watts, amps & volts???

msgieser
msgieser Registered Users Posts: 24 ✭✭
in Off Grid Solar & Battery Systems #1
I'm confused about finding out what kind of max. amps to expect out of solar panels.

If I have (3) 280 watt, 24 volt panels feeding thru an mppt charge controller into a
12 volt battery bank are the batteries going to see a max (under ideal conditions) 35amps or 70 amps? The 24 volt to 12 volt has me confused (not too hard to do!) Thanks!
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: watts, amps & volts???

    With an MPPT controller it's a matter of panel Watts derated divided by system Voltage. The derating factor varies with any given site, but typical is 77%

    So three 280 Watt panels is 840 Watts and that would derate to 646 Watts (840 * 0.77). Divide that by 12 Volts and you get 53.9 Amps as the most you might expect to see.

    However, that's just a "ballpark" figure. Wiring losses, controller efficiency, actual battery Voltage, ambient temperature, et cetera can all alter this either up or down.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #3
    Re: watts, amps & volts???

    you might do better to think in terms of wattage delivered at a certain end voltage minus operational losses.

    3 x 280w = 840w

    840w x .77(average derating) = 646.8w

    646.8w / 14.4v(rough figure for 12v system at the high end of charge) = 44.91a output

    now every system is different and somewhat unique so this rough estimation can vary. for instance, if you are running resistive losses in the wires to the cc then this will detract from the output some or if your controller is better or worse in its efficiency than the figured 95%.

    a phrase many like to use is, your mileage may vary, and this holds true here, but this gives a good rough figure to start with.

    edit to add: you beat me to it coot and it seems my typing is slowing down as it took too much time for my post to appear after yours.:cry::roll:
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: watts, amps & volts???

    Niel;

    I'm on the cable system at the moment. When I get back to satellite country I'll be slowed down! :cry:
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