Mini camper build solar system design

Jarhead55
Jarhead55 Registered Users Posts: 6 ✭✭
First off this is my first post, hello from the Alabama gulf coast.

I am an engineering type but know nothing about electricity or solar. I want to be able to go off grid boondocking and have all the comforts when doing so.
 
I am converting a 6'x12' enclosed cargo trailer into a camper and will be putting solar panels on it. I have 8 renogy 100w 12v panels and all will fit on top on the roof rack. I am also considering adding 6 more of those panels on a hinged rack on both sides of the trailer. This would not only add 600w to the system but would also act as an awning and keep the sun off of that side of the trailer thus keeping it cooler. If needed I too I can mount 3 100w panels on the fiberglass bed cover on my pickup. 

Panel information:
  • Maximum Power: 100W
  • Maximum System Voltage: 600V DC (UL)
  • Optimum Operating Voltage (Vmp): 18.9V
  • Optimum Operating Current (Imp): 5.29A
  • Open-Circuit Voltage (Voc): 22.5V
  • Short-Circuit Current (Isc): 5.75A

I doubt I would need 2.3kw is to run my 1250w 10.9a Whynter 14,400btu portable air conditioner during the day while still charging batteries and running 12v lights, iPad and phone charging, water pump and refrigerator as well some other 120v items like a television, Xbox one (for the grandkids), MacBook and so on. But I also understand that panels won't be 100 percent efficient due to their relative position to the sun through tout the day. My thinking is just the more panels the better.

Like I said I don't know anything about this stuff. All I've done if figured out the maximum number of 100w 12v renogy panels I could possible mount on the trailer and truck. Past that I have know idea about the charge controller, inverter, batteries and all the rest of the neccasary parts and pieces.

I am the kind to over think/do things so I expect here hear that I'm being rediculous in my expectations so bring back to reality if that's the case.

I do have a Yamaha 2000w inverter generator for backup.

Thanks for all the help in advance.

Regards,

Jh55

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Welcome to the forum JH.

    I always like to start with your loads, then design the system to support your loads. And, off grid A/C systems (and even refrigerators) are energy hogs and not always a good fit for off grid use. Add that trailers have limited spacer and weight capabilities, makes things even more difficult.

    But, you have what you have, and lets see what it can do. I am going to go "conservative"--Basically designing for a full time off grid home. It will give you a battery bank ~2x larger (two days off grid storage and 50% maximum discharge for longer life)--For various reasons, this tends to work out as a pretty close to optimum system. However, with flooded cell lead acid batteries, you can go with a 1/2 size (1/2 the AH battery bank I am going to suggest below) for an RV. The batteries will not last as long (for seasonal usage, may not matter anyway, RV batteries have a hard life and a 1/2 size bank that lasts 1/2 as many years--Kind of a wash expense wise). There are other battery technologies that can work very well (LiFePO4) for RVs (and boats, etc.)--But that will be for another post/discussion (and more $$$, at least up front for Lithium battery bank).

    Start with the array, and design a system around it. You have 14x 100 Watt panels (possibly 3x more). Assume mounted flat, but if you can tilt the array (especially if you go north during winter--upwards of 1 hour of sun per day for Alabama) can give you more energy.
    http://www.solarelectricityhandbook.com/solar-irradiance.html

    Montgomery
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a horizontal surface:
    Jan Feb Mar Apr May Jun
    2.32
     
    2.90
     
    4.06
     
    5.01
     
    5.54
     
    5.64
     
    Jul Aug Sep Oct Nov Dec
    5.70
     
    5.14
     
    4.58
     
    3.84
     
    2.68
     
    2.17
     
    Pick 5 hours a day minimum for 5-6 months of "summer" camping:
    • 1,400 Watt array * 0.52 off grid system eff * 5 hours of sun per day minimum = 3,640 WH per day
    If you can run your A/C at 800 Watts, that will give you around (3,640 WH per day / 800 Watt load=) 4.55 hours per day of A/C. And you are out of power.

    Anyway, say you want to have two days of storage of ~2,000 WH per day (small fridge, lights, computer, no A/C for cloudy weather), a battery bank would be:
    • 2,000 WH per day * 1/0.85 inverter eff * 1/12 volt battery bank * 2 days storage * 1/0.50 max discharge = 784 AH @ 12 volt battery bank (or 392 AH @ 24 volt battery bank--same stored energy, just different battery configuration)
    That is not a small battery bank (around 8x 6 volt @ 200 AH "golf cart" batteries).

    Anyway--I will stop here... Is this system going to meet your needs? Or too large/expensive, or you need more power? Things like using a Propane powered fridge can save ~1,000 WH per day (for other loads). A mini-split A/C system is much more "off grid system" friendly (or other smallish inverter-A/C system).

    Go with a 1/2 size battery bank, and it may not run your loads (if they have high starting surge, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Jarhead55
    Jarhead55 Registered Users Posts: 6 ✭✭
    Hello Bill,

    Thanks for for such a fast and excellent response. I was thinking that trying to run the 1250w 10.9a portable AC on solar was going to be a real challange. Also didn't know if the 12v or 24v system was the the best way to go. I figured I may have to run the AC off of the gen set or grid power and everything else on solar. I have a nice maxx fan on the top of the trailer and good 12v box fan to move air in the trailer if AC isn't possible.

    So without the AC will 8 panels on top and 800ah battery bank be enough for the 2 day reserve or would I still need the 12 on passenger/sun sides of the trailer?
  • Jarhead55
    Jarhead55 Registered Users Posts: 6 ✭✭
    I've seen that some people say that you need at least as many watts in panels as you have in ah's so your batteries charge as fast as possible. Don't know holds any water. I'm ignorant to it all.
  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    You do need enough panel to charge batteries to full at least every few days. Factors like season, tilt, climate, loads, and type of battery all affect the ratio. The watts=AH ratio seem high for most situations though.

    Say you have 1200 watts of panels and 120ah of battery in a 12v system. Assuming tilt etc means you get 75% of the 1200w rating, or about 900w. At 14.5v charging, that's 62a available for charging and loads. Charging 120ah of battery might take 20-25a of that.
    Off-grid.  
    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
  • Jarhead55
    Jarhead55 Registered Users Posts: 6 ✭✭
    Roger that. I found a good book today, it's basically RV solar systems for dummy's. It seem to explain it all in terms that even I can understand So I won't have to bother you all with all of the simple noob questions but I'll be back when I get stumped. Thanks for the help again.

    regards,

    jh55
  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,036 ✭✭✭✭✭
    JH55. can you share the name of the book with members?

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Sizing the system really depends on your energy usage. I suggest that if the battery bank is over ~800 AH, you probably should go up to the next voltage (i.e., 800 AH @ 12 volts = 400 AH @ 24 volts).

    The details do matter... If most of your loads are 120/240 VAC, then bank voltage does not matter too much (i.e., you do not have a bunch of 12 volt loads like HAM radios, 12 VDC adapters for electronics, etc.).

    Is the trailer heavily insulated? Getting a smaller A/C unit (window possible?) can work. We have at least one poster here that runs 4x 6 volt @ 200 AH golf cart batteries for his daytime A/C load (~200 AH @ 24 volts, as I recall).

    http://forum.solar-electric.com/discussion/comment/298553#Comment_298553

    Hopefully, Photowhit can drop by and give you some suggestions.

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Jarhead55
    Jarhead55 Registered Users Posts: 6 ✭✭
    The book is Mobile Power Made Easy, here's a link to it on amazon. $7.99 on kindle.

    https://www.amazon.com/gp/product/B0716WGW59/ref=oh_aui_d_detailpage_o00_?ie=UTF8&psc=1
  • Jarhead55
    Jarhead55 Registered Users Posts: 6 ✭✭
    Thanks for the suggestion BB I am already leaning toward the 24v system for several reasons.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    800ah @12V=
    400ah @ 24V= 8, 12V marine deep cycle $100 batteries wired series / parallel  (or just 4, and replace them yearly)
    200ah @ 48V   which could be 8, 200ah, $100 golf cart batteries.   What's going to be easier to wire up, or obtain batteries for ?
     
    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

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,