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Thread: Solar Refrigerator

  1. #1
    Junior Member
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    Default Solar Refrigerator

    I'm so new it hurts. Have refrigerator uses 100 watts. Plan to build my own panels. Need to know how many 18V panels are needed and how many T105 deep cycle batteries needed to run the fridge full-time. I get about 4.5 - 5 sun hours/day, and want enough charge to a) run the unit for up to 4 no-sun days and b) still keep the batteries charging. Please help! I am not well-versed in electrical stuff (or solar, really). Thank you

  2. #2
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    Default

    First, you will have to measure your fridge, since it does not run all the time.
    100w for 13 hours a day is different than 100W for 4 hours a day. Is your fridge 12Vdc or 120Vac ? If it's AC, get a Kill-o-watt meter (about $25) and plug the fridge in, and measure it for a week. 2x a day, open it, take out a bottle of cold water, and put in a bottle of room temp water. This will give you an idea of how much power you can expect it to draw.
    If it's 12Vdc, it's much harder to measure it's consumption, as you will need an expensive battery monitor.

    Or we can assume worse case, it runs 18 hours a day (75% on)
    100 x 18 hrs = 1800watt hours from the batteries.
    4 days = 7200wh consumed. Since you only want to pull batteries down to 50% (any more severely shortens their life) you need 14,400 wh in the battery bank, so converting to amps (divide by 12 ( watts/volts ) ) = 1200AH

    A t-105 battery is 6V, 220ah and can hold (volt x amps) 2640Wh. the earlier 14,400wh divided by 2640 means you need 5.4 batteries. Since you need them in PAIRS, you need 6 batteries, of 3 parallel strings of 2 . [ 2, 6v in series gives 12V ]

    So, the voice of experience will now tell you it's foolish to plan for 4 days, because:
    1) extra batteries
    2) by day 3, the batteries have already had 2 days to sulfate and be damaged, even more damage by day 4.
    3) it will take a lot of solar to recharge the 6 batteries in 1 sunny, 4 hour solar day.

    You need to consider a generator you can start up, and power a battery charger with on day 3.

    Continuing on 4 day assumption, you have 2 hours to get the bulk charge into the batteries, and 2 hours for the absorption stage, which is shortchanging the batteries, but that's your prescribed scenario.

    You have 7200wh to replace, and adding all the losses (recharge efficiency, PV losses, controller losses) you have to HARVEST 14400wh in 2 hours (7200W each hour). Using 200W panels, at about $500 each, that's only 72 panels. Whoops! 3 days looks a lot better. That will both boil your batteries, and still leave them low at sunset.

    Who told you this would be cheap ??

    I've laid out the numbers above, you can play with them and see what you can afford.
    Since the dawn of time it has been mankind's dream to blot out the sun.
    Montgomery Burns

    "Always listen to experts. They'll tell you what can't be done and why. Then do it."

    spreadsheet based voltage drop calculator:
    http://www.solar-guppy.com/download/...calculator.zip
    http://www.solarpaneltalk.com/showth...oss-calculator

    http://www.mike-burgess.org/PVinfo_2.html

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,
    battery lugs http://tinyurl.com/LMR-BigLug
    Setting up batteries http://tinyurl.com/LMR-NiFe

    gear :
    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 || || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

  3. #3
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    Feb 2011
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    Default So how do others do it?

    Thank you (I think ) Some people power their entire place with solor. Since there are often periods of no-sun days I would assume they store enough to cover that. But according to your post, a simple 100W fridge would be virtually impossible to run on solar. I do not doubt your figures, but I'd like to know how it IS done. I am simply trying to plan for refrigeration in a world where both electricity and fuel supplies are interrupted long-term. Which means no generator. I just want to be able to refrigerate food, long term. Any ideas that won't require winning the lottery just to keep a slab of bacon cold? By the way, fridge can run either AC or DC.

  4. #4
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    As you can see from my .sig, I have a 3KW PV array, and a 48V 400Ah battery bank.
    I run a 1/2hp water pump 3 hours a day in summer, and a fridge. My fridge is an Energy Star rated fridge, and uses about 400KWh a year. This is a little over 1Kw daily. I also have a generator used in cloudy weather. I will be building a house soon, and increasing my array and battery bank so I can live there full time. I currently have to shut down after 1 cloudy day if I don't start the generator.

    You have to look at what your fridge uses and re-calculate your solar and battery need.
    Since the dawn of time it has been mankind's dream to blot out the sun.
    Montgomery Burns

    "Always listen to experts. They'll tell you what can't be done and why. Then do it."

    spreadsheet based voltage drop calculator:
    http://www.solar-guppy.com/download/...calculator.zip
    http://www.solarpaneltalk.com/showth...oss-calculator

    http://www.mike-burgess.org/PVinfo_2.html

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,
    battery lugs http://tinyurl.com/LMR-BigLug
    Setting up batteries http://tinyurl.com/LMR-NiFe

    gear :
    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 || || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

  5. #5
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    Join Date
    Feb 2011
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    Default Thanks...

    Thank you. But I just do not understand how some folks run a home on solar when I can't even run a small fridge with any consistency. Seems like solar is a complete waste of time. Maybe I'll go with wind - I have the components for a system that can generate about 60Kwh/month, or nearly 700/year. But it can be a pain to maintain.

  6. #6
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    Dec 2010
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    Qld Australia
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    Default

    I think the problem in what you asked for is that you wanted to allow for 4 days with no sun, that is where the battery bank becomes very big and the panels to charge it back up become very numerous.

    I live on stand alone solar but use a generator and charger to keep my batteries from getting to low when there is little sun, and the genset runs bigger appliances etc.

    The reply was also based on a worst case as there is not the required info for a proper reply.

    So you may well be able to run your fridge on solar but you will need to know how much power it actually uses as suggested, the area you live to factor the sun hours etc.

    If you can provide the correct info then this will allow for a good estimate of the requirements, if you have wind or water power avail this can be factored in.

  7. #7
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    Default The fridge

    No way to tell useage - not currently using it and would use it strictly DC. However...looking at the Coleman Powerchill as another option. Built to use on boats, trucks etc. Doesn't list the wattage but it says it can run on one battery (marine) for about 18 hours - about 8-9 hours if you only run the battery down to 50%. Other than that I have no real info except the amps are .6 - 2.3. Again, my panels would be 18v. As for the wind turbine, I would really rather avoid that and keep the components on hand just in case a greater need arises someday.

  8. #8
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    Default

    The coleman power chill is listed as having "Thermoelectric Cooling (Peltier Element)." To me that is not good for low power consumption. Its not only about how many amps a
    fridge uses to run but how much power it uses to keep it cold in a 24hr period.
    Generally element types are not low in power consumption and take a long time to cool. Units with a compressor may even use more amps to run, but over a 24hr period they will use less power to keep the temp down as the compressor can cool faster, so it does not run for many hours in the day.
    To say a fridge will run on one battery for X time really means nothing, there are to many variables.
    Stand alone solar stuff is very expensive, without actual power consumption figures, over extended periods, to base systems on, its all really just guess work.
    You can set up a system without good data but you will either spend a lot more than you needed, or usually the system will not be correct and the batteries will be dead in a very short time.

  9. #9
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    Default

    Many of the off grid guys use propane fridges and stoves because of this problem.

    Russ

  10. #10
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    Join Date
    Feb 2011
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    Default No can do (propane)

    If you read my thread you would uinderstand the purpose is to be prepared in the event of no electricity OR fuel for a substantial period of time - such as a solar flare knocking out the grid for months. No power, no propane deliveries. No gas pumping. Not much of anything. But still would like to keep food from spoiling.

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