upgrade redirected by Mom....DC Fridge?

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bmet
bmet Solar Expert Posts: 630 ✭✭
in Solar Beginners Corner #1
My mother has asked me a couple of times if her fridge can be powered by solar. I tell her NO, not with her current appliance. This gets me to reconsider my upgrade path, as now I am looking at 24VDC refrigerator. I've seen a couple that advertise to run on 4 Amps, and I'm stumped on the math. If two 200W panels(in parallel) would yield 12-13 Amps for a few hours a day, that could leave 8 Amps left over for charging battery

So 8A x 14.4 volts charging = 115W
115W x 4 'good' hours = 460W

Now I am stumped on what to do with that number. What size battery can be fully recharged on 460W, and still have enough capacity to run the fridge for the other 20 hours of the day?

I can estimate the fridge use over a 20 hour period, for example.

Refrigerator:
4 Amps x 20 hours x 12 volts = 960 watt hours

I thought DC fridges were supposed to be much more efficient, but a 4 amp constant draw sounds like a lot. This brings me to my next question. Does that energy rating represent a constant draw, or only when compressor runs? I'm really confusing myself. Please help.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #2
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    Re: upgrade redirected by Mom....DC Fridge?

    4 amps @ 24 volts continuous? That's 96 watts continuous X24 hours = over 2.3 Kwh / day and would require a substantial solar/battery system and deep pocket$. That's horrible!!!! Flee from that fridge and do some more checking. The most efficient fridges will have a compressor which will cycle on and off. The one you were looking at obviously does not. There are several different refrigeration systems, and they're not all efficient by any means.
    There ARE very efficient DC fridges, but all things considered, you may well be better off with a good, high efficiency standard AC fridge and run it via inverter from a solar system.
    Good thing you checked before purchasing.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #3
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    Re: upgrade redirected by Mom....DC Fridge?

    tell me why her current 'frige can't be run by solar or is it a case of you just need to upgrade the pv and battery system to accommodate it?
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  • Urbandialect
    Urbandialect Solar Expert Posts: 107 ✭✭✭✭
    #4
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    Re: upgrade redirected by Mom....DC Fridge?

    Cheap man's solution to problem, put the refigerator on a timer.. 2 hours on 1 hour off, or 1 hour on 2 hours off, 2 hours on 2 hours off.. etc
    The timer is a device that you plug your refigerator in to, then you set it to the setting you like then plug the device into the inverter, it will shut off and on however you programed it ... think christmas lights. :)
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  • bmet
    bmet Solar Expert Posts: 630 ✭✭
    #5
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    Re: upgrade redirected by Mom....DC Fridge?
    niel wrote: »
    tell me why her current 'frige can't be run by solar or is it a case of you just need to upgrade the pv and battery system to accommodate it?

    Her current fridge is a 40 yr. old appliance with an unknown expiration date. She wanted to replace it with something newer and more energy efficient. I've read that DC refrigerators use some type of variable frequency compressor that's a better solution to the standard AC appliance on an inverter. On one site, the manufacturer claims there product can run on a single panel, but that product is the size of a styrofoam ice chest.

    Wayne,

    Thank you for correcting my numbers, I got my 12s and 24s mixed up. What I've read about these DC powered refrigerators is that they are super expensive, but are supposed to be energy efficient. The one retailer I've called didn't know anything about their consumption outside of what's printed on the product card. Another solar retailer carries refrigerators that are energy star rated, but none of them DC. Other sites won't list a price, but are happy to have your contact info.

    When it's time to replace my mom's fridge, I'd rather do it with a product able to be run off-grid. Thanks for your time.
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  • Slappy
    Slappy Solar Expert Posts: 251 ✭✭✭✭✭✭
    #6
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    Re: upgrade redirected by Mom....DC Fridge?

    bmet, can you post a link for this fridge?
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  • PhilS
    PhilS Solar Expert Posts: 370 ✭✭✭
    #7
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    Re: upgrade redirected by Mom....DC Fridge?
    Urbandialect wrote: »
    Cheap man's solution to problem, put the refigerator on a timer.. 2 hours on 1 hour off, or 1 hour on 2 hours off, 2 hours on 2 hours off.. etc
    The timer is a device that you plug your refigerator in to, then you set it to the setting you like then plug the device into the inverter, it will shut off and on however you programed it ... think christmas lights. :)

    If I did such a system I suspect that overall I'd be losing. My Sears fridge, when first plugged in, starts with a defrost cycle. With a timer, it would start that defrost cycle every time power was turned on.

    All fridges aren't the same, but a timer system should be checked with a Kill-a-watt meter over a few days to see if it was actually saving power or not.

    Phil
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  • halfcrazy
    halfcrazy Solar Expert Posts: 720 ✭✭✭
    #8
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    Re: upgrade redirected by Mom....DC Fridge?
    PhilS wrote: »
    If I did such a system I suspect that overall I'd be losing. My Sears fridge, when first plugged in, starts with a defrost cycle. With a timer, it would start that defrost cycle every time power was turned on.

    All fridges aren't the same, but a timer system should be checked with a Kill-a-watt meter over a few days to see if it was actually saving power or not.

    Phil

    This is typical of a lot of the new electronic fridges. I would be very Leary of putting any newer fridge on a timer if it is like mine it would do a defrost cycle every time it turns on. This would cause the daily usage to go from 1kwh to probably 3kwh or more.

    I also am not a huge fan of dc appliances they seem to be expensive and proprietary. A good old Kenmore from sears with a good energy star rating will be at least one quarter the cost and not much less efficient.
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  • Urbandialect
    Urbandialect Solar Expert Posts: 107 ✭✭✭✭
    #9
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    Re: upgrade redirected by Mom....DC Fridge?
    PhilS wrote: »
    If I did such a system I suspect that overall I'd be losing. My Sears fridge, when first plugged in, starts with a defrost cycle. With a timer, it would start that defrost cycle every time power was turned on.

    All fridges aren't the same, but a timer system should be checked with a Kill-a-watt meter over a few days to see if it was actually saving power or not.

    Phil

    Well there goes that ideal
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #10
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    Re: upgrade redirected by Mom....DC Fridge?

    Personally I don't like the idea of putting a timer on a fridge, I would be concerned the temperature wouldn't be kept low enough for food safety. That's the job of the thermostat, to cycle the compressor as needed to maintain temp. Food poisoning can be bad, and worse, much worse.
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  • cptdondo
    cptdondo Solar Expert Posts: 103 ✭✭✭
    #11
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    Re: upgrade redirected by Mom....DC Fridge?

    You're looking for a fridge with a Danfoss BD-5 compressor, possibly with the ASU controller from Isotherm.

    Mine uses about 17 Ah on a normal (72 degree) day, up to about 50 Ah on a roasting hot day. This is in a parked RV with no cooling, so the fridge is working in high ambient temps, with air temp in the 90s or even higher.

    The ASU controller monitors voltage; when it senses charge voltage (greater than something like 13VDC) it kicks into high freeze mode and freezes a cold plate down to 15 degrees. When it loses charge voltage (ie it's running on battery power) it switches into a high-efficiency mode where it only cools enough to keep the internal temps barely adequate.

    It controls the speed of the compressor as well as the run time to minimize energy usage.

    Prepare to spend $$$$; an undercounter-sized unit like mine is about $1200.
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  • bmet
    bmet Solar Expert Posts: 630 ✭✭
    #12
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    Re: upgrade redirected by Mom....DC Fridge?

    Thank you for your response. In the various products around the internet, I've yet to see a fridge/freezer combination for under 3 grand. The fridge-only, or freezer-only appliances are exactly where you mention. I understand temperature relates to AH required, in this case it would be in a TuffShed. As a comparison, one appliance's specs state 80 watts as input power, regardless if its 120VAC, 12VDC, or 24VDC. (That doesn't make sense to me). Other units advertise their input as you do, in AHs. Which is a more realistic statement? In a small tabletop fridge that uses electrical 'superconductor' technology (no compressor), the input power is a constant 1.1 Amps.

    I get confused trying to hop-scotch back and forth between amps, amp-hours, and watts. Usually I miss a decimal point or forget to figure 12 vs 24 volts. :confused:
    cptdondo wrote: »
    You're looking for a fridge with a Danfoss BD-5 compressor, possibly with the ASU controller from Isotherm.

    Mine uses about 17 Ah on a normal (72 degree) day, up to about 50 Ah on a roasting hot day. This is in a parked RV with no cooling, so the fridge is working in high ambient temps, with air temp in the 90s or even higher.

    The ASU controller monitors voltage; when it senses charge voltage (greater than something like 13VDC) it kicks into high freeze mode and freezes a cold plate down to 15 degrees. When it loses charge voltage (ie it's running on battery power) it switches into a high-efficiency mode where it only cools enough to keep the internal temps barely adequate.

    It controls the speed of the compressor as well as the run time to minimize energy usage.

    Prepare to spend $$$$; an undercounter-sized unit like mine is about $1200.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #13
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    Re: upgrade redirected by Mom....DC Fridge?

    In my opinion, when you're looking at that much $ for a DC fridge, you would definitely be further ahead going for a common every day, but high efficiency Energy Star fridge and put a bit more $ in PV to run it, if necessary. The results will be roughly the same, but you'd be $ ahead and if the fridge quit in a few years, you wouldn't be looking at another 3 grand to replace it. Re energy consumption, you should be looking for the lowest kwh per month, or year.
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  • RandomJoe
    RandomJoe Solar Expert Posts: 472 ✭✭✭
    #14
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    Re: upgrade redirected by Mom....DC Fridge?

    My first inclination (and what I did) would also be to just get a standard fridge - save lots of money on the fridge - and run it via inverter. But running a (standard) fridge will require a fairly substantial solar setup. Mine uses about 1.6kWh/day. As keeping the food cold during an outage was one of my primary motivators to installing my solar system, I focused on what I'd need to accomplish that during my initial designs. In simplest math (which leaves out some inefficiencies) I needed enough solar panels to replace *at least* that 1.6kWh/day which with 4.9 hrs/day of sun (my winter minimum) is 1600Wh / 4.9 hrs = 326W in panels.

    Nameplate ratings of panels are optimistic at best - my chosen 135W panels are more realistically 96W, so 326/96 = 3.4 panels so 4 135W panels plus mounting hardware, charge controller, inverter, wire, all kinds of miscellaneous components... And don't forget, a fridge's running current isn't very high - generally around 100W - but it takes about 10X that to get it started! I had to get a 1500W inverter just to get mine to start.

    Leaving us with the battery bank: how low are you willing to take it each night? I wanted to ensure I could run 3 days without any sun (say very stormy weather or an ice storm) and not take the bank below 50% SOC. So 1.6kWh/day x 3 days = 4.8kWh / 12V battery bank = 400Ah to 50% SOC, so double that for total capacity = 800Ah battery bank. That's eight T-105 6V 220Ah batteries, in four parallel strings. (Or, if you want 24V, two parallel strings. A single 8-battery string for 48V.)

    That's what I wound up doing, installing everything myself in a small off-grid arrangement inside my otherwise grid-powered home. Worked just fine, not quite as fully capable as the numbers above suggest since I did leave out some inefficiencies that will eat up some power each day. Mighty expensive way to run a fridge, though! :p Think this much of the system was around $5,000 - again, completely self-installed so no labor costs.
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  • mikeo
    mikeo Solar Expert Posts: 386 ✭✭✭
    #15
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    Re: upgrade redirected by Mom....DC Fridge?
    My first inclination (and what I did) would also be to just get a standard fridge - save lots of money on the fridge - and run it via inverter. But running a (standard) fridge will require a fairly substantial solar setup. Mine uses about 1.6kWh/day.
    There are a few EStar fridges out now that use less than 900 watts per day. They arn't large but in the usable 16 to 18 cubic ft range. Prices run in the 600 to 700 dollar range. Examples: Frigidaire LGUI1849L* and Kenmore 9704388*, 18.34 cubic feet, 334 kWh/yr.
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  • bmet
    bmet Solar Expert Posts: 630 ✭✭
    #16
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    Re: upgrade redirected by Mom....DC Fridge?

    Thank you for those two references. A Google search led to this web site listing of various EnergyStar appliance at a glance.

    http://www.energystar.gov/index.cfm?fuseaction=refrig.display_products_html
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #17
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    Re: upgrade redirected by Mom....DC Fridge?
    mikeo wrote: »
    There are a few EStar fridges out now that use less than 900 watts per day. They arn't large but in the usable 16 to 18 cubic ft range. Prices run in the 600 to 700 dollar range. Examples: Frigidaire LGUI1849L* and Kenmore 9704388*, 18.34 cubic feet, 334 kWh/yr.

    be careful here as bb had mentioned the frigidaires not lasting as long as they should without problems and be sure as to who made that sears frig as sears don't make them themselves.
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  • rplarry
    rplarry Solar Expert Posts: 203 ✭✭
    #18
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    Re: upgrade redirected by Mom....DC Fridge?

    Bmet
    If you are just looking for a refer to put into a shed, then maybe a chest freezer to refer conversion will work for you. I did one about a year ago, only cost me $150 or so and only uses 200wh a day in cooler weather and 400wh in hot weather. Here is a link to the info: http://forums.bajanomad.com/viewthread.php?tid=47172
    Mine works really well as a drink cooler and for extra food when we run out of room in the house refer.
    Larry
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  • bbbuddy
    bbbuddy Solar Expert Posts: 135 ✭✭✭
    #19
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    Re: upgrade redirected by Mom....DC Fridge?

    We are in a 40 foot 5th wheel, and never turn the AC on, so high ambient temps in summer. When our propane fridge died we had to decide whether to get a new one or go with 110v.

    The high price of a new propane fridge turned us toward putting that $ into solar.

    We now run a 10 cubic foot 110v fridge, and 12 cubic foot 110v chest freezer on 800 watts of solar. I do turn off the inverter when I go to bed, and turn it back on when I get up, and everything stays cold just fine during those 8 hours.

    We also run a TV/sat system at night maybe 4 hours, and a computer during the day probably 6 to 8 hours.

    The only time the 800 watts is not enough is a totally cloudy day, or when I have to do laundry or fill the 3000 gallon water tank from the well.

    Now I know that if and when the fridge dies in the future, it will cost about $350, not $1400. And a WHOLE LOT easier to buy and replace...
    Magnum4024PAE, 2 Midnite Classic 150s, 3100watts solar, 432ah lifepo4 battery.  Off grid since 2004.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #20
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    Re: upgrade redirected by Mom....DC Fridge?
    bmet wrote: »
    ... As a comparison, one appliance's specs state 80 watts as input power, regardless if its 120VAC, 12VDC, or 24VDC. (That doesn't make sense to me). Other units advertise their input as you do, in AHs. Which is a more realistic statement? In a small tabletop fridge that uses electrical 'superconductor' technology (no compressor), the input power is a constant 1.1 Amps. ....

    I think you are speaking of Thermal Electric Cooler or Peltier Junction heat pumps.

    They consume 100W of power, to provide 10w of cooling, very inefficient. Needs a lot of power, and dissipates it as heat.
    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 ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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