Battery Size

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  • mrtim
    Junior Member
    • Jun 2023
    • 2
    #1

    Battery Size

    I recently purchased a solar system kit from Northern tool so I could get some power out to a shed that I have in the back of the yard. one thing I didn't know much about was what to buy for a battery that goes with the system and Northern tool didn't provide any sizing information. the manufacturer of the system is now telling me that I need 100ah for my 110 watt system and I think I have learned that it's bad for solar batteries that continually drop down to less than 50% rated capacity. I think I have ruined the first battery I bought that had a 36ah as it no longer appears to take a charge.

    Advice?

    Tags: None
    • SunEagle
      Super Moderator
      • Oct 2012
      • 15126
      #2
      Originally posted by mrtim
      I recently purchased a solar system kit from Northern tool so I could get some power out to a shed that I have in the back of the yard. one thing I didn't know much about was what to buy for a battery that goes with the system and Northern tool didn't provide any sizing information. the manufacturer of the system is now telling me that I need 100ah for my 110 watt system and I think I have learned that it's bad for solar batteries that continually drop down to less than 50% rated capacity. I think I have ruined the first battery I bought that had a 36ah as it no longer appears to take a charge.

      Advice?
      Hello mrtim and welcome to Solar Panel Talk

      If you are using a FLA type battery you will need to have about 1/10 the Ah rating in charging amps. So my guess is that your 110 watt panel system is about 6 amps so a 60Ah battery will work for you. But depending on your loads and need for your shed you may need a bigger battery and more panel wattage to charge it.

      Have you determined you daily watt hour needs? That is the beginning step to size a solar/battery system.

        Comment

        • mrtim
          Junior Member
          • Jun 2023
          • 2
          #3
          yes about 20

            Comment

            • SunEagle
              Super Moderator
              • Oct 2012
              • 15126
              #4
              Originally posted by mrtim
              yes about 20
              Then a 60Ah battery should safely get you about 30 watt hours a day (60Ah x 12V x .2)/5 = 28.8 wh. That formula is using a 20% discharge rate and 5 days of no sun. You will get more watt hours if you get more usable sunlight or if you discharge below 80% SOC. Hopefully that works for you. But your battery life may be less due to a higher discharge. The number of cycles and discharge amount should be listed by the battery manufacturer.

                Comment

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