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The average domestic fridge uses 350kWh of electrical energy per year and would need 300 watts of solar panels to supply it. A 100Ah would also be needed as reservoir to supply compressor motor surge current and to run the fridge through the night when the solar panel generates no power.
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How to work out what size solar panel for a refrigerator
Domestic fridge compressors draw power in cycles, as the motor stops and starts according to the temperature fluctuations inside.
For solar panel sizing it’s best to use the average energy used over a period of time, but sometimes the current draw will be low and sometimes high.
For this reason I recommend supporting correctly sized solar panels with a deep-cycle battery and an inverter. The battery acts as a power reservoir to supply high compressor starting currents.
Video – How many watts does a refrigerator use on average
How much power does a fridge use?
Instantaneous power draw by any fridge is misleading, because the compressor motor only runs about 50% of the time.
Newer model compressors tend to run for longer but they are much more efficient and don’t draw as much power overall. I carried out current draw test on an old fridge compared to a new fridge in this post.
I founds that a 10 year-old fridge took twice as much power as a new one. This is important because it pushes up the amount of solar power and battery support needed to run an old fridge.
A battery is needed as compressor motors cycle on and off, and draw 3 times as much power at start-up. At other times it won’t run at all and draw zero amps.
The battery acts as a reservoir to supply the power peaks associated with compressor cycling. Because of this stopping and starting, it’s difficult to assess how much power a fridge takes at any point in time.
The best way to assess energy consumption is to use the manufacturer’s estimate from the appliance label. Most fridges use between 200 and 900kWh/year.
I’m using a fridge energy consumption average of 350kWh/year for this post.
How much power do solar panels generate?
Solar panel power generation depends on irradiance, or the peak-sun-hours, for any geographic location.
A good average value often used by professional solar panel installers is 4 peak-sun-hours per day.
A 100 watt solar panel will generate 100 watts x 4 peak-sun-hours x 365 days = 146kWh/year.
The table below shows the energy generated by solar power systems in various locations:
Table – 100 watt solar panel power output by location
City | New York, NY | Birmingham, UK | Lisbon, PT | Brisbane, AU | Nairobi, KN |
Irradiance (peak-sun-hours/day) | 4.086 | 2.165 | 5.163 | 5.275 | 3.955 |
100W solar panel output per year (kWh) | 149.1kWh | 79kWh | 188.5kWh | 192.5kWh | 145.8kWh |
What Size Solar Panel Is Needed For A Fridge?
If average fridge energy consumption is 350kWh per year we will need:
350kWh / 146kWh = 2.4 solar panels each rated at 100 watt.
The inverter will have losses and it’s always best to over-estimate solar power sources, so I would use 3 x 100 watt panels, with 500 watt inverter and a 100Ah deep-cycle battery.
Solar Panel Sizing For Fridge – Calculator
What size solar panel for RV battery?
The average RV battery is 200Ah at 12 volts, so equivalent to 2400 watt-hours (Wh) of energy. Leisure batteries of this type are often lead-acid deep-cycle, which means they can be discharged up to 80% without damage.
Usually deep-cycle lead acid type are discharge to about 50% to maintain a long life. Either way, it effectively means you only have 50% or 80% x 200Ah for normal use.
Alternatively, a lithium iron phosphate battery can be discharge up to 95%, so you would enjoy 190Ah capacity if you bought a 200Ah model.
Let’s stick with the lead-acid and I’ll work out what size solar panels would be good to keep the battery topped up.
If using a 200Ah (2400Wh) battery at 80% discharge rate this means severely restricting power usage to 80Ah (960Wh) per day.
How many solar panels to run an RV?
A 100 watt solar panel in a location with average irradiance of 4 peak-sun-hours will generate 400 watt-hours/day or 0.4kWh/day.
Number of 100 panels for this RV = 960/400 = 2.4 which means 3 panels.
So it looks like the answer is 300 watts, but is it?
Remember that the RV will still be drawing some power so that needs to be supplied at the same time, so in fact you’d need twice the amount of panels. Most RVs don’t have room for 600 watts of solar!
The only alternative is to increase the battery capacity to extend boondocking time, or reduce consumption even more.
What size solar panel for electric fence?
A typical electric fence battery of 36Ah could be charged by a trickle charger using a 40 watt solar panel. 36Ah equates to 432 watt-hours (Wh) and at 80% discharge a 40 watt solar panel would recharge the battery in a little over 2 days.
A typical electric fence battery is about 36Ah capacity at 12 volts and are most commonly lead-acid deep-cycle leisure-type batteries.
Without topping up, such a battery at 80% discharge would power a smaller size electric fence for 3 to 4 weeks and then would need re-charging.
In normal operation, livestock owners would have two batteries, changing them out when one needs recharging. Obviously this takes time that could be save by installing a solar charger.
There are no surge current demands on a fence set-up and a basic solar trickle-type charger with over-current protection would do. A 40 watt solar panel would be sufficient.
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Related Questions:
Can a 100 watt solar panel run a refrigerator?
A 100 watt solar panel would be able to power a fridge for a limited time and would need batteries for energy storage. A 100 watt solar panel produces about 400 watt-hours of energy per day, assuming irradiance of 4 peak-sun-hours. Irradiance depends on location.
What size battery to run fridge?
The average refrigerator needs 40 watts of power each hour which equates to 960 watt-hours of battery capacity over 24 hours to run a fridge. 960 watt-hours equals a battery capacity of 80Ah, therefore a 160Ah deep-cycle lead-acid battery with DoD of 50% would be needed.
Resources:
Which are the most efficient solar panels?