On average, full-size refrigerators (16 – 22 Cu. ft.) consume between 1500Wh and 2000Wh (Watt-hours) of energy per day.
To run a full-size refrigerator on solar, you would need 300 to 400 watts of solar power. The exact amount of solar power you need mainly depends on the energy consumption of your refrigerator, and on your location.
However, it’s a tiny bit more complicated than that. To run a refrigerator on solar power, you need a solar system that consists of:
- Solar panels
- A battery bank: To store energy during the day and use it at night or when sunlight is scarce.
- A solar charge controller: To maximize power production and protect the solar panels and the battery.
- An inverter: To convert low voltage DC power into higher voltage AC power that the refrigerator can use.
In this article, I’ll show you a few easy and simple steps you can take to:
- Efficiently determine how much solar power you need to run your refrigerator.
- Correctly size the components of the solar energy system.
How many solar panels do I need to power a refrigerator?
To run an average-size refrigerator on solar power continuously, you would need a solar array that produces around 1500-2000Wh of energy per day. A solar array that produces this much energy would consist of 3 to 6 – 100 watt solar panels. The more sunlight you get each day, the fewer solar panels you would need.
However, to accurately determine how many solar panels you need to power your refrigerator, you mainly need to know 2 things:
- An estimation of your refrigerator’s daily energy consumption.
- The amount of sunlight your solar panels would receive each day (Peak Sun Hours).
First things first.
How much energy does a refrigerator use?
The amount of daily energy that a refrigerator uses depends mainly on its size. The table below shows the estimated energy consumptions of different fridges with different sizes:
|Model||Size (Cu. ft.)||Estimated Annual energy consumption (kilo-Watt-hours)||Estimated daily energy consumption (Watt-hours)||Estimated solar power needed (Watts)|
|4.5 Cubic Feet||237 kWh/year||650 Wh/day||100 – 200 W|
|12 Cubic Feet||312 kWh/year||854 Wh/day||150 – 300 W|
|Frigidaire FFHT1425VV||13.9 Cubic Feet||332 kWh/year||909 Wh/day||150 – 300 W|
|20.6 Cubic Feet||653 kWh/year||1790 Wh/day||300 – 500 W|
|27.4 Cubic Feet||728 kWh/year||1994 Wh/day||300 – 500 W|
New refrigerators in the U.S. come with EnergyGuide labels that estimate the Annual Energy Consumption of the fridge. For example, the EnergyGuide label below is from a 20.6 Cu. Ft. refrigerator:
Estimated Annual Energy Consumption of 20.6 Cu. Ft. fridge (Source)
The label specifies an estimated yearly electricity use of 653 kWh. To get an estimate of the daily energy consumption of the fridge, we can simply divide by 365 (number of days in a year):
Estimated Daily Energy Consumption (Wh) = 653 kWh ÷ 365 = 1.790 kWh/day = 1790 Wh/day
But what if the EnergyGuide label is not provided? Here’s another way you can estimate your refrigerator’s daily energy consumption.
How to calculate refrigerator electricity consumption?
To avoid confusion, here is a reminder of what the difference between electrical power and electrical energy is:
- Electrical Power: measured in Watts
- Electrical Energy: measured in Watt-hours
If I have a 60 Watt light bulb that I leave on for 5 hours a day, the light bulb uses 60 watts of power for 5 hours, and the energy it consumes per day is calculated as such:
Daily Energy usage = Electrical Power x Usage Time = 60 Watts x 5 Hours = 300Wh (Watt-hours)
So to estimate how much energy (Watt-hours) a refrigerator uses, we need to know:
- How much power it consumes (Watts)
- How much time does it run for (hours)
So, How many watts does a refrigerator use?
Older refrigerators can use up to about 700 Watts of power, while the newer and more energy-efficient ones only use about 150-300 Watts. However, the power usage of a refrigerator still mainly depends on its size.
You can find the wattage of your refrigerator on the manufacturer’s specification label. For example, the image below shows the electrical specifications of a 29.3 Cu. ft. LG fridge:
On the specification label, the wattage of the refrigerator is usually specified under Rated Input. However, in some cases such as this one, the manufacturer does not specify the wattage.
In this case, you can calculate the wattage by using the voltage and the amperage:
Watts = Volts x Amps
Since the Rated Input is in watts, all you have to do is find the rated voltage (volts) and rated current (Amps) and multiply them.
Rated Input (Watts) = Rated Voltage (Volts) x Rated Current (Amps)
Following our example:
Rated Input = Rated Voltage x Rated Current = 127 Volts x 2.4 Amps = 305 Watts
Now that we know how much power this refrigerator uses when it’s running, we need to know how many hours it runs per day.
How many hours does a refrigerator run per day?
Refrigerators have running cycles (Duty cycles), which means that they don’t really run 24 hours a day. The compressor – which is the main electrical component in a refrigerator – turns ON and OFF in a way that maintains the temperature inside the fridge at a certain level. This duty cycle depends on a few factors, such as:
- Ambient temperatures: In the image above, you can see that whenever the room temperature increases the compressor has to work harder to maintain the internal temperature of the fridge. This results in power surges and longer running times.
- Usage: When the refrigerator’s door is open, the cool air escapes and is replaced by warmer air, which increases the overall temperature inside the fridge. Every time this happens, the compressor starts running until the low-temperature setpoint is achieved.
- How full the refrigerator is: The emptier the refrigerator, the more air it has to cool down. This means that the emptier the fridge, the more duty cycle
There are more factors that come into play here, such as size, age, and the condition of the fridge. All of these factors make it very hard to track the run time and duty cycle of the refrigerator.
However, the duty cycle of a fridge is usually around 0.33 on average. Meaning that in 24 hours, the compressor only really runs for 8 hours. Older refrigerators can have a duty cycle as high as 0.5, which means 12 hours of run time in 24 hours.
So if you know the wattage of your refrigerator, you could easily estimate how much energy it consumes using this simple formula:
Estimated Daily Energy Consumption (Wh) = Rated Input (Watts) x (Run time/day)
Following our example of the LG refrigerator:
Estimated Daily Energy Consumption (Wh) = 305 Watts x 8 hours = 2440 Wh (Watt-hours)
If you suspect a longer run time, you could use 10 or 12 hours instead of 8.
Now that we know how to estimate a refrigerator’s daily energy consumption, we need one more piece of information to accurately determine how much solar power we need to run our fridge: The amount of sunlight that the solar panels would receive.
How to measure sunlight for solar panels?
Sunlight (i.e., Solar irradiance) is measured in W/m2 (Watts per square meter). In solar energy applications, since it’s kind of hard to track the amount of sunlight received each day, the term Peak Sun Hours is used to represent the average amount of solar energy a certain area receives each day (kWh/m2/day).
Ok, but what is Peak Sun Hours?
In general, Peak Sun hours is a unit that measures the yearly average solar energy that a location receives daily. It represents the number of hours for which a certain area receives 1kW/m2 of sunlight.
For example, an area that receives an average amount of solar energy of 5kWh/m2 per day, can be said to receive 5 Peak Sun Hours per day.
Peak Sun Hours help us determine how much energy solar panels would be able to produce in a certain location. Energy Production per day (Watt-hours) = Solar Panel Wattage (Watts) x Sun Peak Hours For example:
- If we placed a 100W solar panel in an area that receives 5 Peak Sun Hours a day, the solar panel would produce 500 Wh of energy per day.
- If we placed a 300W solar panel in an area that receives 4.5 Peak Sun Hours a day, the solar panel would produce 1350 Wh of energy per day.
How many Peak Sun Hours do you receive in your location?
There are many resources online that can help you find the number of peak sun hours in your location. The map below provides the annual average daily peak sun hours in the U.S. (Click here for a higher resolution) You can also check other resources on the official website of the National Renewable Energy Laboratory (NREL).
For more precise information, you can use NREL’s PVWatts calculator. All you have to do is submit your address (or the address of your camping location for example) and it will give you the yearly and monthly average peak sun hours:
If you’re going to use the solar panel all year, use the peak sun hours from December. This will make sure your solar panels will be able to run the refrigerator throughout the year.
For this particular address that I submitted in the tool, a 100W solar panel would produce 545 Wh/day on average throughout the year. And the same panel would produce 379 Wh/day throughout the month of December.
Now let’s see how you can use this information to determine the amount of solar power that you need.
How much solar power do I need to run a refrigerator?
To determine how much solar power you need to run a refrigerator, divide the daily energy consumption (Watt-hours) of your refrigerator by the number of peak sun hours you get each day (hours).
Solar power needed (Watts) = Estimated Daily Energy Consumption (Wh) ÷ Peak Sun Hours (hours)
Here are a few examples of different refrigerators, their daily energy consumption, their location, and how much solar power would be needed for each of them to run:
|Model||Size (Cu. ft.)||Estimated daily energy consumption (Watt-hours)||Location||Estimated peak sun hours per day||Estimated solar power needed (Watts)|
|4.5 Cu. ft.||650 Wh/day||Denver, CO||6.5||100W|
|San Fransisco, CA||6.5||100W|
|12 Cu. ft.||854 Wh/day||New York, NY||4.5||190W|
|San Jose, CA||6.5||131W|
|Frigidaire FFHT1425VV||13.9 Cu. ft.||909 Wh/day||Los Angeles, CA||6.5||140W|
|20.6 Cu. ft.||1790 Wh/day||Charlotte, NC||5||358W|
|Los Angeles, CA||6.5||275W|
|27.4 Cu. ft.||1994 Wh/day||San Diego, CA||6.5||306W|
What size battery to run a refrigerator on solar power?
To run a refrigerator on solar power you’re going to need a battery bank that stores the excess energy generated by the solar panels during the day to use during the night, or when there’s not enough sunlight in general. The size of the battery bank needed depends mainly on these factors:
- The daily energy consumption of the refrigerator.
- The type of battery: The most common types of batteries for these applications are Lead-Acid and Lithium batteries. The main difference between these 2 types is how deep each type can be discharged without being permanently damaged.
- Days of Autonomy: This is essentially an energy backup plan. Days of autonomy stands for the number of days that you suspect a low solar input and would have to rely on the battery bank to run the refrigerator.
To better understand these factors, consider the following example:
I have a 14 Cu. Ft. refrigerator that consumes around 900Wh of energy on a daily basis. I want to run this fridge on solar power and still haven’t decided between a Lithium battery or a Lead-Acid battery.
But I know that batteries are rated in Ah (Amp-hours) and are usually rated at 12V. So the amount of daily energy (in Amp-hours) that I need from the battery bank is:
Daily energy needed (Ah) = Daily energy needed (Wh) ÷ Voltage Daily energy needed (Ah)
Daily energy needed (Ah) = 900 Wh ÷ 12 V Daily energy needed (Ah)
Daily energy needed (Ah) = 75 Ah
Now let’s what size each type of battery would have to be to supply this amount of energy every day.
If I use a lead-acid battery, I can only discharge it to 50%. So if I want my refrigerator to have access to 75 Ah every day, this is the size I need the battery to be:
Battery size (Ah) = 75 Ah ÷ (50/100)
Battery size (Ah) = 150 Ah
If I use a Lithium battery, I can use 80% of its rated capacity:
Battery size (Ah) = 75 Ah ÷ (80/100)
Battery size (Ah) = 94 Ah
So assuming that the solar panels get enough sunlight every day, above are the sizes each type of battery would have to be to supply 75 Ah of energy to the refrigerator each day.
However, there will be some periods where the solar panels don’t get enough sunlight. In this case, I would need to have a backup plan.
The Days of Autonomy factor helps us determine how big of an energy backup plan we need. For example, 2 days of autonomy would mean that the battery bank could supply 2 days’ worth of energy without receiving any energy from the solar panels.
The more days of autonomy the bigger the backup and the more expensive the battery bank will be. In this particular example, I will go with 2 days of autonomy. This means that I need to multiply the battery capacity by 2.
Battery size (Ah) = 150 Ah x 2 = 300 Ah
A good fit here would be 3 of these WindyNation batteries.
Battery size (Ah) = 94 Ah x 2 = 188 Ah
For a lithium battery bank with this capacity, I would go with 2 of these Battle Born batteries.
But what if I need more days of autonomy? Won’t the refrigerator shut down? Will the battery bank be damaged from over-discharging?
If the days of autonomy you choose to go with turn out to be not enough you can always add more batteries. As per battery protection, the inverter connected to the battery can prevent over-discharging through the LVD (Low Voltage Disconnect) feature.
In the next section, I explain why you need a solar charge controller and how you can choose the right one for your system.
What size solar charge controller do I need to run a refrigerator on solar power?
Solar charge controllers are electronic devices that connect the solar panels to the battery and are used in solar energy systems to maximize power production and protect the battery. There are 2 types of solar charge controllers that you could use:
In this section, I will focus on MPPTs as they are a more efficient technology.
Related: MPPT charge controller calculator
If you’re going to use an MPPT, the size of the solar charge controller you need can be calculated by dividing the wattage of your solar array by the voltage of your battery bank.
MPPT Amperage Rating = (System Wattage) ÷ (Battery Bank Voltage)
I have a refrigerator that consumes about 900 Wh of energy per day, I get 5 peak sun hours per day so a 200W solar panel will be a great fit. I’m going to use 2 12V-100Ah lithium batteries wired in series, which means my battery bank will be rated at 24V nominal.
MPPT Amperage Rating = (System Wattage) ÷ (Battery Bank Voltage)
MPPT Amperage Rating = 200 W ÷ 24 V
MPPT Amperage Rating = 8.33 A
For this particular example, the MPPT charge controller I choose needs to be able to put out at least 8.33 Amps. A good fit would be this 10A EPEVER MPPT charge controller.
Please note that when sizing your MPPT charge controllers you also have to take the Maximum Input Voltage of the controller into account.
For more details about this please refer to this article: How to choose the right MPPT charge controller for your system
Now that we know how much solar power, what size battery, and what size charge controller we need to run a refrigerator, one more essential component is left to discuss.
While solar panels produce DC power, most refrigerators need AC power to run. An inverter is used to convert low voltage (12-48V) DC power into higher voltage (110-130V) AC power.
Inverters are rated in Watts; for example, a 500W inverter is capable of supplying 500 Watts of power continuously. When choosing an inverter for your refrigerator, make sure the inverter can handle both the running wattage of your refrigerator and the power surges required to start up.
Power consumption of a 150W refrigerator.
The good news is, inverter manufacturers usually specify both of these capacities for their inverters, the maximum continuous power, and the peak power.
So, to determine the size of the inverter we need to run a refrigerator, we have to know:
- The refrigerator’s running wattage
- The refrigerator’s starting wattage (power surge)
The running wattage can be calculated using the voltage and the current on the spec sheet of the fridge:
Running Wattage = Rated Voltage x Rated Current
The starting wattage of a refrigerator is not usually mentioned by the manufacturer on the specification sheet, which means we can only estimate. However, – on average – the starting wattage of a refrigerator is 3 to 10 times its running wattage.
The higher multiple you go with, the safer the estimation, the bigger the inverter.
For the following example, I will multiply by 10.
Starting Wattage = Running Wattage x 10
A more precise way would be to use the Locked Rotor Amps (LRA) rating on the compressor. For more information about this, please refer to this article: How big of an inverter do I need to run a refrigerator?
For example: Let’s consider this LG refrigerator. The running wattage:
Running Wattage = Rated Voltage x Rated Current = 127 V x 2.4 A = 305 W
The starting wattage:
Starting Wattage = Running Wattage x 10 = 305 W x 10 = 3050 W
Now, all we have to do is find an inverter that could supply both 305 Watts of continuous running wattage and 3050 Watts of starting wattage.
This 2000W Renogy inverter will do the job for sure. It has a 2000W continuous power rating and a 4000W peak power rating.
However, for most refrigerators, the starting wattage is more likely to be 5 times the running wattage. So for this particular example, it would be appropriate to round that calculated starting wattage down to 3000W.
This Aims 1500 Watts Inverter seems to be a good fit. It can supply 1500 Watts of continuous wattage and handle 3000 Watts of peak power.
If you don’t want to take any chances, refer to this article on How to size an inverter for your refrigerator. The article explains a more precise way to determine the starting wattage of your refrigerator.
Another important thing to note is the input voltage of the inverter and its waveform.
If you’re planning on having a 24V solar system, make sure to check if the inverter is designed for 24V. You’ll also have to make sure it’s a Pure Sine Wave inverter.