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Refrigerator runtime calculator

A power station runs a fridge for usable watt hours divided by average fridge watts. Enter your station and either your fridge watts or its energy label. You then see the runtime in hours, whether it lasts overnight and a full 24 hours, and the station size needed for a full day.

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Your station and your fridge

Choose how you know your fridge use. The label path is best when you have the kilowatt hours per year figure.

Kitchen with an open refrigerator and dishwasher

How the calculator works

  • Watts path. average watts = running watts × duty cycle. Daily energy = average watts × 24. At 150 W and 50 percent, that is 75 W average and 1,800 Wh a day.
  • Label path. daily energy = kilowatt hours per year × 1,000 ÷ 365. At 365 kWh a year, that is 1,000 Wh a day and about 42 W average.
  • Usable capacity = capacity × inverter efficiency × (1 minus the reserve). With the defaults, a 1,000 Wh station gives 765 Wh, the same 0.85 planning basis as our runtime calculator.
  • Runtime = usable capacity ÷ average watts. The 24 hour size divides one day of energy by efficiency and reserve, then adds the same 20 percent margin used across the site and rounds up to a common station size.

Runtime does not prove the station can start the fridge. Before you rely on it, check the station surge rating against the compressor start. Many fridges need roughly 800 to 1,200 W for a moment, and it varies by appliance. To add lights, a router or a CPAP to the same station, use our power station runtime calculator. To plan panels to refill it, use our solar charging time calculator.

How long food stays safe if the fridge goes off

A power station buys time, but it helps to know how much time the fridge already has on its own. The USDA and CDC say a refrigerator keeps food safe for up to 4 hours with the door closed. A full freezer holds a safe temperature for about 48 hours and a half full freezer for about 24 hours.

After that the test is temperature. FoodSafety.gov says perishable food that has been at 40°F (4°C) or above for more than 2 hours should be thrown out. So a station that keeps the fridge at or below 40°F for part of each day, with the door kept shut in between, can protect food even when it cannot run the fridge nonstop. Keep an appliance thermometer inside so you can see the temperature without guessing. Our guide to how long food lasts in the fridge without power lists what to keep and what to throw out, food by food.

Frequently asked questions

How long will a power station run a refrigerator?

Divide usable capacity by the average watts of the fridge. A 1,000 Wh station at our 0.85 efficiency and 10 percent reserve gives 765 Wh usable. A fridge averaging 75 W therefore runs for about 10.2 hours, and one averaging 42 W from a 365 kWh a year label runs for about 18 hours.

Should I use running watts or the energy label?

Use the energy label if you have it, because kilowatt hours per year already includes compressor cycling. Divide it by 365 for kilowatt hours a day. Use running watts with a duty cycle only when you have no label, because a fridge compressor commonly runs about 30 to 50 percent of the time, and more in a hot room.

What duty cycle should I use for a fridge?

Start at 50 percent if you only know running watts. With 150 W running, that gives 75 W average and 1.8 kWh a day. Lower it towards 30 to 40 percent for a modern efficient fridge in a cool room, and raise it in hot weather or with frequent door opening.

Will the station start my fridge?

Runtime is only half the check. A fridge compressor can need roughly 800 to 1,200 W for a moment at startup, and this varies by appliance. The station surge rating must clear that plus anything else running. Check the fridge label or manual and the station surge rating on the maker page.

What size power station do I need to run a fridge for 24 hours?

Take the daily watt hours, divide by 0.85 for efficiency and by 0.9 for the reserve, then add margin. A fridge using 1.8 kWh a day needs about 2,353 Wh of rated capacity before margin, which rounds to a 3,000 Wh class station with the 20 percent planning margin this tool uses.

Sources

Figures are typical values for planning, not a substitute for your appliance labels or an electrician's load calculation.

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