Solar powering a refrigerator

[randallhilton]

With the aim of moving to solar for some of our energy I'm looking at the energy efficiency of the super efficient refrigerators. From what I can tell, the solar ready refrigerators are smallish, with much more insulation etc. And they cost more than conventional refrigerators that are twice their size.

Currently, we have a nearly new 25 cubic foot side by side which I know to be vastly more efficient than the 15 year old unit it replaced. This week I plugged it into a Kill A Watt (http://www.discountpv.com/meters/p4400.htm) meter and low and behold, here's what I have learned so far:

It runs at less than 150 watts. (I'm sure this will be higher during summer months)
It uses a little less than 1.5kwh per day.
When in defrost cycle, it's using over 600 watts.
When a door is opened, three 40w bulbs punch 120w worth of heat into the box.

So, what I'm thinking is that if I want to "solarize" this fridge I could take out the light bulbs and unplug the defrost heater, both of which would go a long ways towards reducing the KWH per day. I suppose I could stick on some external insulation for good measure (but then I'd have to figure out what to do with all the fridge magnets we have!) ;D

Then, I discovered one other bit of information: We're currently running the freezer right at 0 degrees F (summer time) and -5 during cooler weather. The high efficiency units I find on the market seem to use 10 to 15 degrees F for the freezer temp when doing their calculations. So, if I raise my freezer temp to that level, the efficiency should climb quite a bit since the heat transfer from outside to inside would be less.

Bottom line: It appears that my department store fridge is actually MORE efficient per cubic foot than a $3,000 unit that's considerably smaller. Am I missing something? ???

[kawalekm]

Hi Randall
When you plugged in the kill a watt, did you make the reading while the compressor motor was running? One thing particular about electric motors is that they use many more watts of power during startup, then after they've been running a while. One hundred fifty watts might be the amount of power it's consuming while in rest-mode.

If however that reading is full power consumption, then I think you might be able to make your idea work.
Good luck to you,
Michael

[Michael32170]

I'm not sure how well this will work. Here is my electrical data for my whole house.


Averages$107.86 $46.71 $4.40 $16.93 $13.61 $20.43 $3.37 $2.42 2,811.0 435.8
Max Values$188.48 $130.31 $48.10 $48.90 $23.42 $23.65 $3.91 $3.66 15,100.0 1,112.0
2002 Tot$999.92 $320.78 $117.93 $198.06 $173.17 $144.67 $27.24 $18.07 46,300.0 4,717.0
2002 Avg$124.99 $40.10 $14.74 $24.76 $21.65 $18.08 $3.41 $2.26 5,787.5 589.6
2003 Tot$1,204.81 $2,622.18 $159.05 $868.42 $684.11 $1,142.28 $185.15 $134.47 130,792.3 22,736.5
2003 Avg$100.40 $26.87 $13.25 $20.82 $14.15 $19.79 $3.39 $2.14 4,291.7 349.5
2004 Tot$1,177.66 $535.28 $0.00 $170.62 $153.73 $249.17 $40.52 $28.35 20,732.3 4,510.5
2004 Avg$98.14 $44.61 $0.00 $14.22 $12.81 $20.76 $3.38 $2.36 1,727.7 375.9
2005 Tot$1,277.03 $638.06 $0.00 $180.49 $133.51 $254.25 $40.19 $30.53 25,100.0 5,061.0
2005 Avg$106.42 $53.17 $0.00 $15.04 $11.13 $21.19 $3.35 $2.54 2,091.7 421.8
2006 Tot$1,491.71 $847.96 $0.00 $172.35 $144.98 $252.68 $40.20 $33.54 22,600.0 6,534.0
2006 Avg$124.31 $70.66 $0.00 $14.36 $12.08 $21.06 $3.35 $2.80 1,883.3 544.5
Min Values$68.93 $15.20 $0.00 $12.35 $10.47 $16.92 $2.89 $1.73 1,100.0 169.0

[randallhilton]

Hi Randall
When you plugged in the kill a watt, did you make the reading while the compressor motor was running? *One thing particular about electric motors is that they use many more watts of power during startup, then after they've been running a while. *One hundred fifty watts might be the amount of power it's consuming while in rest-mode.

good question. I have the Kill A Watt where I can check it out every time I walk past. When nothing is on, it's zero. When the compressor comes on it varies between 140w - 150w. Interestingly, I thought there were two interior light bulbs at first but when I opened the door, the KAW read 134 watts so I knew I had an extra bulb (which I found) plus, these bulbs are running hotter than their label says. :o Obviously, the lights don't run for long but heat is heat. I can hang a flashlight by the door.

What has me befuddled is that it seems like the defrost cycle is the biggest energy difference between the high dollar/high efficiency units and the off the shelf models. I remember that our old fridge also had heaters around the door facings to prevent sweating but this new one doesn't have that because the seals and insulation are better.

It's beginning to look like we might be able to eat our ice cream and have it too! :D

[CarolAnn]

Randall,
Have you considered a chest refrigerator? There is an article about an Australian man who bought a $40 digital thermostat and installed it on a chest freezer. After reading it, I know that's what I want to do!

http://www.treehugger.com/files/2005/07/man_retrofits_f.php

It sounds very simple - and it's truly efficient & not too expensive to do. All of the ready-made chest fridges I found were "frost free" - which is kind of stupid, when you're doing it to save energy in the first place.

If you'd try it on a smaller scale, here's how to turn a mini-fridge into a chest fridge. (The cold air doesn't roll out with the chest design like it does with an upright.)

http://www.instructables.com/id/How-to-Convert-a-mini-fridge-to-a-chest-refrigerat/

[randallhilton]

Randall,
Have you considered a chest refrigerator? . . .

. . . If you'd try it on a smaller scale, here's how to turn a mini-fridge into a chest fridge.

I wasn't thinking in terms of the absolute minimum electrical demand, just trying to figure out if our big fancy unit could be operated with a reasonable solar investment. Now you have me thinking a little harder. The fact of the matter is that I have a background which includes refrigeration service so in concept, I'm 100% on board with fiddling with the t-stat on a chest freezer. To simplify the task, I might recommend just getting a "piggy back" switch sort of like this one (https://www.hardwareworld.com/15-foot--Remote-Switch-Cord-pGJXKIN.aspx) to plug in the refrigerator cord. Cut the switch off the cord and wire it into the new, adjustable t-stat. BUT before trying that, it might be possible to simply adjust the freezer t-stat high enough that it becomes a refrigerator by itself (I don't know if it will adjust that much).

A note about flipping the compressor over like they did in your second link: It might be worth trying on a free fridge but it looks to me like the condensor coil will be lower than the compressor. If the compressor oil migrates into the coil, it won't be able to come back into the compressor. This may eventually kill the compressor but long before that, I suspect the efficiency would be compromised as the oil fills the condensor coil. It might take a year or two to find out.

Anyway. . . this is very helpful stuff!

[DavidOH]

Sounds like my numbers.
When the power was out a while back, I checked the load on the generator.
Freezer 151 watts
Ref/Frez 143 watts 1.2 amps

[not-a-bot]

we got a new westinghouse {china}
freezer with a danfoss compressor
that is so good on power it didn't make sence to go with a sunfrost, it was cheaper to get 240 watts of panels.
read the back of the freezer to see what it draws ours is 150 watts, 5.7' chest freezer, $170 at home depot.be sure you are not covering the radiator before adding insulation ours uses the skin as radiating surface.

[Ocala]

I still use mine today and will be hooking it to my solar soon

http://www.shtfmilitia.com/viewtopic.php?t=176

[Anon001]

I still use mine today and will be hooking it to my solar soon

http://www.shtfmilitia.com/viewtopic.php?t=176

I can't get your link to work???

[12vman]

Server must be down.. ::)

[DavidOH]

I still use mine today and will be hooking it to my solar soon

http://www.shtfmilitia.com/viewtopic.php?t=176


The server is up , the link is working.

Cool! *8) *Your chest Refrigerator is working!
Yes, you did cut your electric about in half.
Thanks for posting the numbers.

"Feb 2008 28 65° 42° 588 $66.95
Feb 2007 31 63° 44° 1,285 $145.28
Difference -3 2° -2° -697 ($78.33)"