Solar refrigerator.

patrickp8616
patrickp8616 Registered Users Posts: 6 ✭
in Solar Beginners Corner #1
Ive tried to figure the math but cant. I need to know how many panels, MPPT Controller size & battery bank to get to operate an "Engle 12 vdc 2.8 amp Refrigerator" 24/7. The specs say it runs between .7 to 2.8 amps. Theres only me so I would only open it 3-4 times a day.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Solar refrigerator.

    You'll never get exact power consumption numbers for anything, especially not a refrigerator. Part of this is because they operate with a thermostat (except the cheap ones) and so have a duty cycle which is variable.

    So you need a margin for error.

    If it draws 2.8 Amps for 24 hours that's 67.2 Amp hours. If it's duty cycle is 1/3 of the time (typical but not absolute) then it will only draw 22.4 Amp hours. Which do you pick? That would depend on what would happen if you run out of power (how critical the load is and what back-up power is available).

    As it is 67.2 Amp hours would be a minimum 134.4 Amp hour battery, or up to 268.8 Amp hours for 25% DOD. A compromise in between these sizes is likely as batteries don't come tailor-made. In all likelihood the bargain GC2's at 220 Amp hours would do the job.
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  • patrickp8616
    patrickp8616 Registered Users Posts: 6 ✭
    #3
    Re: Solar refrigerator.
    Cariboocoot wrote: »
    You'll never get exact power consumption numbers for anything, especially not a refrigerator. Part of this is because they operate with a thermostat (except the cheap ones) and so have a duty cycle which is variable.

    So you need a margin for error.

    If it draws 2.8 Amps for 24 hours that's 67.2 Amp hours. If it's duty cycle is 1/3 of the time (typical but not absolute) then it will only draw 22.4 Amp hours. Which do you pick? That would depend on what would happen if you run out of power (how critical the load is and what back-up power is available).

    As it is 67.2 Amp hours would be a minimum 134.4 Amp hour battery, or up to 268.8 Amp hours for 25% DOD. A compromise in between these sizes is likely as batteries don't come tailor-made. In all likelihood the bargain GC2's at 220 Amp hours would do the job.

    Thats great so far. Now, how much panel do I need? PS, Its a dual 12 / 24 vdc system, would I be better off at 24 vdc?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Solar refrigerator.
    patrickp8616 wrote: »
    Thats great so far. Now, how much panel do I need? PS, Its a dual 12 / 24 vdc system, would I be better off at 24 vdc?

    You're always better off at 24 Volts if 12 isn't needed; higher Voltage is more efficient and allows handling the equivalent power with lighter wire gauge.

    If you're going to recharge 220 Amp hours @ 12 Volts under typical conditions you need approximately (22 Amps * 12 Volts / 0.77) 343 Watts of panel on an MPPT controller or (22 Amps * 17.5 Volts) 385 Watts on a PWM controller. This is right near the 400 Watt threshold where the GT panels & MPPT controller become more cost-effective. Naturally you need to find panels that fit the Wattage requirements, and it's always better to have more rather than less.

    If you were going to do 220 Amp hours @ 24 Volts you'd have to double up the batteries and the panels to provide the power. As a result you'd have twice as much capacity as you need for just the refrigerator.
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