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Refrigerators are more energy efficient than ever, but they are still among the most energy intensive appliances. If you are living off the grid or plan to, can you run a standard home fridge on an inverter? And how many batteries and solar panels will you need to run it for 24 hours?
A 22 cubic feet refrigerator can run off a 2000 watt inverter, and it will also need a 300ah battery and 600W solar panels. A 4AWG or 1/0 AWG wire must be used to minimize energy loss.
How to Calculate Inverter Size for a Refrigerator
The following examples are for a typical 22 cubic feet refrigerator running at 120 volts. You can however replace the figures with your own but still use the same formulas and conversions.
Modern refrigerators use 300 to 800 watts, but the surge wattage is 2 to 3 times higher. A fridge with 600 running watts likely has a 1800 surge watt, so a 2000W inverter is the minimum needed.
A typical 1000W inverter has a surge watt capacity of 2000W, so it might be able to run a 22 cu ft fridge. However you will be pushing the inverter to its limit and that could strain the system. With a powerful inverter like the Renogy 2000W Pure Sine Wave, you can turn on the fridge and not worry about any overload indicator lights flashing.
This is why it is important you always take a look at the surge watts of any appliance, whether it is a refrigerator, air conditioner, etc. Usually manufacturers highlight the running watts only so the fridge looks so efficient. However, a fridge that uses only 300W actually needs 1200W, a 500W fridge uses 1500W and so on.
The surge watts can vary by fridge model, but for our calculations it is better to double or triple the amount as stated above. Even if it is just for a split second, your inverter must be able to supply that power. Remember that inverters have two values, the surge and running watts. In our case here, the surge watts has to be at least 2000W.
How Many Batteries Do I Need to Run a Fridge Off an inverter?
Inverters draw power from batteries while running, so your battery bank determines how long you can operate your fridge.
To run a residential fridge for 24 hours, you need 600ah lead acid batteries. Only 300ah of those amp hours are usable on a lead acid battery, but that is enough. The surge watt is only for a second or less so it does not count when computing battery requirement for a fridge.
Battery capacity is in amp hours, but it is easy to convert to watts.
Amps x volts = watts
Watts / volts = amps
An energy efficient refrigerator may use 200 to 300 watts an hour. Factor in the on/off cycle and a fridge probably runs for eight hours a day. 300 x 8 = 2400 watts.
A 600ah battery bank has 300 usable amp hours. 300ah is 3600 watts (300ah x 12V = 3600), more than enough. You can get a couple of CHINS 300AH\ lithium batteries and they should be enough.
There are factors to remember about running batteries on solar:
- Lithium batteries have a discharge rate of 70%, 80% or higher. So while it more expensive, you can a smaller size compared to lead acid. Some batteries are in 24V, 36V or 48V. You can replace the 12V with any of these, but the results will be very different. You should run the numbers before you buy a battery bank for your inverter.
- This 600ah battery bank can only run a refrigerator for 24 hours if it is fully charged. If you are going to connect a washing machine or other appliances, it will not be enough.
- And even if you only run the fridge, the battery is still good only for 24 hours. You need a solar array to keep running the fridge on the batteries and inverter continuously.
How Many Solar Panels Do I Need to Run a Fridge Off an inverter?
While the inverter draws from the battery, the battery needs to be charged and recharged by the solar panel. How many you need depends on the fridge wattage and how long you intend to run it.
Going with our example earlier, we want to run a refrigerator for 24 hours a day. We have a 2000W inverter and a 600ah battery bank. The fridge has a total of 2400W running watts, so 600W of solar panel power is recommended.
You can use any solar array combination as long it is 600W:
- 3 x 200W
- 2 x 300W
- 6 x 100W
- 4 x 150W
Solar panel ratings are based on peak output, but in reality this will vary throughout the day. On a perfect day you might get 3000W with 5 sun hours, but more likely it will be 2500 to 2800W.
Either way that should be enough to recharge that 600ah battery and keep the inverter running. You may be able to get by with less power, but you can never tell with the weather. It is better to have more solar panels available in case of a sudden downpour or clouds pass by.
Important Reminders For Running a Fridge Off an Inverter
So the math is easy enough, determine the refrigerator running and surge watts and get an inverter that matches or better yet, surpasses it. But there are few more things to consider.
200W Inverter is for the fridge only. The 2000W inverter size given here is for the refrigerator only. It is true that the surge watts is just a moment, but you should not connect any other solar appliances to the inverter while the fridge starts up. That might overload the system and cause severe damage.
If you are only going to run a fridge on a 200W inverter, that is good. But if you want to run an 80W laptop, a 60W solar TV and some 10W light bulbs, add the total wattage to check if the inverter is sufficient.
Pure sine vs. modified sine wave inverter. A modified sine wave inverter is suitable for basic electronics, but for a refrigerator, pure sine wave is better . These inverters do a better job of drawing power, though they cost more.
Modern appliances are often made for pure sine wave inverters. Check your fridge if it is compatible with modified sine. If it is, be prepared for some energy loss and less than efficient operation. With pure sine wave, you pay more upfront but operation will be smoother.
Use thick wire for the inverter. Use AWG 4 to AWG 10 for 1000W to 2000W inverters. The manufacturer will recommend a size range so you should go along with that. The larger, thicker wires work best. Do not settle for flimsy wires because the system may not run.
You could have the right inverter size, solar panels and battery bank, but if the wiring is too small, the fridge will not work. The cable wires are responsible for transferring the energy between the inverter, battery and solar panel, so it needs to be the optimum size.
Inverter for Refrigerator Buying Guide
Check the refrigerator power draw. This is usually given in watts ,so if it is, just buy an inverter that can match or exceed the surge watts. If the power draw is in amps, multiply it by the volts to get the wattage. If your 18 cu ft fridge draws 6 amps, 6 x 120V -= 600 watts. Multiply 600 x 3 and you have 1800, the surge watts and minimum inverter size you need.
Inverter surge and running watts. The rule of thumb is the inverter surge watt limit is double its running watt capacity. A 1500W inverter is usually good for 3000W surge watts. The key word is usually, because some inverters may not. Check both numbers. As long as the inverter surge capacity is greater than that of the refrigerator surge wattage, it will work.
Battery Bank Size. Decide whether to buy led acid or lithium. You can start by comparing the pros and cons. Next, calculate the capacity. You only need to calculate the running watts. If a 22 cubic foot fridge uses 500 running watts and 1500 surge watts, only the 500 watts needs to be counted.
Usage. Will you run the refrigerator solely from the inverter and battery? Then you need a large solar array to recharge the system. You may also want to consider a backup power source in case the panels cannot produce power (due to rain or snow for example). A gas or solar generator may be worth considering.
Warranty. The inverter is often the most sensitive part of a solar component. While solar panels have great warranties, inverter warranty will b shorter. Go over the details and find the one that offers the best coverage.
There is no getting around the fact that refrigerators consume a lot of power. For RVs and off the grid homes, smaller, portable fridges are available that run on less power. But if you need a residential refrigerator, you have to invest in a powerful inverter and battery bank.
I am an advocate of solar power. Through portablesolarexpert.com I want to share with all of you what I have learned and cotinue to learn about renewable energy.