# Solar Powered Deep Freezer Fridge

WolfMT Registered Users Posts:

**21**✭✭ Here is the plan:

15 Cubic foot Freezer Converted to Fridge

1000w Pure Sine Inverter (Tripp Lite)

320w Solar Panels

4 each 6 volt batteries

no charge controller yet

looking at 30A controller MPPT

Any thoughts??

15 Cubic foot Freezer Converted to Fridge

1000w Pure Sine Inverter (Tripp Lite)

320w Solar Panels

4 each 6 volt batteries

no charge controller yet

looking at 30A controller MPPT

Any thoughts??

## Comments

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33,546adminAnd, we do not know how much energy the freezer will use as a refrigerator... Just to be relatively conservative, lets guess 500 WH per day. 2 days of storage, and 50% maximum discharge (longer battery life) on a 12 volt battery bank:

- 500 WH per day * 1/0.85 AC inverter eff * 2 days storage * 1/0.50 max battery discharge * 1/12 volt battery bank = 196 AH @ 12 volt battery bank

So--While you should be able to run with a 200 AH @ 12 volt battery bank (2x 6 volt @ 200 AH golf cart batteries)--With a flooded cell battery, I would recommend a 480 AH @ 12 volt battery bank to support ~1,200 Watt starting load (AGM can use the 200 AH @ 12 volt battery bank).Suggest 5% to 13% rate of charge for battery bank--And 10% or more for full time off grid (vs weekend/seasonal system usage). The solar array for such a battery bank would be:

- 480 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 452 Watt array minimum
- 480 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 903 Watt array nominal

- 480 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 1,175 Watt array "cost effective" maximum

Note, the larger the battery bank, the larger the suggested minimum array.Then there is sizing array based on energy usage and by season... You did not say if this was for backup power, full time off grid, inside or outside, generator backup, other power usages (LED lighting, cell phone charging, laptop computer, etc.)... A nominal system design would look like (assuming Missoula Montana):

http://solarelectricityhandbook.com/solar-irradiance.html

## Missoula

Measured in kWh/m2/day onto a solar panel set at a 43° angle from vertical:Average Solar Insolation figures

(For best year-round performance)

- 500 WH per day * 1/0.52 off grid system eff * 1/3.75 Hours of sun per Feb day = 256 Watt minimum array (Feb break even)

If, you expected 500 Watts per day, and little to no genset backup, then you should run daily power usage to 65-75% of designed power output (to allow for some bad weather), and if you pick December as break even month:- 500 WH per day * 1/0.65 daily power usage * 1/0.52 off grid system eff * 1/2.37 Hours of sun per Feb day = 624 Watt array minimum (12 months per year)

If we go back to suggested minimum solar array for battery bank (based on starting surge current), it was ~903 Watt array for 10% rate of charge with a 1,200 Watt minimum AC inverter....So--Without knowing much about where you are located, if you will use genset for winter/bad weather, etc... At this point, I would be suggesting a ~903 Watt minimum array (note, solar math is not that exact.... I am using 903 Watts so you can see where I am pulling the numbers from -- Anything within ~10% is pretty much "exact" in solar power estimate).

And possibly a larger AC inverter (1,200 Watts minimum)... It is possible that your 1,000 Watt Tripplite will work fine for you--I just do not know.

Also, with a 903 Watt array--You will have lots of extra power for much of the season...

- 903 Watt array * 0.52 off grid AC system eff * 3.75 hours of sun (9 months of the year) = 1,761 Watt*Hours per day

That is enough to keep a cabin well lite and the folks entertained (laptop, cell phone, LED TV) and probably a 12 volt RV water pump for plumbing (surface water, or use deep well pump + cistern + genset or a "solar friendly" deep well pump).Your corrections/questions about my guesstimates?

-Bill

295✭✭✭1,386✭✭✭✭Consider buying the freezer somewhat larger than needed (it doesn't add much to the energy usage) and then fill all the unused space with water jugs. This should allow turning it off for significant periods (perhaps 3am to 9am), saving some wear on the batteries and generator.

I am available for custom hardware/firmware development

3,830✭✭✭✭However...wattage while running varies a bit. Didn't expect that. Up to 80 watts while running. Only had it a week.

21✭✭21✭✭21✭✭21✭✭3,830✭✭✭✭33,546adminDo you want simple or computer logging or even Ethernet?

-Bill

21✭✭21✭✭21✭✭3,830✭✭✭✭33,546admin-Bill

21✭✭21✭✭33,546adminSay you want 3x panels in parallel at 26 amps for 20 feet with 1% to 3% voltage drop. Using a basic voltage drop calculator:

http://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=1.296&

voltage=18.5&phase=ac&noofconductor=1&distance=20&distanceunit=feet&eres=26&x=62&y=166 awg:

Voltage drop:

0.41Voltage drop percentage:

2.22%Voltage at the end:

18.09

2 awg:Voltage drop:

0.16Voltage drop percentage:

0.86%Voltage at the end:

18.34You can see that is pretty heavy copper cabling... If you instead put 3x panels in series (2 is really recommended for MPPT--A bit less MPPT controller heating/losses):

http://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=13.17&voltage=55.5&phase=ac&noofconductor=1&distance=20&distanceunit=feet&eres=8.65&x=50&y=11

16 awg:

Voltage drop:

1.39Voltage drop percentage:

2.50%Voltage at the end:

54.1112 awg:

Voltage drop:

0.55Voltage drop percentage:

0.99%Voltage at the end:

54.95So--An MPPT controller will allow you to use much less copper for your wiring run (probably 14 AWG or heavier wire recommended for mechanical strength).

A nice 30 amp MPPT charge controller (not cheap @ $290):

https://www.solar-electric.com/midnite-solar-kid-mppt-solar-charge-controller.html

And a simple 30 amp PWM charge controller ($90)

https://www.solar-electric.com/midnite-solar-brat-pwm-solar-charge-controller.html

Notice the besides saving on the costs of copper at higher array (and battery) voltages (higher voltage means lower current)--The charge controllers are typically rated for a maximum current... On a 12 volt battery bank, you are looking at a ~480 Watt maximum array with 3x panels (in series or in parallel) and a 30 amp controller. With a 24 volt battery bank, the same controllers will manage a 2x larger array (~960 Watts--Or a bit more for MPPT).

Doing a couple of paper designs to see what works best (price/performance/needs) for you. With PWM controllers, you are typically limited to "12 volt" (Vmp~18 volt) panels on a 12 volt battery bank. With MPPT you can use "Grid Tied" panels with Vmp~30 volts or higher on the 12 volt battery bank--"GT Panels" are around 1/2 the cost per Watt vs "12 volt" panels... Spend less on solar panels (and wiring) and spend more on MPPT charge controller(s)--You need to do a paper design to see what works best for you.

Typically--Less than 400 Watt systems work out fine with PWM controllers. And >800 Watt arrays, typically MPPT charge controllers end up being a better choice.

-Bill

21✭✭