Appliances such as refrigerators have compressors on board run by electric motors. A motor can have 3 states – resting, continuous running or starting. The surge current drawn when the compressor motor starts in an average size fridge increases the power needed to 700 watts.
As a general rule, 100 watt solar panel can run a refrigerator for a short time only and would also need a battery. 100 watts of solar panels can generate on average 400 watt-hours of energy per day. A refrigerator with combined freezer needs 2000 watt-hours/day.
When the compressor motor is resting the only current taken by the refrigerator is for the on-board lights and electronics, or when the door is opened. At this time the current drawn from the supply will be tiny.
When the motor starts, after the door has been open for example, it will take several times more current in amperes than when running continuously.
Some very small domestic refrigerators have a power rating as low as 65 watt, so would a 100 watt solar panel run this? We’ll find out below.
There are two ways we can determine power needed to run this appliance – read the nameplate or run a physical test to measure the current drawn in amps.
How Many Solar Panels Do I Need To Power A Refrigerator?
Many fridge nameplates only give the current rating in amperes. How does this relate to the power rating in watts? Loosely speaking, watts = volts x amps, so in the U.S. a refrigerator at nominal 110 volts and nameplate current of 4 amps would have a power rating of 4 x 110 = 440 watts.
Use The Nameplate Current Or Measure With An AC Clamp Meter
Important Note: Volts x amps is only an approximation. In circuits with magnetic components such as electric motor windings volts and amps are slightly ‘out of phase’.
How much out of phase is called the circuit Power Factor. Sometimes this is given, but mostly not.
In addition to the above, all continuously running appliances have a Duty Cycle expressed as a decimal. For example, if a fridge motor runs only 70% of the time, then it’s duty cycle is 0.7.
This is important when considering solar panel size. This number and the surge current when the motor starts are critical for designing a suitable solar panel installation.
How does a refrigerator work?
Refrigerator Duty Cycle And Surge Current.
Imagine a fridge with duty cycle of 0.7 which normally runs at 3 amps. 70% of the time it draws 3 amps from the solar panel and 30% of the time it draws 0 amps. So far, so good, but when it starts up the motor pulls 9 amps for 10 seconds.
This means that 70% of the time it is using 330 watts, 30% of the time 0 watts, but hidden inside that 70% is the short time when the motor starting current is high, approximately 3 times more than normal.
So, should we buy a solar panel rated at 100 watts to make sure it can supply the short-time load?
Before moving on we need to clarify exactly how much power we can get out of a 100 watt solar panel.
How Much Power Can A 100 Watt Solar Panel Produce?
The answer sounds obvious, but it’s not. It depends on several factors.
Solar Panels Standard Test Conditions – Full Insolation at 25 Degrees C
Mid-day sun should be great for output, but if the temperature goes high then down the output comes! Most areas don’t actually get optimum insolation for many hours during the day, if at all.
The actual output in watts will vary dramatically during the day and possibly never hit the 100 watt rating.
Related Questions
How Much Power Does It Take To Run A Refrigerator?
Many fridge nameplates only give the current rating in amperes. How does this relate to the power rating in watts? Loosely speaking, watts = volts x amps.
In the U.S. a refrigerator at nominal 110 volts and nameplate current of 4 amps would have a power rating of 4 x 110 = 440 watts.
How Many Solar Panels Would Be Needed To Run A Refrigerator?
For example, we could say that 200 watts of solar might run the fridge during peak hours during the middle of the day, but what about morning and evening?
There is no sun at night, so you need some way of storing energy that the panel produces. You also need to think of power in terms of kilowatt hours (kwh). You’d be better off with a 300W mono solar panel.
What Else Do I Need To Run A Refrigerator From Solar Panels?
You need solar panels, an MPPT solar charge controller and battery storage capacity to run a refrigerator from solar panels. Use the solar panel calculator on this page to make sure the size of each component is correct.
RV solar panels – What size solar panel do I need to run a 12v fridge?
The average 50 to 70 litre 12v Fridge consumes about 35Ah to 45 Ah and pulls a current of between 4 amps to 6 amps.
Let’s say that a 12 volt fridge average power usage is:
12 volts x 5 amps = 60 watts
Energy used per 24 hours = 60 watts x 24 = 1440 watt-hours
A 100 watt solar panel with irradiance value of 4.5 peak-sun-hours generates:
100 watt x 4.5 = 450 watt-hours
Solar power required = 1440/450 = 320 watts
Fridges pull more current when the compressor motor starts, so extra power is needed. Also, most energy is used during the day when the door is open and closed a lot, say perhaps 70 to 30 power usage split between day and night.
Together with RV solar panels of around 320 watts, a 100Ah deep-cycle battery would be required both to ensure enough power for the compressor motor surge and also power an 12 volt fridge through the night.
What size solar panel do I need to charge a 12 volt battery?
A standard 12v 50Ah auto battery at 20% discharge will need 2 hours to recharge with a 100W solar panel. A deep-cycle lead-acid 12v 50Ah battery at 50% discharge will require 4 hours recharge time using a 100 watt solar panel. The charging current will 5.75 amps using an efficient MPPT controller.
How Many Solar Panels Would Be Needed To Run A Refrigerator?
This question needs to be modified a little to read ‘How many panels would it need to run a refrigerator over a 24 hour period?’
For example, we could say that 200 watts of solar might run the fridge during peak hours during the middle of the day, but what about morning and evening? There is no sun at night, so you need some way of storing energy that the panel produces.
You also need to think of power in terms of kilowatt hours (kwh).
Sizing Solar Panels For A Fridge – Calculator
Enter the annual energy usage in KWh for your fridge. This can be found in the manufacturer’s specs. The calculator will instantly show you how many solar panels you need to run a fridge, but also how much battery capacity you will need to run it 24 hours a day.
Using Location Irradiance To Calculate Energy Generated By 100 Watt Solar Panel
A more accurate assessment of the average 100 watt panel energy generation capacity can be found by using the actual irradiance at you location.
This is done by looking up historical irradiance data from the site Global Solar Atlas. Simply enter your city and state, and read off the direct irradiance value. This is also known as peak-sun-hours.
Multiply the solar panel power by the peak sun hours and you have the energy produced by the panel per day or year:
For Orlando peak sun hours = 1806/year x 0.1 = 180 kWh per year
What Else Do I Need To Run A Refrigerator From Solar Panels?
How many watts does a refrigerator use?
Most refrigerator manufacturers give an estimated power usage in kwh for a whole year. Let’s say our fridge is estimated to consume 800 kwh over the year. Simply divide this by 365 to get the daily usage:
800 / 365 = 2.19 kwh
Now divide by 24 and multiply by 1000 to arrive at the watts:
2.19 / 24 x 1000 = 91 watts
So this fridge averages 91 watts per hour over a 24 hour period.
Elements of a Complete Solar Panel Control System – MPPT or PWM Solar Charge Controller, Inverter and Batteries
Solar Panels Plus Batteries
It isn’t possible to run a refrigerator over a 24 hours without batteries (remember the night time?) so we need to work out how much battery capacity would be needed.
The fridge uses 2.184 kilowatt hours per day. On average, assume 4 hours of sunshine per day, so a 100 watt solar panel will generate 400 watt-hours.
Dividing 2184 Wh by 400 Wh gives us 5.46 solar panels, so you would need 600 watts of solarpanels to continuously run the refrigerator.
Converting DC to AC and Charging The Batteries
In addition to the solar panels and batteries, you would also need an inverter to change the dc volts to ac. Choose and inverter that can handle twice as much load as your appliance.
A solar charge controller connects between the solar panels and the batteries to ensure continuous safe recharge.
Web Story – Can A 100 Watt Solar Panel Run A Refrigerator?
How Much Power Does It Take To Run A Refrigerator?
Many fridge nameplates only give the current rating in amperes. How does this relate to the power rating in watts? Loosely speaking, watts = volts x amps.
In the U.S. a refrigerator at nominal 110 volts and nameplate current of 4 amps would have a power rating of 4 x 110 = 440 watts.
How Many Solar Panels Would Be Needed To Run A Refrigerator?
For example, we could say that 200 watts of solar might run the fridge during peak hours during the middle of the day, but what about morning and evening?
There is no sun at night, so you need some way of storing energy that the panel produces. You also need to think of power in terms of kilowatt hours (kwh). You’d be better off with a 300W mono solar panel.
What Else Do I Need To Run A Refrigerator From Solar Panels?
You need solar panels, an MPPT solar charge controller and battery storage capacity to run a refrigerator from solar panels. Use the solar panel calculator on this page to make sure the size of each component is correct.
RV solar panels – What size solar panel do I need to run a 12v fridge?
The average 50 to 70 litre 12v Fridge consumes about 35Ah to 45 Ah and pulls a current of between 4 amps to 6 amps.
Let’s say that a 12 volt fridge average power usage is:
12 volts x 5 amps = 60 watts
Energy used per 24 hours = 60 watts x 24 = 1440 watt-hours
A 100 watt solar panel with irradiance value of 4.5 peak-sun-hours generates:
100 watt x 4.5 = 450 watt-hours
Solar power required = 1440/450 = 320 watts
Fridges pull more current when the compressor motor starts, so extra power is needed. Also, most energy is used during the day when the door is open and closed a lot, say perhaps 70 to 30 power usage split between day and night.
Together with RV solar panels of around 320 watts, a 100Ah deep-cycle battery would be required both to ensure enough power for the compressor motor surge and also power an 12 volt fridge through the night.
What size solar panel do I need to charge a 12 volt battery?
A standard 12v 50Ah auto battery at 20% discharge will need 2 hours to recharge with a 100W solar panel. A deep-cycle lead-acid 12v 50Ah battery at 50% discharge will require 4 hours recharge time using a 100 watt solar panel. The charging current will 5.75 amps using an efficient MPPT controller.
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