Runtime by power station size: Refrigerator (full size)
| Power station size | Typical runtime | Realistic range |
|---|---|---|
| 300 Wh | 4 h 15 min | 2.8–6.4 h |
| 500 Wh | 7 h 5 min | 4.7–10.6 h |
| 1,000 Wh | 14 h 10 min | 9.4–21.3 h |
| 1,500 Wh | 21 h 15 min | 14.2–31.9 h |
| 2,000 Wh | 28 h 20 min | 18.9–42.5 h |
| 3,000 Wh | 42 h 30 min | 1.2–2.7 days |
Why a 150 W fridge doesn't use 150 W all day
The label on a refrigerator, or a watt meter reading taken while it hums, shows the running watts: often 100–250 W. But the compressor only runs part of the time. Once the inside is cold, it switches off until the temperature creeps back up. Over a day, most modern fridges use 1–2 kWh, which works out to an average of 40–90 W.
That average is what drains a battery, so runtime estimates that divide capacity by the label watts come out far too short.
The startup surge decides which stations work
When the compressor kicks on, it draws a spike of several times its running power for a fraction of a second, typically 600–1,200 W for a full-size fridge. If the power station can't deliver that spike, it shuts off or the fridge fails to start. In practice:
- 300 W stations (like 256–300 Wh units) often can't start a full-size fridge, even when the running watts look fine. Some cope with small or inverter-compressor models.
- 1,000 W+ stations with a pure sine wave inverter generally start household fridges without trouble.
Inverter (variable-speed) refrigerators ramp up gently and have much smaller surges. If yours is one, check the manual: it is usually stated on the spec sheet.
Find your fridge's real number
- Look for the yearly kWh figure on the EnergyGuide label (US) or energy label. Divide by 8,760 hours and multiply by 1,000 to get average watts. For example, 500 kWh/year ÷ 8,760 × 1,000 ≈ 57 W.
- Or plug the fridge into a watt meter for 24 hours and read the kWh. Divide by 24 to get the average in kW.
Put that average into the calculator above instead of the default for a much better estimate.
Make the battery last longer during an outage
- Keep the doors shut. A closed fridge stays cold for about 4 hours with no power at all.
- Run it in shifts: power it for an hour or two, then unplug it for a few hours. The food stays cold and the battery lasts far longer than running it non-stop.
- Turn off ice makers and door heaters (the "energy saver" switch on some models).
- Fill empty space with jugs of water. Thermal mass holds the cold.
- Pair the station with solar panels: see the solar recharge time calculator to check how much a day of sun puts back.