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Looking online for what inverter size to run freezers can be frustrating because most provide information about refrigerators. If you want to only run a chest freezer for instance, you can do so with a smaller inverter than what you would need for a typical refrigerator.
A 15 cubic foot chest freezer needs at least a 420W inverter to run, while a 20 cubic foot model requires 450W. A portable freezer with a 3.1 cubic foot capacity can run on a 140W inverter, while a 3000W inverter is the minimum requirement for a conventional refrigerator with freezer.
Inverter Size For Freezer Calculation
There are many types of freezers and they come in different shapes and sizes. You also have to take into consideration how long you intend to run the freezer. But we can make some general assumptions.
The calculation is: get the maximum wattage used by the freezer and add 25% to it. The result is the ideal inverter size.
You can get a larger inverter, but it does not make sense money wise, unless you are going to run other appliances with the freezer. The 25% rule is not set in stone, but it provides enough reserve power in case of a power spike.
Needless to say there are scores of freezers in various specs, so we cannot cover them all here. The following is a guide for some freezer sizes and what inverter you should use.
|Freezer Type||Watts||Recommended inverter Size|
|Refrigerator with Freezer 17 cu. ft.||1800W||3000W|
|Chest / Deep Freezer 15 cu. ft.||335W||450W|
|Chest / Deep Freezer 20 cu. ft.||350W||450W|
|Chest / Deep Freezer 3.1 cu. ft.||120W||150W|
|Portable Freezer 1.1 cu. ft.||80W||100W|
|Upright Freezer 3.1 cu. ft.||140W||175W|
For the recommended inverter size, we have rounded off the results. For instance 350 watts plus 25% is 437 watts, but you won’t find an inverter with that capacity, so your best option is a 450W to 500W unit. One we can recommend is the BESTEK 500W Power Inverter as it can run freezers without a problem.
The freezer power requirements listed above are for energy efficient freezers. Whether it is a freezer, microwave, solar stove, or any appliance, make sure it is Energy Star compliant.
if you have an old freezer and it is not energy efficient, consider buying a new one. The money you pay for a new freezer is going to be worth it, because the power consumption difference between the two is significant.
All the inverter sizes given here and in the succeeding examples are for the freezer only. We are assuming you will only use the freezer on the inverter. If you are going to run a freezer off an inverter in an off grid system, make sure there are enough batteries.
How Long Can an Inverter Run My Freezer?
An inverter can run a freezer for as long as it has sufficient power to draw from. The power source can be a solar PV system, batteries or a generator. Each setup will produce different results.
With Batteries and Inverter
A 15 cu. ft. freezer can run for 5 hours on a 300ah 12V battery and a 450W inverter. This assumes the battery has a 50% discharge and the inverter is used solely for the freezer. A 3.1 cu. ft. chest freezer can run for 10-12 hours on the same setup. We recommend the 300ah Ampere Time 12V Battery with its long DOD, solid performance and is well worth the price.
Let us try another scenario.
Suppose you have a 20 cu. ft. 350W chest freezer. We already know what inverter size it needs, which is 450 watts. To run this on an off the grid solar PV system, we need a battery that can deliver at least 335 watts.
A 300ah 12V battery is 3600 watts (300 ah x 12V = 3600W), but with a 50% discharge only 1800 can be used. If the freezer uses 350 watts an hour, that 300ah battery will last for around 4 hours before it drops to 50%.
In real of course the computation is not that clear cut. We have to account for inverter energy losses, power lost during solar cable transmission, battery age, etc. But 4 hours is a reasonable assumption to make, though you should always have more reserve power if you want to run the freezer longer.
The runtime will be longer if you use lithium batteries or 24V batteries . These are more expensive than 12V lead acid batteries but you do get more running time. So it really depends on your budget and how you intend to use the freezer.
You also have to check what type of voltage works best for the freezer and inverter. Most freezers run fine on 12V or 24V batteries, but some inverters may be optimized for specific volts. Before you purchase, look up the inverter specs if it will work with your appliances.
With Batteries, Inverter and Solar Panels
A 350W solar panel can run a 20 cu. ft. chest freezer for up to 5 hours or longer, depending on how much sunlight is left. A 400W solar panel is the better choice in case the PV is unable to deliver full power output.
Solar panels are like inverters in that there are losses incurred during the energy conversion process. Some power is lost when solar power is transferred to the battery and in the cables too. Also, solar panel output is affected by the movement of the clouds or anything that might block the sun.
For these reasons it is unrealistic to expect a 350W solar panel to produce 350 watts every hour for 5 hours a day (or more depending on how many sun hours your area receives). If your freezer uses 335 watts, a 350W PV may suffice during summer. But if you want to be sure, go for a 400W or even a 450W solar array.
It does not matter if you use a single 400W panel or connect 2 x 200W panels. As long as the total output is higher than 335 by at least 15%, it should be good. Just like inverters, you will need a larger solar array if you will run appliances with the freezer.
A lithium battery offers better discharge rates and longer lifespan than FLA or AGM. While they will certainly work with freezers, the higher price tag is a concern. For many, FLA batteries are sufficient for freezers.
On a Grid Tied Solar System
In this setup the inverter works with the solar PV system and the grid, converting DC power produced by the solar PV so it is compatible with the grid. You can run the freezer as long as you like because the power company serves as a large battery.
You can run the freezer on your solar array all day, and when the sun goes down you can switch to the power grid or a solar generator . Grid tied inverters simplify the process, which is why this is the most popular solar PV configuration for homes.
You still have to make sure the inverter is the right size for the freezer. However you don’t have to worry about recharging batteries on a grid tied system. With access to both solar and electrical power you can run any freezer as long as your solar array and inverter can handle it.
Grid tied solar PV systems are the least complicated setup, so it is no wonder it is popular. The disadvantage though is if the main power goes out, you will not have access to solar power either. This is why some prefer to run their freezers in an off grid system.
Which Freezer is Best For Solar Inverter Power Systems?
Chest or deep freezers are more energy efficient than upright freezers. However, upright freezers have shelves that make it easier to organize the items you place there. So it really depends on what you need and how much power your system has.
While a chest freezer is the best in terms of energy use, there are other factors to consider such as the capacity, dimensions and what solar PV setup you have. here are some suggestions.
For Household Use. If you don’t want to use a regular refrigerator, a 15 or 20 cu. ft. chest freezer is the best option. It uses less energy than an upright freezer of the same size, and it won’t consume as much power from the inverter.
For Camping and RVs. A portable freezer is ideal here. Sizes vary from 1 cu. ft. 3 cu. ft. 5 cu. ft. and so on. Most of these run on 100 watts or so, and you probably will not need an inverter. Just hook it up to a solar panel and/or battery and the freezer should run. Some of these portable freezers may require an inverter though, so do some research first.
Off Grid Cabin / Small House. There are a lot of variables here. For a single or couple, a small freezer and inverter will be enough. However others might need a full sized freezer. You have to calculate the freezer capacity you need before you decide to buy one and run on a solar inverter.
While freezers consume different amounts of energy, one thing is clear and that is they require much less solar power than a refrigerator. So it comes as no surprise it is popular choice if you want to cut on power cost..