Refrigeration on Solar Systems

Nationally, refrigeration represents some 11% of Australia's domestic energy usage and on stand alone systems (or off-grid systems), it is often 2 – 3 times this figure. The panels and batteries to run a large fridge can cost up to several thousand dollars

Most Efficient 230V Fridges / Freezers

Electrolux is the Aussie winner in this category with their Eco range of fridges and freezers. They are the only range of refrigeration in Australia with both a 5 Star (current rating) and 3.5 Star (new rating). The Eco range is made in Australia. Their upright fridges are from 420 litres up to 700 litres and they also have a 360 litre upright freezer. They all use a new non-synthetic refrigerant R600A.

There are quite a few models, including:

Alternative freezers include Fisher and Paykel, Westinghouse and Lemair who make 200 – 216 litre chest freezers using between 334 – 349 kWh/year. In the fridge range, leaving out a couple of imported fridges costing several thousand dollars, the nearest 'energy competitors' would be:

12 Volt & 24 Volt Fridges

There is a fairly large range of small chest fridges made mostly for the camping market. The better quality ones use a Danfoss compressor. There are also a few very efficient larger chest fridges made for specialist applications. These can often cost $2,000 – 3,000. Their appeal as a ‘family fridge’ is limited, however some are very energy efficient. Most are either a fridge or a freezer. If it has both, most have a very small freezer.

A further innovation is the use of eutectic fluid in some of these fridges. In the old days this used to be a brine solution. The idea with the eutectic fluid is similar to the esky freeze packs you put in your deep freeze for camping trips.

Eutectic refrigeration is often used in fishing vessels. The basic principle is that when the engine of your boat or vehicle is running (and therefore generating power), you run your fridge so that the eutectic fluid goes below 0°C. This then keeps your fridge cold for a further 24-48 hours (while your engine is off). The advantage of a eutectic fridge in a solar set-up is that you can time the fridge to come on in day light hours only (when your solar panels are generating power). This lowers the system voltage a bit and helps to get a bit more amperage from your panels.

More importantly, it helps reduce the battery inefficiency which results from storing power in your batteries during the day to run the fridge at night! And the last bonus is that 1-2 days holding capacity of your fridge is a bit like having some more battery storage.

We have monitored a chest type 73 litre eutectic fridge for a one year period in our area. If you are not familiar with our location, Nimbin is fairly close to Brisbane. Basically it is a sub tropical climate with typical summer day temperatures around 32°C and winter day temperatures about 20°C. The average daily current consumption @ 12V in Winter is 8 - 11 Amp hours, in Spring & Autumn = 12 - 16 Amp hours and in Summer = 17 - 20 Amp hours.

There are also a number of upright fridges made. These generally use a standard 230V type of fridge cabinet fitted with a Danfoss compressor. These are expensive – approx $2,000 for a 220 litre model.

Until a couple of years ago, it was generally agreed that if one wanted an upright fridge on a solar system, one needed to buy a 12/24V one which was expensive with limited choice of models and features available.

Fortunately for both the environment and those living on off-grid systems, 230V fridges have been getting more efficient over the years. Virtually any fridge you buy today uses some 50% of the power that a typical fridge used a decade ago.

Star Label Efficiency Ratings

All 230V fridges sold in Australia must be tested for efficiency and labelled according to AS/NZS 4474.2. They show a number of Stars to give the lay person a good idea of what models are best - the more Stars, the higher the efficiency. Find the rating of your fridge/freezer.

For those with more advanced electrical knowledge, the label also gives the power used per year (kWh/year). This figure is very useful to us when designing a stand alone solar system. We usually divide this yearly figure by 365 to get a daily figure.
The test standard for a fridge measures the power used to maintain the test temperature for a 24 hour period with an ambient temperature of 32ºC for a full 24 hours. This includes the power used for auto defrosting. The inside temperature is first standardised at 3ºC and -15ºC for the freezer, no food is in the fridge and the door/s are kept closed throughout the test. While this is just a test standard or bench mark that appears to be somewhat unrealistic, I have been told that it approximately simulates the average usage pattern in an average house in an average location in Australia.

Some years ago we tested a number of fridges in ‘real life situations’ and we generally found that they used less in this area than the Star label indicated.

In the past week, we have tested 3 fridges to compare the Star label usage versus a real life usage pattern. The three fridges tested were:

The RPC test was conducted for 3 days at room temperatures between 24 – 29º C. The Waeco was first brought down to test temperature with four 6 packs of drinks inside. Thereafter, power was measured by removing one six pack and replacing it with a room temperature one daily. The door was opened 6 – 8 times a day. The Westinghouse and Electrolux were tested in my home ie one person using them. Interestingly, the RPC test results were 89 – 92% of the Star label for all 3 fridges tested.

Measured power consumption of the 420 litre Electrolux

We measured the power consumption of two identical fridges over a period of 12 months. One fridge was sitting quietly at home, while the other operated at RPC headquarters.

• Start up current: 7.46 A (1790 W)
• Continuous current: 0.67 A (161 W)
• Power consumption according to Star Label: 956 Wh /day

Note: The staff fridge uses more power in the summer than the private one because it freezes up to three litres a day of water which is used by our Installation Teams in their eskies.

Want to measure your fridge? Get an Energy Meter.

AC versus DC Refrigeration?

The advantage of a DC fridge is that they are generally quite efficient and you don’t need an inverter which can result in some 15% efficiency losses – probably less if lights, TV etc are on at the same time.
The inverter will probably need to be left in 'Run' or 'On' mode, rather than on 'Standby' to keep the electronics running in the fridge. This could typically add a further 180Wh/day to your daily load. However you may want to have your own inverter on anyhow to keep LCD clocks etc going on appliances.

Your inverter may need to be larger than you would otherwise need. The 420 litre Electrolux uses 161 Watts when on and up to 1790 surge on start up.

These 3 power consumptions were measured in the USA

If you are happy with a chest fridge, then a 12/24 Volt DC fridge is probably your best bet.

However, once your desire reaches to a 220 litre or larger upright fridge, you really need to consider the 420 litre Electrolux. Its power consumption compared with the 12/24V Waeco fridge is about the same even considering inverter losses, it is stainless steel and almost twice the volume for $400 cheaper!

You can see from the above example that the Electrolux may be the way to go if you want an efficient 230V upright fridge. The only disadvantage with the Electrolux range is cost – about $1,600 for the smallest 420 litre model. They are an upmarket range, with a stainless steel finish, glass shelving, ice-cube maker etc.

You might get a more economical white fridge for perhaps $600 cheaper that uses an extra 100 kWh/year. If you are on the grid, the yearly cost is another $22. If you have a stand alone, or off-grid solar system, it would mean an extra $1,000 – $2,000 worth of solar panels and batteries, so in other words it is cheaper to spend an extra $600 for the Electrolux fridge.

We are often asked "what is required to run a fridge only on solar panels". To run a 349 kW/hr per year fridge, ie the large 420 litre Electrolux, would require 450 Watts of PV solar panels, and 500Ah @24V battery storage with a 700 Watt inverter assuming that nothing else is running off the inverter.

Oh, and by the way, we don't have any shares in Electrolux nor do we sell any 230V appliances.

US Fridge Observations - By Laren Corie

Many YahooGroup members have referred to this chest fridge PDF.

There seem to be things at that link that do not make mathematical sense. There are also strong practical reasons why only a couple of tiny companies make chest refrigerators, on the whole planet. Freezers are opened very seldom, however they are usually done as chests, while refrigerators, which are opened many more times are virtually always built as uprights. That little observation should send up a warning flag, about the validity of chest refrigerators, for most homes. Refrigerators are not being designed upright, to cheat the public. So, before anyone blindly swallows the koolaid about these chest conversions being some wonderful solution, you really need to educate yourself about why virtually no refrigerator manufacturers are making them.

We have looked seriously at this subject. I would not consider using one. And, if I had one, I would replace it with a new upright.
Any tiny energy savings (maybe a couple of dollars per year) is far outweighed by the inconvenience, waste of critical floor area in the kitchen, and shortened life, since many chest freezers are not designed for very many door openings, and can not handle the condensation (we have reports of rust in the interiors, water build up, in the bottom). In fact, most of the energy savings appear to be due to their lack of auto defrosting, rather than their chest configuration.

Probably the three most important bits of information about refrigerator energy efficiency are that:

1) Since 1991 standard refrigerators have been improving in energy efficiency, at an amazing rate, so that current standard refrigerators are as, or more efficient, compared to older refrigerators, as fluorescent bulbs are to incandescent bulbs.

2) Simple, low-cost refrigerators are generally more energy efficient, than expensive refrigerators with fancy features.

(I will throw in another point here. Size seems to matter less than many other characteristics) which supports the idea that door opening is not as critical a factor as insulation value, surface area, and compressor efficiency.

3) The yellow tags (energy usage ratings) do not represent some manufacturer's exaggeration, toward the low end. In fact it is literally the opposite. The yellow tags represent how much electricity the refrigerator used inside of a 90°F/32C test cell. That might have been fairly representative, of normal usage sometime in the past, for a family of four, in a warm climate, with a lot of warm soft drinks going into the fridge, and kids standing and staring, holding the door open. But, for energy aware people, especially in an adult household, in a cool climate, the yellow tag number is nowhere near what the actual energy consumption will be. In the real world, the refrigerator will use much LESS electricity. In a 68°F/20C room, with the door opened maybe fifteen times during a day, you can expect the refrigerator to use only about half as much electricity as the yellow tag states. And, it would not be unrealistic for it to use less than 40% of what the yellow tag says. We have a member of my RefrigeratorAlternatives YahooGroup, who lives in Michigan (US) (who also monitored a chest conversion for a couple of year), who reports that his upright uses 61% LESS energy than the yellow card number.

I just bought an Energy Star refrigerator (CEE tier 3) that Home Depot was selling (online including free delivery and setup). It is 16.6ft³ (470 litres). The yellow tag says 324kWh/yr, which is so little that it is literally 18% below the bottom level of its category (30% better than Energy Star). Take 50% off that (not unrealistic), and at the US national average of 12½¢ per kWh, it will cost $20US/year to operate. It is important that an upright, with its big door storage, and easily accessible shelves, even in the separate door freezer, plus crisper drawers, will not require close to as much time with the door open, as the extreme awkwardness of a chest refrigerator. And, if you convert the freezer to a refrigerator, what are you going to use as a freezer, another separate unit? That definitely will not be energy efficient. The fridge that I just bought is nearly four times (3.86) the size of the little 4.3ft³, that I have been using, but it will likely use only about half the electricity, due to my cool climate, and the fact that I use a refrigerator very efficiently. I am using the little one the same way, in the same climate, and have monitored its energy usage at close to the yellow tag rating for the larger unit. And, with the amazing sale price, government Energy Star- CEE rebate, and the $30 that my local utility will pay me for my old one, it only will cost me $229US for this big extremely efficient refrigerator.

After that, it will save me about $15/year on my electric bill. Obviously, from solely an electricity cost standpoint, spending about $250 (including tax) would not be a great investment, even at such a low price. But, my current refrigerator is barely big enough, for just me, living alone (don't want that to continue forever) with diligent loading. And, at about fourteen years old, it has a limited future life. But, there is an even greater factor, which does convert quite directly into monetary savings. My nearest grocery store is an 18 mile round trip. I also buy a significant portion of my groceries further away, because many of the prices are better. So, I think that it is relatively safe to estimate a savings of about one gallon of gasoline, per week, because this big refrigerator and freezer allow me to stock up. If that estimate is high, I am still leaving off the savings from stocking at sale prices, and wear and tear on my vehicle. So, with increased size, and immanent replacement, it make sense for me to replace my already energy efficient little refrigerator, while the rebates and sale price are available.

Laren Corie
Natural Solar Building Design and Solar Heating/Natural Cooling/Energy Efficiency Consultation since 1975

Gas Fridges / Freezers

LP gas fridges are an option – a 240L gas fridge or gas freezer will typically use a large (45kg) bottle of gas every three months so the yearly running cost is ~ $550/year. There is some maintenance to keep the gas jet clean, the fridge fumes should be vented outdoors and a gas fridge can struggle a bit in tropical heat. The gas bottle can run empty at inconvenient times of the day or night. Some of these fridges are often known as 2-way or 3-way in that they can also run off 12V or mains power electricity. These use the electricity to first make heat similar to the gas flame. Depending on size, they typically draw 10 - 25A @ 12V and will run non stop for 24 hours per day. This type of fridge is okay to run on gas but is too power hungry to run it off solar.

Refrigeration Conclusions

1) The Star label gives a good indication of expected power consumption. Actual power consumption in non-tropical areas will probably be 10 – 20% less than the Star label rating, particularly in the cooler months.

2) Running an old fridge on a solar system is not a cost effective option. If you are on the grid you can reduce your carbon footprint and power bill by buying a new efficient one – unfortunately at the expense of increasing landfill.

3) For those living off-grid, LP gas is an option but it is somewhat inconvenient and the annual running cost is around $500.

4) If you are off the grid, your best long term option is either a small/medium 12/24 volt chest fridge or freezer or the most efficient 230 volt model you can buy if you want an upright model over 220 litres.

5) If you can minimise fridge power usage by:

• limiting the amount of warm food and drink placed in it, try and keep your groceries and drinks cool on the way home etc
• keeping an upright fridge full, use water containers, esky coolers etc – these act as a 'cold sink', taking up 'air' space that would otherwise fall out when you open the door
• keep the door seals in good condition
• allow plenty of air circulation around the outside of the fridge.