We recently bought a solar generator for backup power during power outages. In this article we answer the question “how long will a solar generator power a refrigerator?” using our own recently purchased solar battery kit as an example. In this 5 minute read you’ll learn how big a solar generator you need to power a fridge, and how long it will run your fridge for, from a single battery cycle. We clarify how much power a large and small fridge need and what kind of solar generator will keep your food cold until the lights come back on.

How long will a solar generator power a refrigerator? TL;DR

The answer to the question ‘how long will a solar generator power a refrigerator?’ depends on a few factors.

• The size and energy demands of the fridge,
• the capacity of the solar generator, and
• the intensity of sunlight in your area are all important.

Using our own solar generator and fridges as an example, we found:

1. 300 watts of solar panels and a 1500 watt lithium battery will deliver enough power to run a 600+ litre side-by-side refrigerator for up to 8 hours on a single charge. This is enough time to keep your fridge cycling and food cold over a 24 hour period.

If the power is still out after that, you’ll need a battery with BMS (battery management system) on board that can charge from solar panels and discharge, simultaneously.

2. For a small 205 litre fridge, 200 watts of solar panels and a 1000 watt lithium battery will do the job. This size solar generator will run a small fridge for 6 hours (our small fridge is less energy efficient). 6 hours is sufficient cycle time to keep the fridge and food cool over a 24 hour period in cooler weather.

It’s important to note that a refrigerator doesn’t run continuously over a 24 hour period. But it still uses a considerable amount of energy. Especially to start up from room temperature – called the ‘starting watts’.

Our example doesn’t cover starting watts, just running watts. This is because we use our solar generator for power outages, to keep the fridge running when it is already cold. We don’t have to power it up from room temperature.

Depending on your battery, you may also need an inverter and a charge controller.

To work out what size solar generator you need to run your own fridge, follow these steps in order:

1. Start with finding out the energy demands of your refrigerator. It’s on the nameplate.
2. Then estimate how long it will need to cycle over a 24 hour period. We provide some guidance on this below.
3. From there, you can calculate what size battery you need.
4. Finally, you can work out what size solar panels it will take to charge the battery.

Steps 3 and 4 can be done with a few simple formulas. Down below we show you how.

Solar Generator Basics

If you’re considering using a solar generator to power your refrigerator, it’s important to understand what components you need to build a solar generator and the basics of how they work.

Components of a Solar Generator

A solar generator consists of several components that work together to generate, regulate and store electricity and turn it into the type of power your fridge will need. These components include:

• Solar panels: Solar panels convert sunlight into electricity. They are typically made up of photovoltaic cells that absorb sunlight and convert it into DC or direct current electricity. Solar panels come in different sizes and can be wired together to increase the overall power they output.
• Charge controller: This component regulates the amount of voltage and current that flows from the solar panels to the battery. They’re typically found in 12 volt and 24 volt systems that are common in campervans, RVs and camping equipment. You may not need a charge controller if your battery has a battery management system (BMS) onboard.
• Battery: The battery stores the electricity generated by the solar panels. Solar panels are typically used with a lithium-ion battery that can store a large amount of energy in a compact size unit.
• Inverter: The inverter is responsible for converting the DC electricity produced by the solar panels and stored in the battery into AC electricity that can be used to power your refrigerator. An inverter may be built in to your solar generator battery.

How Solar Generators Work

A solar generator works by converting sunlight into electricity through the use of solar panels. The solar panels generate DC electricity, which is then stored in a battery. A charge controller regulates the amount of voltage and current that flows from the solar panels to the battery, preventing overcharging and extending the life of the battery.

When you need to use the electricity stored in the battery, the inverter converts the DC electricity into AC electricity that can be used to power appliances and electronics. Sometimes the inverter is separate to the battery. Sometimes batteries have inverters built in.

If you have an ‘AC outlet’ on your battery, chances are the inverter is built in.

The amount of electricity that a solar generator can produce and store depends on several factors:

• the size (in watts) of the solar panels,
• the battery’s rated capacity and power output, and
• the peak sun hours of PSH where the solar generator is located.

When choosing a solar generator to power your refrigerator in a power outage, it’s important to make sure your solar generator can produce and store enough power in one cycle to meet the daily energy needs of your fridge.

So next, lets look at what our daily energy needs are, for two different size refrigerators.

Our solar generator set up

The solar generator we used for this post is the Ecoflow River 2 Pro with 220 watt bifacial solar panels. Altogether the kit cost us AUD$1998. Here are some key stats on The Ecoflow solar generator unit:

• LifeP04 battery capacity
• 220 watt bifacial solar panels (150 watts reverse side ambient light)
• Can deliver up to 1800 watt hours a day with solar charging
• Power capacity of around 800 watts
• Surge output of 1600 watts
• Max solar input of 220 watts

We bought the Ecoflow solar generator as backup power for a Tiny House we own.

How much power does a refrigerator use?

When it comes to powering your refrigerator with a solar generator, you need to first work out the power requirements of your fridge. You can usually find the energy consumption of your fridge on the nameplate, located at the back of the unit. Or look up the manual and specs for your model of fridge online.

Here are some factors that determine how much power your fridge requires in a day:

Fridge Types

You might have a full-size refrigerator, small fridge or mini bar fridge. Full-size refrigerators will have a freezer compartment and require the most power. But small fridges can also use quite a bit of power if they’re not energy efficient, as you’ll see with our example.

Capacities

The capacity of a fridge refers to the amount of space it has for storing food and drinks. The larger the capacity, the more power the fridge will require.

Full-size refrigerators typically have a capacity of 18 to 25 cubic feet, while mini fridges have a capacity of 1.7 to 4.5 cubic feet.

Cycling times

Your fridge doesn’t run all day. It cycles on and off in the most energy efficient way, to maintain a core temperature.

The amount your fridge cycles depends on the make, it’s efficiency, how much you store in it, and how many times you open and close the door. The less you open the fridge, the less it cycles and the less energy it uses.

If you’re in a blackout and keeping the fridge closed, we assume it will cycle on 35% of the time. This can go up to 80% depending on those factors we list out above.

Starting watts

It’s important to note that refrigerators also require more energy to start them up. This is called ‘starting watts’. It measures the amount of energy required to start the compressor from room temperature.

Starting watts can be up to three times the running watts for a fridge. For example, a full-size refrigerator may require 1500 watts to start but only 500 watts to run.

To start a fridge up from room temperature using your solar generator, you need to size your solar panels and battery to have enough surge power (rated capacity) to cover the starting watts of your fridge.

If the fridge is already cold and you’re using your solar generator as back up power in a black out, you won’t need to cover starting watts.

We used out solar for the latter. So no need to account for surge power on start up.

How much energy our refrigerators use

The energy consumption of a refrigerator is measured in watts and depends on its size, type, and age. And the way you use it. Newer models and better brands are generally more energy-efficient than older ones.

We’re going to assume for this example that your fridge is already cool, and you’re using the solar generator to keep it that way in a power outage. So we won’t take starting watts into account.

Lets look at how much power our 2 different size fridges need.

Full size refrigerator:

Our full size, energy efficient Samsung 617 litre fridge uses 420kWh (kilowatt hours) of power per year according to Samsung.

Averaged out, that’s 1.15kWs or 1150 watts per day.

Now we’re going assume it runs 8 hours a day, based on 35% efficient cycling. It has a 4 start energy efficiency rating.

So the fridge might use around 143 watts per hour for 8 hours a day.

Small refrigerator:

Our small, 205 litre, less energy efficient Hisense fridge uses around 130 watts of power per hour when cycling. We assume this fridge cycles less because it’s smaller and we barely use it. To use it 6 hours a day it needs 780 watts of energy (130 watts x 6 =780 watts). But 6 hours of cycling should keep it cold over a 24 hour period. You just can’t ‘set and forget’ the battery.

How big of a solar generator do you need?

In this section, we’ll discuss how to calculate the size of the solar generator you need to power our two different sized Samsung and Hisense refrigerators.

Afterwards, you can follow the same process to calculate your own solar power needs.

What size battery to run a refrigerator?

Once you know how long your fridge cycles each day and the average daily watt-hours required to run it, you can calculate the size of the battery – or ‘battery capacity’ – you need. Always start with the battery first.

The battery capacity is not the only thing to look at when picking a battery for your solar generator. There are a few other factors that matter, such as:

• Battery chemistry (and hence its depth of discharge)
• The battery’s maximum discharge load (max output)
• Energy losses from the solar panel to the battery (around 10%)

Lithium-ion batteries are a popular choice for solar generators because they have a high energy density and a long battery cycle life. So we will use a Li battery in our calculations. This is important because lithium-ion batteries can be discharged to a lower level (80%) than lead acid batteries (50%), before they need to be charged again. Some lithium battery types – like LifeP04 batteries – can be discharged to between 90% and 100% without harming the battery.

The maximum discharge load sets the upper limit for how much power the battery can output at any one time. It is measured in watts in Australia, and typically in Amp Hours in America. You find these numbers on the name plate or in the battery specs.

Since the energy use of your fridge is in watts its a good idea to convert Amps to watts, so you’re comparing apples with apples. The conversion is easy, using the formulas in this post “What size solar panel do I need to charge a 100 Amp Hour Battery?’

So lets look at what battery will run our two different fridges.

Full size fridge:

In our full size fridge example, the solar generator needs to run the fridge for 8 hours a day and will use 1150 watts to do that.

So the battery needs a daily output capability of at least 1200 watts at an 80% depth of discharge.

The battery also needs to have a maximum discharge load above 150 watts (given our fridge uses 143 watts at any one time when it runs).

Accounting for depth of discharge, we want a battery with a capacity of 1500 watts to run our full size fridge on a single cycle for 8 hours per day. (1500 watts x .8 DoD = 1200 watts).

If you have a LifeP04 battery with 90% DoD, you can get away with a smaller battery. 1300 watts should do it.

Small fridge:

For the small fridge, it will run 6 hours a day.

We need 800 watts or power from the battery in one day, at 80% depth of discharge.

So we need a battery with a capacity of 1000 watts (1000 watts x .8DOD = 800 watts). The battery should also have a maximum discharge load above 130 watts.

We’ll account for energy losses next, when we calculate solar panel sizes.

What size solar panels to power a refrigerator?

The amount of energy your solar panel can output depends on its rated power, efficiency, and also the peak sun hours in your location.

For the Full Sized fridge we need a solar generator that can produce more 1150 watts in a day on average. We want to oversize our solar panels slighty too. We’ll talk about why later.

Portable solar panels typically come in sizes of 100 watts. To calculate how many watts of solar a 100 watt solar panel can output in one day, we use a formula:

Daily Power Output = panel watts x peak sun hours (PSH) per day.

Now if you want to know more about peak sun hours, have a read of this article “What will a 100 watt solar panel run?“.

Assuming you are in Sydney Australia, your peak sun hours are 5.3 hours per day. This averages out how much good sunlight you can expect in a day in Sydney.

So lets plug that in to our formula:

Daily Power Output = (100) panel watts x (5.3) PSH/Day

So 1 x 100 watt solar panel will produce 530 watts of power per day in Sydney.

Now around 10% to 20% of that power will be lost in the storage process. Factoring that in, our 100 watt solar panel will provide 477 watts of energy into our battery per day.

Now just divide the watts our fridges need each day by our daily solar output.

Full size fridge:

1200 watts / 477 watts = 2.5

So we need 250 watts of solar panels, or 3 x 100 watt solar panels to charge our 1500 watt battery from 80% depth of discharge in one day (if we’re in Sydney). This will give us enough power in a day to run our full size fridge!

Small fridge:

800 watts / 477 watts = 1.7

We need 170 watts of solar panels or 2 x 100 watt solar panels to charge our 1000 watt battery from 80% depth of discharge in one day (in Sydney). This will give us sufficient power each day to run our small fridge from the battery.

Oversizing your solar panels

Now these are all averages and typical performance figures. What your solar panel actually produces in a day will depend on the sun and the performance of your make and model of solar panel. It might prodce less one day, and more the next.

The message here is, if you are worried about not having enough power, oversize your panels slightly. Also, buy quality solar panels from trusted brands and do the same for your battery.

What size charge controller for a 100 watt solar panel?

The size of the charge controller you need for a 100W solar panel is determined by the solar panel’s voltage and the charging current required for your battery. Here’s how to work it out:

1. Calculate the Amps (current) you need from your charge controller: Divide the solar panel’s wattage (100W) by your battery voltage. Lets say you have 12V lithium battery.

100W / 12V = 8.33 Amperes

2. Add a conservative margin: It’s always good to add a margin for potential power fluctuations. We suggest adding 25%.

8.33A * 1.25 = 10.41 Amps

So for a 100 watt solar panel and 12 volt battery, a charge controller rated at least 10 Amps is fine. Standard sizes are 10 Amps, 15 Amps or 20 Amps.

If your battery is a different voltage, use the same process above with the alternate voltage.

Recap

In summary, a solar generator can power a fridge for enough time to keep it cool over a few days, in a black out. The size and power of solar generator you need depends on the size and wattage of your refrigerator and how you use the fridge. It also depends on the sunlight available. You can right size your solar generator to your fridge. Or something a little bigger can power a freezer too and some lights. Our EcoFlow River 2 Pro can run our tiny house for 3 hours on a single charge. It charges from our solar panels and discharges simultaneously. If you’re looking to run your fridge over a few days, we highly recommend this feature.

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