

We have four 100w panels on the roof, all laying flat, two along each side. The two on each side are wired in series, and the two pairs are wired parallel to each other.

The main reason I chose series/parallel is that it raises the voltage and helps eliminate voltage drop - it also allows a slightly smaller conductor.

Kind of a crap shoot which two panels were in series and which two were in parallel though. So, I put the two on each side in series assuming that the sun would usually be coming/going over our trailer in that way since most of the time we end up parked north/south on our favorite campgrounds.

I did the same arrangement with my 4 panels. Was concerned about 4 panel in parallel voltage drop with existing AS roof wire to MPPT gauge.
I also noted too, that with this config the solar controller to turns on sooner. There is a min voltage threshold for the MPPT to turn and turn off..so I noted that the array came online earlier in the day (took less light to reach threshold voltage) and same for system cutout later in day. But I’m sure that is traded off for partial shade inefficiency with series / parallel. 1 panel in shade effecting partner panel’s output in sun.

[Nishad]

Another reason to consider is shading. Shading varies throughout the day and across the roof, especially on a moving RV. I have 8 x 100W Renogy panels on my 25' Airstream in a 4S2P configuration, which works well. It harnesses solar energy from sunrise to sunset, with minimal amounts during shoulder times. I'll be changing it to 2S4P for better shade efficiency, as my two air conditioning units partially shade the panels.

[vanderwielen]

10 100watt panels on the roof of any airstream 'is not' common. SMH

[kb0zke]

I had three 365W panels on the Reflection, and lacked only about 2" of being able to put the fourth one on. Last year, on our way to Escapade, we spent several days boondocking with those panels feeding out two 24V 200AH batteries. We had a 16 cf residential refrigerator and used the microwave and electric skillet just as if we were plugged in. No problems at all. Batteries never went below 60%.


The reason for asking now, even though I'm not going to do the upgrade until later, is that I want to do something with my current solar controller. It is a Victron, but no bludtooth, and just stuffed into a corner. There also is no disconnect between the panels and the controller. If I'm going to remount it I may as well add the disconnect and get the larger controller now.

[uncle_bob]

Hi

If you go to series connections, you need to make sure your controller will handle the max output voltage of the "stack". It's not always obvious just how high that voltage actually can be. We tend to focus on the loaded / max power output voltage. A *very* rough starting point for the sort of panels we tend to use would be 32V.

Why mention this? If you are shopping for a new solar controller, and *might* go series .... bump up to that higher voltage unit. Better to have some "room just in case".

Bob

[kb0zke]

That's my thinking, Bob. I could just buy the biggest Victron I can find and be fine, but I suspect that doing so may result in spending far more than necessary. I also don't want to buy one and then find that it is slightly too small. That's why I'm asking the experts.


I've gotten two suggestions: 2s5p and 5s2p. Each have some good arguments. Any preferences?

[JeffKim]

A clarification, your solar wiring is 8AWG.

Maybe telling you what you already know department:

It sounds like you're trying to plan ahead and get a controller beefy enough to handle 10 panels on the roof and for now has the Smart capability. It's a pretty easy swap BTW.

Somebody tell me if I'm wrong: most 100W panels are in the 24V open circuit and 5A short circuit range. Looking at the scenarios, if you go with 5 in series connected in parallel that's roughly (5x24V) = 120V and 2x5A = 10A. All connected in parallel is 24V and 5Ax10 = 50A. However, the wire size calculator says 20' is about all you can go RT at 50A without rewiring, so doesn't seem like a good option. With 8 panels and 40A, possibly.

Soo... with the series/parallel at 120V/5A a Smart 150|35 should be fine (a Smart version of the standard issue 150|35). With the all parallel then there's a 100|50 ($184) version. Covering all bases is 150|60 but then it's about twice the cost ($350) of the 150|35 ($184).

[Nishad]

https://youtube.com/@cleversolarpower?feature=shared

https://youtube.com/@exploristlife?feature=shared

Both excellent resources.

[JeffKim]

If anyone is following along, missed the 2s5p. That's 5x5A = 25A and 2x24V=48V and 8AWG is plenty. A 100|30 ($128) would be adequate. Or maybe I'm all wet?

With this configuration, what is the effect of shading?

[JohnTF]

A lot depends on what your upgrades are going to be .

One is higher voltage = lower gauge wire , now the voltage of the system - charge controller , batteries , inverter etc.

I've been doing alternative energy stuff since the 70s , it use to be stay under 48 volts - because arcing becomes an issue --- seems that has been left behind , and I do not have an answer for the higher voltages these day [ being ok ] ?

So seems choices are 24v or 48v , then lots of gear forces a choice of locking you into picking --- lots of gear [ like charge controllers will do 12v or 24v , but do not do 48 & below ? ] .

Another thing to research is shading , is helped or hindered by series or parallel , so depending on shading of at min. other things on the roof ?

Seems as though your current batteries are doing what you want - how are they wired - for 24v ?

I choose to stay at 24v for my trailer , if I was going to like a large class A - i would give 48v more thought ?

Victron has a BlueTooth add-on for your controller .

You can also use multiple Victon controllers - so just adding another for extra capacity .

[Jum]

Originally Posted by JeffKim

If anyone is following along, missed the 2s5p. That's 5x5A = 25A and 2x24V=48V and 8AWG is plenty. A 100|30 ($128) would be adequate. Or maybe I'm all wet?

With this configuration, what is the effect of shading?

You're looking at the PV side only, but the 100|30 is solar input 100volts max and charge output 30amps max. 1000watts at ~14volts is 71.4amps, so the controller would limit it to 30amps max.

I am putting 800W (8x100 Renogy) on our Argosy and using 2x 100|30 MPPT with the panels 2S2P to each controller.

[OrangeCrush]

Originally Posted by JeffKim

If anyone is following along, missed the 2s5p. That's 5x5A = 25A and 2x24V=48V and 8AWG is plenty. A 100|30 ($128) would be adequate. Or maybe I'm all wet?

With this configuration, what is the effect of shading?

That is what I would do. Partly to minimize shade impact but mostly because I would not want to be messing with 120V DC open circuit potential with 5 series panels. I agree the 8 Gauge is fine for this as rough numbers (50 ft RT, 5 amps per panel, .63ohms/1000ft) is 5*5*.63*50/1000 =0.788 volts drop. That results in an approximate .788/40 ~ 2% loss which is reasonable to me.

[strangepod]

Originally Posted by uncle_bob

Hi

If you go to series connections, you need to make sure your controller will handle the max output voltage of the "stack". It's not always obvious just how high that voltage actually can be. We tend to focus on the loaded / max power output voltage. A *very* rough starting point for the sort of panels we tend to use would be 32V.

Why mention this? If you are shopping for a new solar controller, and *might* go series .... bump up to that higher voltage unit. Better to have some "room just in case".

Bob

Yup, agreed..

[uncle_bob]

Originally Posted by kb0zke

That's my thinking, Bob. I could just buy the biggest Victron I can find and be fine, but I suspect that doing so may result in spending far more than necessary. I also don't want to buy one and then find that it is slightly too small. That's why I'm asking the experts.


I've gotten two suggestions: 2s5p and 5s2p. Each have some good arguments. Any preferences?

Hi

If you go with 5 panels in series and use the "32V" number, you are up at 160V max voltage. That's more voltage than anything I know of in the Victron lineup. The normal configurations (as noted above) would be 2s, and 4s ( so 24 V and 48V).

Is the "real number" for max voltage on your panels below 32V? Maybe it is. It might be 28V. You then are about 10V *under* the rating on the high voltage Victron. Do make sure that the number you use is for *your* minimum temperature. A number at 70F is *not* what you want to use. Voltage goes up as temperature goes down.

You can do the math on the cable loss. Your output will vary over a wide range with a trailer mounted array. How much do you want to spend going from 4% wire loss to 1%? The efficiency of your solar converter is "unknown" if you want a "good to < 2%" sort of number. Yes, if you go crazy, you can exceed the wire ratings.

Ideally, I'd design for >20% below any rating either on current or voltage. Once you get to 40% below, that's probably "enough".

Fun !!!

Bob

[JeffKim]

Originally Posted by Jum

You're looking at the PV side only, but the 100|30 is solar input 100volts max and charge output 30amps max. 1000watts at ~14volts is 71.4amps, so the controller would limit it to 30amps max.

I am putting 800W (8x100 Renogy) on our Argosy and using 2x 100|30 MPPT with the panels 2S2P to each controller.

Thanks, yes I'm all wet. I thought the numbers corresponded to the PV side. Please ignore any of the advice above.

Some links to solar controller calculators I found:
https://www.victronenergy.com/mppt-calculator
https://explorist.life/solar-charge-...er-calculator/

[kb0zke]

Thanks, everyone. I'm leaning toward the 2s5p arrangement, but I suspect that I'll be at or slightly above the capacity of the wire from the roof to the solar controller, and I suspect that running a new wire is not going to be easy. I'll see if I can figure out exactly what wire I have coming into the existing solar controller. That will at least let me know what the maximum current I can have from the new array.


From what I've been able to glean from various sources, an Airstream's curved roof cuts down on solar panel efficiency quite a bit, so the more capacity up there I can start with the more I'll actually have going into the batteries.


Any more suggestions or ideas?

[richard5933]

Originally Posted by kb0zke

Thanks, everyone. I'm leaning toward the 2s5p arrangement, but I suspect that I'll be at or slightly above the capacity of the wire from the roof to the solar controller, and I suspect that running a new wire is not going to be easy. I'll see if I can figure out exactly what wire I have coming into the existing solar controller. That will at least let me know what the maximum current I can have from the new array.

From what I've been able to glean from various sources, an Airstream's curved roof cuts down on solar panel efficiency quite a bit, so the more capacity up there I can start with the more I'll actually have going into the batteries.

Any more suggestions or ideas?

This is only true if you're installing the panels so they lay along the roof's curve. Mine are mounted with higher mounts on the outside edge to keep them flat, and this is how I've seen many people mount rigid panels on an Airstream. Of course if you're using flexible/non-rigid panels this is not an option. By mounting them flat the curve of the roof is taken out of the equation.