Have you ever thought; Can a 100 watt solar panel run a refrigerator? The idea seems very attractive because 100w solar panels are small and light. Popping one on the roof or mounting one in the garden and hook it up to run the refrigerator.
Are you thinking you might want to do something like that to save on fuel bills? Or do you want to be more energy self-sufficient or environmentally friendly? I will be exploring the possibilities in this post but there is a bit more to it than you might think.
Can A 100 Watt Solar Panel Run A Refrigerator?
“Because a refrigerator has to be powered over a 24 hour period the answer is no. A 100 watt solar panel is actually an undersized panel. It means it’s not capable of directly powering any AC appliances on it’s own. It is designed to be primarily used with a storage device such as a 12 volt battery. The 100 watt solar panel would be used to charge the battery. This would then provide electricity to power the refrigerator via an inverter”
Big residential solar panels fixed to a roof directly power appliances through an inverter. The inverter converts the direct current (DC) the solar panels produce. To alternating current (AC) which household appliances use.
A 100 watt solar panel is designed to charge a battery which can then be attached to an inverter. The battery has a limited capacity and would quickly drain trying to run a household refrigerator.
100 watt solar panels are usually called portable solar panels This is because they have a limited output and are primarily used to charge;
- Recreational vehicle and boat house and starter batteries
- Portable power stations/generators
- Electronic devices and appliances with built-in batteries. Such as smartphones and portable fridge freezers
- Installations where batteries can be used to provide power for outhouse buildings. Such as sheds, garages and workshops. Or power for a house that has limited roof space. Or provide power for specific appliances such as a household refrigerator.
How Many 100 Watt Solar Panels Would Be Needed To Run A Refrigerator?
As I mentioned earlier a refrigerator needs to be run over a 24 hour period. So to achieve this goal with 100 watt solar panels. A combination of multiple 100w panels would be required along with batteries, a solar controller and an inverter.
Unfortunately this will require some mathematical theories and calculations to work it out. Please be patient with me. You will see the math is very easy to follow and I will not make it ‘techie’. You will understand it I promise.
The first thing we need to find out is how many watt hours a standard fridge freezer will use per 24 hour period. Then we need to find out how much capacity that equates to in battery usage. Finally we need to calculate the amount of solar input required to keep the batteries charged.
For our theoretical calculation we are going to use an imaginary 28” wide 13Cu.Ft.115V refrigerator freezer. With an energy usage rating of 320Kwh (kilowatt hour) per year pulling 2.4 amps. A 100Ah 12V lithium iron phosphate battery and 5 hours of full sunlight per day.
How Many Watt Hours Per Day Will Our Imaginary Refrigerator Use?
To find out how many watt hours our refrigerator would use per day. We need to divide the 320 Kwh energy usage per year by 365 the number of days in a year. So we multiply 320 (Kwh) by 1000 to find out the number of Kwh expressed in watt hours (Wh). This is because there are 1000 watt hours in a kilowatt hour.
320 x 1000 = 320,000
Then 320,000 ÷ 365 = 876.71
So the number of watt hours per day our refrigerator will use is 876.71 but we will round it up for convenience sake to 877Wh. I hope you are still with me and your eyes haven’t glazed over.
How Many Amp Hours (Ah) Will Our Imaginary Refrigerator Draw From The Battery?
Because battery capacity is expressed as amp hours (Ah) and the refrigerator usage is expressed in watt hours (Wh). We now need to convert Wh the fridge uses into Ah battery capacity usage.
This is achieved by dividing the number of Wh the refrigerator consumes (877Wh) by the battery voltage (12V)
877 ÷ 12 = 73
So the number of battery amp hours our fridge will consume is 73Ah over a 24 hour period.
How Many Watts of Solar Power Will Be Needed To Keep The 100Ah Battery Charged.
This will require a slightly larger calculation to find this out. We need to divide the total number of watt hours per day (877). By the solar panel wattage (100w) multiplied by the number of sun hours in a day (5).
877 ÷ (100 x 5 = 500)
Then 877 ÷ 500 = 1.75
This figure of 1.75 is the number of 100w solar panels that would be required to keep the 100ah battery charged. But there is a caveat to that. We should always overestimate the amount of solar power required by 20%
This is because of environmental, irradiance, solar panel power output and efficiency variations. It all means we now have to multiply the number of solar panels by 20% and add it to the total.
1.75 x 20% =0.35
Then 1.75 + 0.35 = 2.1
This means the required amount of 100w solar panels is 2.1 or 210 watts of solar power. Sorry about all the math if you find it tedious but I hope it was easy enough to understand.
What Is The Reality of Running A Refrigerator With 100 Watt Solar Panels?
The theoretical facts and figures we have explored up to now are ok. They give a good indication of the number of 100 watt solar panels that would be required to run a refrigerator. But they are theoretical and things often work differently in reality. Real world applications often throw up unforeseen complications and road blocks.
Running A Refrigerator With 100 Watt Solar Panels In The Real World.
In this case one 100Ah lithium iron phosphate battery and 2.1 100w solar panels is not going to cut the mustard. You may have noticed for instance that the amp hour capacity usage of the battery is 73Ah. This battery depletion over a continuous 24 hour period would eventually deplete the battery to 0%.
This would occur even with the solar panels charging the batteries everyday. Because eventually the charge going in would be outstripped by the amps going out. This means that one day you would wake up to the refrigerator powerless.
A Possible Solution
A possible solution to this would be to have a second back-up battery fully charged on standby. When the battery charging the refrigerator capacity becomes dangerously low. It could be swapped out for the back-up battery. The depleted battery could be re-charged to 100% with a separate 100 watt portable solar panel.
This could be done continuously for many years. Because the lifespan of a lithium iron phosphate battery is around 10 to 11 years of 24/7 use.
2.1 X 100 Watt Solar Panels Are Probably Not Enough To Keep The 100Ah Battery Charged
2.1 x 100 watt solar panels will probably not sustain the 100Ah batteries charge. This is because in the real world it isn’t sunny everyday especially in more northerly latitudes. Clouds, rain, snow and any other type of unfavourable weather conditions can hamper solar collection.
It is true that during these types of conditions the solar panels will still charge the battery. But at a much reduced rate. So to compensate for this I would be thinking more along the lines of 3 x 100 watt solar panels.
Other Factors to Consider
There are other factors that can affect solar collection such as the panel’s location relative to the sun. The seasons, irradiance and solar panel efficiency all play a role in reducing solar panel output.
You probably don’t know that if a solar panel gets too hot it loses efficiency. This can be a problem in baking hot conditions. So being out in the desert is no guarantee of maximum efficiency and power output.
The reality of running a refrigerator with 100 watt solar panels is not as straightforward as it might first appear. Taking everything into consideration just powering a normal sized fridge/freezer. May take time and money but it is a great first step to becoming energy self-sufficient.
Are There Portable Applications That Will Run A Refrigerator?
You might by now be feeling that running your home refrigerator with solar power might not be your cup of tea. But there are portable refrigerators on the market that you can use in and around your home. Or when you are out and about having adventures.
While their capacity isn’t going to be as large as a domestic fridge/freezer. They can be used for emergency back-up, chilling drinks for backyard parties, tailgating and camping. For a freezing capability you want the compressor type.
For cooling there are thermoelectric coolers that can be powered from your vehicle cigarette port. Or rigged to work with solar panels via a portable power station.
There are now even portable fridge/freezers that have built in lithium ion batteries. They can be re-charged by a 100 watt portable solar panel, AC mains or vehicle cigarette port. And are capable of providing indefinite 24 hour off-grid refrigeration. Great if you are a boondocker or spend lots of time on the road.
My Closing Thoughts
I think I mentioned it at the beginning of the post. That there was a bit more to running a refrigerator with a 100 watt solar panel than might first appear. It will probably take a lot more money, DIY skills and time than you thought.
I didn’t go into the inverter or solar charge controller. You would also need these to complete a solar system to run a refrigerator. I will leave it for another post. In the meantime for further reading take a look at this post;
I hope you enjoyed this post and have found it helpful. If you have any questions about how to run a refrigerator with solar panels. Or want to leave your own personal review, please feel free to leave a comment below.