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Offgrid solar setup for pool pump only- battery and calcs check

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  • Offgrid solar setup for pool pump only- battery and calcs check

    Hey folks,

    I have a project i am working on right now to try and take my pool pump off the grid. I have 5 SPR335's that I plan on using for the project, likely i will not need all of them ( the spot i have has space for 3 so that is what i have done the math on) so the others will be saved for another project. They didn't cost me anything and i don't want to tie this into the grid for a bunch of reasons so the why for this project can be saved for later.

    I have 2 pumps, a 1HP pump for the big filter and a 3/4HP pump for the pool bottom shark cleaner. If we assume the 1HP pump runs for about 3 hours and 3/4HP pump runs for about 3 hours as well.

    Using this website i would be using about 174kwhs a month to run these 2 pumps. http://www.myconserve101.com/energyS...poolPumps.aspx. Does this seem accurate to folks?

    My calculations have annual production of 3x 335 panels at about 1,254kwhs with some shade and 1,456 with better assumed exposure, I need to get a suneye down there to get better accuracy. This is going to leave me a bit short so i may have to reconsider the number of panels.

    I am the most stuck on the batteries and what type to choose to power the pumps with the above production assumption. Should i go with a deep cycle battery or a dual purpose? I need some help on calculating how many batteries i need to run the pumps for long enough.

    I have an electrician friend that is going to help me wire it all up with charge controller etc.

    Is there anything that i am overlooking at this stage?

    Thanks for everyones help.

  • #2
    Yeah, those numbers look like they are in the right ballpark.

    Can you control when the pumps run? If you can make sure they are both not on at the same time, that will help. Also, if you can run them during the day when they can be powered more directly by the sun, the batteries will not be so deeply cycled and they should last longer.

    I hope your "why" is solid. The batteries are much more expensive than the panels, and lead to other expenses, so getting free panels doesn't do much to help with the long term financial consequences of moving a load this large off grid.

    As for sizing... 174 kWh / mo = ~5.8 kWh day. If you run at 48 V, that is 120 Ah. If the system runs at night and all of the energy needs to come from the batteries, figure at least 3 days, and more like 5 days of capacity, so 600 Ah of 48 V battery. Maybe 8 of these would get you going?

    I agree you will need more panels. 600 Ah of batteries should have 60 A of charge current at 48 V, which is more like 10 of those Sunpower panels.

    If you stay on grid, or use a generator, you can avoid the multipliers and efficiency losses that make going to batteries so expensive. Those panels would be nearly enough to offset the load, and in a grid tie scenario with net metering, there might be a TOU plan that would encourage you to run the pumps at night when the electricity is cheaper. In that case, the more valuable energy you generate during the day might turn out to be enough to offset the cheap consumption.
    CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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    • #3
      Originally posted by Birdmanjon View Post
      .. My calculations have annual production of 3x 335 panels at about 1,254kwhs with some shade and 1,456 with better assumed exposure, I need to get a suneye down there to get better accuracy. This is going to leave me a bit short so i may have to reconsider the number of panels....
      You cannot use yearly production numbers for an off grid system. You need to plan for worst case. Rerun the calculations using the insolation numbers for the worst month that you plan on running the system.

      BTW - 3 panels is not going to be enough. You will need at least all 5 if not a couple more.

      WWW

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      • #4
        I'll assume you run the pool pump from Memorial day to labor day...or close to that. Your cleaner booster pump doesn't need to run every day so delete that and run it once a week on a sunny day after the batteries are fully charged. You're looking at 12-15K to build what you want, minus 1K for the panels you already have, but you'll need more.
        1150W, Midnite Classic 200, Cotek PSW, 8 T-605s

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        • #5
          Originally posted by Birdmanjon View Post
          Hey folks,

          ....
          Is there anything that i am overlooking at this stage?

          Thanks for everyones help.
          Just the fact that even with free solar panels it will be costing you 5 to 10 times as much to generate a kWh from those batteries then purchasing it from the Utility Grid.

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          • #6
            Originally posted by SunEagle View Post
            Just the fact that even with free solar panels it will be costing you 5 to 10 times as much to generate a kWh from those batteries then purchasing it from the Utility Grid.
            It sort of depends what he's paying for electricity- $0.06 in TX vs. $0.36 in HI would make a big difference.

            Also, I am willing to bet that the real need for pool filtration tracks more or less in parallel with PV production- Sunny summer time the pool gets more use and wants to grow algae a lot more than cloudy winter time. I think the battery system would just need to provide enough storage to efficiently use that day's production.

            If he can't connect to the grid for some reason, and his avoided cost for electricity is high, it might almost make financial sense. Otherwise it's a hobby.

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            • #7
              Originally posted by jimqpublic View Post
              It sort of depends what he's paying for electricity- $0.06 in TX vs. $0.36 in HI would make a big difference.

              Also, I am willing to bet that the real need for pool filtration tracks more or less in parallel with PV production- Sunny summer time the pool gets more use and wants to grow algae a lot more than cloudy winter time. I think the battery system would just need to provide enough storage to efficiently use that day's production.

              If he can't connect to the grid for some reason, and his avoided cost for electricity is high, it might almost make financial sense. Otherwise it's a hobby.
              For the OP to run both those pumps (1hp & 3/4hp) even for only a few hours a day will require a pretty big & expensive battery and solar panel system. Even at $0.36/kWh he would not get back what he spent for those batteries when they fail after 5 years.

              Most people do not just have a pool without a home. So I presume his house has grid power. Going off grid to just run his pool pumps is not an economical way to go.

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              • #8
                Originally posted by jimqpublic View Post
                It sort of depends what he's paying for electricity- $0.06 in TX vs. $0.36 in HI would make a big difference.
                Not really, still very ignorant and foolish. On the mainland a good 5-year battery will cost you 60 to 75-cents per Kwh. Higher in Hawaii. But that is only if you use it 365 days per year. Occasional use of 4 month out of the year and you still have a 5 year calendar life driving that cost up 300% or $1.80 to $2.10 per Kwh. Higher in Hawaii. There is no economic justification taking anything off grid if you already have it in the USA. Pretty much in any country even Islands. Very few countries hav elower electric rates than the USA, Same for batteries. Go to a country with higher electric rates and batteries will be equally higher.
                MSEE, PE

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