Solar Pool Pump (3-phase DC vs VFD AC)..need help with decision

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ArmyChief
ArmyChief Registered Users Posts: 18 ✭✭
First of I would like to introduce myself and show my appreciation for such a compilation of experts in the solar field. :clap2:

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?

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,477 admin
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    Re: Solar Pool Pump (3-phase DC vs VFD AC)..need help with decision

    Welcome to the forum ArmyChief!

    The forum is a community based on all of the posters here. Everyone brings something different and it is a joy to read (and the little moderation we ever need to do makes it pretty easy. Mostly just spam patrol).

    I think you are on the right track looking at ROI.. Just make sure you include maintenance costs too. Electronics will need replacing every ~10 years, many times because repair parts/services are not available after 5-10 years (at least have the funds in the bank so no surprises).

    Next, are you looking at doing the pump with off grid inverters and battery bank? It almost always costs a lot more for off grid power vs utility or grid tie power (usually around $1-$2+ per kWH when initial costs and down the road replacements are included--10 years for electronics, 5-10+ years for batteries, the extra losses from battery+inverters give you a ~52% end to end efficiency from solar panel spec to AC power vs ~77% for a Grid Tied system--Plus solar, of both types, does give you the 30% federal tax break--for now).

    Grid Tied solar, cheaper, more reliable, less service -- Does have one major down side, no power if the utility power/grid is lost. Still need generator and/or other solar power system for emergency power (there hybrid "hybrid" GT inverters which can be somewhat more cost effective if you need emergency power--but still expensive to install).

    Regarding you water heater... Assuming you need A/C much of the year (cooling/humidity control), look at heating systems that take the energy from your central air heat pump--Or even a stand-a-lone GE or other brand heat pump water heaters. Will be about 2-3 times as efficient as standard resistance heating, and cooling the room and dehumidifying are the "side effects" of generating the hot water.

    One poster here believes that a Grid Connected heat pump water heater is a better long term deal than solar hot water (pumps, tanks, thermal collectors, leaks, complexity, debugging, etc.).

    Anyway--A little more about your power needs and what you are looking for (saving money, emergency backup power, going green, getting off the grid, etc.).

    In most cases, "extreme conservation" is cheaper than generating your own electric power. In some cases, having a Grid Tied solar power system can be a wash or even same money vs grid power (in my area, summer peak "time of use" rates are around $0.30 to $0.50+ per kWH, and GT solar cost me around $0.15 per kWH). But much of GT solar depends on your local rates and the billing plan supported by your utility. Mine, I get 100% retail payment for anything extra I get (credit to bill, not cash). In some areas, you will be credited for the wholesale cost of electricity--Which can be down to the $0.05 per kWH range.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ArmyChief
    ArmyChief Registered Users Posts: 18 ✭✭
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    Re: Solar Pool Pump (3-phase DC vs VFD AC)..need help with decision
    BB. wrote: »
    Next, are you looking at doing the pump with off grid inverters and battery bank? It almost always costs a lot more for off grid power vs utility or grid tie power (usually around $1-$2+ per kWH when initial costs and down the road replacements are included--10 years for electronics, 5-10+ years for batteries, the extra losses from battery+inverters give you a ~52% end to end efficiency from solar panel spec to AC power vs ~77% for a Grid Tied system--Plus solar, of both types, does give you the 30% federal tax break--for now).

    Bill, no sir...going totally grid-tied..supplementing my grid usage with solar
    BB. wrote: »
    Grid Tied solar, cheaper, more reliable, less service -- Does have one major down side, no power if the utility power/grid is lost. Still need generator and/or other solar power system for emergency power (there hybrid "hybrid" GT inverters which can be somewhat more cost effective if you need emergency power--but still expensive to install).

    I have a propane powered 16KW generator already..that I will be bringing to Florida..hooked up to a buried propane tank
    BB. wrote: »
    Regarding you water heater... Assuming you need A/C much of the year (cooling/humidity control), look at heating systems that take the energy from your central air heat pump--Or even a stand-a-lone GE or other brand heat pump water heaters. Will be about 2-3 times as efficient as standard resistance heating, and cooling the room and dehumidifying are the "side effects" of generating the hot water.

    When I built my last house in Florida, I had a Waterfurnace Geo-Thermal with the a desuperheater..provided most of my hot water. I quickly figured out SW Florida is not optimal for Geo-Thermal. However, I did not know they made HVAC heat pumps that also could be tied to my hot water system.
    BB. wrote: »
    Anyway--A little more about your power needs and what you are looking for (saving money, emergency backup power, going green, getting off the grid, etc.).

    Saving money....I do not think, quite yet..I am up to the task of going off grid..or completely green..just lowering my monthly utility bill.

    Thanks Bill
  • BB.
    BB. Super Moderators, Administrators Posts: 33,477 admin
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    Re: Solar Pool Pump (3-phase DC vs VFD AC)..need help with decision

    The GE water heater (and other brands) is an electric water heater with a refrigeration compressor and condenser mounted on top of the tank.

    And the new air sourced a/c systems are efficient enough to maker ground sourced systems not worth the costs.

    Check with your local utility about their gt solar rules. That can make or break the gt install.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ArmyChief
    ArmyChief Registered Users Posts: 18 ✭✭
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    Re: Solar Pool Pump (3-phase DC vs VFD AC)..need help with decision
    BB. wrote: »

    Check with your local utility about their gt solar rules. That can make or break the gt install.

    -Bill

    There are rules?....Does that mean they charge you to be more self-sufficient? If one..hypothetically that is, was not making enough power to feed the grid back..just supplement thier use...could they tell?...hypothetically of course
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
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    Re: Solar Pool Pump (3-phase DC vs VFD AC)..need help with decision
    ArmyChief wrote: »
    There are rules?....Does that mean they charge you to be more self-sufficient? If one..hypothetically that is, was not making enough power to feed the grid back..just supplement thier use...could they tell?...hypothetically of course

    Usually they do not charge you more, but they may not pay you for the power you send them.

    Its very difficult to make power without occasionally feeding the grid unless your system is tiny, in which case its not worth the effort. This problem has recently come up on this forum where the power company (in Spain) charges the customer to feed the grid. An expensive solution was EMMA by coolpowerproducts.com. For that amount of money you might as well deal with your utility and get the permits.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • ArmyChief
    ArmyChief Registered Users Posts: 18 ✭✭
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    Re: Solar Pool Pump (3-phase DC vs VFD AC)..need help with decision
    vtmaps wrote: »
    Its very difficult to make power without occasionally feeding the grid unless your system is tiny, in which case its not worth the effort.
    --vtMaps

    vt,

    Why do you say generating less energy than needed (so no feeding the grid) is not worth the effort. In my example, I can completely power my pool pump and provide almost 500 Wh during daylight back to offset the home ussage...without feeding th egrid...for about $2000-$2500. When I lived in Florida 6 years ago and did an FPL energy audit..my pool pump alone was costing my $80-$100 a month. So payback..just using the pool pump usage would be about 2-3 years. That's not worth the effort?...not arguing..just trying to realize your statement.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
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    Re: Solar Pool Pump (3-phase DC vs VFD AC)..need help with decision
    ArmyChief wrote: »
    Why do you say generating less energy than needed (so no feeding the grid) is not worth the effort.

    Virtually all solar electric systems need a 'battery' in order to work. In a grid-tied system the grid is the battery. In an off grid system the battery is an expensive, inefficient, short-lived, high maintenance electrochemical device. Off-grid systems are rarely cost effective if the grid is available.

    The one exception to needing a 'battery' is if you can directly power a device from the solar panels. Some motors, pumps and fans can work this way.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • ArmyChief
    ArmyChief Registered Users Posts: 18 ✭✭
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    Re: Solar Pool Pump (3-phase DC vs VFD AC)..need help with decision

    Correct...understand...but I plainly said I was going grid-tied....not off-grid.

    Thanks,
  • BB.
    BB. Super Moderators, Administrators Posts: 33,477 admin
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    Re: Solar Pool Pump (3-phase DC vs VFD AC)..need help with decision

    We are more than happy to discuss the technical ins and outs of solar power (GT, off grid, hybrid, etc.).

    But the whole Utility/State PUC thing is a serious issue. Some places it is very straight forward. $5 per month billing/minimum charge. At the end of 30 days, read meter. If "positive", pay the normal bill. If "negative" (meter spun backwards), credit the money to account and pay the difference (or pay after 1 year the net power used, if net credit in bill, account is set back to zero and billing starts over).

    If you install a GT system without utility approval... They can "ask you" to remove the system, have your home red-tagged, many "new digital meters" will read "forward" when the power is being fed back to the grid (i.e., you generate excess power, then you pay retail for that privilege). This was because in the past, customers would install meters upside down for part of the billing cycle to run the meter backwards (theft of power).

    In California, we had the situation for awhile where people were forced to Time of Use billing--and if they installed a small GT system (to try it out)--Their bills actually increased.

    But, in general, solar GT power can, for many people, equal the cost of utility power, and for some (with tiered power rates were we pay more as we use more power), it can save significant amounts of money.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ArmyChief
    ArmyChief Registered Users Posts: 18 ✭✭
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    Re: Solar Pool Pump (3-phase DC vs VFD AC)..need help with decision

    Bill,

    Thanks..I've contacted a local Solar installer in the area to determine the best route. It appears something is "amidst" in Florida when it comes to FPL and the rebate programs. I do not believe Florida uses meters that spin faster when putting power back...however I project I will never get into the negative area with only 1-2kW of panels.

    I've not seen anyone discuss the pro's/con's of a solar DC pump vs VFD AC pump. Service, ruggedness, efficiency..etc..again .. thanks
  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
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    Re: Solar Pool Pump (3-phase DC vs VFD AC)..need help with decision
    ArmyChief wrote: »
    Correct...understand...but I plainly said I was going grid-tied....not off-grid.

    Thanks,
    ArmyChief wrote: »
    There are rules?....Does that mean they charge you to be more self-sufficient? If one..hypothetically that is, was not making enough power to feed the grid back..just supplement thier use...could they tell?...hypothetically of course
    If you are grid tied you have to do so with the approval of the Utility Provider. How can they tell ?? If you have a Smart Meter and most do or soon will, anything you generate will be added to the meter usage instead of subtracted. You have to have a net meter even if you do not feed into their system. It was evident to me when the usage went up 300 KWH in a week and I had to pay for generating it.

    Of course you can set your pool up as a separate system and not tie it to the grid system.
  • ArmyChief
    ArmyChief Registered Users Posts: 18 ✭✭
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    Re: Solar Pool Pump (3-phase DC vs VFD AC)..need help with decision

    Thanks Blackcherry...this is why I am meeting with a licensed Floria Solar installer...to discuss the options.

    The latter is the SunRay system I spoke about earlier
  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
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    Re: Solar Pool Pump (3-phase DC vs VFD AC)..need help with decision
    ArmyChief wrote: »
    Thanks Blackcherry...this is why I am meeting with a licensed Floria Solar installer...to discuss the options.

    The latter is the SunRay system I spoke about earlier
    Try putting a post down in " Solar Water Pumping " People with a interest and knowledge will post there. It won't get as much play as here , but you might get a better answer. You might want to search that part of the forum, I know it's been discussed.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
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    Re: Solar Pool Pump (3-phase DC vs VFD AC)..need help with decision
    ArmyChief wrote: »
    Correct...understand...but I plainly said I was going grid-tied....not off-grid.

    And I said that it is very difficult to go grid-tied without feeding the grid (unless your system is tiny). --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
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    Re: Solar Pool Pump (3-phase DC vs VFD AC)..need help with decision
    ArmyChief wrote: »
    I've not seen anyone discuss the pro's/con's of a solar DC pump vs VFD AC pump. Service, ruggedness, efficiency..etc..again .. thanks

    I run a VFD AC pump for my well and chose to go this route not because of DC vs AC, but rather because I think a single integrated system with 1 solar system for all the loads, is more versatile than a DC pump with it's own dedicated solar panel. Same conclusion you came to basically :)

    This way, when the weather is lousy I can choose to not run the well pump and save the energy for the more important loads at home. And if I have surplus power I can choose to run the well pump longer.
    The other things I like about the VFD approach is that you can choose to run the pump at variable speeds instead of full speed only. This is likely to have a positive effect on the longevity of the pump. The lorentz system will also vary the speed, but it will be based on the available solar, not on what you choose the speed to be.

    For repairability, both the lorentz and VFD approaches have the controller and pump separate which means less costly repairs if one of the units fail (some other DC pump systems have the controller integrated into the pump). With the VFD you have the option of choosing a wide range of devices and pumps, all interoperable. With lorentz, you're stuck with their controller and their pump- not necessarily a bad thing, just depends on the price of their kit :)