Panel size ...tradeoffs

System
System Posts: 2,511 admin
in Advanced Solar Electric Technical Forum #1
I plan to add a solar charger for a 4D (185AH) gel battery which has only one purpose: to power a NorCold fridge ..drawing 3 Amp. Estimate the unit runs between 8 and 12 hour per day, depending on ambient temp. ..with most of the load during the day.

The question I am trying to resolve is: do I go with a Kycera KD-135 or the KD-180?
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  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    #2
    Re: Panel size ...tradeoffs

    Bob,

    A couple of factors will greatly influence the answer to your question:
    1) Local insolation data. Can you give us an idea about the intended system's location?
    2) 135 is a "12 V" module (36 cells), and the 180 is a "16 V" module (48 cells). What kind of charge controller are you planning to use?

    More later,
    Jim / crewzer
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,623 admin
    #3
    Re: Panel size ...tradeoffs

    Also, is that 3 amps at 120 VAC, do you need/have an inverter picked out (some inverters can waste serious amounts of power).

    Besides your location, do you have a goo place to install solar panels with, at least no shade/shadows from 9am-3pm?

    And, solar power varies over the season (summer/winter sun angles, local weather conditions, etc.)--so do you want the panels to handle 100% of the power, or 90% of the power with generator backup?

    Lastly, is the fridge already energy efficient? Conservation is almost always cheaper than building out a solar RE power system. And, is the system setup in a cost effective installation... Fridge used 365 days a year (good for Solar PV)... Used just weekends during the summer--generator+battery bank or Propane powered fridge may be a better solution (more cost effective).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    #4
    Re: Panel size ...tradeoffs

    Bill,

    I assumed (perhaps wrongly) that Bob was referring to a small NorCold AC/DC unit like one of these (in the middle of the page):

    http://www.thetford.com/HOME/PRODUCTS/NorcoldIncRefrigerators/tabid/195/Default.aspx

    HTH,
    Jim / crewzer
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,623 admin
    #5
    Re: Panel size ...tradeoffs

    Jim,

    I am sure you are correct... But asking voltage and current always makes things less confusing (at least for me).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #6
    Re: Panel size ...tradeoffs

    Running an absorption fridge on electricity is way more "expensive" than running it on LP. My Dometics use ~1500 btu/hour, with duty cycle of ~50% at 75f ambient, or less than 18k btu/day. (Full size dometic, not one of the little ones) That translates to less than 1 quart of Lp per day. A 20# bbq tank holds between 4-5 gallons for comparison.

    The same fridge draws 325 watts on AC and the duty cycle is considerably longer, say 75% making 5.2 kwh/day. (that 325 watts would be ~2.7 amps at 120vac. 3 amps at 12 vdc would only be ~36 watts. I don't think 35 watts would be enough to heat the ammonia boiler enough to begin to cool, I could be proved wrong however).


    Both run times can be reduced significantly by adding both a condenser and a evaporator fan, as well as adding ridged foam around the cabinet.

    I have been struggling with the idea of running my dometics on my Pv for a number of years, and the investment in additional Pv/battery/inverter just doesn't make sense. I do on occasion plug it in to the inverter when I have a full battery and full sun, but it just doesn't save enough LP to make much sense.

    A new energy star compressor fridge can be had that will draw ~.5.75 kwh/day. As I have suggested before, if this is a full time installation, consider getting the compressor, part time consider LP

    Tony
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
    Re: Panel size ...tradeoffs

    Purely in terms of one panel over the other, if the larger one fits the space and fits the budget go for it. You can never have too much PV! :D
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  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    #8
    Re: Panel size ...tradeoffs

    The NorCold fridges in the "middle" of the page linked above are all compressor type units with adjustable thermostats. Running DC current specs generally appear to be in the 1.5 A to 3 A range at 12 VDC nominal.

    3 A at 12 V nominal for 12 hours/day would put net energy requirement at 432 Wh/day.

    The two modules have identical current specs. All else being equal, the larger module will be able to deliver more energy/day if the OP is planning on using an MPPT controller. If he's planning on using an PWM controller, then performance from the two will likely be identical.

    We just need a bit more info from the OP.

    Regards,
    Jim / crewzer
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