What pump to use for 24/7 pumping 5 GPM at 12 ft head?

[thane]

I need to pump water from a hand dug well into a pond during the dry season ( Jun, Jul, Aug, Sep ).

Well is 20 ft deep, 5 ft in diameter, water level 12 ft

The discharge head will be about 12 ft (much less if slow drawdown), with a run of 100 ft.

Preliminary testing indicates a well recharge rate of 400+ GPH (need more testing).

The flow requirement for the pond will be 7000 gallons per day ( 300 GPH,  5 GPM ) due to evaporation.

I have no grid power nearby, but it's the highest sun during those months and the location gets 6-8 hours of unobstructed sun.

I think my best bet will be 24/7 pumping with batteries, charged by PV at the lowest rate of 5 GPM.

Any ideas on which pump would work?  DC? AC?

I'm concerned about 24/7 pumping for 4 months killing pumps.

Plus, I obviously want to right size the pump to the task and use the least PV panels and batteries.

[damian]

Water pumping systems have been my bread and butter for about the last twelve years so I know a few things about the subject in general.  There are many specifics that influence each situation that will modify all I will say but here are a few generalities.  A good pump can run 24/7 for a long time.  The biggest factor influencing pump life is how clean the water is that you are pumping.  Grit equals less pump life.  If you have a lot of grit you should look at some kind of sock for the pump to live in that will take the grit out.  My favorite pump for off grid is the Grundfos SQF series.  They are extremely efficient, tough, and will run on AC or DC.  In general I would say, if you are starting from scratch don't use batteries.  If the well is deep enough to sustain some drawdown its recharge rate will increase as the static level drops.  So if you can pump only during the day and go array direct you will have a far simpler system.  The only reason to go battery is if your well will not keep up.  What I am trying to say is if you draw the well down somewhat that will increase your head somewhat but that is a smaller factor than the added cost and complexity of batteries.  Lots of variables.  You're looking at evaporative losses from the pond but if it is not lined then your seepage losses could be a bigger factor.  If the pond is lined and you can estimate evaporation well then you can go array direct with a simple float switch in the pond to cut off pumping at full or just let the excess spill from an overflow.  If you run an SQF array direct it will simply pump as much water as it can with the power available so you will move the most water from the well when your evaporation is the most.  All of this depends on the well being able to keep up so you may want to get a pump and a generator and do a pumping test to see what the well will actually do.  Again, there are lots of variables.  The well capacity in June may not be what it is in August so inquire with neighboring well owners if they are they to try to get an idea of how wells in your area produce seasonally.  In summary, try to dial in the well production rate and think about going array direct.

Damian

[thane]

Thanks Damien.

I would prefer going array direct.  I'll have to really work the well over and find out what maximum GPM it can sustain... in June through Sept.

Most of the solar pumps are designed to go deep.  I would like to "right size" this for higher volume low head.  The head will run between zero and 10 feet.  I don't want to overkill (read overpay) the system.

It looks like this summer may be best used as a data gathering season... and implementation next year.


Also, do you know if the Grundfos SQF pumps will work with other PV panels using their controller/switch box?

[damian]

Hi Thane,

Yes the sqf pumps will work with any panels.  The smaller ones (up to 11 gpm nominal) are helical rotor pumps which means they are positive displacement devices.   If you were to use, say, an 11 sqf, it will do 10 gpm at 15 feet of head with 200 watts input.  Though it will pump up to 300 feet of head, running it at lower head just means it will use less power.  It will be no less efficient at that lower head.  One cautionary note on efficiency though, these pumps will run on 36-300 volts ac or dc but will be a little less efficient with lower voltage supplied, (less than 120 vdc or vac), so the best thing would be to supply it with ~200 watts worth of panels configured to supply about 120 vdc.

Damian

[hydrosun]

What is the pond being used for? 7000 gallons per day in evaporation sounds like a lot. How big is the pond, and how do you know how much water is lost in evaporation? On swimming pools most of the heat is lost in evaporation so there are floating pool covers when not is use to cut the evaporation losses. It also keeps the water warmer. If your use can handle slightly warmer water then you could decrease the amount of water needed to be replaced by using some sort of cover. That would be cheaper than pumping water.
I've worked on Grundfos SQ pumps with a similar pump head as the SQF with over a million gallons pumped and still working great.  It makes sense to use the higher priced grundfos instead of the shurflo pumps that will have to be replaced every 2000 hours when the diaphram fails. 
You'll have to see if your well will keep up with increased day time only pumping to pump without batteries.  Other wise you will have to charge batteries during the day and run a SQ pump through an inverter and batteries to keep a steady 5 gpm for 24 hours a day to match your well production.
Chris

[thane]

What is the pond being used for? 7000 gallons per day in evaporation sounds like a lot. How big is the pond, and how do you know how much water is lost in evaporation?

The pond is about 2 acres in surface area. In my region evaporation loss is about 1 inch per week (+/- due to wind, etc.). One inch on my pond is about 50,000 gallons... divide by 7 days... about 7000 gallons per day.  I have done copious testing and measurement over the last 4 years.

But, now I need to get more data on the well during the next few months.  I plan on doing draw-down and recharge tests every 2 weeks during July, August, September.

[damian]

Just one thing I need to mention.  Grundfos SQ series pumps are centrifugals and this means they will not be efficient over a wide range of heads.  Even the smallest SQ, a 1/3 hp 5 GPM model, will see maximum efficiency at ~95 feet of head.  Please note that the SQF series is entirely different than the SQ series.  The SQF pumps were developed specifically for off grid/RE applications whereas the SQ series is a derivation of the SQE series which were developed as primarily on grid constant pressure pumps.  The SQF needs no inverter and will be vastly more efficient in your application than an SQ series.  As I stated in an earlier post, the smaller SQF pumps, up to model 11 SQF will be very efficient and long lived at a variety of heads.  Additionally the SQF pumps have a built in low water cut off feature.

Best of luck with your well testing. 

Damian

[Ungrounded Lightning Rod]

With well water and a lot of pond evaporation you may need to overpump and spill a bit of water into the local drainage.  Otherwise you may end up with a salt pond and dead ground around it after a while.  B-b

(I'm not an expert on this so do your own literature survey.)