Using Refrigeration in Solar Systems

Your choice here is reasonable however all refrigeration is somewhat of a disappointment when it comes to solar electricity. Unfortunately refrigeration is not a highly efficient commodity at this time. It is also a relentless load, consuming power whenther the sun shines or not and if you want it to work correctly you cannot turn it off when you feel like it.

Refrigeration choices are outlined below along with their advantages and disadvantages (as well as my opinion). All prices are in Australian dollars and are an average sort of figure gained from casual inquiry. We do not sell any of these appliances and you may find prices vary greatly in your area of the world.

1. Gas or Kerosene refrigeration. This is obviously not an electrical load! It is perhaps a suitable choice for some people. Gas refrigerators are expensive to buy and operate and you will need to consider the cost in your particular situation.
   My opinion... I hate the things! I have had several and they all used a lot of gas. The gas heating section requires regular cleaning and maintenance and mine always seemed to run out of gas at the most inopportune time. A comparative cost in Australian dollars is as follows. Purchase price around $2750.00 for a 220 litre fridge. Gas use = 4 x $120.00 gas bottles per year = $480.00 per year running cost. Given a maximum refrigerator life of 20 years; at today's gas prices (in my area) the cost of this refrigeration would be $9600.00 in gas alone! Over a 20 year period solar/electrical refrigeration is most definitely cheaper.

2. Conventional household refrigerator. These are the cheapest refrigerator on the market due to the volume sold worldwide. The average examples are not highly efficient and need an inverter of suitable size to power them.
   Purchase price: $600.00 - $1500.00 + Running cost average = the output from 3 x 120 watt solar panels per day for a 220 litre version up to 6 x 120 watt panels per day for a largish family size refrigerator averaged over 1 year.
   Beware if you are going to take this route. You must be careful in your choice of refrigerator due to inverter requirements. An inverter converts battery power into household power and this conversion uses energy even if no appliance is connected to the inverter. Good inverters have a standby (auto start) system fitted to avoid unnecessary electrical use when no power is being used from them.
   With no other electrical load plugged in the refrigeration cycle should work as follows: The refrigerator thermostat switches on the refrigerator to start the refrigeration process. The inverter senses that there is an electrical load and starts up from standby to run the refrigerator. The refrigeration process completes itself and the thermostat turns off the refrigerator. The inverter senses the loss of electrical load and returns to standby.
   Most modern fridges have either, some or all of the following: Auto defrost, frost free, electrical spike suppresser. All these items must be disconnected to allow the inverter to turn off when it is not required. This process is often as easy as a simple wire disconnection. In addition to the above, if you want your inverter to return to standby when it is not in use the refrigerator will have to have a manual control dial for the temperature.

3. The electronic controls fitted to some refrigerators require constant power and keep an inverter on. Manual control dials are temperature controlled switches requiring no electricity for the switching process. An inverter for a refrigerator must be rated at least 3 times the refrigerator power consumption. This is because initially the power requirement to start the refrigerator is often 3 times higher than the power required to run the refrigerator once it is running.

4. Buy a conventional refrigerator and have it converted to operate directly off the battery (i.e.: 12 or 24 Volts). This process is relatively easy for a refrigeration mechanic and some refrigeration businesses specialise in the conversion. The ac driven motor and refrigeration compressor are removed and replaced with a high efficiency dc driven compressor unit. Cost for conversion around $600.00 - $1000.00. You must consult the refrigeration mechanic prior to purchasing your refrigerator. The result is a higher efficiency refrigerator, the losses from the inverter are eliminated and the new compressor (which probably cost you as much as the fridge) is a better unit than that previously fitted.

5. My opinion: This is what I should have done. The refrigerator I brought is not particularly suited to conversion process (I consulted the mechanic after purchase!). Converting your fridge to DC can also free up the use of a small inverter if that is all you have. Its not much fun to be watching television or using a computer from your inverter then have it shut down because this load plus the refrigerator start up load exceeded your inverter rating. Generally the gain in efficiency is most in fridges at or under 230 litres in capacity. It is of the opinion of the refrigeration mechanic I consulted that anything larger than this may even be more efficient on ac power. A possible 20% reduction in refrigeration array size is gained from this process.

6. Buy a purpose built high efficiency refrigerator that is designed for a solar system. If you can afford it this probably is the best choice. These high efficiency refrigerators seem to cost heaps! Around $2500.00 for 220 litre.

7. Make your own! This is not as hard as you would imagine. A conversion that is becoming popular is a converted freezer unit. Small freezers use less power than refrigerators. This is because of the top loading design and the fact that they are often insulated better. If you can live with a top loading fridge then convert a small chest freezer. All that is required is a different thermostat to keep your goods at the correct temperature. Most refrigeration mechanics should be able to perform this operation however it would be sensible to consult the mechanic prior to purchasing your freezer.

8. Go without refrigeration. This actually suits some people. I am not one of them.

Finally I will leave the mathematics up to you as to what will cost you how much when. In a perfect solar system all appliances would be of the highest efficiency available regardless of cost.

It is also worth considering that a refrigerator has a life of maybe 20 years. Most solar panels will last 40 years or more. It is up to you whether you buy efficient refrigeration or extra panels or adopt my route and use a direct charging system when the solar input is low.

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