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Watts after the sum total of all inefficiencies for a small/budget off grid system

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  • Watts after the sum total of all inefficiencies for a small/budget off grid system

    Would it be a fair initial guesstimate for me to assume that my 4 x 250 Watt panels when coupled to a budget 24V MPPT charge controller, batteries, and a low priced 1500W inverter will likely yield me something close to 620 Watts per sun hour after all of the various system inefficiencies are factored in?

  • #2
    MPPT Eficiency 67%
    PWM at best is 50%

    You can get MPPT efficiency ya little higher with proper design and equipment selection, but 67% is close enough.Bu tin real world operation cradle to grave is way less than 50% because you cannot even come close to utilizing the power.
    MSEE, PE

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    • #3
      Originally posted by Sunking View Post
      MPPT Eficiency 67%
      PWM at best is 50%

      ...But in real world operation cradle to grave is way less than 50% because you cannot even come close to utilizing the power.
      Part of what Dereck is referring to here is that once you have gotten your battery bank out of the Bulk charge stage, the reduced current it can accept during the remaining hours of charging will typically mean that your CC is deliberately not taking all of the potentially available power from the panels.
      This is one of the major frustrations of off-grid power budgeting.
      If you can arrange your load scheduling to use some or all of the otherwise unused panel power after Bulk is over, then your overall efficiency will be higher.

      (Taking a slightly different perspective, you can calculate efficiency as the ratio of the usable output power from the CC to the DC input to the CC. Or you can lower the efficiency number by always dividing by the current maximum output of your panels rather than just what the CC is currently asking of them.
      And if you take into account the fact that you have to put more watts into the batteries than you get back, the overall system efficiency goes even lower. Then multiply in the the conversion efficiency of the inverter if you have AC loads.)
      SunnyBoy 3000 US, 18 BP Solar 175B panels.

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      • #4
        I was initially looking at it this way:

        Panels: STC (ideal theory) to PTC (real world practice) = 0.90
        MPPT charge controller: 0.96
        Batteries: 0.84
        Inverter: 0.88
        Wires: 0.98

        Putting them together: 0.90 x 0.84 x 0.88 x 0.98 = 0.65, or 65%

        But I can now see where returning 65% would mean utilizing every Watt produced which can possibly be recovered, and that can never be done.

        PS: From the time I initiated this post until now I have actually received my 4 x PV modules (solar panels), and they are 260 Watt panels (vs. the 250 that I was looking at purchasing).

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        • #5
          Realistically way less then 50%. You cannot possible utilize all the potential power. Most of it is never used and lost forever like rain in the dessert.
          MSEE, PE

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          • #6
            Originally posted by Sunking View Post
            Realistically way less then 50%. You cannot possible utilize all the potential power. Most of it is never used and lost forever like rain in the dessert.
            Plants grow in the dessert so how can rain not be used and lost forever?

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            • #7
              Originally posted by SunEagle View Post
              Plants grow in the dessert so how can rain not be used and lost forever?
              Well, most of the rain in Texas was eventually lost to the ocean, not to absorption and it also did a lot of damage on the way out.

              I heard that the total local rainfall was enough water to cover the entire state something like six inches deep.
              SunnyBoy 3000 US, 18 BP Solar 175B panels.

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              • #8
                Originally posted by inetdog View Post
                Well, most of the rain in Texas was eventually lost to the ocean, not to absorption and it also did a lot of damage on the way out.

                I heard that the total local rainfall was enough water to cover the entire state something like six inches deep.
                I saw that report. Considering the size of Texas that is a huge amount of water. Too bad it couldn't have been siphoned to CA.

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