Increasing solar on rooftop -- choosing new panels for optimal efficiency and space utilization

MG1965 Registered Users Posts: 1

Hi folks,

I full-time RV with solar power. The camper came with a 150 watt panel on the roof (of unknown provenance, but probably the Kyocera KD, as it looks very similar) and two (2) 12v Lifeline 150 amp hour AGM batteries. The RV dealership installed an additional 170 watt panel (Zamp) and a 30 amp Zamp charge controller (ZS30A). The camper has a WFCO 8945 converter, and I have a Honda eu2200i generator.

For the most part, my system works well enough. I live in the camper full-time. I only need to whip out the emergency generator if there have been successive cloudy days and my batteries are starting to get close to 50%. This has worked for the past six months. However, things are not ideal, and there is a specific issue I have identified.

Even with daily full sun (in winter in Southern California), my batteries are never fully charged in the course of the day (although they also never go below 12.5v unless we have two days without sun). I have oriented my rig such that the panels both face south, but they are flat on the roof (not tiltable), and there is a rooftop AC unit between them (so one panel is partially-shaded in the morning, and the other is partially-shaded in the afternoon -- see picture below). I do get 14.4v charging. I am thinking that I should add another solar panel. My charge controller can handle 510 watts, so perhaps I should add an additional 190 watt panel (for 510 watts in total)? This would go in front of the AC unit, so it would not be shaded at any point if I were facing due south (see picture below).

This is the space where I can install more panels. It’s pretty much the only spot available on the roof. The clear, flat area in front of the AC unit measures 28”x86”. This model of truck camper has a full walk-on roof, so the panels can be installed wherever there is space.

The table below represents my maximum daily electrical requirement:  running the furnace all day long in freezing weather when I am staying inside all day long… which I haven’t actually done yet, and doing things I don’t do every day -- which is explained in the “notes” section of the below table.  Note that I don’t have any inverters besides a 150 watt cigarette-lighter type, and I don’t have any high-draw inverter appliances (like a toaster, hair dryer, coffee machine, etc.).  I make tea and coffee with a kettle on the propane range.


I concluded that the best thing for me to do would be to add an additional 190 watt panel (for a total of 510 watts, which is the limit of my charge controller) and wire the three panels in parallel, which should work since they are all 12v panels, right?  The panel I am looking at is the Go Power 190 Watt panel.  The respective VMP’s of the Kyocera 150 watt, Zamp 170 watt, and Go Power 190 watt are: 18.2v, 18v, and 20.4v. The respective IMP’s are: 8.25A, 9.4A, and 9.3A. If I installed the Go Power 190 watt panel on the roof and wired the three panels in parallel, the voltage of all three panels would drop to 18v (the lowest of the three), which would reduce the output of the 190 watt panel by almost 22%, correct? And if I wired them in series, all three panels would drop to the lowest amperage (8.25A), which would reduce the output of the panels together by 8%, correct?

So it seems I would be better off installing two Go Power 80 Watt panels, which have a VMP of 18.4v or 17.5v and an IMP of 4.35A or 4.57A (the documentation is different on the Go Power website and in the owner’s manual, which contains the latter set of numbers). If my calculations are correct, installing the four panels in parallel would mean only a 1% - 2% loss of output. That seems much more reasonable to me, even though I would be sacrificing 30 watts on the roof (versus a single 190 watt panel). One significant advantage of two smaller panels is the fact that they would be easier to fit on the very limited real estate on top of my truck camper. Does all that sound correct?

I first want to better understand the problem and what is being done and why before I spend my money. Thank you in advance for any replies and information or suggestions.

Here is a marking on the unknown 150 Watt panel. I tried googling the code, but it didn’t give me any results.  I wrote to Kyocera, as well, and I hope they get back to me with confirmation that this is their panel.


  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    Assuming the Zamp CC is a PWM type, putting panels in series isn't really an option.  With shade, likely unwise anyway.

    We usually consider 10% to be "close enough" in matching panels.  The 190w at 20.4v is a bit more than that (I get ~12%), but IMHO still in the ballpark.  One option would be to put it on a separate small pwm controller.  If there's any way of tilting it for a better winter angle though, I suspect that would make a bigger difference.
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    You need to add 2 more columns to your spreadsheet, watts ( which is V * A ) and Watt Hours (watts * hours) for each device, then add up the watt hours for a more understandable load estimate.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    gen: ,

  • BB.
    BB. Super Moderators, Administrators Posts: 33,476 admin
    Assuming all of your loads are 12 VDC... Then solar panel wise:
    • 104 AH per day * 12 volts = 1,248 WH per day @ 12 vdc
    • 1,248 WH per day * 1/0.61 panel+battery+controller eff * 1/4.0 hours of sun per day (good summer day) = 511 Watts of solar panels minimum
    Lets say you vacation in western Virginia with array mounted flat to roof:

    Average Solar Insolation figures

    Measured in kWh/m2/day onto a horizontal surface:


    That would cover your power needs daily (long term average) April through September... Note, solar power is highly variable, so you should still plan on a backup genset or cutting back on energy usage during days of less than "optimum" weather (suggest that base loads should never be more that ~50-65% of projected solar harvest (base loads--Those loads that you "need" every day vs optional loads that you can do without/justify genset use to help power).

    With PWM controllers, the Vmp 17.5 to 20+ volts is fine to parallel. Note that Panel Wattage is Power=Vmp*Imp. With PWM controllers, Vmp-panel-load is closer to 15 volts or so, so the "extra" voltage from a Vmp=20 volt panel is not giving you anything extra vs a panel rated at Vmp=17.5 volts (don't "pay" for the extra name plate wattage--Only pay if it fits your space, good quality, and works with your setup).

    Note that Vmp-spec (and Voc-spec, etc.) are "marketing numbers" with panels at ~75F... Panels run much hotter than that under full sun, and Vmp/Voc fall as panels get hot (and rise in sub freezing weather).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset