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  • How to calculate the capacity of storage battery?

    In stand alone solar system, how do you calculate the capacity of storage battery? Is that any formula?

    Please make an example. Thanks so much for any answers.

    Helen

  • #2
    The battery manufacturer makes that calculation when they design the battery, and then they put a label on the battery with the specs.

    example 12V 110Ah @ 20 hour rate


    In reality, you can only use half the power stored, otherwise, you severely shorten the life of the battery. There is a good battery FAQ here:
    http://www.windsun.com/Batteries/Battery_FAQ.htm That will answer a lot of questions I hope.

    Mike
    Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister

    Comment


    • #3
      hi, Mick90250,

      Thanks for your answers, but I think you did not catch what I said. You know if I want to make an off-grid system, I need to figure out which capacity of battery I should use.

      Ok, let me make an example,
      Load :2* 11W lamp; 10 hours working time per day.
      system voltage:12V
      Rainy days: 3 days

      Then how will you calculate the capacity of the battery?

      Comment


      • #4
        Originally posted by solarf.helen View Post
        hi, Mick90250,

        I want to make an off-grid system, I need to figure out which capacity of battery I should use.

        Ok, let me make an example,
        Load :2* 11W lamp; 10 hours working time per day.
        system voltage:12V
        Rainy days: 3 days

        Then how will you calculate the capacity of the battery?
        Much better question. I knew you were not going to manufacture a battery.

        Batteries have a shorter life, the deeper you discharge them. example:
        1000 cycles 10% discharge
        800 cycles 20% discharge
        300 cycles 50% discharge
        80 cycles 90% discharge

        Generally, discharge to no less than 50%, and size 1 day to about 10%

        You are asking for 3 days. I 'll assume 12V CFL, so no inverter losses

        Your load is 22W for 10 hrs = 220W hour x 3 days = 660w hour consumed in 3 days

        So a battery bank of 1320wh would be the minimum size.

        Working all in watts, allows conversion back to any voltage. Volt x Amp = watts

        12V = 110A
        24V = 55A

        So a standard group 24 size battery would be just under the spec, but a group 27 would
        http://www.mysears.com/DieHard-Marin...ze-27M-reviews
        just make it. at 105A.

        Then you have to recharge it with something.
        Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
        || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
        || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

        solar: http://tinyurl.com/LMR-Solar
        gen: http://tinyurl.com/LMR-Lister

        Comment


        • #5
          Cycles vs Life

          Originally posted by Mike90250 View Post
          Batteries have a shorter life, the deeper you discharge them. example:
          1000 cycles 10% discharge
          800 cycles 20% discharge
          300 cycles 50% discharge
          80 cycles 90% discharge
          Generally, discharge to no less than 50%, and size 1 day to about 10%
          .....
          Then you have to recharge it with something.
          Last edited by MarineLiner; 07-17-2009, 11:35 PM.

          Comment


          • #6
            Originally posted by MarineLiner View Post
            so it differs with "cycle" in the AC (Alternative Current, Hertz/cycle).
            and Depth of Discharge (DOD) is what i just know.
            Right, battery cycles, are:
            a) Discharge to some value
            b) Recharge back to full
            = one cycle

            Not the same thing as AC powerline frequency (cycles)
            Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
            || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
            || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

            solar: http://tinyurl.com/LMR-Solar
            gen: http://tinyurl.com/LMR-Lister

            Comment


            • #7
              Originally posted by Mike90250 View Post
              Right, battery cycles, are:
              a) Discharge to some value
              b) Recharge back to full
              = one cycle

              Not the same thing as AC powerline frequency (cycles)
              So with that said that means that the average battery coming in with a 50% discharge would last less than a year?

              Comment


              • #8
                It's a giodeline to start. Same batteries, same site, but more batteries, sized to only 20% dishcarge, should last over 5 years. (Deep cycle batteries, not Kmart deep/starter batteries)
                Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
                || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
                || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                solar: http://tinyurl.com/LMR-Solar
                gen: http://tinyurl.com/LMR-Lister

                Comment


                • #9
                  need help.. confusing

                  which is ri8.. case1 or case2?
                  CASE I:
                  our fan needs 220 v and 0.2 A for an hour = 50 watts.
                  a 12volt 7AH battery @20 hour rate -> 7/20 = 0.35 A.
                  The battery can sustain a 0.35A load for 20 hours.
                  But we can use only the 50% capacity of battery so tat it doesnt get damaged.
                  So 0.35A load for 10 hours.
                  If we consider the losses in invertor, the time will be around 3 hours.
                  CASE II:
                  power consumed by the fan is 50watts.
                  lets consider that we want the fan to run for about 3 hours in battery.
                  power required = 50 watts * 3 hours = 150watt hours
                  So, the battery capacity should be 150 watt hours.
                  what we need : Two 12volt 7AH in parallel. (in parallel v is constant and I= 7+7, so P=12*14=168 watt hours)
                  Loses in invertor will occur. We can not drain the full power from the battery.

                  Comment


                  • #10
                    welcome. Lets' un-confuse this a bit.

                    power consumed by the fan is 50watts.
                    power required = 50 watts * 3 hours = 150watt hours
                    Good so far. If you use only 50% of battery, then you need a 300 watt hour battery.
                    At 12V, that would be a 25amp hour battery.

                    Now to recharge that battery, to account for all the system losses, you need to have a PV panel with a wattage nameplate that, when multiplied by your SUN hours
                    use PV watts to find out your hours http://www.nrel.gov/rredc/pvwatts/about.html
                    Ths solar SUN hours are quite different than when the sun is up , most areas get 6 or fewer hours.

                    Anyway, you need to harvest 300 watt hours, divide by ____ sun hours = ______ watts of PV

                    If you use an inverter , add 30% to the needed 300W harvest, you will need to harvest about 400 wh

                    Hope this helps
                    Last edited by Mike90250; 04-22-2012, 10:26 AM.
                    Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
                    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
                    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                    solar: http://tinyurl.com/LMR-Solar
                    gen: http://tinyurl.com/LMR-Lister

                    Comment


                    • #11
                      Originally posted by Mike90250 View Post
                      Anyway, you need to harvest 300 watt hours, divide by ____ sun hours = ______ watts of PV
                      First of all, thank you mike. Really thank you. You cleared my mind.
                      lets say in here we have 10 sun hours. so i should buy a 12 volt 30 watts panel?

                      Comment


                      • #12
                        There is no place on the planet that gets 10 sun hours a day. You are confusing daylight hours with sun hours.
                        When panels are tested they are exposed to a light = 1000W per square meter. that gives them the watts of the panels.
                        Sun hours are the calculated amount of light in watts per square meter /1000.
                        Mike gave you a link to find the sun hours for your area. use it to find the sun hours for the lowest month of your year at your location and use that number to calculate how many watts of panels needed.
                        Rich
                        WWW.solarsaves.net

                        NABCEP certified Technical Sales Professional

                        http://www.solarpaneltalk.com/showth...Battery-Design

                        http://www.calculator.net/voltage-drop-calculator.html (Voltage drop Calculator among others)

                        www.gaisma.com

                        Comment


                        • #13
                          Originally posted by Naptown View Post
                          There is no place on the planet that gets 10 sun hours a day. You are confusing daylight hours with sun hours.
                          When panels are tested they are exposed to a light = 1000W per square meter. that gives them the watts of the panels.
                          Sun hours are the calculated amount of light in watts per square meter /1000.
                          Mike gave you a link to find the sun hours for your area. use it to find the sun hours for the lowest month of your year at your location and use that number to calculate how many watts of panels needed.
                          Except NREL uses the term 'insolation' which is generally kW/m2/day

                          To dumb it down people all the insolation value sun hours. 5.5 kW/m2/day is sometimes referred to as 5.5 sun hours
                          [SIGPIC][/SIGPIC]

                          Comment


                          • #14
                            100MW wind farm

                            Guys i am working on design of a 100 MW wind farm and i need to know the calculations about energy storage of the system using batteries?

                            Precisely speaking,

                            What kind of batteries should be placed ?
                            What should be the ratings of battery in terms of power output in times of high demand.(Power out to the grid)

                            Please help me

                            Comment


                            • #15
                              Originally posted by maxi_da1 View Post
                              Guys i am working on design of a 100 MW wind farm and i need to know the calculations about energy storage of the system using batteries?

                              Precisely speaking,

                              What kind of batteries should be placed ?
                              What should be the ratings of battery in terms of power output in times of high demand.(Power out to the grid)

                              Please help me
                              I will answer your question for $10,000 USD
                              MSEE, PE

                              Comment

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