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  • Validation of purposed solar

    Good Day All,

    Been working out he calculations for my RV solar and would like input, validation, corrections, improvements if you don't mind.

    I travel my RV 9 months a year and am in one place for longer than a week.

    Currently have 4 Trojan T105 batteries -- 440Ah

    Wish list for Solar is:

    Renogy Poly 320w 24v panels x 2 in Parallel should be 640W or 26 amps at controller

    MPPT controller - Blue Sky 3024 DiL and adjust charging to batteries specs 14.82 / 15.5 / 16

    Usage is as follows: 24hour in non frugal mode is 3Kwh measured by Kill A Watt meter -- amp hour drain on Batteries over 24hours 300Ah

    I believe I need to recover the evening Drain of MAX 200Ah - this drain is lights, residential fridge, charges, TV DVR etc.

    From what I have read here, the recovery formula is Watts x sunlight hours useable, x efficency

    My calculations mean 640 x 5 x .66 = 2112 or 211Ah

    I believe this will work as designed but I am open to any and all comments suggestions improvements.

    Appreciate the input,

    NutinElse2do aka Richard

  • #2
    The output of any solar panel can be seriously reduced below the nameplate wattage if the panel is not at the correct angle and point due South without any shade. There will be days that you will not get those 5 hours of usable sunlight so you probably will not see even 2112watt hours of production from that 640 watt system. That will mean you won't be able to recharge your battery bank back up to 100% most days if you use 2400 watt hours at night (200Ah x 12v = 2400wh).

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    • #3
      In a more real world situation what I should I expect this setup to produce?

      I am sure I can lower my evening usage but if 640W is only going to get me say 1200 watt hours of production I may have to return to the drawing board.

      Comment


      • #4
        Originally posted by NutinElse2Do View Post
        In a more real world situation what I should I expect this setup to produce?

        I am sure I can lower my evening usage but if 640W is only going to get me say 1200 watt hours of production I may have to return to the drawing board.
        It is hard to say. Some days you will get a lot of production but other days you will get less.

        The question is how will the panels be oriented to the sun and how many useful "sun hours" will you get during the Winter months?

        Panels that are flat mounted or get some shade will have a reduction in production of watt hours.

        The months of November to February will see much less "sun hours" then the months of May to August.

        If the panel array was adjustable for the winter months and are always pointed South without shade you will get more output.

        It is not easy to live totally off grid and predict how much power you will get when the amount of solar generation is a fluid variable.

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        • #5
          Appreciate the input, my winter months November to February are usually spent connected to shore power so that is not an issue.

          I was also going to add a tilt kit if needed to obtain more horsepower when further North in the US.

          Again appreciate the input.

          Comment


          • #6
            Originally posted by NutinElse2Do View Post
            Appreciate the input, my winter months November to February are usually spent connected to shore power so that is not an issue.

            I was also going to add a tilt kit if needed to obtain more horsepower when further North in the US.

            Again appreciate the input.
            You are welcome.

            Hang around the forum and continue to learn and contribute your experiences concerning solar technology.

            Comment


            • #7
              Originally posted by NutinElse2Do View Post
              In a more real world situation what I should I expect this setup to produce?

              I am sure I can lower my evening usage but if 640W is only going to get me say 1200 watt hours of production I may have to return to the drawing board.
              FWIW. I have a setup somewhat similar to yours-though mine is a 24v system.
              2 320w panels wired in series
              2 12v 200ah AGM in series

              I use roughly 1.2-1.6kwh on average daily. The system produces anywhere from 1.6-2kwh daily.
              Last edited by Suprasoup; 11-12-2017, 02:33 AM.

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              • #8
                I can give another point of reference for daily solar production:

                My rig has a 1200W, 48V array, which is fixed flat on the roof of our 25' fifth-wheel, which means it is "tilted" about 10 degrees rearward - basically flat-mounted, but we usually point the back of the trailer South to make that tilt work in our favor. Our system went online in March 2015 and has been operating nonstop since then with the exception of 4 months last winter (seasonal job at ski resort - no sun!). So that's around 850 days' operation. The charge controller's "Lifetime" total is currently at 2081.1 kWh. So we've averaged 2448 Wh per day over that ~2 year period. So, about 2x the array's rated power per day. Although we see 800-900W frequently, i've only seen 1kW coming in once - but we push the envelope a lot and venture to some pretty non-solar-friendly places. Like the rainy tree-covered pacific Northwest...and Yukon territory, north of the 60th line of latitude : ) But we also spent a winter in the desert, too. So this number represents a range of behaviors, from solar-smart to solar-stupid : )

                Probably the strongest dividing line in the RV-solar community is tilting vs. fixed. I personally don't think tilting is worth it unless the way you camp means you are up on the roof a lot anyway. Panels that tilt can't be mounted as densely as if they were flat, to protect from self-shading. Since Wattage is pretty cheap now, i think it's better to max out on fixed panels at a high array voltage with MPPT, make sure they won't ever be shaded, and just keep 'em clean. In Yukon territory, we got rained on all summer, but made 100-200 Watts in the overcast conditions, from about 3 in the morning 'til 11 at night ... which is still 2kWh/day! Tilting makes no difference in overcast conditions, but MPPT does ; )

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