Refrigeration is a tough problem to solve for people who live off grid. The refrigerator does not care how sunny it is out. You can’t conserve on refrigeration use like you can with other things such as lighting and television. Your off grid system needs to match the demands of your refrigerator or you will kill your batteries dead dead dead!
There is also a lot of misinformation floating around due to most people’s lack of electrical knowledge. In this post I will help you to understand the electrical and physical concepts you need to understand when selecting an off grid refrigerator.
There is a fellow that reviewed what he thought was a great off the shelf Kenmore fridge on YouTube. It only consumed “30 watts per hour or 720 watts per day”. Thats pretty much nonsense to anyone not schooled in electrical theory…even if you are, its still nonsense. What he meant to say, was that his fridge draws 30 watt hours (per hour) or 720 watt hours per day. Few can relate that to how many amp hours his Kenmore fridge uses without some math.
To derive the amp hour number you can divide the watt hour number by the voltage of your battery bank. In my case I use 12V batteries, so 30/12 gives me 2.5 amp hours of consumption each hour or 60 amp hours each day. Wait a minute…I thought this was supposed to be an efficient fridge! When you compare it to the Sundanzer DCR50 which uses only 9 amp hours per day you realize that this Kenmore fridge is total crap for off grid folks!
The Kenmore fridge he reviewed is actually a pretty good fridge (power-wise) when compared to other fridges designed for on grid use.
The most important component in an off grid refrigerator is insulation. Thick insulation keeps things cold longer which allows the compressor to run less….very simple.
The second most important factor is the efficiency of the compressor. In other words how much power does it use and how long must it run to cool the refrigerator contents. Unfortunately, this is not something thats easily determined from manufacturers spec sheets. The small compressor used in the Engel 12V coolers run for between 2.5 and 3 minutes to maintain 40 degrees with the outside air temperature of 70 degrees just to give you a point of reference.
Another factor that plays a large role in power consumption is the temperature where the fridge is located. If it’s in a 90 degree sun room the difference in temperature between inside and out will be large. This means it will run more and use more power. On the other hand, a fridge kept in a cool basement at 60 degrees will run very little.
Another factor that consumes power is opening and closing the door and putting new things in the fridge. Off grid fridges tend to be chest style so that the dense cold air stays inside the fridge. When putting something into the fridge make sure it’s not hot! Let those leftovers cool to room temperature or your fridge will spend the next 4 hours trying to maintain the inside temperature.
How cold does it need to be?
Also consider how cold your fridge really needs to be. The FDA recommends you keep the fridge temp to 40F or below for safety. If your fridge temperature is set any lower than 40F degrees, then you are wasting power. Get an accurate thermometer and adjust the fridge temperature setting accordingly. You will likely need to wait 12-24 hours each time you make an adjustment to allow the temperature to stabilize.
Do you need a freezer?
Thats right do you? If you are like me I buy groceries each week. Hot pockets stored in the fridge taste the same as those stored in the freezer. If you plan to use your frozen foods up in a week then why do you need a freezer…keep them in the fridge. The answer is probably “I need a freezer for ice cream and ice cubes”. My advice is to lay off the ice cream (advice I wish that I could follow better) and learn to live without ice cubes. There is an awful lot of power that can be saved if you can learn to live without a freezer.
The reason I’m talking about refrigeration is that I have just completed work on a DIY off grid fridge made from a 12 Engel car cooler. My next post and my video of the week I’ll show you that project. Needless to say it uses far less than 60 amp hours per day. I’ve also developed an online web app that will help you calculate the amount of power you refrigerator will consume. Stay tuned!