One of the challenges of off-grid living is how to power a fridge. This blog post looks at our experiment on hacking a freezer to work as a fridge that uses very little energy.
Although a fridge takes relatively low power (around 50 Watts) it needs to be plugged in all day. A fridge uses power to get down to the set temperature and then switches off. Assuming that a typical fridge is powered for 8 hours out of every 24 hours, the total energy consumed by a fridge is around is 50 Watts x 8 hours = 400 Watt Hours a day.
12 V fridges are handy, but are quite expensive - costing hundreds of pounds.
A 100 Ah leisure battery has 50 % of 100 A x 12 = 600 Watt hours of energy stored - so would just about be enough to keep the fridge powered.
An often suggested way of running a fridge at much lower power is to hack a freezer to run as a fridge. Freezers generally have much better insulation than fridges and so use a lot less energy.
Fridges keep the inside temperature below 5 deg C and freezers keep the inside temperature below - 15 deg C. The device shown below can be programmed to switch the freezer off when the temperature gets down to around 4 deg C and come back on again when the temperature rises above 5 deg C.
The temperature sensor is placed inside the freezer, which is plugged into the Refrigeration Equipment socket and the Inkbird plugged into the mains. The freezer will start up and then stop once the temperature gets below 4 degrees C.
I used a small tabletop freezer for this trial. (The results with a chest freezer should be even better, as they are better at retaining the cold as it stays at the bottom). The rated energy consumption for a 24-hour period when working as a freezer was 412 Watt hours a day. Here is the rating plate for the freezer and a photo of the inside. It is only a small one - 35 litre capacity.
Having set this up, the power usage was monitored with a power meter - shown below.
We ran the trial over 5 days and then worked out the energy used. This came out as an amazingly low 120 Watt hour per day. Just for comparison, we tried the power meter on the WiFi router, which turned out to be using 200 Watt hours per day - much more than the hacked freezer.
If this freezer as a fridge is the only appliance being run off the power inverter, then a 12V fridge might be a better option. But if a power inverter is already in use then this is a great way of having a small off-grid powered fridge.
PARTS USED
Inkbird Temperature Controller - around £35 from Amazon
Power Meter (optional) - around £16 from Amazon
Cookology Table Top freezer - around £95 from Amazon
Alternative Temperature Controller
I used a lower-cost device and did the wiring myself.
Elitech Temperature Controller STC 1000 - around £14 from Amazon
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