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Thread: Solar Pool Pumping (3 Phase DC vs VFD AC)

  1. #1
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    Default Solar Pool Pumping (3 Phase DC vs VFD AC)

    First of I would like to introduce myself and show my appreciation for such a compilation of experts in the solar field.

    I'm a current returning Army Warrant in the Electronics MOS arena and building a home in SW Florida. It is my plan to offset the utility bill by installing Solar PV panels and Solar Hot Water & Pool heating. As most, I am trying to calculate the cost vs benefits vs ROI. I want to do most of the work myself, as I feel I am some what qualified. My first dilemma is this:

    The Pool Pump:

    The plan is to have a small pool (10,000-12,000 gallons) with a roof top solar collector for pool heating with a small 4 person spa. I calculated approx 30 gallons per hour needed to turn the pool over once in a 6-7 hour day. I was going to use a Haywood EcoPump with a about 1KW of solar panels fed through either 4 Enphase MC215 inverters or a 1.5 KW grid-tie inverter. Based on my research and calculations..the pool pump for most of the day would only draw approx 200-300 Wh...so theoretically during that time, I would be offsetting my A/c and other electrical uses in the home with about 600-700 Wh of energy (using 90% eff as a basis). Not sure what a new Carrier 21 Seer A/C unit uses in low speed and high speed compressor mode, but 600-700 watts..is still offsetting). Total for the solar and inverters should be about $2,000, not including installation.

    Sunray has a solar pool pump system that they say is more efficient than using a VFD AC drive. Theirs is a Lorentz dc pump (PS600) connected directly to the PV panels through a MPPT controller. This would save $$ on JUST the pool pump energy, but provide no offset to the house during lower pump needs. Their philosophy is pump at max available speed based of PV panel ... pump all day..more water turnover..better. However, I belive I can achieve the same running the Haywood at 30 GPM speed (1400 RPM or so) AND provide excess energy back to home to offset other loads..mainly HVAC.

    Lastly, the SunRay system would cost almost double vs the 1KW panels and inverters. I think the Haywood with the 1KW panel setup and inverters is a smarter way to go, less cost and would reduce total overall home energy cost.

    Is my thoughts and math correct...Am I on the right track...or am I missing something?

    Thanks for any assistance,

    Doug

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    Quote Originally Posted by ArmyChief View Post
    First of I would like to introduce myself and show my appreciation for such a compilation of experts in the solar field.

    I'm a current returning Army Warrant in the Electronics MOS arena and building a home in SW Florida. It is my plan to offset the utility bill by installing Solar PV panels and Solar Hot Water & Pool heating. As most, I am trying to calculate the cost vs benefits vs ROI. I want to do most of the work myself, as I feel I am some what qualified. My first dilemma is this:

    The Pool Pump:

    The plan is to have a small pool (10,000-12,000 gallons) with a roof top solar collector for pool heating with a small 4 person spa. I calculated approx 30 gallons per hour needed to turn the pool over once in a 6-7 hour day. I was going to use a Haywood EcoPump with a about 1KW of solar panels fed through either 4 Enphase MC215 inverters or a 1.5 KW grid-tie inverter. Based on my research and calculations..the pool pump for most of the day would only draw approx 200-300 Wh...so theoretically during that time, I would be offsetting my A/c and other electrical uses in the home with about 600-700 Wh of energy (using 90% eff as a basis). Not sure what a new Carrier 21 Seer A/C unit uses in low speed and high speed compressor mode, but 600-700 watts..is still offsetting). Total for the solar and inverters should be about $2,000, not including installation.

    Sunray has a solar pool pump system that they say is more efficient than using a VFD AC drive. Theirs is a Lorentz dc pump (PS600) connected directly to the PV panels through a MPPT controller. This would save $$ on JUST the pool pump energy, but provide no offset to the house during lower pump needs. Their philosophy is pump at max available speed based of PV panel ... pump all day..more water turnover..better. However, I belive I can achieve the same running the Haywood at 30 GPM speed (1400 RPM or so) AND provide excess energy back to home to offset other loads..mainly HVAC.

    Lastly, the SunRay system would cost almost double vs the 1KW panels and inverters. I think the Haywood with the 1KW panel setup and inverters is a smarter way to go, less cost and would reduce total overall home energy cost.

    Is my thoughts and math correct...Am I on the right track...or am I missing something?

    Thanks for any assistance,

    Doug
    Basic starting points:

    1. Solar thermal heating is usually the most economical form of solar energy use in terms of savings and up-front expense (Return On Investment.) You are on the right track there.

    2. If the you are grid-connected, the most economical use of solar PhotoVoltaic (PV) investment is to set up a grid-tied system and offset your utility power consumption (assuming that you get Net Metering or a favorable Feed-in Tariff from the utility.) Trying to directly drive a load like a pool heater pump from the solar system does not make economic sense.

    3. Depending on the amount of power used by the pool pump, the cost savings in cheap utility-priced power by using a DC pump may not come close to paying for the panel and battery investment. For an off-grid user (who cannot connect to the grid at any reasonable cost), looking hard at every power need does make sense.
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

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    Quote Originally Posted by inetdog View Post
    3. Depending on the amount of power used by the pool pump, the cost savings in cheap utility-priced power by using a DC pump may not come close to paying for the panel and battery investment.
    inetdog,

    Thanks for the quick reply. Not sure if you looked at the SunRay system i mentioned above...but it is a non-battery, non grid-tied, PV->MPPT Controller->DC Pool Pump system..in that the pool pump runs all the time there is sun..and varying speeds depending on sun and panel wattage.

    Are you familiar with the DC pump and controller used? Is it "better" (relative..i know}, then a AC VFD pump and supplementing the pump wattage with PV solar?

    Thanks,

    Doug

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    Quote Originally Posted by ArmyChief View Post
    inetdog,

    Thanks for the quick reply. Not sure if you looked at the SunRay system i mentioned above...but it is a non-battery, non grid-tied, PV->MPPT Controller->DC Pool Pump system..in that the pool pump runs all the time there is sun..and varying speeds depending on sun and panel wattage.

    Are you familiar with the DC pump and controller used? Is it "better" (relative..i know}, then a AC VFD pump and supplementing the pump wattage with PV solar?

    Thanks,

    Doug
    I am not familiar with that product, but others here might be.
    But in any case, I would look at the cost of the panels and the pump and then compare it to buying a normal AC pump and spending the difference on panels to be added to a grid-tie system.
    Will it be more economical to spend money up front so as not to pay for power for the pump at all or to pay for it at utility rates and generate more PV to offset your usage?
    Where will the panels for the pool pump be and would you rather have panels on your roof?
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

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    Quote Originally Posted by ArmyChief View Post
    Not sure if you looked at the SunRay system i mentioned above...but it is a non-battery, non grid-tied, PV->MPPT Controller->DC Pool Pump system..in that the pool pump runs all the time there is sun..and varying speeds depending on sun and panel wattage.
    Doug that is the part you are missing. A GTI systems utilizes all the power that is collected. Does not matter to you where that power goes. Any excess power goes out and you get credit. If you are using more power than the panels can generate you are buying but offset by what you are producing. In the END it is your NET use. That means lowest possible amount of power from FPL.

    Your pool pump does not need to run 24 hours per day, use a timer and most efficient induction AC motor.
    MSEE, PE

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    Quote Originally Posted by Sunking View Post
    Doug that is the part you are missing. A GTI systems utilizes all the power that is collected. Does not matter to you where that power goes. Any excess power goes out and you get credit. If you are using more power than the panels can generate you are buying but offset by what you are producing. In the END it is your NET use. That means lowest possible amount of power from FPL.

    Your pool pump does not need to run 24 hours per day, use a timer and most efficient induction AC motor.
    Sunking..thanks for the reply.. wasn't really missing that fact...since I was leaning to the grid-tied procedure. Appreciate all your inputs. Now..to go enphase micro-inverters or a line inverter.......

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    Quote Originally Posted by ArmyChief View Post
    Sunking..thanks for the reply.. wasn't really missing that fact...
    OK chew on this. Which is less expensive and has the fastest ROI? One system or two systems?

    Kind of like having two wives.
    MSEE, PE

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    Quote Originally Posted by Sunking View Post
    OK chew on this. Which is less expensive and has the fastest ROI? One system or two systems?
    One of course..which is why I've been leaning toward PV panels on a grid-tie system. Just curious if anyone has any info on the DC pump I quoted.

    Quote Originally Posted by Sunking View Post
    Kind of like having two wives.
    Two wives could be fun ....but would be more expensive !

  9. #9
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    Quote Originally Posted by ArmyChief View Post
    Just curious if anyone has any info on the DC pump I quoted!
    Cannot help you on the pump question, but what I do know is the specialized pumps for solar systems are DC and very expensive. AC motors are much less expensive, more reliable/efficient, and last a lot longer in my experience.

    Good luck to you.
    MSEE, PE

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    Thanks Dereck

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