Running a fridge or freezer on an inverter or solar
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Keeping food cold is one of the main reasons people buy backup power. Fridges and freezers are easier to run than their reputation suggests, but they have two quirks that catch people out.
A fridge doesn’t run all the time
A fridge’s compressor switches on and off to hold the temperature. It might draw 100–200 W while running, but only run for part of each hour. So its daily energy matters more than its wattage.
The easiest way to find it:
- Energy label: many fridges show energy use in kWh per year. Divide by 365. A fridge rated 300 kWh a year uses about 0.8 kWh a day.
- Plug-in power meter: leave it on the fridge for 24 hours and read the kWh. This catches the effect of your kitchen’s temperature and how often the door is opened.
Older fridges and chest freezers in hot rooms can use much more than their label suggests. Measuring is worth it. See how to find your appliances’ watts.
The starting surge
When the compressor starts, it briefly draws several times its running power. Your inverter has to supply that surge on top of everything else running at the time. If the inverter is too small, or is a modified sine wave model, the fridge may fail to start, hum, or trip the inverter.
- Choose a pure sine wave inverter for fridges and freezers. See pure sine vs modified sine.
- Check the inverter’s surge rating, not just its continuous rating.
- Inverter-type fridges, with variable-speed compressors, start gently and are much easier on a backup system.
How long food stays safe without power
If the power goes out and you can’t run the fridge, keep the doors shut. The US Department of Agriculture’s food safety guidance says:
- a closed refrigerator keeps food cold for about 4 hours;
- a closed, full freezer holds its temperature for about 48 hours, or about 24 hours if it is half full.
This matters for sizing: if your outages are usually short, a modest battery that runs the fridge for a few hours may be all you need.
Tips for running a fridge on backup power
- Keep it full. A full fridge or freezer holds its temperature better, so the compressor runs less. Bottles of water fill empty space.
- Give it air. Leave space behind and above it so it can shed heat, and keep the coils clean.
- Keep the door seals tight. A worn seal makes the compressor run far more.
- Set sensible temperatures: colder than necessary wastes energy.
- Put the fridge on its own circuit from the backup system, if your installer can, so it keeps running when heavy loads are switched off.
Add your fridge and freezer to the calculator, using your measured daily energy if you have it.