Solar System Help

Tank3333Tank3333 Registered Users Posts: 6 ✭✭

I am new the forum and new to Solar Power.  It's actually an interesting topic but very confusing as well.

I need some opinions/information on an issue I am having with a solar system setup in my 5th wheel trailer.

I purchased a new 5th wheel trailer that came with a residential fridge so I need continuous power to run as it won't run on propane. 

Currently the trailer is at a permanent site with shore power so the only time I need to use solar is if/when the power goes out. We are out there every weekend (20 weekends in summer) and last year the power went out 3 times for a maximum amount of 4 hours total throughout the year so not much.  We do however plan on using the trailer to travel with so I would like to get this figured out before we are on the road having issues.

My current system doesn't seem to be charging/holding a charge, it was hooked up the first weekend in May last year and I started watching my voltage on my batteries drop slowly for a couple months.  I recharged the batteries and tried to diagnose the issue.  I haven't been able to find anything wrong, of course I am not a solar guy.  I am however very mechanically inclined and learn very quickly.

Doing the calculations on my current system I believe it is too small for the job.  The system was recommended and installed by the trailer dealer and I believe they were wrong but would like some opinions on it.

My current system is as follows:
2 - 160watt solar panels
EWC-30amp 12v Controller
Xantrex FreedomX 1200 Sinewave Inverter
4 - 6v 225AHr Deep Cycle Batteries (12v system)
Average peak sun hours per day is 4 to 5.

This system will only be running a fridge 640kWh per year. 

1. Will this system run my fridge 24 hours a day, 7 days a week if I need it too if I get the 4 to 5 hours of peak sun?
2. Should it be working for what I am using it for now, when the shore power goes out and we need to power the fridge?
3. What are the best ways, steps to diagnose to see if my batteries are getting the power they need?

I really appreciate all the help.

Thank you,


  • EstragonEstragon Registered Users Posts: 4,478 ✭✭✭✭✭
    1.  Short answer, no.
    2.  Yes (maybe), for an outage of a few hours.
    3.  For a start (assuming flooded golf cart size batteries), check the electrolyte (acid) level in the batteries. Remove the caps on top and shine a flashlight into each cell (3 per battery) to see if the liquid covers the metal plates.  

    If the plates are covered, check the voltage with a multimeter and note.  If ~12.6 or higher, turn off (or better yet disconnect) all charging sources and loads, leave them overnight, then check the voltage again.

    If the plates are uncovered to the point you can't see any liquid, they may be unrecoverable.  If just low, you could try adding distilled water to about 1/2 way between the top of the plates and the bottom of the cell opening.
    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
  • mike95490mike95490 Solar Expert Posts: 8,863 ✭✭✭✭✭
    >   640kWh per year

    That's about 2Kwh daily ! 
      So you need batteries that can store & deliver 6kwh.  6v*200ah=1,200wh ber battery  x 4 batt = 4.8kwh in your existing batteries
      You need solar that can harvest about 3kwh (plus whatever other loads you have) daily  We'll go with 4 sun hours, which is optimistic.
       So that's about 1,000w of panels (they only produce 80% of nameplate in real life)

    This is going to be a pretty big PV upgrade.  you could go smaller on the PV and use a generator or vehicle engine to make up the charge.  The 4 existing batteries are likely shot, golf cart batteries are about the same thing as you have now, true deep cycle and less expensive.

    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: ,

  • Tank3333Tank3333 Registered Users Posts: 6 ✭✭
    Thank you Estragon, 

    That's what I thought, I knew I should have asked around before taking the dealers word for it.

    I have checked the battery fluid level and it is good.  I've also tested the batteries with a battery tester and they do hold a charge and test good. I believe it has something to do with the hook up of the panels, controller, inverter or either a draw or not getting power to the batteries.
    Just not sure where to start that testing.  May be time to get someone out to check it once we open the trailer in the spring.  

    Thanks again,
  • EstragonEstragon Registered Users Posts: 4,478 ✭✭✭✭✭
    2 x 160w panels, with proper tilt and no shade in most climates will produce ~ 160 x 2 x .75 x 4hrs = 960 watt-hours/day.  Fridge as rated is 640kwh/yr ÷ 365 = 1750wh/day, or double available pv power (before various system losses).  

    2 strings of 225ah [email protected]  For decent life, you don't want to draw below 50%, so about 225 x 12v = 2700wh useable capacity.  If the batteries are in like-new condition, enough to run the fridge for a day or so.  Solar wouldn't be able to run the load and catch-up charge the battery alone.  With shore power carrying the fridge load, solar would take ~ 3 days of good sun to charge batteries.
    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
  • Tank3333Tank3333 Registered Users Posts: 6 ✭✭
    I want to thank you guys for the feedback and information, this is a huge help. 

    Greatly appreciate it.
  • EstragonEstragon Registered Users Posts: 4,478 ✭✭✭✭✭
    If the solar system is working properly, it should bring the bank voltage up to ~14.5ish volts (fairly quickly with a more or less full bank), hold it there for a while (maybe an hour or so), then drop to ~13.5v for as long the sun allows.  There are variations based on controller settings, etc., but that's the basic idea.
    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
  • BB.BB. Super Moderators, Administrators Posts: 30,716 admin
    What you really need to do is measure/understand your loads... And get the most efficient loads you can (and turn off stuff when it is not used--computers, satellite receivers, etc.).

    For your AC loads, a Kill-a-Watt type meter is the place to start. You plug the refrigerator in and find out it uses ~1.0 to 1.7 kWH per day (1,000 to 1,700 WH per day). Using LED for lighting (either 12 VDC or 120 VAC) vs filament bulbs (most new stuff is LEDs these days).

    And you will find the refrigerator uses more energy on a hot day, making ice, cooling stuff from market/stove top, etc....

    More or less, the dividing line between a "small system" (~1,000 WH or 1.0 kWH per day) and a "medium size" system (~3,300 WH per day) is the refrigerator, and surprisingly, the DC central heat system/fan in cold weather:
    • ~8 amps * 12 volts = 96 Watts 
    • 12 hours per night * 0.50 duty cycle * 96 Watt load = 576 WH per night (rough guess)
    Or about 1/2 the energy used by a refrigerator per day.

    Also watch out how much energy the AC inverter uses "just to turn on". For your size system, 10-20 Watts "Tare Load" is pretty common:
    • 20 Watts * 24 hours per day = 480 Watt*Hours per day
    Again, another load that can be almost 1/3 to 1/2 the refrigerator load (and if you have a larger inverter, it can be 40+ watts load).

    Here is the basic math for a 3.3 kWH per day system (about a "near normal" electrical existence in a very energy conservation minded home/cabin/RV).

    For a full time off grid Flooded Cell Lead Acid battery system, you want  around2 days of storage and 50% maximum discharge (for longer battery life).
    • 3,300 WH per day * 1/0.85 AC inverter eff * 2 days storage * 1/0.50 max discharge * 1/24 volt battery bank = 647 AH @ 24 volt battery bank
    • Or around 4x 6 volt @ 220 AH "golf cart batteries in series" (for 24 volts) * 3 parallel strings (for 660 AH battery bank) = 12 "golf cart" batteries (just to give you an idea of what we are looking at here)
    We will need to calculate the size of your solar array with two methods. The first for 5% to 13% rate of charge for the battery bank. 5% is OK for summer/weekend use. 10%+ recommended for full time off grid. The second based on your loads and hours of sun per day harvest.
    • 660 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 1,243 Watt array minimum
    • 660 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 2,486 Watt array nominal
    • 660 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 3,231 Watt array "cost effective" maximum
    Say you are around Calgary Canada and you tilt the panels for optimum year round harvest (if you tilt them more, you can harvest a bit more in winter. Less, more harvest in summer). Note that far north, very poor solar harvest in winter (use utility power/genset/ice box/etc.):

    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 39° angle:
    (For best year-round performance)


    Let's toss the bottom 3 months of solar harvest (assume using genset/conservation/etc.). February at 2.99 hours of sun is pretty reasonable amount (it is not horrible):
    • 3,300 WH per day load * 1/0.52 off grid system eff * 1/2.99 hours of sun (Feb) = 2,122 Watt array "break even" February harvest
    More or less, I would be suggesting a ~2,486 Watt array minimum based on our rules of thumb design (loads, "optimal" FLA battery bank, residential type power usage).

    Now, you may not be able (or want to) put that large of battery bank and solar array on your Trailer... Then, the choice may be to run batteries and AC inverter at night, and genset during part of the day when traveling and dry camping.

    I will stop here... A lot of information (and some math) to go through here. And I have made a bunch of guesstimates--So you probably have to corrections and questions too.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Tank3333Tank3333 Registered Users Posts: 6 ✭✭


    Thank you so much for the information.  I am currently going through everything I have learned so far on this site.  There is a lot of information I didn't take into account with a solar system. 

    I know I will have some questions and will be back.

    Thanks again everyone.

  • Tank3333Tank3333 Registered Users Posts: 6 ✭✭

    I do have one quick question about batteries.  Another topic I need to get more familiar with.

    For the system I have now, the batteries are hooked as follows.  2 strings of 6 volt batteries hooked in Series then together in parallel.  Is this the proper way as it makes a 12v system or do I want them in series to make a 24v?


  • WaterWheelWaterWheel Registered Users Posts: 337 ✭✭✭
    Since your FreedomX inverter wants 12v battery power you want to wire the batteries for 12v.

    Conext XW6848 with PDP, SCP, 80/600 controller, 60/150 controller and Conext battery monitor

    21 SW280 panels on Schletter ground mount

    48v Rolls 6CS 27P

  • BB.BB. Super Moderators, Administrators Posts: 30,716 admin
    Adding batteries in series "adds voltage". 2x 6 volt @ 200 AH in series gives you 12 volts @ 200 AH

    Adding batteries in parallel "add AH/capacity". 2x parallel of (the above) 2x 6 volt @ 200 AH batteries gives you a 12 volt @ 400 AH battery bank (4x batteries in series/parallel).

    As WaterWheel says, your battery bank needs to be "matched" to the input voltage of the AC inverter (and any other loads you may have).

    RVs tend to have 12 VDC battery bus and loads... Good for "smaller" systems up to ~800 AH @ 12 volt battery bus. And good for ~2,000 Watts of loads (AC inverter, etc.).

    For larger systems, a 24 or 48 volt battery bank is usually a better choice. You don't need as heavy of wiring, and solar charge controllers are rated at 80 amps (example) at 12/24/48 volts... In another words, an 80 amp controller * 12 volts = 960 Watts of charging energy. At 24 volts, it is 1,920 Watts of charging. And 48 volts it is 3,840 Watts of charging power... One controller ($600) will manage more power at higher voltages.

    Anyway, back to designing for your energy needs. The stuff that came with the RV may not be "optimum" for your usage. Highly suggest to get your needs defined and then look at what you have and what you will need. Getting random parts without a plan is difficult to put everything together in a mix&match system.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Tank3333Tank3333 Registered Users Posts: 6 ✭✭

    Thank you,

    I am currently reviewing my full system and will be making a lot of changes replacing my current system.  I have learnt a ton from you guys and believe I have a very good starting point. 

    The good thing is I don't have to update the system this year as we won't be pulling the trailer out until starting the 2020 season.  I will have some time to evaluate my needs and see where that takes me. 

    I am sure I will be back for more information at some point.

    Thanks again,

  • BB.BB. Super Moderators, Administrators Posts: 30,716 admin
    And let us know what you end up with and how it works out for you.

    Nice to have feedback on our suggestions and for others to learn.

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