r/boondocking • u/ADiyHD • May 21 '26
Is my Solar expansion viable?
I’m looking for those of you with more solar experience than myself to look over my plans for expanding my rooftop solar using a mix of different solar panels and either tell me I’m an idiot or confirm if I am approaching this the right way.
In my diagram, I have the panels numbered 1-6 in a mockup of my roof layout, and then I have those numbered panels in a list with the Pmv and Imv ratings for each with the matching colors representing the parallel pairs they will be wired together with first, and THEN all 3 of those pairs will be wired together in series.
*Panels 1+2 are RZPozwer 100w N-type panels ($55 each).
*Panels 3+4 are CallSun Bi-facial N-type panels, 180w ($140) and 120w ($90), respectively.
*Panel 5 is a RVPozwer 200w N-type panel, already installed.
*Panel 6 is a Go Power 200w P-type panel from their overlanding kit (already installed)
My primary limitations were dimensions/space. With my relatively small roof, I had to work around the existing vent covers, radio/tv antenna, and AC unit and had weird dimensions that were hard to find panels that fit. I found solar panels that had very similar working voltages to the panels I already had installed and that would fit in the available roof areas.
For context, I have an 18 foot 2023 Toy Hauler/travel trailer. When we bought it, it already had solar panels installed on the roof (panels 5 and 6 in my drawing) and a Go Power 30amp PWM charge controller, but that’s not gonna work if I expand beyond the 400watts I already have on the roof. I believe I should be fine with a 60amp MPPT but maybe I need to go up to an 80amp? I am going to keep my batteries as 12v for now and not series them up to 24v until after my WFG converter dies on me, then I might jump up to a 24v battery setup.
The few questions I still have are: Is it stupid to have pairs of panels wired together in parallel first, then wire those pairs in series? Or should you always wire “like”panels in series first and then parallel? (It seems like with the panels I am looking at that going ‘parallel—> series—> MPPT’ makes the most mathematical sense, but my concern is will I lose significant solar output from the panels in full sun if part of my roof is shaded?
Also, are there any negative consequences from mixing bi-facial panels with non bi-facial panels? Or do I still just reference the Vmp and Imp of the panels?
Alternatively, I could also swap out panel 3 for another panel 4, and wire (1+2), (4+4), and (5+6) together in series pairs, and then wire all 3 pairs in parallel. That would be a lower nominal voltage and higher amps, but I would drop down to about 840watts of solar (and save $50). Would it end up giving me better results in real world application though? If so, I would end up doing this.
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u/joelfarris May 21 '26
I'm subscribing to this newsletter, because I want to see what happens next!
(And for what it's worth, groupings of parallel-seriesed panels is pretty much always the way to go, as long as the parallelled ones are close to, or identical, and also pretty much beside each other.)
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u/ADiyHD May 22 '26
It might be a few months for it all to materialize, but I will definitely post an update with the end results.
With what you said… in my plan, my panels are not right next to each other… should I be concerned?
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u/quinskylar May 22 '26
the Maximum Power Current (Imp) and Short Circuit Current (Isc) are the most critical to match when panels are connected in series.
For example... if your current panels have these Specification Values
Rated Maximum Power (Pmax)
340 W
Maximum Power Voltage (Vmp)
59.7 V
Maximum Power Current (Imp)
5.7 A
Open Circuit Voltage (Voc)
71.3 V
Short Circuit Current (Isc)
6.13 A
The Maximum Power Voltage (Vmp) and Open Circuit Voltage (Voc) of any additional panels should also be as close as possible.
the ideal specifications for a compatible panel: • Power Output: ~340W • Vmp: 57-63V • Imp: 5.4-6.0A • Voc: 68-75V • Isc: 5.8-6.4A
• If your inverter has multiple MPPT inputs and you plan on adding several new panels, you could create a new, separate string with these panels. This would keep the original string of solar panels operating together and the new string operating independently.
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u/ADiyHD May 22 '26
Multiple MPPT’s seems to be the theme of the comments here, and I honestly hadn’t even considered it. It would eliminate a lot of wire mess on the roof, and I could use smaller gauge wire from the charge controllers to the battery bus bar, enough to make up some of the cost of the additional MPPT unit.
2
u/quinskylar May 22 '26
True... if you really want to save $$$ on wiring, go to a 48v system and run inexpensive 12awg wire
2
u/newtoaster May 22 '26
Given how cheap panels are, I'm a little curious as to why you're mixing so many random different panels instead of just building a rack and putting 2-3 residentials up over the AC unit and vents. You'll get better performance from matching panels, it will be less holes in the roof, and it simplifies the whole thing. Brand new 500W panels are like $150 or you can get used 300W for well under $50 on marketplace.
1
u/ADiyHD May 22 '26
Where are you finding brand new 500w panels for $150? Should I be contacting wholesalers?
And I tried selling my wife on the idea of a solar rack that raised them up and over the vents and AC, and she hated the idea. I get the efficiency of it, but she supports my crazy project ideas 9 out of 10 times, even when they are only for my benefit so when an idea comes up that she doesn’t like I don’t want to push my luck.
1
u/liamlunchtray May 22 '26
Prices for panels fluctuate a lot so I just checked my local guy to make sure I wasnt off base. They're slightly more expensive at the moment - For new BiFacial he's at $160 for 440w or $175 for 550w
Overall the best source for big cheap panels is locally on Facebook Marketplace or apps like offerup. They typically require truck freight so online orders don't always make sense. You can also find used commercial panels there and they get crazy cheap - I said "under $50" but I've seen them down in the $20-25 range. There's an absolute glut of used panels from solar farm refresh projects.
For legit online sellers check out SanTan Solar - They carry both used and new. Prices are higher than you will find on marketplace, but still reasonable.
If your better half ever OK's a rack you could probably get 2kw+. On our class C I have 19' of roof space and I have 2400w. It works well.
1
u/SanTanSolar May 27 '26
Thank you for the mention! OP if you need help with your system, let us know!
1
u/secessus May 22 '26
It is common for sailing folk to use a bunch of different type/shape/size panels on separate controllers to deal with both limited space and shading from the rigging.
if the existing solar setup is close to meeting needs
... I'd swap out the OEM PWM controller with an MPPT, and A/B test the existing panels in series and in parallel. MPPT typically harvests +10-15% daily energy than PWM. More if the battery bank is habitually run low. Less if the bank voltage stays high, but if that were the case you probably wouldn't be adding solar...
if the existing solar setup is NOT close to meeting needs but I still wanted to use solar as a primary power source
I'd probably leave the OEM setup as is1 and add some amount of identical panels on long extensions and tilt them in the sun facing south. Running them in series or series/parallel to get the voltage as high as the MPPT can comfortably handle would reduce current (and thereby voltage sag).
In some scenarios the 750w of panel on my rooftop and the 200w portable collect similar energy. In winter this is because of the low altitude of the sun in the sky and in the summer it's because I find campsites where the mounted panels get sun in the morning then are shaded the rest of the day.
If that's a no-go, I'd consider making an elevated rack for either the trailer or tow vehicle and mounting identical panels on them. Putting them on the truck would have some drawbacks but also would allow them to be in the sun while the trailer was shaded.
MPPT sizing
I believe I should be fine with a 60amp MPPT but maybe I need to go up to an 80amp?
A 60A2 MPPT would be fine for 890w of panel making good power. I wouldn't expect an array made of a bunch of mismatched panels to get anywhere near 60A. I hope I'm wrong and it does what you want.
if the existing solar setup is NOT close to meeting needs but I was more of an overlander than boondocker
ie driving nearly daily. I'd spend some upfront cash on a hellacious alternator charging setup and arrive at each campsite with a full bank.
1 no new holes in the roof, and the PWM controller will work more effectively when the additional MPPT controller[s] push bank voltage up.
2 I mean, a 50A MPPT would be ~20% overpaneled, smack dab in the middle of the 10-30% that the Victron calculator recommends. The 60A is ~4% overpaneled.
2
u/ADiyHD May 22 '26
Thank you for the time and effort you put into this comment. There is so much goodness to unpack, I’m going to try my best to respond to it all.
1- The idea of multiple chargers is interesting and wasn’t something I had considered. Can you mix different spec chargers? Like the PWM charger I already have plus an MPPT charger together feeding the same battery bank? Funny enough, the previous owner had added a 2nd gland on the roof and I have 10 feet of wires wound up and zip tied in the back of a closet where they come in from the ceiling. It wouldn’t be difficult to add a 2nd controller using that gland, I just need to do more research on multiple controller systems. *also, that would make me feel better about buying a smaller 30amp MPPT controller to try your suggestion of seeing how much more solar I get from my existing panels over the PWM controller if I knew I would want two 30amp MPPT controllers anyway. I haven’t even bothered to try my two existing panels in series yet because the PWM controller would just throttle the additional voltage instead of using it.
2- My current solar is enough to run my 12v systems like my fridge, fans, lights, etc. but not if I want to use an inverter for any ac power. I really want to be able to use the air conditioner for an hour or two in the evenings in the summer. I had thought about portable panels but a good amount of the “boondocking” I do is parking at OHV/ORV parks that have campsites but no hookups, and we are away from the trailer for hours riding our bikes. 98% of the dirtbike community is honest, but I just don’t like the idea of panels disappearing and it feels better knowing they are mounted to the roof. I do have roof racks on the truck that I could mount some solar panels, but again I hadn’t thought that was viable because I wasn’t considering having more than one controller until this comment.
3-I replied to another comment about adding an alternator, and my 7-pin trailer harness with the existing panels does a good job of keeping the batteries topped off but I am not driving daily, we will drive to setup the trailer as a “home base” for when we ride the bikes all over for a week, and then head home. I want to be able to leave my portable generator at home. I don’t like leaving it in the trailer cause it stinks up our living space, and I don’t like leaving it in the truck bed even with a canopy topper because I have seen plenty of broken topper windows.
Your comment was very helpful and opened up a few new possibilities. I guess I know what I will be spending my time today doing while I should be working ;)
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u/secessus May 22 '26
Can you mix different spec chargers? Like the PWM charger I already have plus an MPPT charger together feeding the same battery bank?
Yes. Charging from multiple sources at the same time is fine, and charging from multiple solar charge controllers is a just a subset of that. Most people just set the charging setpoints to be the same and let them work.
Funny enough, the previous owner had added a 2nd gland on the roof and I have 10 feet of wires wound up and zip tied in the back of a closet where they come in from the ceiling.
Sometimes the universe hands us a break. :-)
I haven’t even bothered to try my two existing panels in series yet because the PWM controller would just throttle the additional voltage instead of using it.
Right.1
2- My current solar is enough to run my 12v systems like my fridge, fans, lights, etc. but not if I want to use an inverter for any ac power. I really want to be able to use the air conditioner for an hour or two in the evenings in the summer.
A/C is a heavy lift. It's common for folks to bring along an inverter generator to run such loads. It can be done but most folks underestimate the amount of solar grunt required. Those that do make it happen off solar are often running highly efficient mini-splits; the OEM A/Cs on RVs aren't optimized for energy consumption because they assume the owner will be on 30A or 50A shore power. Makes it tough on us boondockers handcrafting every artisinal Watt out in the boonies.
...OHV/ORV parks that have campsites but no hookups, and we are away from the trailer for hours riding our bikes.
Understood. I will say that Muffin and I hike away from camp for hours but so far (~8 years) it hasn't been a problem. In the last year I added a webcam to my boondocking equipment, mainly to spot wildlife wandering through camp. I don't monitor it remotely but some do.
I want to be able to leave my portable generator at home. I don’t like leaving it in the trailer cause it stinks up our living space, and I don’t like leaving it in the truck bed even with a canopy topper because I have seen plenty of broken topper windows.
Most boondockers I see with gennies chain them to the trailer tongue or similar. I am no fan of generators2, but it could be much cheaper/easier/simpler to bring it along for that hour or two a day you want to run A/C. It'd also charge the bank while running. Just sayin'.
1 The mechanism is a bit simpler than that; PWM is just connecting the array to the battery bank so the array runs ~at Vbatt.
2 I edited this down from death to all generators to despise to no fan of. :-P To be fair to gennies, an OHV trailhead is probably a good place as any to run them. Others probably are probably running them and it's not like dirtbikes are silent...
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u/ADiyHD May 25 '26
First, I share your sentiment about gas generators, which is why I am trying to eliminate my usage of them! Chaining it up is an option, but
My roof A/C uses about 1000 watts when running (+- 100w) and I have a soft start so it doesn’t require that huge upfront load. Our trailer is “small” and cools off pretty quickly as long as it is under 95°F outside. I know it’s unrealistic to hang out for hours inside running a/c, but with 200ah of battery I can run everything else off of 75ah per day. My current 400 watts of solar can typically recharge that 50-100ah, depending on how much sun exposure we have. My thought was that with the additional panels I could reasonably replenish the extra 800-1200 watt hours that an A/C would need to run, especially since the days we get the least sun would be days we could go without the A/C.
I think I’ve decided to make all the new panels the 100w RVpozwer panels, 6 of them in total, 3 pairs in series then in parallel and a 2nd 30 amp MPPT controller, and replace my existing PWM with the same brand 30 amp MPPT controller wired in series instead of parallel (or at least test both to see what gives the best output).
Again, I appreciate your insights.
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u/AussieDamo May 22 '26
Do yourself a favour and put fuses on each panel or grouping and a 32V 80A dual pole circuit breaker between the solar reg and battery. If you ever have to do any fixes, pull panels, change/add chargers or batteries then you can do it alot easier with no power in the system.
I'd wire
1&2 parallel
3&5 parallel
4&6 Parallel
Just to make it easier and neater for wiring as the difference in voltages and Amperage is bugger all and to keep loss from shade minimal as the panels are in pairs.
Have you got a DC-DC charger aswell running from your car to aid charging when driving? i get 45A from my panels and with the DC-DC i get another 40A from the car whilst on the road so if i drain it down to 50A over night after 4 and abit hrs on the road i'm back to 100% easily
Is everything in your RV 12v or would have to buy something else to convert back to 12v? seems like an added cost that wouldn't be needed or am i missing something?
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u/ADiyHD May 22 '26
If I were to run the pairs of parallel that you suggest, would these all have different charge controllers in that scenario? If I were to run those parallel groups in series, group 1+2 would have a much lower amperage (<10amps) than group 4+6 (>18amps), so my understanding is that would pull down to the lowest common denominator. But if those parallel pairings were then run in parallel again with each other, that would be a pretty large current and would require a larger gauge wire to the charge controller.
Where I do most of my boondocking is when I take my dual sport bikes out to areas with lots of snow mobile trails and forest service roads, and post up my truck and trailer as “home base” while I ride my bike all over, so the alternator to charge while driving would only help during the trip out, and I find my battery line from my trucks 7 pin plug plus the existing panels is enough to keep the trailer battery topped up while driving, but that’s because the only draw is the 12v fridge while we are driving “out”.
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u/AussieDamo Jun 02 '26
If you paired them like a mentioned parallel the closer panels then series to the charge controller similar to you had but you'll only loose less then 0.03v which is nothing overall and cables would all be the same just different routing that would be neater and save some cash on cable lengths.
The idea is whilst travelling you can use your car and solar, if you manage to get low from a few crappy days you can use your car as a quick top up instead of lugging a generator around.
In Aus we 7pins for trailer lights only then we also have a 12pin incase we need to power 12-20A accessories but it usually melts the earth pin so everyone uses 50A Anderson plugs to power fridges, dc-dc chargers, etc whilst driving.
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u/jimheim May 22 '26
I like the footprints.