View Full Version : Refrigerator for off grid
July 10th, 2008, 12:31 PDT
I am thinking of adding an electric refrigerator to my off-grid house. I see quite a few "EnergyStar" models around for 400 to 450 kwh/yr offered (18 cu ft). I presently use propane.
Is that reasonable run on a 800 watt array? I am living on a 400 wat array now, and can easily add 800 more. We are very energy efficient.
What are people's recommendations?
July 10th, 2008, 13:06 PDT
Your answer lies in how many other loads you have. If you do the math, you can calc, what your usage is, your solar input is, your desired reserve etc.
You can also find fridges that will draw as little a .75kwh/day I believe.
I wish that I had bitten the bullet and spent the extra for a good electric fridge when I built our new place, but I had it in my mind that I would need too much solar. Propane fridges are way more expensive to purchase, but I got mine pretty cheap, so now I'll stick with it. As it turns out, the increase in efficiency of Fridges in the last few years makes them very competitive. If you are off grid in only a part time occupancy, the advantage goes to propane however IMHO.
Do your math and come to your own conclusion,
July 10th, 2008, 13:07 PDT
From what I have seen, the Energy Star ratings seem to assume around a 90F room--if your home averages cooler, then the energy use will even be less.
Assuming your weather is similar to Portland ME, then 1,200 watts of solar panel on an off-grid system (battery) (default efficiency of 0.52) will give (http://rredc.nrel.gov/solar/codes_algs/PVWATTS/version1/) you:
Month Solar Radiation
(kWh/m2/day) AC Energy
(kWh) Energy Value
1 3.73 "sun" 74 kWhrs per month
2 4.85 87
3 5.25 101
4 5.17 92
5 5.33 96
6 5.37 89
7 5.73 96
8 5.56 96
9 5.18 89
10 4.34 79
11 3.14 57
12 2.96 58
Year 4.71 "hrs of sun" 1014 kWhrs per year
Assume that your fridge (worst case) uses:
450 kWhrs / year divided by 12 months/yr = 37.5 kWhrs per month
And the rest is available for use in the rest of your home. I would guess you would use less than 30 kWhrs per month in the winter...
Since your fridge needs power 100% of the time (or else, spoiled food)--I would suggest a good Battery Monitor (http://store.solar-electric.com/metersmonitors.html) (if you don't already have one)...
You can accurately tell when you have problems with power (fire up the generator) and how much you have left for the rest of the home. And you can program it to turn on a switch for a warning light/bell--if needed.
This should be a much nicer solution vs the propane powered fridge.
PS: I should also add that some folks have used a modern Energy Star AC chest freezer (http://www.wind-sun.com/ForumVB/showthread.php?t=9&highlight=chest+freezer+fridge) and a separate temperature controller to use as a refrigerator... Very power efficient. You can use the search function here and find a few more threads.
July 12th, 2008, 6:38 PDT
Ive come to a pretty easy way for calculating extra solar panels for off gridders in my sunny loacation in Spain and also a payback Electric v LPG of about 3 years
I have a 550 kwh American Fridge Freezer and I write off 800 watts of PV just for this.
An A+ Large Fridge Freezer rated at 250 kwh a year I calculate 400 watts of PV just for this.
An A+ Frige Freezer at 178 kwh a year I calculate 300 watts of PV a year. (Best rated Refer Ive come across to date)
Looking at the last example .
Cost of Frigdge 250 + Cost of PV Panels (300 watts)1350 (4.5 euro a watt) Total 1600
Similar Sized LPG Fridge Freezer for comparison.
Cost of LPG Refer 950 euros LPG @ 12 bottles a year at 16 euros a bottle (todays price) equates to 180 euros a year to run
After 3 years of LPG use the cost of your refer +gas is 1526 euros by the end of year 4 its 1718 euros
Assuming that is LPG stays the same when in fact its doubled in the last 3 years
The figures are not to the watt accurate but I use this when helping people to decide which way they should go Gas or Electric other factors bounce in and out also but a three year payback usually seals thier decision.
July 14th, 2008, 8:58 PDT
Some folks have modified chest freezers for use as refrigerators. This works very well because the cold air doesn't "fall out" of a chest freezer when the door is opened. If you're buying new, you also have the advantage of shopping around for the most energy efficient chest freezer you can find. The modification is simple; add a thermostatically controlled switch to control power to the freezer. Sorry I don't have a link to the discussion, but you should find it if you search this forum.
July 14th, 2008, 10:48 PDT
re mod chest freezers
You now have manual "defrost" and bail out, no freezer section, and increased chances of rust out from the trapped water. And no warrenty after you modify it. You might be able to use some sort of external thermostat to control it with, and save your warrenty.
All sorts of variables, it's not a cure-all. And re-cooling a slug of "air" after you open the door, is relativly easy. "Air" does not hold much heat, compared to a glass of ice water.
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