Solar Generator

Crystal Solar Expert Posts: 128 ✭✭✭
edited March 2019 in Solar Beginners Corner #1

I've been throwing the solar generator idea around. I currently live in my camper van...yes in Minnesota and by choice. Thankfully on the really cold nights I've been offered a place to stay. Anyways now spring is on it's way and I would like to have a small solar system to run a few LEDs lights, phone, tablet, and 5 amp dc cooler.

I was wondering if the idea of getting one of those "goal zero" type solar generators, charging it with a panel and then hooking up a car battery charger to it to charge the camper van battery would be an efficient idea.

I'm looking to keep it simple and portable. I like the idea of the lightweight affordable lithium ion batteries the units offer.

Any suggestions are appreciated.

Thank you in advance!


  • BB.
    BB. Super Moderators, Administrators Posts: 33,398 admin

    You need to know your energy usage... All of the stuff you listed are "small loads"--Until you hit the 5 amp DC cooler--That can take a lot of energy.

    For a "typical" DC cooler, they use a Thermoelectric (Peltier) Cooler--Basically dissimilar metals that when you put current through them they get cold (at one junction, and hot at the other). Many coolers, you can reverse the plug and use them to keep things warm too.

    Anyway, this type of cooler uses 5 amps 24 hours per day (and are not very efficient vs a standard compressor type refrigerator/freezer):

    • 5 amps * 12 volts * 24 hours per day = 1,440 Watt*Hours per day

    Or as much energy as a typical full size Energy Star Home refrigerator.

    Mostly, "Solar Generators" tend to be smaller systems that can only supply maybe a 1,000 WH (80 AH * 12 volts = 960 WH battery bank--Just a guess/example)--Which would not even supply power to your cooler for 1 full day.

    In the end, you need measure your loads (using a KIll-a-Watt type meter, or a DC AH/WH meter, or similar) to see what you need. And pencil out a system that will supply the energy you need. Then start picking equipment (don't pick the equipment first and see if it will work).

    Here are some examples of various types of units:

    • Thermoelectric cooler--inexpensive, small cooling unit, lightweight, typically cool ~40F below ambient (keep drinks and food "cool" in average weather). Not energy efficient
    • 3 way refrigerator (DC, AC, propane) absorption--Running propane, pretty fuel efficient (~1 lb or so of propane per day). AC and DC modes, very inefficient. Can have issues with ventilation (propane flame) and cleaning combustion area.
    • DC compressor (12/24 volt models common)--Most efficient DC electric solution. Low maintenance, not cheap. Can use a smaller solar power system--But still need to measure your loads and plan an off grid system to support it (DC fridges can also be run from solar panels only--Cools only when sun is up, some sort of metal plate, frozen water, etc. to "store" cold when no sun).
    • And, of course the 120 VAC home refrigerator/freezers--Energy Star models are pretty efficient. Need an AC inverter for solar. Need a "Medium Size" solar power system (neither small or cheap).


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭

    Helped out a farmer who needed a refrigerator ad a few lighs, rather than using an inverter I ordered a small DC compressor refrigerator, it's pretty small, much like the thermoelectric cooler, but unlike them it does not need to run all the time. The solar side is a 12V 130Ah battery and 160W PV. They are not cheap in comparison to a small AC refrigerator about double what they cost, but it eliminates the inverter cost, it's self consumption and inherent efficiency losses.

    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • Crystal
    Crystal Solar Expert Posts: 128 ✭✭✭


    Would like to get a propane fridge...I can vent it out easily. Just need to find an affordable one.

    I guess my main question it efficient to get the solar charger and plug in the van battery charger to charge in-house battery to run the lights and devices? I will be charging the solar generator with a panel.

  • BB.
    BB. Super Moderators, Administrators Posts: 33,398 admin

    Generally, running a parked car/van and charging batteries is not very fuel efficient. And it makes wear and tear on your vehicle too (added maintenance). Also, vehicle charging systems don't really charge at high enough voltage (usually 13.8 to 14.4 volts for car, 14.75+ needed for "good charging" of a flooded cell lead acid battery).

    Now--You can run a DC to DC or AC to DC battery charger from your van to quickly/properly recharge the battery bank--But that is with added costs of an AC inverter and possibly a second battery charger.

    If you are driving the van a couple hours (say round trip once or twice a week to town), it can be OK (again with a DC or AC input battery charger--Not directly connecting to the battery bank--In general).

    To know what makes sense for you--Need actual loads and charging conditions.

    I think you are up north (near Fargo ND)?... Obviously, during winter, you may have less than 3 hours a day... But February through October, you are >3.5 hours of sun per day.

    You simply need to figure out how much energy, per day (by season) you need, then figure out the rest of the math. I guess that you would be OK with 500-1,000 WH per day... A 12 volt Flooded Cell Lead Acid battery bank with 2 days storage and 50% maximum discharge:

    • 500 WH per day * 1/12 volts * 2 days storage * 1/0.50 max discharge = 167 AH @ 12 volts

    A Li Ion battery, you may get away with a 100 AH battery bank.

    ~And regarding sun:

    • 500 WH per day * 1/0.61 DC system eff * 1/2.25 hours of sun (Fargo December) = 364 Watt array December "break even"

    You will probably need a genset during winter--Especially when the weather turns bad.

    And, for a reliable system, I would suggest a minimum of 10% rate of charge for full time off grid:

    • 167 AH * 14.5 volts charging * 1/0.77 panel+controller deratings *0.10 rate of charge = 314 Watt array nominal

    A pair of 6 volt @ ~200 AH golf cart batteries in series (12 volts @ 200 AH battery bank). Or, less (167 FLA or AGM @ 12 volt)--Or ~100 AH @ 12 volt lithium battery bank. And, if you need power in winter, a backup genset of some sort (possibly even your vehicle short term) would be a good idea.


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Crystal
    Crystal Solar Expert Posts: 128 ✭✭✭
  • Crystal
    Crystal Solar Expert Posts: 128 ✭✭✭
    edited March 2019 #7

    I think this will fit my needs with appropriately sized panel.

    I can then plug a car charger into this and charge the inhouse battery for the camper van. I plan on increasing battery bank if needed.

    Any more advice is appreciated!

  • BB.
    BB. Super Moderators, Administrators Posts: 33,398 admin
    edited March 2019 #8

    I am always very leary of these lithium battery packs. Usually, they do not really even list their actual capacity (Amp*Hours and no voltage listed) and they give capacity for "larger" battery packs in mAH (1,000 mAH = 1 AH) to make them look good.

    For example, 444 Watt*hour and 20,000 mAH... The math:

    • 444 WH / 20 AH = 22.2 volts battery bus (???)

    While it is possible that there is a 22 volt battery bus internally (6x 3.8 LiFePO4 cells in series), I am not sure there is (would require power supplies to charge and discharge from a 12 volt source). So, I don't really trust the original specifications.

    And a 22.2 AH battery (at 12 volts?) is probably 1/4th the capacity of your car battery.

    Now--If you only need 20 AH @ 12 volts or 400 WH maximum battery bank to run your stuff over night... Then a Li Ion battery bank can be pretty nice (no electrolyte levels to check, faster charging, etc.). It certainly would run some 12 volt LED lighting, tablets, and cell phone charging for a couple nights (assuming it has a 12 volt output).


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭

    And when you get the box, it's the size of a portable 1TB hard drive. Wow, 20Ah - or add 0's and call it 20,000mAh yeah, that's much bigger !

    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: ,