Life off the grid requires a few adjustments in lifestyle and habits for most people. One of the most crucial is called “load shifting,” which is simply running large loads only when there is extra power coming in that can’t be stored, thanks to a fully charged battery bank.
Unfortunately, some very critical loads can’t be shifted. Refrigerators and freezers are two of the worst offenders—they turn themselves on and off based on internal temperature, without any regard to the status of your battery bank or incoming power.
In the world of off-grid living, the answer to “Which refrigerator is the right one?” is almost always, “It depends.” What’s the most efficient power source—120 VAC or low-voltage DC? What sizes and models are available? What’s the most efficient arrangement of doors, compressors, and compartments? Is propane a better option? Here are a few points to consider before you buy.
I had to add another 1 kW of PV to run a conventional AC-powered, upright electric fridge/freezer, which replaced the 20-year-old propane model I started my off-grid life with. That big freezer up top opened new worlds for me—like the frozen-food aisle at the local wholesale club and freezing wild game from hunting. Extra bread on the counter that is at risk for growing mold or going stale? Freeze it! Herbs in the garden? Cut ’em up, put them in ice-cube trays with a little water, and pesto-freezo!
But different households have different energy budgets (and different levels of expendable income). My conventional 120 VAC refrigerator/freezer from a big box store cost me $800, plus about $700 to expand the PV array, $500 for a new controller, $2,500 for additional batteries, and another $1,400 for a new inverter I didn’t realize I would need (see “Off-Grid Fridge Vagaries” sidebar). These additions, though, helped the efficiency and performance of my entire home’s energy system. Here are some options and considerations to weigh when you’re choosing a refrigerator and/or freezer for your off-grid home.
High-Efficiency Upright Refrigerator/Freezers
If having high efficiency in a standard format (i.e., upright fridge/freezer) is your priority, high-efficiency uprights come in both DC (12, 24, or 48 V) and 120 VAC versions. They feature efficient compressors, thick insulation, tight door seals, clever ways of removing condensation from the interior using natural ventilation—without running heating elements—and more. Even blank door and side panels are available so you can customize them to your décor.
Expect to pay between $3,000 and $4,000 for a full-size, 19-cubic-foot two-door fridge/freezer. The DC versions are a bit more efficient, as they won’t have inverter losses. One advantage of a DC refrigerator compared to an AC one is that an inverter doesn’t have to be sized to handle the compressor motor startup surge—see the “Powering an Off-Grid Electric Fridge” section. Another advantage is, if the inverter fails (for example, from a nearby lightning strike), you still have refrigeration.
Going DC requires a DC circuit in your kitchen, which is likely not already wired. Either way, these appliances are an investment that will serve you well for at least a couple of decades. The downside, in addition to the price, is that you’ll need to order these units and have them shipped and, unless you can find a local dealer, you won’t be able to inspect the product until it’s paid for and at your doorstep.
Are these specialty units really worth the extra cost, with conventional models available from the local big box store? It depends on both your situation and your budget.
Manufacturers: Northern, Nova Kool, SunDanzer, and Unique
Chest-Type Freezers & Refrigerators
If you’re looking for the highest efficiency, have plenty of floor space, and don’t mind some access inconveniences, chest-type freezers and refrigerators are a great match. These appliances capitalize on dense, cold air settling to the lowest point—unlike an upright model, in which cold air spills out the bottom every time you open the door and is replaced by room-temperature air. Combined with thick insulation, chest refrigerators are excellent, efficient choices, and at a much more reasonable cost ($1,000 to $1,500) than specialty vertical models.
Chest refrigerators have a couple of downsides. You’ll have to practice loading them so that frequently used items are readily accessible, though they come with wire baskets to help you stay organized. And, they don’t come in combination fridge/freezer models—you’ll need to buy separate units. I’ve seen some innovative kitchen solutions to this issue with the chest refrigerator on a sturdy shelving unit in easy reach, with the freezer on a heavy-duty slide-out shelf underneath it. Others may put them side-by-side, with handy shelving or wall cabinets above. Your creativity and adaptability will be key to living well with a chest refrigerator and freezer solution.
So how much room will you need? A conventional 20.1-cubic-foot refrigerator/freezer combo, for example, allocates about three-fourths of this capacity (15 cubic feet) to fresh-food storage and the remainder (5 cubic feet) to freezer space. At about 8 cubic feet, SunDanzer’s chest refrigerator offers about half of the capacity of a conventional refrigerator.
Manufacturers: Dometic, Nova Kool, Phocos, SunDanzer, Steca, and Unique
Many U.S.-sold appliances have caught up with European ones in energy efficiency. You can now choose from a wide selection of refrigerator/freezer models, sizes, and colors, and base your decision on those factors plus the Energy Star rating and yellow EnergyGuide sticker. That’s what I did.
I didn’t want to spend money on a specialty off-grid fridge, was leery of tackling making my own built-ins, and didn’t have the kitchen space for a chest fridge and freezer, so I shopped by size, estimated kWh usage, and color. The model I chose offers 19 cubic feet of capacity, uses about 350 kWh per year (just under 1 kWh per day), and cost about $800, delivered. Once we finally learned to get along power-wise and energy-wise (see “Off-Grid Fridge Vagaries”), I was satisfied with the investment.
Be aware! When used off the grid, refrigerator “features” that no city dweller would do without can cause excessive energy use and unexpected problems. Here are a few things to look out for when selecting a standard electric refrigerator for off-grid use:
Top freezer, bottom freezer, or side-by-side configuration? Top freezers are the most efficient, as warm air rises while cold air sinks. Bottom freezers need a fan to make this heat exchange, but tub-style bottom freezers hold cold air better than door-style top freezers. Side-by-side freezer/fridge models are the least efficient, spilling more cold air from both compartments whenever opened. These should be avoided.
Ice makers. These cost you about 10% to 15% in increased energy usage as they have electric valves, actuator motors and, possibly, heating elements, to make sure the ice cubes fall cleanly into the bin. They also require a pressurized cold-water connection. I was willing to sacrifice that extra energy usage for the convenience, but you may not be able to. Refrigerator/freezers without ice makers (or in-door cold water dispensers for that matter) may be less expensive, but may have to be special ordered.
An automatic defrost cycle runs heating elements for an hour or so every few days to prevent ice crystal buildup. This is essential for the fridge’s proper function, but can often turn on when a battery bank’s state of charge is low. Time to run the generator for a couple of hours! In older refrigerators, it was possible to simply disconnect the heating element wires and defrost manually when needed, or install a switch so the defrost cycle could be turned on when it was warranted. In newer computer-controlled models, this can cause error codes that shut the entire defrost system down. In my case, I was again willing to expend the extra electrical energy for the convenience but had to sort out the bugs in the system first. It can be difficult to find full-size refrigerators that don’t have the automatic defrost feature—without it, unless you regularly defrost manually, the ice buildup can cause the fridge’s efficiency to plummet more than the efficiency losses from the defrost cycle itself.
Anti-sweat condensation control systems also use heating elements to keep moisture from condensing on the outside of the refrigerator in warm, humid climates. They should be avoided in any off-grid power system.
Powering an Off-Grid Electric Fridge
Continuous and surge load. The yellow EnergyGuide sticker will give you an idea of how many kWh the fridge will use annually. You can extrapolate its daily energy requirements by dividing by 365. For example, an EnergyGuide sticker on a conventional fridge/freezer estimates 404 kWh per year—divided by 365, that’s 1.1 kWh/day.
The appliance’s nameplate rating (usually located inside the main compartment, next to the model and serial numbers) will tell you the maximum wattage it can draw. This includes when the defrost cycle and ice maker are running—but most of the time, it will be far less. A typical compressor load for a full-size fridge would be about 150 watts from the compressor, and 350 watts during defrost. Don’t assume that a smaller refrigerator will have lower continuous or surge ratings, either—dorm-sized models can draw as much as full-size ones. Always refer to the nameplate and EnergyGuide ratings.
When starting up, the compressor surge load will be significantly higher—often well over 1,000 watts (see sidebar), so make sure your inverter can handle it. Unfortunately, you won’t find surge load information from the refrigerator’s nameplate or in the spec sheet, so a bit of guesswork is involved. It’s possible to add a “hard-start capacitor,” which lowers the surge to the compressor, but many modern, efficient refrigerators already have one—adding another can damage the compressor.
Inverter waveform. Many modern refrigerators won’t run properly on a modified square wave inverter, with possible problems ranging from the internal controls not functioning properly (disabling the auto defrost cycle and the ice maker) to a drastic shortening of the compressor lifespan.
Propane refrigerators use heat to generate cooling, without electricity. Propane (and even kerosene) refrigerators have been around since the early 1930s, using an absorption cooling system developed by Michael Faraday in 1824. The advantages of a common fuel source and quiet, reliable operation were huge for rural areas that had not yet been electrified, and still relied upon iceboxes and ice deliveries.
Propane refrigeration has downsides, though. Besides being a nonrenewable fossil fuel requiring drilling, refining, and transport (i.e., pollution, pollution, and pollution), propane’s price can fluctuate wildly and you may be subject to annual tank-rental fees and propane delivery charges.
With propane units, such amenities as automatic ice makers, water dispensers, and automatic defrost cycles are rare or unavailable. From the moment you first light the pilot flame, ice starts forming on the interior condenser plates. As it builds up into a miniature glacier and starts creeping ominously, it’s also impacting cooling efficiency and increasing your propane use. The only way to make the glacier recede is to remove the food (to some place that will keep it cold), fill pots and pans with hot water, and close them inside. As the water cools, this process is repeated—usually all day. You may have to do this two to three times a year, depending upon the humidity and how often you open the door. Some modern propane refrigerators have a defrost setting that bypasses the cooling system and sends burner heat directly to the compartment plates, but this still makes for a long defrosting process.
Don’t even think about jabbing at the condensers with a screwdriver or other tools to knock the ice loose—you are likely to puncture the coils, thereby ruining the fridge or freezer. You can use an electric hair dryer and complete the task in couple of hours. But if you are off-grid and can’t spare the hair dryer’s 1,500 W, it’s hot water for you. Watch your toes.
Small rural gas cooperatives may deliver to your off-grid location—and also disclose their prices. I recently switched to a rural company after years buying fuel from one of the biggest national propane corporations. The corporate rate was $3.76 a gallon. The cooperative charges $1.79 a gallon, delivering to exactly the same location.
Portable propane tanks are an option, but you’ll be doing a lot of work swapping out tanks, even with an automatic tank-switching device. A full-size (19 cubic feet) propane fridge/freezer will burn through 1.5 to 2 pounds (0.36 to 0.47 gallons) per day, and possibly more depending on your ambient indoor temperature.
Three-way propane refrigerators, which can use propane, 120 VAC, or 12 VDC, are common in RVs, come in compact sizes, and may seem like a flexible off-grid option. Some can automatically switch between the energy sources depending on what’s available. But don’t be fooled—these units work fine with propane, but are all very inefficient when used electrically. They do not have high-efficiency compressors and instead use an electric heating element in lieu of the propane flame. They are intended for use in an RV or boat with a 120 VAC shore power connection, or for short periods of time on 12 VDC until you can go to town and get your propane tank refilled.
With all that said, propane refrigeration can still be an excellent option—and sometimes the only option—for homes, cabins, and RVs with smaller (or non-existent) off-grid power systems. If a home doesn’t already have a large PV system and battery bank, installing all that equipment just to have electric refrigeration may not make much sense.
Rebates for energy-efficient appliances • dsireusa.org
Energy Star rebate-finder • energystar.gov
Enervee • enervee.com
“Off-Grid Appliances—Ultra-Efficiency Required” by Ian Woofenden in HP140 • homepower.com/140.106
“Converting a Chest Freezer to a Refrigerator” from Build-It-Solar • bit.ly/FreezerConvert
American Council for an Energy-Efficient Economy • aceee.org