Selection of solar panels and batteries

  1. is there any procedure ( formulae ) to select the power rating of solar panels and ampere hour rating of batteries ??????
  2. jcsd
  3. mfb

    Staff: Mentor

    It depends on the application.
  4. it is to charge a battery which inturn provides the supply for a 12 V 100 W DC motor ...... the operating time of the motor is 5 minutes intermittent cycle of 4 cycles in a day
  5. mfb

    Staff: Mentor

    Well, that helps a bit, but it is still a bit vague:

    100W for 5 minutes are 100W*300s= 30kJ = ~8.3Wh. This is the minimum requirement for your battery, unless you want to rely on sunshine directly at the time of the motor operation.
    8.3Wh at 12V correspond to 8.3Wh/(12V) = .69 Ah.

    In general, your battery won't get fully charged between cycles, so I guess you'll need more capacity. If your solar cells are sufficient to provide the power for a day even if it is cloudy, a capacity for 4 cycles could be sufficient. Otherwise, you could need more capacity.

    The required peak power rating of the solar cells depends on the amount of sunshine you get, and the battery capacity. The average energy per day has to be at least the required energy for the motor operation, but there should be some additional safety factor for cloudy days/weeks.

    Matching the voltage is another thing you have to take care of - if the output voltage of the solar cells is not 12 Volts, you get some conversion losses.

  6. can a 20 W solar panel and a 24 Ah battery will be more than enough for this operation ???? considering our place in India we get a minimum 5 hrs of intense sunshine a day ........
  7. mfb

    Staff: Mentor

    20W*5h = 20J/s*5*3600s = 360kJ. Should be more than sufficient, especially with the large battery that can store enough energy for a few days.

    Just keep in mind that you need some controlled way to charge the battery with the right voltage and current range.
  8. hmm yes .... i'll be using a 12 V 10 A charge controller ............
    can i go for a 12 V 12 Ah or a 12 V 24 Ah battery ????????
  9. mfb

    Staff: Mentor

    Sorry for the late reply: both should work.
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