Home Backup

One of the most frequent questions we get is “what do I need to keep the fridge or freezer running during a power outage?” Well, that depends a lot on what fridge or freezer you have, so let’s dive into the deep end and see if we can make this a bit clearer.

Power Explained

Power is measured in Watts – you may have seen this on light globes, where there are several wattages available. The larger wattage equates to brighter light, for the same types of light globe. Other appliances will also have a wattage printed on a label somewhere showing how much power they use.

To work out how much power an appliance uses over time, we multiply the wattage by the time (hours). As an example, a 23 Watt light bulb running for 30 minutes uses 23 x 0.5 = 11.5 Watt hours. For a 2000 Watt heater running for 2 hours, the calculation is 2000 x 2 = 4000 Watt hours.

Power Ratings

So, what about my fridge? Most appliances these days have an annual power rating – just Google ‘Energy Ratings’ and you will probably be able to lookup your fridge model. Once you have the annual figure, divide that by 365 to get the daily power consumption.

For example:

240 Volt 700 litre side by side fridge freezer – 1250 Wh per day.
240 Volt 400 litre upright fridge/freezer – 930 Wh per day.
240 Volt 300 litre chest freezer – 940 Wh per day
240 Volt 120 litre bar fridge (no freezer) – 330 Wh per day.
12 Volt 50 litre portable refrigerator – 300 Wh per day.

You can see that the smallest fridge uses about one quarter of the power of the largest fridge, so it makes a big difference to what size power station you need.

Selecting a Yeti Power Station

If we wanted to run the 700 litre fridge for one day, we would need at least Yeti 1500X (1516 Wh) but the 400 litre fridge would only need a Yeti 1000X (983 Wh).

Stepping up to a Yeti 3000X (3032 Wh) would give you two days for the 700 litre fridge, over three days for the 400 litre fridge and nearly ten days for the bar fridge.

What about solar panels?

Adding some solar panels to the mix will allow you to extend the run times for any of the power stations.

Solar panels are rated by the power they produce, in Watts, under controlled conditions. Solar panels are rated using the amount of light at the equator at midday, at 90 degrees to the panel and a temperature of 25 degrees Celsius.

When we use those same panels, we are unlikely to get same power since panels in the sun get hotter (less efficient), the angle of the sun to the panels changes over time, we don’t all live at the equator and it isn’t midday all day!

The real-world output from a solar panel is between 50% and 80% of the rating – so a 100 Watt panel will give you between 50 and 80 Watts. Melbourne in Winter gets about 3.1 ‘good sun’ hours per day, Sydney 3.8 and Brisbane 4.5. In summer these all go up to about 6 hours per day.

To collect enough solar energy to run that 700 litre fridge for a day (1250 Wh), in Melbourne in Winter, we need 1250 Watt hours/3.1 hours = 403 Watts from the panels for those 3 hours. If we say we get 70% of the rated power from the panels, then that is 403/0.7 = 576 Watts – plus some extra as things aren’t 100% efficient, so call it 600 Watts worth of panels.

The same calculations for the 400 litre fridge are 930/3.1 = 300 Watts. At 70%, that is 428 Watts worth of panels.

Summary

All these calculations are theoretical and are provided for educational purposes.

You will likely want to add some additional battery and solar capacity to allow for cloudy weather, etc.

It is always a good idea to speak with one of our sales professionals if you are unsure of any aspect of your project.

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