Running a fridge or fridge/freezer on solar power
|Appliances in our test
||Whirlpool American fridge/freezer v Steca PF166
|Run it on rating
||Well worth it!
If you're already thinking that's not a fair comparison you're probably right but it's what we have in our house and therefore easier for me to measure. Besides which this is more about the feasibility rather than a side by side appliance review/comparison. Also one of the main disadvantages of upright fridge/freezers is all the cold air "falls out" when you open the door (open the door with nothing on your feet) The Steca PF166 is a chest fridge/freezer so it doesn't suffer from this problem. And neither would a mains powered fridge freezer for that matter.
The Whirlpool consumed 840 Watt hours over a 24 hour period. Although that's quite efficient for mains appliance that's a lot of power that would need to be generated by a solar panel and stored in a battery.
Battery sizing for the mains powered fridge/freezer
A medium sized solar/leisure battery can store about 1440 Watt hours of power. Because it's not a good idea to drain batteries excessively we can divide that by two (leaving 50% of charge in it) That gives us 720 Watt hours of useful power which is well under the 840 Wh (Watt hours) we need to run it. Plus it's not sunny every day so at least 3-4 days worth of reserve power must be available. Here's how I would calculate the battery size/capacity
840 Watt hours per day x 4 days of no sunshine = 3360 Watt hours
Double the size so we get a better battery life means 3360 x 2 = 6720 Watt hours
Watts are Volts multiplied by Amps so:-
A single 12Volt 200Ah (Amp hour) battery has the capacity to deliver 12V x 200Amps = 2400 Watt hours
or approx three batteries.
It's generally not a good idea to connect too many batteries in parallel. Which is what we would have to do to get 12Volts from three batteries. Batteries charge/discharge more efficiently when connected in series so connecting two 6 Volt solar batteries to get 12Volts is better. The more powerful the battery the heavier it gets so higher power 6 Volt and 2 Volt models versions are easier to source, move and install.
Two 280 Amp hour 6 Volt batteries will give us 2 x 280 Ah x 6Volt = 3360 Watt hours
Connecting another two in parallel is ok and will give us 6720 Watt hours to run our fridge/freezer. Even better would be to connect the four 6V batteries in series to give 24 Volts
Four 280 Amp hour 6 volt batteries in series gives us 4 x 280 x 6 = 6720 Watt hours. Exactly the same as having two pairs in parallel but much better for the batteries. To learn more about connecting solar batteries and how to connect them visit our help pages
on this subject.
Number of solar panels required for the mains fridge / freezer
We have already calculated the power consumption and how big the batteries need to be so we know that after 4 days of little sunshine 3600 Watt hours of power need to be put back into the batteries. A 100 Watt solar panel will produce about 75 Watts in good conditions. If the panel is in full sunshine for 5 hours it will produce 5 Hours x 75 Watts = 375 Watt hours of power. So that's 10 solar panels? Well no not quite because some of the time the sunshine will be running the fridge as well as charging the batteries. So probably 6-8 will suffice. That's still a considerable number of solar panels just to run a fridge freezer.
Battery sizing for the Steca Solar Fridge
The Steca PF166 , when used in Freezer mode (-18C) consumes about 300 Watt hours per day and when it's in fridge mode (+3C) it consumes an incredible 72 Watt hours. So if you had two of them one as a fridge and the other as a freezer total power consumption is less than half the mains powered fridge. In fact in most circumstances the PF166 will run off two 80 Watt panels and a small 90 Amp hour battery.