Towards a better tinyhouse

Inventing to freedom?

Cheaper solar powered fridge

with 3 comments

I just came across this interesting solar powered fridge. Bigger than you need for a tinyhouse, though, drat. They have smaller models, though they require batteries.

If you check the manufacturer’s website, you can see this one does not require a battery, saving you something like $400 on the batteries and charger (maybe more, depending on which batteries you use), and the weight and bother of them. Plus batteries wear out, adding another maintenance item. It’s not cheap as fridges go, but I bet it compares favorably with a propane fridge, which can be $2 a day to operate (2 lbs propane), I think, plus the bother of getting more propane, and the environmental aspect.

I wish they made more battery free models… If you have a solar electric system that is sufficiently large to support the peak power requirement of a normal fridge, you can do load balancing, though, which will nearly eliminate the fridge’s load on the battery system – all you have to do is add some sort of thermal storage, frozen salt water being the obvious (maybe you could just drill a hole from the freezer section to the fridge section to thermally couple them enough, though this would reduce efficiency just slightly) use an outlet timer to turn the fridge on when solar power is available, and ideally keep it off on cloudy days… But a normal fridge will require more solar panel, I estimate about 240w of solar panel theoretical minimum, if the fridge uses an average of 24 watts (check the energuide label, take the kwhr/year and divide by 8.76), or about 480$, plus the marginally larger inverter and mppt controller.

So all things considered, this looks like an economical option, even if it is a bit too big.

edit: Another potential option I was thinking about was converting an absorption (propane powered) fridge to run off a solar thermal panel. I think you could do this, because judging by the efficiency of these units, they are single effect units (presumably ammonia?) and the input temperature should be in the 85 deg c. range, which can be collected with a vacuum tube collector. You’d need to intercept about 6 m^2 of solar with 60% collector efficiency and an average input of 70 watts per m2 over the whole 24 hr day if the unit takes 225 watts average.

Edit: It might be worth looking for a used “compressor cooler”, which are used on boats. They require a quarter as much power as a 12v dc thermoelectric cooler (those things are very inefficient), and can produce ice. They are expensive new, but apparently they are fairly common on boats, so it might be worth checking your local adds. they would require a battery, though.

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Written by gregor

September 8, 2010 at 19:15

Posted in Uncategorized

3 Responses

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  1. I am trying to go as green as possible and hope to be almost completely off grid within the next two years.Thanks for posting such an interesting article..I had no idea that solar refridgerators were even an option for me!

    fallenangel39

    September 8, 2010 at 19:19

  2. Gregor,

    Re: solar powered fridge; You might find this fridge/freezer conversion helpful (the whole scheme is discussed in a PDF). Found this at Kent’s Tiny House Blog awhile ago:
    http://mtbest.net/chest_fridge.html

    Best regards,
    Deb

    Deb Hannasch

    September 12, 2010 at 17:05

    • Hey Deb,

      Yes, I had heard that they are much more efficient than fridges, and I know my deep freeze uses only 175 kwhr/year. I would think it would use less if used as a fridge, but might depend on how often it is opened. I know there is some people selling external thermostats for them so they can be easily used for fridges even if the thermostat doesn’t allow it to normally operate above freezing. I read it on wikipedia somewhere , I think . Don’t know if this page is connected to those people.

      However, there definitely some convenience issues going on there, I’m not sure it would be terribly practical to have all the stuff buried, or the need to reach down there – in a freezer it’s much less of a problem because stuff lasts longer in a freezer. In a fridge you know you will be using the stuff at the bottom (or it will go bad) and you need to access it much more often.

      Maybe if you had a wide, shallow one, under the counter, and the counter just flipped up. I’d have to the calculations to see how much energy actually gets wasted as a result of the convecting air when the fridge is open. It might not be that much, but rather a result of the leaking seals and the poorer insulation fridges are usually equipped with.

      gregortheinventor

      September 13, 2010 at 21:52


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