What Size Solar Panel to Charge a 300Ah Battery?

Answer
768 W of solar (5 sun hours)

Refilling 80% of a 12 V 300 Ah battery takes 2,880 Wh. With 5 peak sun hours and 75% real-world efficiency, that needs about 768 W of panels. Use a charge controller rated for at least 80 A.

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Battery voltage
h/day
W
%
Flat mounts, heat and shade: 70–80%.
Solar needed
–
How we calculated this

    For estimating and educational purposes only. Results are approximate and are not a substitute for a licensed professional, the manufacturer's instructions or your local code. Disclaimer

    More questions like this

    50 Ah100 Ah200 Ah400 AhAll quick answers

    Solar watts to recharge a 300 Ah battery in one day

    SunFrom 20% (80% refill)From 50% (50% refill)
    3 sun hours1,280 W800 W
    4 sun hours960 W600 W
    5 sun hours768 W480 W
    6 sun hours640 W400 W

    75% overall efficiency covers heat, wiring, controller losses and non-ideal panel angle. An MPPT controller harvests 15–30% more than PWM.

    Frequently asked questions

    Will a 100 W panel charge a 300Ah battery?

    It adds about 31 Ah on a sunny day, so a full recharge of a 300 Ah battery takes about 7.7 days.

    What charge controller do I need?

    About 80 A for 768 W on a 12 V battery; round up to the next size.

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