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  • 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
    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.
    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 ||

    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||

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

    Comment


    • #3
      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.

      Comment


      • #4
        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.
        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 ||

        || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||

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

        Comment


        • #5
          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.

          Comment


          • #6
            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.

            Comment


            • #7
              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.

              Comment


              • #8
                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.

                Comment


                • #9
                  Many of the off grid guys use propane fridges and stoves because of this problem.

                  Russ
                  sigpic

                  Comment


                  • #10
                    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.

                    Comment


                    • #11
                      Sorry - No one can not help for the survivalist type scenarios.

                      With many things to worry about in the world that is down around number 1000 for me.

                      Solar flares are not of a concern - you are really talking about civil insurrection - in which case an open display of lighting, panels and all will make a wonderful target.

                      Russ
                      sigpic

                      Comment


                      • #12
                        Thermoelectric Cooling (Peltier Element) only gives about a 40f differential from the hot to cold side. And it's about 10x worse power than a compressor fridge.

                        So we really need some accurate figures for your fridge, to calculate the battery and solar requirements.

                        Additionally, when the SHTF, there may not be that much worth cooling after a few weeks.

                        And most mini-fridges are WORSE energy hogs than the 18cf fridge/freezer I have, that is energy star rated.
                        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 ||

                        || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||

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

                        Comment


                        • #13
                          Solar Flare

                          Some may not consider flares a threat but it has happened before and NASA says it is guaranteed to happen again, and probably in the next 12 years. The last big one in the 1860's did little damage because there was no grid. But a SMALL one just 13 years ago wiped out the grid throughout eastern Canada. Bury your head in the sand at your own peril. If another big one hits, as NASA expects, the grid could be down from 5 months to nearly 10 years. No electricity means almost nothing will work, and no communications. Thanks anyway, folks - I'll find a non-solar solution.

                          Comment


                          • #14
                            As a PS to Russ

                            Thanks for your input. However, 1) we are not concerned with insurrection, 2) we live so far in the boonies and so far from the road that lighting would not make a "target", and 3) if we did have lighting (which my posts never even suggested) visibility can easily by avoided by restricting it to a sealed room (cardboard, duct tape etc.) if necessary. Your response simply did not address the question at hand, and assumed far too much. But thank you for taking an interest.

                            Comment


                            • #15
                              Solar flares (the really big ones) will fry the large transformers at main power plants and induce high voltages and currents in long wires. There was an instance of Rail Road track melting from the induced current .
                              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 ||

                              || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||

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

                              Comment

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