How to size your solar panel and battery properly for small electronic project?

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rudy123
rudy123 Registered Users Posts: 1
in Solar Beginners Corner #1
i am working on a solar panel charging project.

The battery i have is li-ion 6600mA, 3.7V battery. Solar panel is 2.8W, 5V and 560mA polycrystaline panel. The charger is a seeedstuiod lipo rider pro charger that outputs 5v to my load.
my load is a 5v 55mA sensor (and controller too).

how do i determine if my solar panel and battery size are enough for my load to run 24 hours/day or not?

thanks
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #2
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    Re: How to size your solar panel and battery properly for small electronic project?

    Welcome to the forum Rudy.

    Very quickly:

    0.055 Amps * 5 volts * 24 hours per day = 6.6 Watt*Hours per day load from sensor

    Assuming your losses/deratings are on the order of 50% for entire system (as good as starting point as any):

    2.8 Watt panel * 0.50 losses+deratings * 4 hours of sun nominal per day = 5.6 Watt*Hours per day

    The battery will store:

    6.600 Amp*Hours * 3.7 volts * 0.80 (3.7v to 5v converter efficiency) / 6.6 WH per day load = 2.96 days of storage

    It will work in a reasonably sunny location/day (~9 months a year in most sunnier areas of the US)... Sort of--Really depends on hours of sun you get for your area and seasonal usage (check PV Watts).

    But if it where my system--I would seriously look at 2-3x larger panel to account for winter (can be in the 2 hours per day of sun average). 3 days of storage--How long do you want the sensor to run in bad weather. Very dark clouds, and your solar panel will output on the order of 1% of it capabilities (aka stormy weather).

    If you are serious about understanding your system--I would highly suggest a DC Amp*Hour/Watt*Hour meter--It will give you much better information to update your design requirements. The only problem with the unit at the link, it only runs "one direction"--It will not run "backwards" when battery is being discharged and "forwards" when battery is being charged.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
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    Re: How to size your solar panel and battery properly for small electronic project?

    The battery is 3.7 Volts and the load is 5 Volts? That looks like a problem to me.

    Otherwise convert to Watts:
    Load of 55mA * 5 Volts = 0.275 Watts * 24 hours = 6.6 Watt hours
    Battery of 6600mA hours * 3.7 Volts = 24.420 Watt hours
    Panel of 560mA * 5 Volts = 2.8 Watts

    So in terms of power with no loss factors the load demand is about 27% of the battery capacity (unless I slipped a decimal somewhere). The panels should be capable of 2.8 Watts * 4 hours or 11.2 Watt hours, almost double the load demand.

    In theory it should work except for that Voltage differential between the battery and the load. If the load can be operated at the lower Voltage, no problem.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #4
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    Re: How to size your solar panel and battery properly for small electronic project?

    There is probably a "boost" converter somewhere in the system... Usually around 80-90% efficient.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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