Panels,Batteries and inverters

System
System Posts: 2,511 admin
in General Solar Power Topics #1
My wife and I are purchasing a boat with solar panels on it. I understand electricity and how solar panels work but I can't seem to find anywhere to explain.

1. If you have 4-100 watt panels how large of a battery bank will they fully charge in 12 hours of sunlight in Florida?

2. Once these bateries are fully charged with a 2000 watt inverter how long will the batteries put out enough power to run 1000 watts of load?

Is ther anywhere that I can get a formula to calculate this?

Gary
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Panels,Batteries and inverters

    Welcome to the forum.
    garystasko wrote: »
    My wife and I are purchasing a boat with solar panels on it. I understand electricity and how solar panels work but I can't seem to find anywhere to explain.

    1. If you have 4-100 watt panels how large of a battery bank will they fully charge in 12 hours of sunlight in Florida?

    400 Watts of panel, roughly speaking would be good for 210 Amp hours of battery @ 12 VDC. The system Voltage is key to what you'll be able to charge; higher Voltage, fewer Amp hours.
    In terms of 'harvest' it is not likely you'll get 12 hours of "equivalent good sun", but if you were then you'd be able to yield about 3-4 kW hours, DC. AC is another issue due to system losses.
    2. Once these batteries are fully charged with a 2000 watt inverter how long will the batteries put out enough power to run 1000 watts of load?

    Is there anywhere that I can get a formula to calculate this?

    Gary

    Rule-of-thumb wise, Array Wattage * hours of good sunlight /2 = approximately how many Watt hours you can expect on the output side. So approximately 2.4 kW hours.

    This is just generalization. Lots of things come in to play when you get into specifics. For instance, as the panels get hot their output goes down. Out on the sunny waters this could be a significant decrease in output. Also there are losses in system wiring, et cetera which need to be considered. And there's the big bugabear of battery-based systems; you can't store it all! Load-shifting can increase 'harvest' significantly, because as the batteries recharge the panel output (and thus over-all 'harvest') goes down.

    So, do you know the nominal system Voltage?
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #3
    Re: Panels,Batteries and inverters

    A 1000 watt load is huge for a 12 vdc battery bank, and it is pretty big for a 24 vdc battery bank.

    Just as an FYI, we live off grid, with 400 watts of PV, we routinely use ~ 5-600 watt/hours of power per day, and can routinely replace that, working out magically to the 50/2* rule of thumb. We have 450 am of battery, 12 vdc.

    Tony
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #4
    Re: Panels,Batteries and inverters
    garystasko wrote: »
    1. If you have 4-100 watt panels how large of a battery bank will they fully charge in 12 hours of sunlight in Florida?


    You will be lucky to get 6 usable charging hours of sunlight. before 9am, and after 3pm, the sun angle is so low relative to the panels, harvest =0 watts.

    Any stays or masts casting a shadow on the panels, will mostly shut down that panels production while the shadow is present :cry:
    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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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #5
    Re: Panels,Batteries and inverters

    One more thing to add, all calculations come from the loads. Do an accurate load calc, then work backward to determine how much battery, how much PV and how much inverter you need. I might also add that a 2000 watt inverter is pretty big, and probably not very efficient to supply smaller loads.

    Tony
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  • bmet
    bmet Solar Expert Posts: 630 ✭✭
    #6
    Re: Panels,Batteries and inverters

    I purchased a 2,000 watt Harbor Freight Tool inverter (just for investigation), and it pulled 2.5 amps just being in standby, can't imagine what a good inverter would use. I never had any intention to keep it, just wanted to see how a large unit would effect my power pack.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
    Re: Panels,Batteries and inverters
    bmet wrote: »
    I purchased a 2,000 watt Harbor Freight Tool inverter (just for investigation), and it pulled 2.5 amps just being in standby, can't imagine what a good inverter would use. I never had any intention to keep it, just wanted to see how a large unit would effect my power pack.

    36 Watts at idle. Boy HF has quality stuff! :roll: :p
    My 3600 Watt Outback uses 20 Watts doing nothing (not standby mode).
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #8
    Re: Panels,Batteries and inverters

    Sure sine 300 draws ~.5 amps powering a load, .005 amps while idle.

    Tony
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