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Lights for a barn

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  • Lights for a barn

    So I have been reading a lot of threads and browsing this forum for a while. I THINK I have an idea of what I need for my set up but want to run it by everyone and see what you think and suggest. I want to be able to run lights in my barn. I will not have them all on at the same time, just whatever part I am in at the time (different bays). I will also only use them for at most maybe 3 hours a night, 3-5 times a week-ish. I do not NEED any plugs, just lights and I live in NC.

    I was looking at a Grape Solar kit that has a 50 watt panel and a charge controller for around $100.

    Power at least one fluorescent light that has two T8 bulbs for 3 hours~ 64w/12=5.3A*3(hours)=16Ah total.
    Deep cycle battery ~ 75Ah

    That panel will produce 4.2Ah. I know it will take ~18 hours to fully charge the battery using that panel. My thought process is, (and I could be COMPLETELY wrong!) that if I use this battery, it will take the panel ~4 hours of sunlight to replenish what I have used that day. So going with a bigger battery gives me the option to use more if I need to because I probably would not need it the following day or so and would give it time to recharge.

    Is this accurate? Let me know if you need me to provide more info or anything.


  • #2
    I would say your calculations are a little off.

    First off 2 x 32watt lamps use more than 64watt due to the ballast losses. For a better estimate I would go with 90 to 100 watts for a 2 lamp fixture.

    Next if you use one of those fixtures for 5 hours (always use the higher number to determine the worse case) you would be burning 450 to 500 wh a night.

    For a 12volt battery that comes to 500wh / 12v ~ 42Ah.

    A FLA or AGM battery should only use at most 25% daily so with 42Ah x 4 = 168Ah battery. The lower the discharge the longer the battery lives as well as it gives you a couple of days to use that battery without sunshine to charge it.

    Now for charging you need to generate somewhere between C/8 and C/12 amps where C = the battery Ah rating. So you need between 14 and 21 amps.

    Using an MPPT type charge controller (which that grape system does not include) you will need ~ 12v x 17amp = 204 watts of panels.

    Worse case is that the estimated watt hour usage is less then what you will really use so up sizing the battery and panel wattage helps keep the battery usage less than 25%.

    That is a quick math to determine your solar / battery system


    • #3
      If you have access to Costco, I think their sale still on for 19.99 for which are brighter than standard 2 fluorescent tubes unit. They are 38W total for the entire unit.


      • #4
        I'd look into using 12V DC LED lights, and use 10 ga romex for the wiring , expensive wires, but simplifies things by not needing an inverter Look at RV or boating supply shops for 12V lighting ideas, Electronic 12VDC ballasts exist for fluorescent lighting, if you need that. Recent LED's aim the light better and are as efficient as fluorescent,
        Powerfab top of pole PV mount (2) | 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