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Determining Amp Hour Rating For Your Solar Batteries



I get a lot of questions from people starting out with solar power on how to get the Amp Hour rating for the solar batteries they will be using. Here is a step by step on that…

  • Determine which appliance or electric device will you power with your solar batteries via your solar power system and get their corresponding wattage input. For example:

light bulb (20watts).

  • Calculate how many hours in a day will you run the above. For example:

light bulb (5hrs/day)

  • Get the watt-hrs/day of each. For example:

light bulb (20watts x 5hrs/day = 100watt-hrs/day)

  • Get the amp-hours per day by dividing the watt-hrs/day value by the voltage of the battery you will use, say 6V or 12V. For example:

100 watt-hrs/day divided by 12V = 8.33 amp-hrs/day

  • Take into consideration the discharge level, usually 50%. For example:

8.33 amp-hrs/day divided by 50% = 16.66 amp-hrs/day or Ah

In conclusion, you will need at the least a 16.66 Ah rating battery to run a 20watt light bulb for 5 hours each day.

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