Explanation Concerning The Advantages Of DC Refrigeration Over AC & Gas, When Used In Solar Installations
Gas: The principle of gas, or evaporative refrigeration, was established over one hundred years ago, so it is a very old technology. It works via a heat source (either gas, kerosene or electricity) boiling a liquid and causing it to turn to a vapour, which upon condensing back to a liquid extracts heat. It is a proven method, but gas fridges are becoming extremely expensive and their performance is generally lacking, but particularly in the hot weather. During this time of the year they must run almost continually, only reducing their energy consumption during the cooler time of the evening. During the daytime, in a family situation, it is not uncommon for them to actually begin to thaw, due to constant opening and closing of the door. Large gas freezers can only reach an average temperature of -8°C to -12°C, which is not good enough for ice-cream, etc. They also use a large quantity of gas, which is not cheap to buy anymore.
Ac 240v: Without going into specific details of operation, 240v AC fridges & freezers are the least desirable type to use in an autonomous house situation. This is due to their high power consumption. We will use a typical 200 watt, 240 volt fridge compressor as an example, and assume it has a 50% duty cycle. Our system voltage is a realistic 24volts DC.
200 watts x 85% inverter efficiency = 235 watts taken from the battery.
235 watts/24 volts = 9.79 amps.
If it runs for 12 hours, 9.79 amps x 12 hrs = 117.5 amp-hrs per day.
We shall now do the same exercise using the same size 24 volt DC refrigerator, which consumes 90watts:
90watts/24volts = 3.75 amps.
If it runs for 12 hours, 3.75 amps x 12 hrs = 45 amp-hrs per day.
As you can see, even if the DC fridge ran constantly it would still not use the AC fridge’s power consumption for running half the day.
DC : DC has the advantage of running directly from a battery, thus it is very efficient. The electronics have over/under voltage protection, thermal protection and pressure protection (in case the unit is disconnected and then reconnected whilst running). Because of its high efficiency, it takes the seasonal changes in solar-charged battery systems to their full advantage. i.e. In the summer, when the days are longer and thus more solar power is available, the fridge may run more because it is hotter. In the winter the reverse occurs, but their main attribute is that they perform just as well as similar-sized 240 volt AC fridges, and yet only consume a fraction of that power.
CONCLUSIONS :
In the long term DC fridges have the following advantages:
They do not require regular maintenance and servicing, as with gas.
They are extremely efficient.
They have no ongoing fuel costs.
If you have to add more solar modules to your system to run the fridge, you are actually buying its complete life’s energy needs.
A wide range of units to choose from.
In most cases cheaper to purchase than the equivalent gas fridge.
The DC freezers reach temperatures of minus 20°C, which is the recommended temperature for storing foodstuffs.
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