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Nov 7 12 10:18 AM

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After checking the power used by my refrigerator I converted a chest freezer into a refrig. The small freezer a Sears was about $250 and was rated at 230 KW per year. All I did was put a external thermostat on and the power into the external thermostat. Set the external to 38 and it works. The old new frig. used about +1000 KW per year +$500? The new set up use’s about 200 $ 100 per year. The new way is not as “nice” no freezer next to, but we also have a freezer and it is smaller, and you have to look for what you want, but about $35 per month is money. We also use it on Solar. Power is Power.

As a note I have checked the top of the frig and the bottom temperature, there is some difference so you may be able to keep ice in the bottom (have not tried that yet).


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#1 [url]

Nov 7 12 10:35 AM

I've wondered how much savings could be had if the fridge was put in a "cold room" or some such to get it out of the ambient temperature. A deep crevasse in the lava which we all seem to have is full of unlimited cool air at about 55 degrees, which could be pulled out with ducting and a little bitty fan to "pre-cool" the environment for the freezer unit. . .there's probably some equation that would tell us. . .haven't got that far with it.

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#2 [url]

Nov 7 12 3:44 PM

That's quite a savings you're showing there Bill.  Bravo!

Wow, 55 degrees! The general rule of thumb that I've learned for ground temperature is that it approaches the average annual temperature for the area.  Seems like your area would approach 68-70 degrees.  If you have 55, that's a pretty big resource.  In an application like you describe Jay, the equation for the heat (Q) that you could harvest would be this:

Q = -hA(Ts – T)


A link for explanation:


Some approximations for "h" (convective heat transfer coefficient):

  • Free Convection - Air : 5 - 25 (W/m2K)
  • Free Convection - Water: 20 - 100 (W/m2K)
  • Forced Convection - Air:  10 - 200 (W/m2K)
  • Forced Convection - Water:  50 - 10.000 (W/m2K)
  • Boiling Water : 3.000 - 100.000 (W/m2K)
  • Condensing Water Vapor: 5.000 - 100.000 (W/m2K)
From here:


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#3 [url]

Nov 7 12 4:44 PM

As I was perusing to see what my fancy (expensive) Austrian-made Steca brand-version of what Bill made -- that is, while trying to find its Kw consumption for comparison; I see that this German company is apparently marketing doohickies (tech term) called: direct methanol fuel cells (DMFC). Oddly enough, it is sort of hard to find much about them on the internet. Nonetheless, it seems like, as a supplement to a modest off-grid electricity rig, particularly in a place with inconsistent rays, that they could be a MacGiver-approved approach. Anybody know much about these things?

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#4 [url]

Nov 7 12 6:34 PM

I am going one more step by putting a frozen turkey in it will it stay frozen for a week or 2 and will the frig stay off and still cool??


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#5 [url]

Nov 8 12 11:52 AM

How old was the refrigerator that you replaced?  In the last five years or so, they've done wonders with making refrigerators more efficient.  Comparing the new "regular" refrigerator we bought when we moved into the new house a year and a half ago to the old "solar" refrigerator we had ten years previously, the new "regular" refrigerator is much more efficient.

If you put one turkey in it, it will slowly thaw out in about a week and probably still be good in there under refrigeration for another week.  However, that's not enough "chill mass" to keep a freezer frozen for very long.  If you filled the whole freezer full of frozen turkeys, wrapped the whole thing so it was very insulated and never opened the lid, it would stay frozen for a long time.  

Way back when, folks used to cut blocks of ice when the river froze and they'd pack them in straw down in deep holes.  That ice would still be frozen even in the middle of summer because of the low ground temperatures, the "chill mass" (I'm sure there's the equivalent term to "thermal mass" for cold things) and the insulation.  But they had a huge mass of ice, not just one turkey.

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#6 [url]

Nov 8 12 1:30 PM

Been there done that. I am finding that I have a lot more water dripping out of the unit, turkey thawing?

The frig was about 8 years old, but when I went looking they all used a lot of power and where very large.
Very time you open the door of a up rite all cold air comes out.


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#7 [url]

Nov 8 12 10:40 PM

Another simple and practical way to improve any old fridge:
Find the temperature sensor (usually a thermocouple) and reroute it to a bottle of water inside. This will reduce how often the compressor cycles on and off due to the added thermal mass of water. The stuff that you're keeping cool is mostly water after all.


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#8 [url]

Nov 14 12 11:29 AM

Hmmm, well, I purchased a new GE 18.5 CF refrigerator form Home Depot about 4/5 months ago and it's rated at 380 KW a little over 1KW a day.  I put my kill-watt meter on it for 2 months and I'm getting about 900W a day average.   So I'm doing a lot better than the advertised power ratings.  

Probably because the fridge is on a "interior" wall.  What does that mean?  Well, when the sun beats down on an exterior wall it will heat up whatever is behind that wall.  Even with insulation it will still radiate heat at night.  So anyway... It stays cooler!  Designed it that way.  Next?  We don't have any kids, and don't open the fridge or try not to open it unless we know what we are going to get out of it. So obviously that saves energy.  Most people open the fridge and spend some time looking around ...  

One other way is we buy a lot of beer and soda (that we don't drink) In case we have company.... We keep it filled up....  You don't have to buy beer and soda, you can just fill it up with jugs of water.  If you keep your fridge full if your not using the space than it's a lot more efficient.   So that's what we do, and obviously if we have a big turkey or lot's of left overs we will just take some beer and soda out till left overs are gone and put it back in. 

Next tip is to replace that stupid 60 watt light bulb with a 3 watt LED.  Big deal you say?  Well... The savings don't come from the light output itself (every little bit helps) but most of your savings is getting rid of that 60 Watt HEATER ... Since a 60watt  incandescent bulb  25W - 110F  40W - 252F  60W - 260F  ...  I almost burned my fingers trying to change out the bulb!   Why would you put 260 degree heater in your fridge?   That is why LED's are so much BETTER!  Because most of the energy used is producing Light waves NOT Heat waves.  

Brings up my last and finial point!  Wait for your dinner to cool down to room temps before throwing it in the fridge.  

There is a guy on CraigsList stone cold in Pahoa that converts standard sears/home depot refrigerators to Maximum energy savings.   What he does is gets a 10 CuFt fridge and disconnects the heater that is used to defrost the freezer.  He says he saves about Half the cost by self defrosting.  He says all you have to do is open the the freezer door (unplug) but I'm sure he also installs a switch on his units if he doesn't I would.  Turn it off and prop open the freezer door for 12 hours once a month ... Just don't forget to close the door and and turn the fridge back on!  But anyway, so he says doing this will almost cut your energy costs in half?    He sells these at almost twice the cost of a new one.  Not sure how hard it is to rewire it and put a switch in it.  Don't really know if there is more to it than that.  But it might be something I may look into myself for a DIY project.  If I could get my fridge to half a KW a day for taking out the heater for defrosting and just propping the door open every month for a self defrost.  I'd be down with that!  :)  

he also sells freezer chests as I was really interested in this at one point.  He told me he can convert the freezer into a fridge but he doesn't recommend it ... I asked why and he said because it grows too much mold?????  Dunno why that would be but that's what he said.  I still might try a freezer chest / refer conversion one day but... Hmmm...  I can live pretty frugal ... But a refrigerator standard size with a freezer is kinda high up on my ONE thing I really don't want to sacrifice ... Bending over shuffling food to get to what you need or finding out the ice cream wasn't low enough and turned into soup or something got shifted and froze that wasn't suppose to.  I just don't think I want to go there.  All and all, So far I've been on Helco for 6 months and I just read the meter not too long ago.  It's at 320 KW!  so far so good we are averaging 2KW a day with a modern connivance I didn't have to give up on my path to solar!  :)

This all being said...  I was @ HD the other day and noticed they had some freezer chests on sale for 170 bucks.  Looked like a really good deal!  Black Friday.  Probably all sold out but can still buy at that price and pick up later....just an FYI.  

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#9 [url]

Nov 14 12 12:31 PM

I was given a SunFrost refrigerator/freezer that runs on 24 volts DC.  The refrigerator doesn't work anymore because one of the refrigerant circuits got clogged up.  The previous owner had a repairman replace the compressor but that didn't fix it so now it has a new compressor on that circuit.  Sort of a spare for the freezer, which still works.  I was planning to cut some holes to allow the cold temps in the freezer to cool the refrigerator.

The main reason the sunfrosts are so efficient is the massive amount of insulation around the cold boxes.  I was glad to get it but I am having second thoughts because my solar set up is based on 48 volts.  Sounds like a simple problem but it is not cheap to get a converter to go from 48 vdc to 24 vdc.  Anyone interested in a 24 volt freezer?

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#10 [url]

Nov 14 12 12:57 PM

I question the merits of disabling auto defrost cycles.  Sure auto defrost is partly for convenience but a heavily frosted freezer is less efficient so there would be a sweet spot where you defrosted just frequently enough to reap the benefits.  If you get lazy and let it go too long you start using too much energy.  There is also the work of transferring all your refrigerated and frozen goods into coolers while you defrost.  I am coming round to the point of view that the new refrigerators are so efficient that any extra money or effort should be put towards a couple more solar panels, then let the reefer do its thing.

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#11 [url]

Nov 14 12 3:16 PM

I believe the Stonecold guy replaces the stock compressor with Danfoss compressor, which is quite a different animal. That compressor is also the key to my 'off-the-shelf' $1500 Steca 'fridge/freezer. 

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#12 [url]

Nov 15 12 2:52 PM

He specifically told me that most of the energy was sucked up in the defrost cycles ... Hence you have to manually defrost it.  Yeah I didn't think about the chore of unloading the freezer but you could unload it into the refrigerator since you don't defrost that portion of it.  I would imagine a 10CUFT top freezer would be rather small. Not much in there anyway. Even an 18cuft is small but it works for 2 people well. I think with a family of four would probably work out ok as well.    I dunno I suppose if push came to shove I could opt for 10cuft refer @ 500 watts a month. I really think for almost twice the space @ 400 watts more and 3 times less expensive is the way to go.   Even tho right now for me the biggest power consumption is the refer.   My connection charges for helco are more expensive than my power usage.  Sad. Yes, I think he would have to change out the compressor so it can be used with a 12/24 volt DC ... Not only that but you'd save on power for not running through a invertor.   So solar friendly for sure.  Just a bit hard to swallow a 1800 price tag.  I think if I bought into that refer I'd see no reason to stay on helco.  I could just put up 4 260 watt panels and a few batts and be done with it!   Save me about 50 bucks a month or 600 a year. Still over 10 years that's 6K bucks.  Not to mention if we have a real wind storm hit us I'll still have power.  :)

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#13 [url]

Nov 15 12 5:04 PM

I saw a 16.5 cf top freezer/reefer at Home Depot for which the yellow tag said 370 kwh/yr.  I don't know the conditions under which they test these so I don't know whether one is likely to get better or worse results, but nominally that's 1 kwh/day.  16.5 cf is plenty big enough for me.  It cost less than $600.  Rather than pay another $1000 for a fancier fridge I would buy another 720 watts of panels that should carry the reefer load entirely.  It's a trade-off but as the PV panels get cheaper and the appliances get more efficient things have reached the turning point where it is easier and no worse really to go all 120 volt appliances.

The 24 volt fridge I mentioned elsewhere was given to me by a guy who gets all his power from hydro.  He opted to buy a 120 volt fridge to replace the 24 volt unit when the 24 volt started having problems.

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#14 [url]

Nov 16 12 10:31 AM

Well, adding the extra panels is easy enough... It's having to buy all the batteries for storage space and maintain all those batteries is where the hard part comes in.   You need the batteries to carry you over for the rainy seasons with no sun.  But I suppose there is probably just no way to getting around NOT having a generator or a kind enough neighbor to plug into when the sun doesn't shine for weeks at a time. 

If your only using 2KW a day how many batteries do you need to carry a person for a 4-7 days?  Maybe it's worth it to buy a generator... Yeah it's a pain to start one when it just seems like a never ending cloud bank.  Sigh.   I guess you need to find a sweet spot at some point of just how many times is it going to cloud up for long periods of time for more than a week?  Even than.........  It's not advisable to flat line you batteries heck I wouldn't want to discharge them with less than 60%.   Tho I suppose if you had enough batteries to carry you for 5 days you'd only have to turn on the generator every 5'th day.   I know it really depends on your location for how many days you can go with out seeing the sun.  But luckily I live a mile from the shore line.  So... I think I'd probably only need to start a generator maybe 5 times a year.  I can't recall too many times I have seen the weather remain cloudy for over 5 days straight. Maybe happens more in volcano I'm sure. 

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#15 [url]

Nov 16 12 1:54 PM

It is true that your battery capacity and your generation capacity must be matched.  I think that the most common error is to add batteries without adding generation to get through the night/cloudy periods.  Ultimately you can't store what you're not generating so that only goes so far.  Adding panels which generate during the day still helps get you through the night because sufficient generation lasts longer into the evening and the batteries ar recharged faster in the morning.  The batteries, even if discharged significantly, suffer less with quick recharges.  However it is true that deep discharging will always shorten the life of batteries.

In theory you should design your system to tide you over the cloudy periods but in practice that can be expensive.  I know I have read in this forum or maybe Sensible Simplicity that the general consensus is that if you make it through the night without abusing your batteries too badly you are doing OK.  If it is cloudy the next day, run the generator.  I know that my system is quite small and that I will be disappointed.  I am pretty sure that for me the next improvement will be another string of panels.  The batteries will take that much before I have to increase my storage capacity.  The charge controller will keep the batteries from being overcharged but can't keep them from being undercharged if you just don't have enough panels.

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#16 [url]

Nov 19 12 4:32 PM

You need batteries that can store power when it's rainy, etc. my system i have 2.5 Kw max solar panels, and 15Kw storage in batteries. You don't want your battery power to go below 20-30 % depending on how you are talking to. I use down to 30% or 24.1 volts in a 24 volt system.
You are going to waste a lot of power on a great day 60- 80 amps and no place to store it, on a bad day no input power and no battery power. My next step is to add panels and batteries. I have 4 more batteries to add and 1.5 Kw panels.


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#17 [url]

Nov 20 12 1:08 AM

Aloha Bill:

I assume that you mean you have 15 kwh storage capacity.  That is 2.5 kw x 6 hrs, or any other product of kw and hrs that yields 15.  Kw is a unit of power, not energy.

I have eight 6-volt Costco golf cart batteries, each rated for 220 amp-hrs.  I have them connected in series so that's 220 amp-hrs x 50 volts= 11,000 watt-hrs, or 11 kwh.  That is at maximum discharge, which I agree is to be avoided.  Discharging them half way I could get 5 hrs of use while drawing 1 kw.  At 500 to 700 watts average input over the course of say 4 to 6 hrs I'll only make 3 kwh on a good day so I can't really discharge them that far on a steady basis.

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#18 [url]

Nov 20 12 10:28 AM

I have found that that your system will not give a 11,000 watts of power ( my system won't ). I don't know why but I just don't get  all that power out. I THINK THEY OVER RATE THE BATTERIES. And if you discharge them at a high rate you will get a lot less.

What is your definition between power and energy?

In physics, power is the rate at which energy is transferred, used, or transformed. The unit of power is the joule per second (J/s), known as the watt


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#19 [url]

Nov 20 12 3:18 PM

Yes, power is energy per unit time.  Power (kilo-watts) is the right unit for  solar panel output or energy use.  It's just that you said your battery bank stores so many kw whereas I think the proper units would be kwh (so many kw x so many hours).

Yes, even as I was writing the bit about 220 amp-hours I was thinking that that must be to a fully discharged condition, something you should avoid like the plague in real life.  You should probably have twice as many batteries so you only need to take them down half way.  I also concur with the bit about how fast you draw the power out.  There are several ratings on batteries that seem to contradict each other until you factor in the losses when discharging at a high rate.  The nameplate amp-hour rating is probably obtained under ideal conditions at a very slow rate of discharge.  In the real world you will lose a lot to resistance.

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#20 [url]

Nov 27 12 3:54 PM

It took the turkey a full week to thaw out. I am real happy with the it is working out, HECO ain't.


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