Off-Grid Refrigeration

By Dan Fink

When buying appliances for a new home or a remodel, most people cruise the big box store looking for the right combination of features, style, color and—as an afterthought—an Energy Star sticker, then maybe a yellow Energy Guide sticker to at least be sure the model they want isn’t one of the worst energy hogs out there.

Off the grid, though, your appliance choices will have a huge impact on how much your renewable energy system will cost, how easy it is to live with and how often you have to run a noisy, high-maintenance backup generator to keep your battery bank healthy. Most renewable energy installers recommend that you choose your appliances before you even begin planning your power system.

Back in the day, it was actually very common for off-gridders to order appliances like refrigerators, freezers, dishwashers and washer/ dryer combos from Europe, and pay exorbitant prices plus outrageous shipping charges. Why? Because back then, U.S. manufacturers lagged far behind Europe in building efficient machines, and all that extra cost paid for itself in the reduced cost of solar panels, batteries and the rest of the power system. Fortunately, manufacturers saw this happening, the government started requiring some basic standards, and now many U.S.- made appliances rank among the best in the world for efficiency.

Energy Awareness

To thrive when living off the grid, you must always be aware of how much energy you are generating, how much you are using and how much you have stored. Remember: houses don’t use electricity, people do. But you can design your house and choose what you put in it in a way that helps you reduce your energy consumption drastically. For example, most off-grid families cultivate the habit of doing chores that require a lot of electricity—for example, laundry, vacuuming, dishes—on sunny days when their battery bank is already nearly full and there’s plenty of power coming in.

But what about appliances that you have no control over when they run? Refrigerators and freezers are essential ones. My electric fridge uses more energy daily than anything else in the house, and I had to expand my solar array to be able to run it. The fridge/freezer combo is reasonably efficient, using about 350 kilowatt-hours per year, which translates to about one kilowatt-hour per day. That’s not a problem most of the time, but during extended periods of

snowy or rainy weather with no sun or wind, it keeps me scrambling. The unit is nothing fancy nor from Europe, just a standard Frigidaire from the local big box store, but I had to visit many stores, make lots of phone calls and do hours of internet research to find the most efficient model at an affordable price.

All refrigerators and freezers are required to have a yellow Energy Guide sticker (Photo 1) from the U.S. Department of Energy that gives you that kilowatt-hours per year figure, but keep in mind your usage may vary depending on the ambient temperature of your house. You can search their appliance database and even download spreadsheets for your own, more advanced analysis, from their website at www.energystar.gov. Go to the Product Finder search page, and have at it. From their spreadsheet, I selected my fridge/freezer sorting by both cubic feet capacity and kilowatt-hours per year, then compaed with what was available locally.

Tricks Of The Trade

Most off-gridders are both satisfied with and proud of their lifestyle, and are eager to share tips and tricks with others. Internet discussion boards are an excellent place to get information and ask questions, for example my company’s board at www.fieldlines.com. Anywhere you go, please search and read past postings before posting, as basic questions have probably already been answered…multiple times. Once you’ve done your homework, you are very likely to find free, expert advice online. Here are a few electric refrigeration tricks I’ve learned over the years:

Try to avoid simple, energy-wasting design mistakes like locating the fridge right next to the oven and range, or even worse, right by the propane space heater or wood stove.

Avoid “side-by-side” refrigerator/freezer combos and through-the-door ice and water dispensers. They waste energy that you had best conserve off the grid.

Don’t be fooled by thinking a smaller refrigerator uses less energy. I frequently see tiny “dorm” refrigerators with only two-to-three cubic feet of capacity that use more energy than my 18 cubic foot model. Official government Energy Guide stickers are the bottom line in predicting energy usage.

Thermal mass is important in case your battery backup storage gets perilously low. Keep the fridge and freezer as full as you can, while still leaving space for air circulation. When I have extra space, I fill plastic jugs with water and put them in the back of each. The frozen ones are very useful in the jobsite lunch cooler, and the cold ones are great for drinking water. However, my favorite thermal mass in the freezer is big packages of local elk, venison and moose…

Don’t be afraid to unplug the fridge and freezer for the night if your battery bank is getting low and you won’t have sun or be able to run the generator until the next day. Since I keep a lot of thermal mass in there, mine can easily keep safe temperatures for 24 hours when unplugged, provided I am judicious about only rarely opening it.

Some folks have gone so far as to put the fridge on a timer, so that late at night when there’s no solar power coming in and nobody will be opening the thing anyway, it’s turned off. I’ve tried it, and it can help. But be sure to put a minimum-maximum recording thermometer in both the refrigerator and freezer compartments so you and your family don’t get food poisoning from thawed and re-frozen or overly warm food. The U.S. Food and Drug Administration recommends that the refrigerator compartment never get above 40°F, and the freezer remain at zero °F or below.

Automatic defrost cycles use a lot of energy for 30 to 45 minutes every few days, which is usually not a problem. On mine you can even see the red-hot heating coils in the back of the freezer turn on. Unfortunately these cycles seem to come at the most inopportune times here (snowing, no sun or wind, generator won’t start), and there’s no way to select when they run. On older refrigerators, off-gridders used to disconnect the defrost heating coils and put a manual switch in, but with most modern computerized models that won’t work. For example with mine, cold air is pushed only into the freezer, and is then pushed down a plenum in the back of the unit into the refrigerator compartment. If that plenum clogs with ice crystals, over a few days the fridge goes to room temperature and the freezer to -20°F. Not good. The best option is to just unplug the fridge until you get some sun or can get the backup generator started.

Technical Problems

When I finally moved to electric refrigeration from propane two years ago, I immediately had to deal with a variety of electrical issues. Modern refrigerators have computers in them, rather than electro-mechanical switches, and we all know how finicky computers can be…. Here are a few technical issues to consider:

Modern refrigerator computers are picky about power quality. If your house runs on a modified sine wave inverter (see Countryside, July/August 2014 issue, page 23), there’s a good chance your fridge computer will balk, with any number of mysterious symptoms and the possibility of damage to the fridge. Pure sine wave inverters provide excellent power quality and run your appliances more efficiently to boot.

Refrigerator compressor motors draw a high startup surge of power. For example, while mine uses at most 350 watts (during the defrost cycle), a 1,000 watt inverter wouldn’t start it up, and the inverter shut down from overload. I ended up having to replace the inverter with a higher-capacity, pure sine wave model.

If you have other loads that use a lot of energy and/or have a high startup surge (for example, your well pump) be sure your inverter can handle all those loads and surges combined. If you exceed its limits, it may shut down until it cools off.

Many modern refrigerators also don’t like the Ground Fault Circuit Interrupters (GFCI) required by National Electric Code (NEC) in kitchen areas where water could be splashed. Mine has a warning about this right in the owner’s manual, and sure enough it wouldn’t run. It was plugged into a regular 120 volt AC outlet, but a GFCI outlet upstream tried to protect everything downstream, even regular outlets.

Code doesn’t require a separate, dedicated branch circuit for refrigerators, but NEC 110.3(B) says: “Installation and Use. Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.” And chances are the instructions in your fridge owner’s manual say to use a dedicated circuit. A great idea if you have one available or are designing wiring for a new house, as it addresses both the startup surge and GFCI issues—but nothing is going to burn down or blow up if you can’t provide a dedicated circuit. Probably.

Propane Refrigeration

I lived with propane refrigerators for 21 years, starting with an RV-size model (about three cubic feet of capacity) including a tiny freezer shelf, then moving to a “mid-size” 10 cubic foot unit (Photo 2) when I built my house. I am so glad to be done with propane, as by nature it comes with a number of problems, extra costs and inconveniences. But if you have a small renewable energy system or a limited budget, it may be your only option, and it certainly does work. A few issues you might run into are:

Gas refrigerators are quite expensive, with prices for a mid-size 10 cubic foot model (photo 3) starting at about $1,200, and larger ones approaching $3,000.

Larger propane fridge sizes can be problematic—some retailers recommend buying two smaller ones instead.

RV “two-fuel” or “three-fuel” fridge models (photo 3) that can be switched between propane and 12 volt DC or 120 volt AC electricity are a viable option, but not when running on electricity. They work fine burning gas, but have terrible electrical efficiency. That electric option might get you through in a pinch (if you have enough energy stored in your battery bank at the time) until you can hook up a portable propane bottle, but it’s a poor choice for everyday use.

Propane is expensive compared to solar electricity, with rapid and unpredictable seasonal price changes. Not to mention maintaining access for the propane truck after a deep snow when your snowplow truck threw a clutch.

There’s no defrost cycle, either manual or automatic. And as the “glacier” of ice crystals builds up on the heat exchanger inside, the burner uses more and more propane until you defrost the interior, while taking up more and more space as it creeps towards the door.

The real defrost “cycle” consists of shutting off the burner and letting it cool, cleaning the chimney, scrubbing the burner orifice with a toothbrush and rubbing alcohol, and putting big pots of boiling water inside to melt the ice, then re-lighting it. You can’t scrape or poke the ice off with sharp metal implements—if you puncture a heat exchanger tube, your expensive fridge will need an expensive repair.

Maintaining and repairing propane refrigerators is turning into a lost art. Only RV repair shops seem to have the knowledge, tools and test equipment to do it anymore, but on the bright side some of these offer mobile service calls to your location.

One tried and sometimes-true trick with a propane fridge that won’t cool is to empty it, disconnect everything, then turn it upside down (on its top) for 24 hours. This does work well occasionally, but not always, and is not exactly an easy procedure.

Old propane refrigerators made by Servel from 1933 to 1957 (photo 4) were recalled by the U.S. Consumer Product Safety Commission (CPSC) in 1990, after dozens of deaths from carbon monoxide (CO) poisoning in Canada and the U.S. occurred over the years. They will send you big orange “Killer Fridge” stickers to paste on the door as you duct tape everything shut, and if you provide a receipt from a landfill or recycling center that the unit was disposed of properly, they’ll send you a $100 check plus a cost of disposal reimbursement. Tens of thousands of Servels have been destroyed.

The cause of those tragic CO poisoning incidents was simply lack of regular maintenance—the burners could clog with dust, debris, mouse poop, burnt moths and such, because of inadequate protective screens and infrequent use, especially in remote locations. Most of those old relics could have operated perfectly for another few decades with regular maintenance…and I have seen models from the 1930s still operating perfectly. When a propane refrigerator burner starts to clog, the odor is very distinctive (I’ve never smelled anything similar) and is detectable before dangerous CO levels are reached or CO alarms go off. Regular maintenance is the key.

If you have any gas appliances in your home at all, old or new, be sure to install combination CO/ propane detectors in every room where propane is used! (Photo 5)

Super-Efficient Refrigeration

The most efficient and reliable option for off-grid refrigeration is to go with a specialized DC unit that runs directly from your battery bank and doesn’t rely on a 120 volt AC inverter. These fridges and freezers were originally developed for transporting and storing vaccines in remote areas of the world. Some are available in 120 volt AC models also. All are very expensive, and once again a few issues often come up with their implementation, for example:

Chest freezers are very efficient because you don’t open them very often, and most of the cold air stays in the tub by the food when you open the top. You can get a chest refrigerator too (photo 6), with pull-up baskets for all your goodies and energy usage at about 1/3 of a regular upright unit. If you can deal with the lifestyle changes needed for organizing your food, these are a great choice. Remember, though, you’ll likely need a second one set to be a freezer. Some custom cabinetry and slide-out shelf innovation can do the trick to combine both, but that won’t be cheap since you are buying two units, and hopefully you can do the cabinetmaking yourself. Check out the SunDanzer brand for a variety of options.

There are also excellent DC upright refrigerator/freezer combos on the market, but the price is also very dear. Sunfrost and NovaKool are popular brands. These units are roughly twice as efficient as standard refrigerators. Sunfrost custom builds each one for you, so a huge variety of colors and coverings are available (photos 7 and 8). They are available in 120 volt AC versions also.

Photos 7 and 8: Super-efficient 12/24 volt DC upright refrigerator/freezer combos (also available in 120 volt AC), custom faced by the factory to match your kitchen. Courtesy Sun Frost

DC units are available only in 12 volt and 24 volt models because of the compressor used. For a 48 volt off-grid electrical system (which most are these days) you’ll need to add a DC/DC converter that drops the voltage to 24 volts.

Beware of 12 volt DC, thermocouple coolers that can also be used as food warmers by reversing the polarity. They are very inefficient, and have difficulty maintaining safe temperatures. Fine for a camping trip, but not for a house.

It’s possible to build your own super-efficient refrigerator, and both Novacool and Adler-Barbour offer component kits at about $1,000 that you can install in your own insulated box (photo 9). These are often used in yachting applications so check marine suppliers for availability, and be sure to read the detailed construction instructions so you know what you’re getting yourself into. And do keep in mind, a big part of the price of any refrigerator is the interior walls and components—with any do-it-yourself application, you must be exceptionally careful that the interior can be easily cleaned and sterilized regularly. If there are cracks where condensation can seep in and mold can start forming in the insulation, you have a health Disaster waiting to happen.

What’s The Best Choice?

That depends on the capabilities of your renewable energy system and capacity of your battery bank, your preferences for size, configuration and style, and (unfortunately) your budget. My preference would be a large freezer compartment and small refrigerator compartment, but I was not able to find anything in an upright unit with that configuration. A SunFrost, either AC or DC, would’ve been great and is available in a half fridge / half freezer configuration, but the $3,600 (plus shipping) price tag was far out of my reach. A pair of SunDanzer chest units would have worked fine, but the cost ($1,600 plus shipping) was still too high, and I would’ve had a major cabinetmaking project on my hands. My house does have a couple of DC circuits in the walls, but if yours does not that would be another complicated project and expense.

So at the end of the day, I settled for the most efficient standard model with a big freezer compartment available at the big box store (photo 10). Life is full of compromises…but I must say, after 21 years of propane refrigeration, it sure is nice to not hassle with defrosting and worrying about expensive propane deliveries. And those magic lights that come on when I open the doors for a midnight snack, and the automatic ice maker…priceless!