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stumpfield
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Water pump power requirement /sizing
10/30/07 06:51 PM
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I have a grundfos sqflex solar pump installed in my well for a little over a year. It has worked well with occasional use powered by a portable generator. The well is 230' deep. The pump is set at 220'. The water level in the well is 80'. The well's flow rate is 2gpm according to my well driller.
I want to install just enough solar panel to maintain a 2gpm flow into a storage tank when the sun is up. The performance curve of the pump said it will require 300watt at 210ft head. 120watt at 90ft. How much panel do I need? A little over 300w or just under 120watt???? Should I use the depth where the pump was set or the static water level? I don't want to exceed the well's flow rate by providing too much power. Thanks for your help.
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Re: Water pump power requirement /sizing
[re: stumpfield]
10/31/07 01:23 AM
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What is the flow rate of the well.
If greater than the pump rate then you can use the 80ft level.
Oversize your solar array to allow for line losses.
Go with close to 150 watts of solar panels.
With more specifics about the pump we could give more info.
Got a website that gives details on the pump?
Pooh Bear
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jimbrown
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Re: Water pump power requirement /sizing
[re: stumpfield]
10/31/07 10:09 AM
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I have a simalar setup except that I have a Dankoff pump. I have installed one just like yours for a neighbor. Warning You can not have too many solar panels. I would put the pump at about 100 or 120 ft and run some where between 200 and 300 watts. I have 240 watts on mine. They make some special panels for those Grunflos that are 66volt panels. If I remember those pumps can run on just about any thing AC/DC from about 12v to 300 volts. The 66 volt work really good if you can find them. Other wise I would probably go with four panels running 48 volts. I have 4 12 volt in series for 48 volts on mine. It pumps about 2 1/2 gallons a min. Warning again it is far better to pump into a storage tank than into a pressure tank. If you pump into a pressure tank you have to consider the pressure as part of the lift requirement.
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jimbrown
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Re: Water pump power requirement /sizing
[re: stumpfield]
10/31/07 05:55 PM
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Attempting to control the rate of pumping by panel wattage will not work. the pump will either pump or it will not. If you go light on the panels it just means that it will take more sunlight to pump than it does with more panels. Thus if your panels are marginal it may only pump from 11 Am till about 2 or 3 PM. With more panels it will start pumping at 9 or 10 and pump untill 4 or 5 depending on where you live. Going small also means that if it is a cloudy day and not much sun you may not pump at all. I guarantee if you run out of water it will always be at night and if your panels are too small and its a cloudy day you may not get any water the next day. It appears that you have a generator for those times, But the purpose of solar is to not use the generator.
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stumpfield
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Re: Water pump power requirement /sizing
[re: Pooh_Bear]
10/31/07 08:02 PM
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Thanks Pooh Bear. The pump is Grundfos SQflex 11 SQF-2 Helical Rotor. The flow rate of the well is 2gpm according to well driller. I think it might be much higher because I can pump with full power with generator power (11 gpm) and the well didn't go dry yet. So, if I plan for 2gpm, it should be safe to not over pumping.
My main question was how to read/determine the meaning of head? Does it go by how deep the pump was set or the water level?
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stumpfield
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Re: Water pump power requirement /sizing
[re: jimbrown]
10/31/07 08:17 PM
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Thanks Jim. I agree with you that it's nearly impossible to control the flow rate with the exact amount of solar panel. The pump already set by the well driller at 220ft. I don't know enough and don't want to mess with it.
This pump can take a wide range of voltage and current. The flow rate is up to 11gpm. The more power, the higher flow rate up to the pump's maximum. With less power, it will pump .1gpm with as low as 40watt at 90ft head. Do I really need to pull the pump up higher to conserve power?
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Re: Water pump power requirement /sizing
[re: stumpfield]
10/31/07 10:39 PM
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There is 3 types of head (regarding pumps).
Suction Head = the distance from the pump to the water surface.
Since you have a submersible pump this figure is irrelevant.
Lift Head = the total vertical distance from the water surface
to the discharge point of the pipe. In your case meaning the
distance from the water surface to the height you are pumping it to.
Total Head = Suction Head + Lift Head.
Your suction head is essentially zero so you only need Lift Head.
So use the vertical distance from the top water level in your well
to the highest point you will be pumping water.
Pooh Bear
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GaryQWA
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Re: Water pump power requirement /sizing
[re: stumpfield]
11/02/07 09:17 AM
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You are forgetting the storage capacity of the well. I.E. a 6" well has 1.47 gal/foot of water in it. If the pump is sized to pump from the depth it is set at in the well, you can plan on using all the water above the pump inlet. If not, then the pump will draw down the well to the level the pump can't move water from.
All the while the pump is moving water up to the house, the well is recovering at the 2 gpm. So you probably have much more water available than a house is going to use unless you use more water than 2 gpm for hours at a time.
Gary
Quality Water Associates
Gary Slusser
Quality Water Associates
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Re: Water pump power requirement /sizing
[re: GaryQWA]
11/04/07 06:09 AM
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That's why you need to know the refresh rate of the well.
If you are pumping 2gpm but the well is only flowing at 1gpm
eventually you will pump it dry if you don't give it time to refresh.
And also you would need to use the lowest point of the draw
down level for head calculations.
Pooh Bear
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egon
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Re: Water pump power requirement /sizing
[re: Pooh_Bear]
11/04/07 06:18 AM
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In reply to:
The Wells flow rate is 2gpm according to my well driller.
From the original post. If the fellow has a large pressure tank and keeps his pump rate at under the 2 GPM he should be able to use the static water level as a very good guide.
We spent many years living with a flow rate of 2gpm for a family of four. 
Egon
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Re: Water pump power requirement /sizing
[re: egon]
11/04/07 10:46 AM
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When our well was drilled almost 10 years ago it had a flow rate of 3gpm. We have 2 houses on that well and a total of 6 people + weekenders.
We are also 18 inches behind on rain for the year. 
Pooh Bear
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stumpfield
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Re: Water pump power requirement /sizing
[re: Pooh_Bear]
11/05/07 01:33 PM
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Thanks for all the info. 2gpm should be plenty of water for us. We have 5000gal water storage capacity located at 20ft above the well then gravity feed down to the house approx. 100ft below. 5000gal could last a month if we use it conservatively. So, let see if I got this right...
Well is 230ft deep. 6" diameter
Pump is set at 220ft.
Water lever is at 80'
Well's flow rate is 2gpm
5000 gal of storage tank capacity 20' above the well.
Total head = 100ft.
So, I need to size based on 100ft head. Add 20% water level uncertainty... I 'm dealing with 120' total head. According to the performance curve of the pump, I need 150w of power. If everything works like it should, I should get a continous 2gpm flow into the storage tank whenever the sun is up.
If the solar panel only produce 2/3 the power (100w) or the water level drops another 100', I'm still pumping .5gpm.
I'm going to start with 150w and see how it goes or should I go with more? When I buy a solar panel that says 150w, does it produce 150w in full sun? or it goes from 0w in morning then peak out at 150w then drops down to 0w in the evening????
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jimbrown
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Re: Water pump power requirement /sizing
[re: stumpfield]
11/05/07 03:43 PM
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It only produces full power in full sun. If it is not full sun it produces less depending on the type of panel. The only way you can get full power all day is to use a tracking mount that follows the sun across the sky. And then there must be no clouds. You are not going to get it to pump at 25 watts and .5 gallons a minute. Because it won't start. Again. Unless you get the special 66 volt panels the voltage will be low and make starting even more difficult. If you go with 12 volt panels I would suggest at least three for 36 volts better yet 4 and run 48 volts. 4 40 watt panels will give you 160 watts at 48 volts. Which should work but in my opinion is still too low. I you really want to go low on power I would start with 3 60 watt panels for 180 watts at 36 volts and then if you need more power add another 60 watt panel for 240 watts at 48 volts. I say again you can't have too many watts (unless you go ridiculous).
You are going to need some type of cut off switch if you do not have one. Something like this works well.
http://store.solar-electric.com/water-floatswitch.html
Edited by jimbrown (11/05/07 04:22 PM)
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Pat
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Re: Water pump power requirement /sizing
[re: jimbrown]
11/06/07 10:08 PM
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Panel output will partially depend on your latitude, the season, (altitude and other air clarity issues) and ambient temperature. Also it matters if you have a tracker, either single or dual axis and if no tracker will you manually adjust the tilt angle a few times a year to track seasonal changes or just set to a compromise like 15 degrees off your latitude and take what you get?
The solar flux can be measured in energy per area (Watts/sqft) Insolation (not insulation) is the amount of solar power available. With no tracker you might get 5 hrs (of equivalent sun) that is, from the predawn glow to the end of evening twilight all the solar power you collect is as if you had full sun for 5-6 hrs (approx.)
In summer with longer days and otherwise good conditions you might net an equivalent of 6 hours or more depending on latitude etc. Panels are typically rated for their output with a standard sun at some specified temperature. This will not happen all day from sunup to sundown but will be about 5-6 hours or whatever you circumstances dictate.
To do the math you need to decide not just how many Watts you need to pump at a rate of 2GPH (or whatever) but how many Watt-hours you need to deliver to the pump to pump the volume of water you need to average at or above your needs. The volume is the critical factor.
For example, if you pump 2 GPH for 5 hours that is just 10 gal, not much if you have flush toilets and like to shower. You may want to size your panels to allow you to pump considerably more that 2 GPH. A higher pumping rate will not necessarily be a problem as you will be pumping the stored water in the well bore (as others mentioned) and that storage will be getting replenished overnight when you are not pumping.
One good thing is that you have no battery storage in your solar electric setup. They are not helpful in your system where your supply pressure is from a gravity head. DO NOT ADD BATTS. They waste energy and will result in less water pumped.
I suspect that you are going to have to size the panels to pump considerably more that 2 GPH or you will have to ration water rather severely. Just for a rough approximation lets assume pump output vs insolation at a given head is linear. If the panels are sized to pump 2GPH then you get 10-12 gal per day. In actuality, probably less since pump efficiency is not entirely linear over a varying electrical input. I did my cruising on a sailboat under rather stringent water use restrictions (on longer outings) and washed dishes and showered with sea water (fresh for a brief rinse only) to extend cruising range. You don't have the option of using sea water.
Note: sea water desalination via RO was available but was too expensive back then for my budget and had too high of input power requirements.
Some panels are much better on overcast days than others, preserving a higher fraction of the "clear day" output. If you have significant periods of overcast you might want to lean toward the panels that do well with longer wavelengths which penetrate overcast better.
Ever notice how on some days although there is significant overcast you can still feel the sun rather well? The right panels will have a good output on those days and worse.
Pat
"I'm not from your planet, monkey boy!"
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GaryQWA
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Re: Water pump power requirement /sizing
[re: Pooh_Bear]
11/07/07 03:28 PM
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Poohbear you are forgetting total dynamic head, that includes the pressure loses in the plumbing with the water moving. The pressure losses vary with the pressure so we use the average pressure. I.E. 30/50 is 40 psi.
To the original poster, I don't give this much chance to work well long term unless you only need a small volume of water moved into the cistern between like 11 AM and 3 PM. That's because you aren't storing any energy in the present design. Now a bank of solar recharged batteries large enough to power the pump at its max open discharge flow rate with a 100-120' of TDH for a number of hours would work but... you'd need charge and possibly other controllers etc.
Here's a link to where I'm thinking I'll be buying a solar system from for my motor home that we live in full time. I still work a lot from 'home', so I have two computers running 12-16 hours a day and running a generator that long is ridiculous, expensive and noisy. So we are sitting in campgrounds more lately than we'd like, saving the money we'd spend on running the generator. By spring we should be in OR having them install the system.
There are other sites but check out the Education section here.
http://www.amsolar.com/
Gary Slusser
Quality Water Associates
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jimbrown
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Re: Water pump power requirement /sizing
[re: GaryQWA]
11/07/07 05:21 PM
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I must politely dissagree. Batteries are totally unecessary and an extra expense. My system has no batteries and will pump 800 to 1000 gallons on most days. I average about 300 to 500 per day. With the size of storage that he has he should not have any problem unless it snows all day for over a week, or does something dumb like I do sometimes and leave a hose or horse tank on all night. I do not have a tracking mount and mine pumps from about 0900 to 1630 everyday at 2 gallons a min or better.
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GaryQWA
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Re: Water pump power requirement /sizing
[re: jimbrown]
11/07/07 08:23 PM
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No problem, you should know much more about it than I do.
Your 800-1000 gallons over 7.5 hours comes in at 1.7 to 2.2 gpm. The 300-500 is .666 to 1.1 gpm.
Gary Slusser
Quality Water Associates
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jimbrown
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Re: Water pump power requirement /sizing
[re: GaryQWA]
11/08/07 08:48 AM
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The 1.7 -2.2 is about what my pump does. The .666- 1.1 is kinda meaningless as it won't pump that slow. It pumps into an 1800 gallon storage tank and simply shuts off when full untill it draws down about 200 gallons. So it normally pumps about 2 gal a min which is what it is rated for. That is kinda what I have been trying to explain to Stumpfield that that once the amperage drops below a certain point the pump will stop and not start. You can't pump .5 gallons a min all day long. You have to pump at rated amounts and then store it.
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Pat
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Re: Water pump power requirement /sizing
[re: jimbrown]
11/09/07 08:23 AM
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Thanks to Jim Brown, I need to modify an earlier post to get right with reality. If you put batteries in the system and charge those when the solar electric output is insufficient to run the pump, then yo can use the stored energy to run the pump when it might not otherwise run. I think spending the battery money on more solar panels would probably be a better investment but batteries could increase your total pumped water quantity if used to store energy when the pump isn't pumping for use when the pump would not otherwise be pumping. Theoretically true but probably not cost effective compared to more panels.
Thanks for the insightful post, Jim.
Pat
"I'm not from your planet, monkey boy!"
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jimbrown
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Re: Water pump power requirement /sizing
[re: Pat]
11/09/07 09:21 AM
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Pat it really depends on what type of system that you have. If you pump into a storage tank then batteries are not needed or desired. if you pump into a pressure tank you will almost always need batteries. I actually have both. But they are seperate systems. The well is all panels and pumps into a storage tank. A seperate system of panels and batteries then uses different pumps (2 12 volt ones) to pump into the pressure tanks. That way my pressure tanks can refill at night. The few people that I know that tried pumping directly into pressure tanks gave up and resorted to a system similar to mine. I can actually graviety feed most of my stuff without the pressure tanks But i do have a two story house so it will not feed the upstairs.
Edited by jimbrown (11/09/07 09:22 AM)
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speedbump
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Re: Water pump power requirement /sizing
[re: stumpfield]
11/09/07 12:44 PM
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In reply to:
The well is 230' deep. The pump is set at 220'. The water level in the well is 80'. The well's flow rate is 2gpm according to my well driller.
I want to install just enough solar panel to maintain a 2gpm flow into a storage tank when the sun is up.
He said he wants to run this pump at 2gpm while the sun is up. To me, this means a lot of drawdown. Because at 80 feet this pump is going to be pumping a lot more that that.
The idea that the pump will do 11 gpm means nothing unless it will do that for a given period of time. The driller said it will do 2 gpm, I would believe him and plan accordingly. The other thing to be sure of is that this pump can't do 2 gpm or more at 220 feet or you may be running it dry.
bob...
Pumpsandtanks.com
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Pat
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Re: Water pump power requirement /sizing
[re: jimbrown]
11/09/07 02:20 PM
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Yes, Jim, I understand what you did and why. My battery comment is true theoretically but not necessarily practical. There are times when your panels are capable of producing power but not enough to run the pump. Your current setup misses the opportunity to take advantage of that generating capacity.
If you charged batteries during the period of time when the panels are producing power below the threshold to run the pump then you would be able to use the stored energy to run the pumps for a while, later. Let's say for simplicity that your panels start making power at 0600 and stop at 1800. Lets also assume your panels make enough power to run the pump from 0930 to 1630. The reduced but finite power the panels can produce between 0600 and 0930 and also the period from 1630 to 1800 is currently not harvested by your system. If that generating capacity were stored (albeit with losses and at unreasonable expense for batteries and controllers etc.) then after 1800 the pumps could be run from the batteries for a while.
I realize you don't have NASA's budget and spending the extra $ on more panels or a better pump is more cost effective most likely than the battery use scheme I detailed. I was just injecting a theoretical observation, not making, necessarily a practical suggestion, and certainly NOT A NEGATIVE comment regarding your system design as yous is THE STANDARD approach.
At our leasehold in Mexico is a solar only area where we had to sign a contract and legal papers declaring that we understand there is no electrical power (commercial grid) destined to be installed in the zone and that we waive all rights to petition individually or as a group to get commercial power in the future. As a result everyone is solar with generator backup. Well in truth some have token solar systems and rely on generators tooooo much.
There are no water wells in this solar only area and with an average of 3 inches of precip per year cisterns for rain water storage are not practical. The odd hurricane now and then provides a bit more that average rainfall but is not a dependable thing. Water is hauled out from nearest town in tank trucks or you can take drums to town and get it from the municipal water plant. There are several RO outfits in town if you want RO water.
There is a split between gravity systems with overhead storage and low pressure vs underground storage tanks with electric pumps (RV/boat type pressure pumps run from solar-battery systems) and a few systems with overhead storage AND pressure pumps. The land is too flat and there are height restrictions (30 ft max) so overhead storage is NOT going to produce much pressure.
Pat
"I'm not from your planet, monkey boy!"
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