solar refrigeration without batteries?

jonr
jonr Solar Expert Posts: 1,386 ✭✭✭✭
in Off Grid Solar & Battery Systems #1
I'd like to avoid battery use as much as possible. So are there refrigerator/freezers that can store enough energy during the day to coast through a hot night? For example, a refrigerator might freeze some blocks of ice to enable it to do that. Or a freezer might be packed with some number of bottles of antifreeze/water mix to keep it cold.

I looked into it and apparently a typical fairly full freezer is OK overnight without power. But a typical refrigerator might only stay cool for 6 hours. Ice storage makes sense.

Part of such an approach would be the system having enough btu/hr capability to get the job done during 1/3 of the day. Ie, it might require a larger compressor and heat exchangers.

Is this feasible?

I am available for custom hardware/firmware development

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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #2
    Re: solar refrigeration without batteries?

    SO how do you power it during the day. All offgrid systems require a battery of some sort just to act as a buffer for starting surges or cloud passing.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
    Re: solar refrigeration without batteries?

    There is a company that makes a refrigerator that is powered directly from PV. I can't speak to its efficiency or practicality though.

    One person here found his best solution was to use an ice maker during the day when there was 'surplus' PV power available and use that to keep the 'frige cold over night.

    And yes off-grid requires batteries for almost everything, but the more you can make use of PV power during the day that would otherwise go unrealized the more efficient the system is. That requires some careful load management.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #4
    Re: solar refrigeration without batteries?

    Ammonia Cycle Solar Fridge - see Crosley Icyball http://en.wikipedia.org/wiki/Icyball

    Make a parabolic reflector to heat the hot side, and you have ice in a couple hours. Maybe even 2 cycles on a really long sunny day.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
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  • Grinnin
    Grinnin Solar Expert Posts: 39 ✭
    #5
    Re: solar refrigeration without batteries?
    jonr wrote: »
    Is this feasible?
    You can search for old articles in Mother Earth News. They did a couple of stories in the'70s on batch ice makers that required no electricity at all. (I haven't seen that mag much since about '80. There may be more recent articles.)

    It's the same evaporation/condensation cycle that a typical 'fridge uses (and the icy-ball too). Solar heat pressurizes the gas during the day. Then at night, when the temperature and pressure drop, the gas passes through a small orfice where the sudden drop in pressure causes local cooling. The ice made at night was sufficient to cool the insulated space for several days.

    In your typical electric 'fridge, the pressure comes from the electric compressor. In an LP 'fridge, the pressure comes from the heat from the flame.

    It is feasable. May be a long-term project, not a simple appliance. Be prepared to work with unfriendly gasses at unfriendly temperatures (for example, amonia at a hundred PSI).

    In addition to the icy ball, see the single-pressure 'fridge that Einstein helped with (perhaps providing more patent advice than inventive genius): https://en.wikipedia.org/wiki/Einstein_refrigerator

    The fellow who started Eos solar in Maine (with a revised design for evacuated-tube solar-thermal tubes) has been working on all-solar refridgeration. I don't know the current status of his work.
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  • unseenone
    unseenone Solar Expert Posts: 61 ✭
    #6
    Re: solar refrigeration without batteries?

    So where are these available to purchase?
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  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    #7
    Re: solar refrigeration without batteries?

    I'm fine with PV solar and if I don't use one of the new refrigerators with inverters in them, then using the batteries to help with motor starting is fine. I think that the big problem is capacity. The typical refrigerator may have a motor and compressor that is just big enough to keep up on a hot day. So running for only 8 hours just doesn't move enough btus and it will fall behind.

    Using a chest freezer as a refrigerator implies some extra capacity. Looking at the numbers, running for only 12 hours out of every 24 should work, even in hot weather. That reduces use of the batteries.

    I'm surprised that commercial solar refrigerators don't offer "no battery" models.

    Holding-Plate-Refrigeration

    A related subject is using ice created during the day to produce AC at night.

    I am available for custom hardware/firmware development

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  • unseenone
    unseenone Solar Expert Posts: 61 ✭
    #8
    Re: solar refrigeration without batteries?

    What are your refrigerator / freezer space requirements?

    What are the temperatures & conditions where the fridge / freezer will be used?

    What's your budget, you can get super efficient, which requires less power for increased costs?

    I was curious why you are so against using a battery.

    If you are adamant SunDanzer makes what they call a "direct drive" refrigerator, which does not use a battery. It has optional ice packs, and is extremely well insulated. It does not require batteries or a charge controller. These are relatively small capacity. I would give SE a call, as they carry some models, so could probably special order you one. http://sundanzer.com/solar-power-refrigerators/vaccine-unit/ They may also offer a DDR165, though I don't see it on their web site, which would give you higher capacity.

    Personally, you can run a decent size high efficiency fridge/freezer on a fairly small battery, and keep a spare on the shelf, which only would need to be maintained periodically (AGM) or a dry LA battery as a backup. For the money you will get a better system, with more versatility.
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,891 ✭✭✭✭✭✭
    #9
    Re: solar refrigeration without batteries?

    Holding plate is the way to go if you have the time and money. My marine holding plate ran for one hour and could make ice for 2 days in the tropics. It was not cheap!

    The link below to the smaller Stecca unit 12v/24v is easily run from a 100 watt solar panel and a 80$ Costco deep cycle.

    http://www.meaglesun.com/en/products/steca-pf-166l-and-steca-pf-240l-refrigerator-and-freezer/

    jonr wrote: »
    I'm fine with PV solar and if I don't use one of the new refrigerators with inverters in them, then using the batteries to help with motor starting is fine. I think that the big problem is capacity. The typical refrigerator may have a motor and compressor that is just big enough to keep up on a hot day. So running for only 8 hours just doesn't move enough btus and it will fall behind.

    Using a chest freezer as a refrigerator implies some extra capacity. Looking at the numbers, running for only 12 hours out of every 24 should work, even in hot weather. That reduces use of the batteries.

    I'm surprised that commercial solar refrigerators don't offer "no battery" models.

    Holding-Plate-Refrigeration

    A related subject is using ice created during the day to produce AC at night.
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    #10
    Re: solar refrigeration without batteries?

    One hour and then coasting for days would be great for use with a generator. Might be something to consider if I came across a commercial walk-in freezer compressor and could build my own insulated cabinet (with ice thermal storage).

    It's interesting that the Steca uses batteries instead of thermal storage. My needs are typical residential refrigerator/freezer. Up to 95F in the day and 75F at night. Looks like I may have to use batteries and live with the cost of larger ones and replacing them periodically.

    I am available for custom hardware/firmware development

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  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    #11
    Re: solar refrigeration without batteries?

    Can a chest freezer be converted into a freezer/refrigerator? It would seem that if a section of the freezer could be insulated from the rest of the freezer, it could have enough heat loss that it would remain a 35F or so. Ie, like really old refrigerators what the freezer section was just a metal box within the refrigerated volume. It might also be better able to coast through 16 hours of no power (ie, run without use of batteries).

    I am available for custom hardware/firmware development

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  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    #12
    Re: solar refrigeration without batteries?

    I did some calculations and batteries to support a typical refrigerator might cost $200/year. So even if a cold plate storage refrigerator (assume a brushless DC motor, doesn't need batteries at all) cost an additional $2000, it would be worth it.

    I am available for custom hardware/firmware development

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  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    #13
    Re: solar refrigeration without batteries?

    Steca makes some reference to a "Steca PF 166 battery free" but I don't see details. Of course once you are down to 15 AH*, batteries aren't that expensive.

    SunDanzer and NASA had a storage refrigerator, but I don't know what happened to it.


    * - assume 24V and no more than 16 hours of battery operation

    I am available for custom hardware/firmware development

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  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    #14
    Re: solar refrigeration without batteries?

    Anyone with a normal refrigerator can get some battery wear reduction by 1) filling any unused refrigerator space with jugs of water and 2) using a timer to turn off the refrigerator for the last n hours of darkness (eg, 2am to 8am).

    I am available for custom hardware/firmware development

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