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Charge controller for large 1766AH, 48V battery bank with 6 hour peak sunshine

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  • #31
    Originally posted by Sunking View Post
    For a DIY it is just not worth the time and effort to try to shave off 5 to 15% of panel power. Well unless you are talking something like a 2000 watt or more system.
    The OP is talking about a 14kW+ system. Worth the effort to do better analysis, and not just trust rules of thumb.
    CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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    • #32
      Originally posted by Sunking View Post
      Sure if I am being paid to do it. Then I would take the time for all factors. But after doing several hundred designs, the difference is so small is insignificant.

      With a grid tied makes no difference if you miss the mark over or under, it still works and every drop of power is used regardless. With a battery system there is only one side you can afford to miss on, the high side. Two designs have to be done. One for summer, and one for winter. You use the larger of the two which 90% of the time is winter. Come up short and you go dark, and destroy batteries, and/or use more generator fuel than necessary. If off-grid you had better have a generator to protect your battery investment.

      So for me if I were being paid I run PV Watts, input a 1 Kw panel, 0% loss, orientation, and tilt. Click Go and see what the shortest days are. In the USA is going to be either December or January. So if 1 Kwh panel in December generates say 3200 watt hours. I know Sun hours is 3.2 is worse case. You cannot use yearly average as that is for Grid Tied only.

      FWIW this is the method John Wiles and a few other pioneers came up with and tested at NMSU. At the time John and his grad students used a simple 100 watt panel with a MPPT Tracker and Dump Load to find Sun Hours. If that 100 watt panel generated 320 watt hours, Sun Hours = 3.2. That was well before PV Watts was ever conceived. John Wiles and his grad students then went on with JPL and NASA and developed PV Watts. No longer need to set out a panel for two months in winter. It is very simple and straight forward and a 5th grader can do it.

      Yes on the Forum I multiply by 1.5 the daily watt hour usage. Works every time and never comes up short which is death. When I crunch the numbers once I know all the equipment, batteries, cable losses I have never ever came in lower than 1.3. For a DIY it is just not worth the time and effort to try to shave off 5 to 15% of panel power. Well unless you are talking something like a 2000 watt or more system. Otherwise 1.5 always works my friend, and 1.4 may fail my friend. Just KISS it.

      Think of it this way JPM. You are the pilot of the plane. Your plane burns 13 gallons an hour. You calculate under current conditions will take 3 hours to get to your destination. As a pilot you want the plane to be light as possible and safe. So how much fuel do you have loaded, 3 x 13 = 39 gallons. Or do you follow the rules and make sure you have at least 52 gallons. DIY uses 39 gallons and crashes most of the time.

      As my wife says, I don't have much of a butt. That is why I wear a belt and suspenders. No butt cracks or falling pants. .
      I think I get the part about designing off grid systems for worst case Dec/Jan. No brainer once explained. If I got into off grid, I might do it different after I dug enough. Until then I'll defer to your judgment. Just sounded like you were applying the logic to all systems.

      With not much of a butt, another good reason your an electron mongering EE and not a plumber. You'd never meet the plumber's crack requirement.

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      • #33
        I've been revising my loads/usage...here is what I will have and my tentative plan:

        Solar Panels: 315W (@STC)
        Power Consumption: 3500W
        Hours of Use: 12 hours
        Daily Wh: 42,000 Wh (42 kWh)

        Inverter Eff: 93%

        Daily Wh Adjusted: 42,000Wh/0.93 = 45162 Wh (45.162 kWh)

        Daily Solar Panel Output (PWatts/SAM with carefully adjusted losses): 2.png



        System Losses: 93% Solar Charger, 80% Battery Bank, 98% Wiring = 0.93*0.80*0.98=0.73

        # of Solar Panels Needed: 45162 Wh/ (1649Wh)/(0.73) = 37.5 Panels = 38 Panels


        From 7AM till 6PM, 38 Panels will provide me with my 45162 Wh to be put back into my batteries

        Agreed or disagreed ?
        Last edited by SillySnakes; 07-05-2017, 09:43 PM.

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        • #34
          Originally posted by SillySnakes View Post

          From 7AM till 6PM, 38 Panels will provide me with my 45162 Wh to be put back into my batteries

          Agreed or disagreed ?
          Sadly (to me), if you just take 42000 * 1.5 you get the same 38 panel result. SMH.


          CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

          Comment


          • #35
            Originally posted by SillySnakes View Post
            I've been revising my loads/usage...here is what I will have and my tentative plan:

            From 7AM till 6PM, 38 Panels will provide me with my 45162 Wh to be put back into my batteries.

            Agreed or disagreed ?
            Agree.

            Personally I think you are out of your freaking mind. You are designing a system to fully discharge your batteries every day. They will not last more than a couple of months. With just one cloudy day you go dark and have to wait for a full day of sun to recharge before you can turn back on the power.

            The battery required to provide you with 42 Kwh a day at 48 volts is 4200 AH, weighing some 13,000 pounds and cost you $30,000 every few years. That is just nucking futs.

            With 5.23 Sun Hours and 42 Kwh daily usage [1.5 x 42000 wh / 5.23 Sun Hours will require:

            Panel Wattage = 12,000 watts
            MPPT Min Current = 12,000 wh/ 48 volts = 250 Amps
            Battery AH Capacity @ 48 volts = 4200 AH weighing 13,000 pounds and cost you some $30,000 every 5 years.

            You will be paying 70-cents per Kwh just in battery cost. The POCO sells it for 10 to 15 cents.
            Last edited by Sunking; 07-06-2017, 12:01 AM.
            MSEE, PE

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            • #36
              Originally posted by sensij View Post
              Sadly (to me), if you just take 42000 * 1.5 you get the same 38 panel result. SMH.
              Hate to say I told you so. There is no need to do all those calculations, It just introduces errors from to many calculations. 1,5 works everytime for MPPT, and 2 for PWM. For Pete's Sake John Wiles and 30 grad students took 3 years to develop the design process for Off-Grid. It is like the Wheel, you cannot improve the design. 1.5 will never leave you short. Any other method might come up short and leave you in the dark and destroyed batteries.

              MSEE, PE

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