[RE-wrenches] Design help for solar water pumping application

Fri Jun 12 01:18:12 PDT 2009

Hi Lee,

I don't know how the two tanks are laid out physically, but if they happen to be installed in a way that you could run one pipeline up to the tank at 200' and go from there to the other tank, you might try using a float valve in the lower tank and a float switch in the upper tank. The lower tank's inlet would just be "teed" off of the pipeline going to the upper tank. The lower tank will fill first, being the path of least resistance. When it is full, the float valve closes sending water through the pipeline to the upper tank. When the upper tank is full, the float switch would turn the pump off.

The distance to the float switch in the upper tank is a bit far, but you should be OK if you use a larger gauge wire than usual. I think that 18 gauge would be fine, but 16 gauge would be better. If it is line-of-site, you might look into doing a wireless control , but that would mean that you need a small PV module and a battery up there.

Go with the 1 ½" pipe

Not to contradict Mark (Ok...I guess that I am!) The Grundfos model 3 SQF-3 will do 600'

As to Allen's comment about array size, he is correct about the pump drawing a max of 900W. However, if you only put a 900W array on the pump, it will only pump at max volume at mid-day. If you put a larger array on the pump, the array will produce 900W in less light (morning and afternoon) and produce a lot more gallons per day (GPD). The GPM figure of a solar pump is really only relevant for making sure that you don't over pump a low yielding well. It's really GPD that counts. That 1.36kW array might produce 900W at 9AM and 3PM, giving you a solid six hours of max output pumping. No problem over sizing the array - the pump will only draw what it needs. If you have really good exposure to the sky, you can use a tracker to increase GPD instead of over sizing the PV.

According to my info, with 250" of head (220' plus pipe friction loss) you can get about 2000 GPD (summer) with the Grundfos model 6 SQF-2 and about 700W of PV in a fixed array, with a peak flow of 4.5 GPM. Adding more PV will give you more GPD. With the model 11 SQF-2, you can get up to about 4300 GPD with a 1750W array at that head. If you needed even more water volume, and the well produced it, you could even put two pumps in the well (with separate arrays). I had one dealer who managed to put two Grundfos pumps down a 5" casing! He said that it all went easy....but I don't believe him. He did have a curious issue though. He said that if he turned one pump off with its CU200, both pumps would shut down, even though the other pump was not connected to that CU200. He couldn't just run one pump. I never did talk to Grundfos about that.

Cheers!

Brian Teitelbaum
AEE Solar

From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Mark Dickson
Sent: Thursday, June 11, 2009 9:40 PM
To: 'RE-wrenches'
Subject: Re: [RE-wrenches] Design help for solar water pumping application

Hey Lee,
Allan is right in that the WINcaps software is a lifesaver and FREE!  Not to contradict Allan, but I do not see a feasible way of using two float switches in separate tanks with only one pump controller.  Also, the 3000' distance is a little far-they usually recommend a max distance of 1600' for the float switches.  Lastly, if you are ever worried about the head, the Lorentz pumps can pump up to 760' --more than double the recommended for Grundfos.

I highly recommend Genpro Energy Solutions as a pump distributor for both of those brands.  They always answer the phone, are personable and return emails (hint, hint Conergy)!

Best,

Mark Dickson
Oasis Montana Inc.
www.oasismontana.com<http://www.oasismontana.com/>

www.grid-tie.com<http://www.grid-tie.com/>

www.PVsolarpumps.com<http://www.pvsolarpumps.com/>
________________________________
From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Allan Sindelar
Sent: Thursday, June 11, 2009 2:28 PM
To: 'RE-wrenches'
Subject: Re: [RE-wrenches] Design help for solar water pumping application

Lee,
You can get Grundfos' WINCaps software from your RE or pump supplier; some will run the sizing for you (Jeremy at Conergy does for us). I didn't check your head and flow, but I would expect that's about your only good pump choice at that head. Add a tracker if you need greater summer output; don't attempt batteries as a solution. If usage occasionally exceeds output, add an IO101 control and allow the pump to run off any AC source at night. A tiny 1,200W inverter/generator will work at sea level. Use a CU200 controller to allow a float or level detector switch to turn off the pump when tanks are full. Mercury-based float switches last longer in signal circuits that carry no current. If you can't use a float switch because the lines are already buried, look into www.P2Flow.com<http://www.p2flow.com/> for pressure transducer-based control. Read the website info, then call Britt there with your specific application. That array sounds oversized, as the pump draws a maximum of 900 watts. Hope this helps.

Allan Sindelar
Allan at positiveenergysolar.com<mailto:Allan at positiveenergysolar.com>
NABCEP Certified Photovoltaic Installer
EE98J Journeyman Electrician
Positive Energy, Inc.
3201 Calle Marie
Santa Fe, New Mexico 87507
505 424-1112
www.positiveenergysolar.com<http://www.positiveenergysolar.com>
________________________________
From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Lee Bristol
Sent: Thursday, June 11, 2009 1:26 PM
To: RE-wrenches at lists.re-wrenches.org
Subject: [RE-wrenches] Design help for solar water pumping application

Solar Water Pumping Wrenches,

We normally don't do solar water pumping but a friend asked for some help designing his system.  He has one well and two 5,000 gallon reservoirs to fill up.  The average usage is expected to be about 2,000 gallons per day but may be higher in the summer.  The tanks will have level detector switches to sense when the tank is full.  The site is near Leesburg, VA.

The problem is to design a control system to turn on the pump when one or both of the tanks needs water and to shut it off when both are full.  The closest tank has a head requirement of 200 feet (pump to tank) and is 300 feet from the well head.  The second tank head requirement is 220 feet and it is 3,000 feet from the well.  The pipes are expected to be 1.25 or 1.5 inch.

A Grundfos SQFlex 6 SQF-2 pump with 1.36 KW solar was recommended, 360 foot head, 360 gph.  I think that this would provide the lift but not the quantity.  Hmmmm, what valves and controls would you all suggest?

Thanks!
Lee

--
Lee Bristol
NABCEP Certified Solar Designer/Installer

Chief Technology Officer
Standard Solar, Inc.
202 Perry Parkway, #7
Gaithersburg, MD 20877
(301) 944-5105
(240) 479-1510 (c)
www.standardsolar.com<http://www.standardsolar.com>
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