E-News Issue #43
Winter greetings to you all. Hope you are all managing to stay warm. Thank you to those of you who wrote in after the last newsletter commenting on my article about power options for Papua New Guinea.
These prices are set to rise by 5% on 1 July so order this month to beat the price rise!
There is an increasing debate on whether or not the extra price of a Danfoss type 12/24V fridge is worth the efficiency gain and the resultant saving in solar panels, battery and inverter capacity.
I believe that the answer is clearly yes, the 12/24V fridge is a better alternative if you are paying the full cost of your solar equipment (e.g. no government rebates etc).
When we looked at this in detail about 4 years ago we compared a 220 litre Kelvinator run with its conventional AC motor and one which had been converted over to 12V. (This was a 3 star fridge rated at 620kWh per year.) After inverter losses we found the AC fridge to use 1.3kWh per day versus 0.5kWh for the Danfoss 12V conversion. The cost over a ten year period was rather dramatic - about AUD$13,000 for the AC fridge versus AUD$6000 for the DC fridge.
However, in the last four years a few things have happened.
Solar panels and sometimes associated equipment is subsidised in some countries such as Australia due to policies to cut back on greenhouse gas emissions. It also appears that AC fridges are slowly becoming a little more efficient.If you are considering buying an AC fridge I suggest you check out www.energyrating.gov.au for power consumption figures.
The star label gives you a figure of kWh per year - divide by 365 to get a daily figure. In general, we find this star label to be fairly pessimistic - in other words if you live in the southern half of Australia and use the fridge 'carefully' you will probably use less than the star label suggests.
A few figures I have come up with:
1) Our 220 litre staff fridge/freezer (1.81kWh per day rating) uses between 1.17 and 2.01 kWh daily (AC measurement).
2) A 362 litre fridge/freezer (1.3kWh per day rating) has been using 0.8kWh per day at 26 to 28 degrees C ambient.
3) A 520 litre Kelvinator fridge/freezer is using 60 - 65Ah @24V in Canberra area (about 1.5kWh per day).
4) A 329 litre Fisher & Paykel (1.39kWh per day rating) is using 1.28kWh at 23 degrees C ambient.
I should also say that the ratings on DC fridges are pessimistic.
You will probably find that you use less power than what is suggested unless you live in a full on tropical region.
All fridge systems need to be designed to suit your local conditions - however, for those of you wanting ball park figures, I'd suggest a 250 litre DC fridge would require about four 80W panels while its 230V counterpart would need eight of them.
You would need to roughly double your battery bank (a recurring cost) and you'd need a good sine wave inverter to run it.
A DC fridge is about AUD$1000 more than a standard AC fridge.
If you can get government rebates on your solar equipment, you might want to consider using an efficient AC fridge - otherwise it definitely pays off to get the more efficient DC fridge.
Cheers from Dave and all the RPC crew.
Dave Lambert (Director)
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