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Thread: What size solar for well pump?

  1. #1
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    Default What size solar for well pump?

    I have a Grundfos 5SQ-180 that is sitting 250' down a 260' well that has a static water level of 30' (so lots of water sitting down that hole). The replenish rate of the well is only about 2 gpm, but I just pump it to the surface into water storage containers (55 gallon food grade barrels) for now.

    For the last year since I have had the well drilled, my little Honda EU2000i has worked admirably (on gas, won't run the pump on propane though), but I really want to get a solar system set up to run the pump.

    I know the Grundfos is a 1/2 hp motor and the pump pulls about 12amps @ 115v.

    With this in mind, I believe i need a 1500 watt inverter (and I can only seem to find modified sine wave inverters below 2000 watts), but what size battery bank would I need to run the pump for say an hour before I was at 50% DOD?

    And how many watts in solar panels would I need if my winter peak sun hours is 1.5? I know I'll also need a charge controller....but am I missing anything else?

    Would a system like this function when it was 10 degrees Fahrenheit out?

    Thanks

  2. #2
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    Based on your specification:

    Panel wattage = 2000 watts
    Charge Controller = MPPT 80 amps
    24 Volt Battery Capacity = 300 AH AGM type
    Inverter = 3000 Watt True Sine Wave
    MSEE, PE

  3. #3
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    Wow, at the US Dept of Energy avg of $8 - $10 per watt, that comes to about $18,000 just to run my well pump. I'm just shocked that it would cost that much.

    If I bought a 1000 gallon propane tank + 800 gallons of propane to fill it = $6500 (roughly)
    6Kw propane generator + installation = $3500 (roughly)

    So about $10,000 total.

    I would only need to run the pump about an hour a day (at 4 gallons of water per minute). The generator consumes .85 gal/hour at 50% load, so if I only used it for the well, I could run that well pump for over 20 years for a little more than half of what it would cost to run it on solar (assuming the batteries lasted 20 years, which I don' think they would).

    After everything I have been finding out about solar power, at least for the area I am in (NE Washington state), I don't ever see a break even point (much less getting ahead). This is depressing.

  4. #4
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    NE Washington is one of the better locations for sun! NW Washington doesn't get enough sun for much of anything but you are better off - if a bit colder

    The cost may be more like 5$ per DC watt

    Look at solar hot water heating or air heating if you want a solar project with better efficiency/return.

  5. #5
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    It's not quite that bad
    Panels about 3500
    Racking (roof mount flush) 600
    Charge controller about 600
    Batteries 800?
    Inverter about 1000
    Total about 6500.00
    Fuel costs 0

    Now for the generator
    About 10K installed
    .85 gallons of propane per day x365 = 310gallons per year.
    Propane here is about $3.00 per gallon so $950 per year in fuel costs.
    figure 6-7 oil changes per yer in there at ?
    With oil changes figured at $20 each and not counting other breakdowns in the generator let's look at life cycle costs over 20 years.
    Total install and operating over 20 years $31,400

    Solar 6500
    If you buy good batteries you should be able to get 5 years out of them.
    So over 20 years $3200
    Inverter and charge controller will probably die and need to be replaced.

    Solar initial investment 6500
    Less 30% federal credit 1950
    Net solar cost 4550
    Battery replacement 4x 800 = 3200
    Inverter and charge controller replacement 1600
    Total install and operating over 20 years. $9350

    The numbers are based on a diy install using UL listed components.
    Last edited by Naptown; 01-23-2012 at 03:57 PM.

  6. #6
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    Quote Originally Posted by Naptown View Post
    It's not quite that bad
    ...
    Now for the generator
    About 10K installed
    .85 gallons of propane per day x365 = 310gallons per year.
    Propane here is about $3.00 per gallon so $950 per year in fuel costs.
    figure 6-7 oil changes per yer in there at ?
    With oil changes figured at $20 each and not counting other breakdowns in the generator let's look at life cycle costs over 20 years.
    Total install and operating over 20 years $31,400
    ...
    I see where you are going with this, but it's not quite that bad with the propane genny either. Propane is only $2.20/gallon here and the maintenance interval on the genny is 500 hours. So the cost for the generator is probably closer to $20K. But that is still double what you came up with for solar costs.

    I'm kind of thinking out loud here...but our house is 300' from the well. How far could I run a line that was pushing 110-120v before the loss was impractical or the size of the cable too expensive to justify?

  7. #7
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    Default Maybe...

    A Wood Gassifier? They ran trucks with them back in the early '40. Scrounge wood from the forest floor, It's still renewable and doesen't put any more CO2 into the atmosphere than if it were left to rot on it's own,...just does it faster.

    Though, I would investagate why that honda won't do the job on propane first. There might be a cheap fix, or at least cheaper than all that money your talking about. Just some thoughts that popped into my head, bounced around a bit, so I had to let them out. Good luck.
    Charlie

  8. #8
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    Quote Originally Posted by Decidion View Post
    I see where you are going with this, but it's not quite that bad with the propane genny either. Propane is only $2.20/gallon here and the maintenance interval on the genny is 500 hours. So the cost for the generator is probably closer to $20K. But that is still double what you came up with for solar costs.

    I'm kind of thinking out loud here...but our house is 300' from the well. How far could I run a line that was pushing 110-120v before the loss was impractical or the size of the cable too expensive to justify?
    300' is 300' whether it is the generator or PV. Voltage drop is a function of draw in amps and distance. To reduce voltage drop you would move the generator or the PV closer to the well or increase the wire size to accomodate.

  9. #9
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    You'd probably be better off to replace your existing pump with a Grundfos SQF series pump, and get the Grundfos CU-200 control box. Then you could run the pump on grid AC, sine wave AC locally produced, or directly off DC from solar arrays.

    Since you are pumping into storage now, this is the idea pump to run directly off solar...skipping the conversion to AC, batteries and all that. You simply put a couple hundred watts ( depends on head, and flow you want ), and when the sun shines, the water flows.

    They also make a generator interface to make it easy to connect a generator to the pump if solar isn't enough to run it ( like extended clouds ). If the generator runs out of fuel, the interface auto switches back to solar.

  10. #10
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    Propane is a less dense fuel than gasoline, I think it's almost 20% less.

    Your startup surge that the inverter needs to supply, is going to be at least 5x the running power

    My 1/2 hp pump, running, pulls 1,000w from the inverter (according to the inverters meter)) so that's at least a 5,000w starting surge.

    I run 240VAC to my pump, 400', over #6 alum wire. Same as #8 copper.

    240V AC 1/2 hp pump is the same watts as 120VAC, but half the amps.

    Voltage drop calc in my .sig will help you a lot, figuring distance, amps and wire gauge.

    Don't forget the wire splice to the underwater cable in the well, you have about 250' of likely #10 wire, unless you are lucky and they installed #8 down the well.

    If you set the pump to only run while the sun is shining, a 600W array could keep batteries charged (making half the power you need) so you can downsize a lot. If you want to pump every day, rain or shine, and night, that's going to cost you.
    Since the dawn of time it has been mankind's dream to blot out the sun.
    Montgomery Burns

    "Always listen to experts. They'll tell you what can't be done and why. Then do it."

    spreadsheet based voltage drop calculator:
    http://www.solar-guppy.com/download/...calculator.zip
    http://www.solarpaneltalk.com/showth...oss-calculator

    http://www.mike-burgess.org/PVinfo_2.html

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,
    battery lugs http://tinyurl.com/LMR-BigLug
    Setting up batteries http://tinyurl.com/LMR-NiFe

    gear :
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV || || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

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