How many panels do Ineed to recharge batteries

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System
System Posts: 2,511 admin
in Solar Beginners Corner #1
I am putting in six ground effect lighting sets rated at 50w each. The lights will be on a dusk to dawn switch. I want to run them on deep cycle batteries and recharge them with solar panels. What I need to figure out is how many panels I need to recharge the batteries. I live in southeastern Arizona, so we do get a lot of sunshine. I assumed, which I know is dangerous, that I would need at least 300w of panels to match the consumption of the lights.
I greatly appreciated any help.
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  • mikeo
    mikeo Solar Expert Posts: 386 ✭✭✭
    #2
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    Re: How many panels do Ineed to recharge batteries
    I assumed, which I know is dangerous, that I would need at least 300w of panels to match the consumption of the lights.
    You will probably need many more panels to cover losses which usually amount to almost 50% in a solar/battery system. Are the lights DC and at what voltage? At 300 watts per hour for 10 hours (just guessing what average dusk to dawn might be) you will need around 3000 watt hours to power them. At 50% loss that translates into almost double that in panels.
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  • System2
    System2 Posts: 6,290 admin
    #3
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    Re: How many panels do Ineed to recharge batteries
    mikeo wrote: »
    Are the lights DC and at what voltage?

    The lights are 12VDC.
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  • Windsun
    Windsun Solar Expert Posts: 1,164 ✭✭
    #4
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    Re: How many panels do Ineed to recharge batteries

    You will need roughly 3x as much panel as your lights consume.

    Even though you might get 12 hours of sun in the summer, the panels do not "see" that much, they only see around 6-7 hours best case. In Winter it is much less, the panels would get around 4.5 to 5 hours full sun per day.
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #5
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    Re: How many panels do Ineed to recharge batteries

    300 watts of outdoor lighting? Why so much? And have you considered LED lighting. Remember, every dollar spent in conservation saves ~ $10 in PV costs. Round numbers, battery based systems run ~$8-12 watt. So a 1200 watt system might cost $12,000. Reduce the load by 75%, you reduce the cost by the same 75%,, say $3000. A much easier nut to crack.

    Tony
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,448 admin
    #6
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    Re: How many panels do Ineed to recharge batteries

    May not apply in your case--but Motion Detector based lights (either for security or just to have them on when people are around) can also save a bunch of energy too.

    Regarding LED lights--the standard White LED in the plastic LED case generally do not last that long in real life (100's to 1,000 hours or so before 50% loss in output--vs the 50,000 hours that everyone prints on their packages).

    Depending on the scope of your project and the ease of getting power too it (if grid power is available, almost always better to use that for powering your lights--And add a Grid Tied Solar Array to your home instead)--It is difficult (i.e., expensive) to light throughout the night. Lots of power, LED's that don't last long, battery maintenance, what about backup power source during stormy weather, etc.).

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