max battery for 50w panel

2680
2680 Registered Users Posts: 15 ✭
in Solar Beginners Corner #1
ok, i know your first response will be i am doing this backwards, but i understand that and have a plan in mind.

if i have a 50w mono panel, and am in the cincinnati area, what size battery (12v) would be appropriate for daily usage.

meaning, how much charge would i be able to get from this setup assuming 50% discharge max per day?

thanks!
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #2
    Re: max battery for 50w panel

    What are the specs on that 50w panel?

    they will give you the answer based on the charge rate you desire. 3%, 5%, 10%? and the number of days autonomy you want
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
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  • 2680
    2680 Registered Users Posts: 15 ✭
    #3
    Re: max battery for 50w panel

    specs: Maximum Power Voltage: 17.5V; Open Circuit Voltage: 22V; Maximum Power Current: 2.86A

    average sun hours here is 3.8 or so. so if i want to use 50% of the battery each night, and charged back full each day, what mah would i need?
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #4
    Re: max battery for 50w panel

    Most battery manufacturers advise that you need at least 110% - 120% of the consumed power to recharge a FLA battery.

    Using 4 hours sunlight and 2.86A you would generate ~11 Ahr, which at 50% DoD will allow you to recharge a ~15 Ahr battery as there is a ~ 70% efficiency de-rating factor to apply...

    NOTE: these are very general, approximate numbers
    YMMV

    HTH
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
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  • 2680
    2680 Registered Users Posts: 15 ✭
    #5
    Re: max battery for 50w panel

    perfect! that's exactly the info i was looking for!

    THANKS!
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #6
    Re: max battery for 50w panel

    The other rule of thumb to be satisfied is that the panel should be capable of delivering current to the battery at the C/10 rate for flooded and higher for sealed.
    Applying that rule gives us a maximum battery size of about 25 AH, even if you want to go larger than westbranch's calculation to get more cycles out of the battery.
    Using your number of 50% discharge, sets the size based on panel energy, but the real determiner there should be how many watt-hours you want to use, independent of battery size.
    SMA SB 3000, old BP panels.
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