When I started living off the grid in 1996, my technology options were limited. However, since that time, there have been many advances that make an off grid life much easier. This is especially true when it comes to off grid refrigeration. Not only have appliances become much more efficient but there are also many more options. Two of the most common options for off-grid refrigeration are propane and electric. But how do you choose?
The decision between these two appliances should begin with a comparison of efficiency and the long term cost of operation. For the sake of comparison, I will discuss the energy consumption of an 8 to 10 cubic foot refrigerator. Household refrigerators range in size from 8 to 30 cubic feet. An 8 to 10 cubic foot unit is sufficient for two people. Add about one cubic foot for each additional family member.
Now let’s get started with our choices for off grid refrigeration.
Unlike the electric refrigerator which uses a coolant, the propane frig relies on simple chemical reactions in order to produce cooling. The flame in a propane refrigerator heats a solution of water and ammonia to the point of boiling. This solution is condensed back to the liquid form and then flows into the evaporator where it encounters hydrogen gas. The resulting chemical reaction that occurs absorbs the heat, which in turn produces a cooling action. The ammonia and hydrogen is then combined with water, which releases the hydrogen gas back to the evaporator and the process starts all over again.
As long as you have a source of propane, you are independent from the grid and this is a viable choice for off grid refrigeration.
Energy consumption of a propane refrigerator.
A 10 cubic foot propane refrigerator uses about 1.5 pounds of propane per day. One pound of propane equals 0.236 Gallons. Therefore, the total use equals 0.354 gallons. This translates into 32,391 BTUs. One BTU equals 0.293971 watts. The grand total is an energy usage equivalent 9,522 watt hours per day.
-Cost of unit: $1,450 as of 2018
-Cost of propane (checked on 12/15/18): 2.499/gallon
-Cost to run this unit for one year:
1.5 gallons x 365 days x 2.499/gallon = $2052 USD
-Total initial set up cost and one year of operation:
$3,492 (not including the cost of the propane tank and installation)
Running cost per year is $2052
Solar electric refrigerators come in AC (standard household current) or DC units. Since the DC units are much more efficient for off grid refrigeration, that is what I will discuss.
The DC units are sometimes referred to as battery powered refrigerators. This is because a battery back up is needed to run the unit when the sun is not shining. These DC refrigerators most commonly come in 12 Volt or 24 Volt. Many of the newer models run off of either voltage and “sense” the voltage of your PV array once connected.
Setting up a small solar array and a battery bank to run this refrigerator is very simple. The system consists of solar panels, a small breaker box, charge controller, batteries, and wiring to the refrigerator unit with an additional in-line fuse. The solar array must be sized on the basis of total energy consumption for a 24 hour period while accounting for 4 sun hours/day.
Energy cost of a solar electric refrigerator
The following example is an overestimation of the equipment needed to run this unit However, if you are living off grid, it is highly desirable to have the extra energy.
-One 160 watt panel: $325 (4 sun hours = 640 watt/hrs/day)
-charge controller: $140
-140 amp hour battery: $400
-DC breaker box and breaker: $40
-SunDanzer 225 liter (8 cubic foot) 198 watt hours per day $1250
Total initial set up cost and one year of operation:
Running cost after one year: $0
-Less initial set up cost
-The system pays for itself after one year
-Astounding efficiency: 45 x more efficient than propane
-Longer appliance life: DC refrigerators last up to 25 years. Propane units last 6 to 10 years
-Electric refrigerators produce no emissions. Propane units have to be vented and produce carbon monoxide
-DC units produce very little heat. Propane units produces about 9000 watts
-Cost of propane can vary considerably. The cost of running a DC electric refrigerator remains constant.
When it come to off grid refrigeration, the choice is clear. You are far better off going with a DC electric unit as opposed to propane. Not only is the initial set up cost much less, but after the first year, your running cost is basically zero. Not to mention the fact that you are not dependent on fossil fuels with a variable cost that you cannot control.
For this post, the cost of solar equipment was taken from Northern Arizona Wind and Sun.
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