Help needed with sprinkler system

Roadrunner

Hello everyone
I have a small question..
Let there be a piece of land of area about 15x15 sq feet ,to be irrigated by sprinkler system. The water source is a tank at ground level, and a solar-powered pump is to be used to drive the sprinkler. Assuming the water pressure required by the sprinkler is 40psi, what will be the typical energy required by the motor, to drive the pump,to drive the sprinkler?
I know my question is very vague and obscure . I am totally new to this pump and motor stuff. I searched everywhere but I couldn't find anything related to energy consumption .
There are no limitations about the gallons requirement etc, I just want to get an idea about the size of the panels required.

BB.

Re: Help needed with sprinkler system

I will take a guess at this...

Two configurations, one without batteries, one with batteries.

First, pick a pump. Here is a 3.5 GPM 40 PSI pump that runs at 9.1 amps and 12 VDC.

Next, I would suggest that you probably should have an LCB (Linear Current Booster). This will optimize and stabilize the solar panel's electrical characteristics to the pump's electrical needs.

To drive this in the middle of a sunny day with a bit of extra headroom (dirty panels, less than perfect sun, etc.):

• 15 volts * 10 amp motor * 1/0.77 panel+controller losses * 1.25 fudge factor = 244 watts of solar array minimum

I think this would work and meet your needs--But I would talk with NAWS (our host) or other dealer to confirm (I do not have any experience with this setup).

If you want to pump water at night/poor lighting conditions, then you would need a battery bank + Solar Charge Controller. And now you need to know how many gallons per day/hours per day of pump operation you will need.

For the moment, assume you would need 1 hour per day of pumping during the spring/summer/fall.

First the battery bank. 12 volts:

• 10 amps * 1 hour per day pumping * 2 days of energy storage * 1/0.50 maximum battery discharge = 40 AH battery bank @ 12 volts

For the solar panels, two ways to calculate the array size... One based on size of battery bank for proper recharging, a second based on how much load and sun you get. First based on battery bank size using 5% to 13% rate of charge:

• 40 AH * 14.5 volts charging * 1/0.77 panel+controller losses * 0.05 rate of charge = 38 watt panel minimum
• 40 AH * 14.5 volts charging * 1/0.77 panel+controller losses * 0.10 rate of charge = 75 watt panel nominal
• 40 AH * 14.5 volts charging * 1/0.77 panel+controller losses * 0.13 rate of charge = 98 watt panel "maximum cost effective"

Next, based on hours of pump usage and hours of sun. Assume that you get >4 hours of sun per day (need your approximate location for more exact estimate) for at least 9 months a year:

• 10 amps * 14.5 volts battery operating voltage * 1 hour of pumping per day * 1/0.61 DC system efficiency * 1/4 hours of sun per day = 59 watt array minimum

So, for the this estimated system, your optimum system would be from 59 watt to 98 watt solar array/panel.

Does this help?

-Bill

niel

Re: Help needed with sprinkler system

i think you may want to ground feed rather than use a sprinkler. pump water to a tank and then feed into special hoses or pvc pipe that drip water at a slow rate directly into the ground.
here's an example,
http://www.homedepot.com/p/raindrip-Poly-Drip-1-2-in-x-500-ft-Drip-Watering-Hose-052050/100137979#.UVsn1zcZSh9

rocmor

Re: Help needed with sprinkler system

The theory says that the energy required to move water at pressure P and flow rate F is E = F*P*k, where k is a conversion factor depending on the units chosen for E, F and P. For the case of the 40 psi pressure as given in the ratings table for the motor suggested by BB, the power (energy per second) required of the motor would theoretically be about 85 watts. You can figure the total energy once you know how many gallons you want to sprinkle on your land. The fact that the pump requires 9.1 amps (109 W @ 12V) is simply a reflection of the overall efficiency of motor and pump when operated at 40 psi, 84/109 = 78%. Actually, that sounds pretty good. Note that none of this takes into account friction losses in hoses, valves, etc., so, a fudge factor is a good idea.

The obvious advantage of running the motor "open", say, to fill a tank, is that you get 3.5 gpm @70W power consumption. Again, knowing how many gallons you need to fill your tank, you can figure out the total energy required. Trying to use a tank and gravity to get 40 psi water to a sprinkler would not be practical as the tank would need to be about 80 feet above your land, and, in fact, you'd end up using as much if not somewhat more energy than if you went direct from pump to sprinkler. In the case you want to use the tank approach, which has its own advantages, Neil's solution makes sense. However, realize that for every 20 feet that the pump has to raise the water to get it into the tank, you have to add 10 psi (round numbers) at the pump, so your motor/pump efficiency and flow rate will drop some.

rocmor

Re: Help needed with sprinkler system

Oops... I should have said niel's solution. My humble apologies.

Roadrunner

Re: Help needed with sprinkler system

Thanx a lot bill,niel and rocmor for your patience !!!
It took me some time to digest the info.. Now I have a much more clear understanding of the topic :-).
By 'pump' do you mean 'motor and pump' together ?

I will think about the drip method..sounds interesting..

BB.

Re: Help needed with sprinkler system

I linked to an Integrated motor + water pump... Just made it easier to relate electricity in to water volume*pressure out.

You could also go about it through defining your water needs, then looking at various pump performance charts to pick the water pump. Then look at the shaft energy to electric motor ratings.

It can be a pretty complex bit of research and design work to find pumps that will meet your needs, and motors (that are "solar/DC compatible") to drive them.

-Bill

Photowhit

Re: Help needed with sprinkler system

With out addressing your specific problem, let me say I'm off in the morning (if it's still available) to pick up a 200 gallon water tank that I'll use for collecting rain water to water my garden. I'll use cinder blocks to raise it off the ground about 3 feet which should allow me to use gravity fed drip irrigation when needed. Drip delivers more water as less evaporates into the air. If I find I need more force or I raise the beds farther. I'll use a bilge pump. They work find if you don't have too much back pressure, some of the ones designed to lift many feet might even work with your sprinkler. In general broadcasting water (spraying) does help remove chlorine, which is naturally a gas, and the plants might benefit if your using public water.

BB.

Re: Help needed with sprinkler system

Out here (SF Bay Area--if not many parts of the country), they converted us all to chloramine to treat our water--Which does not evaporate when exposed to air or boil out of water.

Chloramine

-Bill

westend

Re: Help needed with sprinkler system

Photowhit wrote: »

With out addressing your specific problem, let me say I'm off in the morning (if it's still available) to pick up a 200 gallon water tank that I'll use for collecting rain water to water my garden. I'll use cinder blocks to raise it off the ground about 3 feet which should allow me to use gravity fed drip irrigation when needed. Drip delivers more water as less evaporates into the air. If I find I need more force or I raise the beds farther. I'll use a bilge pump. They work find if you don't have too much back pressure, some of the ones designed to lift many feet might even work with your sprinkler. In general broadcasting water (spraying) does help remove chlorine, which is naturally a gas, and the plants might benefit if your using public water.

This is the most elegant and energy conserving way to irrigate most areas. The OP doesn't state what type of plants are being grown, soil type, or environment but 15' x 15' could be irrigated with a bucket or a sprinkler can in most cases. Most plant species in common soils require about an inch of rainfall (irrigation) per week.

Roadrunner

Re: Help needed with sprinkler system

I have one more doubt...
The solar power keeps varying due to the changing PV current..right?
As the torque of motor depends on the current, it will also vary.
My question is, how will this affect the pump? Will it affect the flow rate or the discharge pressure?
Or , does the pump performance depend only on the speed of motor?

BB.

Re: Help needed with sprinkler system

That is why it is usually better to have a battery in the system, to stabilize the voltage/pump output--But that adds cost, complexity, and things that fail over time.

However, if you are filling a cistern with a pump, you can use the variable pump output to fill the tank over time, then use a separate water pump (battery backed) or gravity to move the water to the point of use.

Solar panel output I*V curves do not match pump motor I*V curves. One way around this is to use a battery, or you can use a Linear Current Booster.

http://www.solar-electric.com/7amplincurbo.html

Used to control and power a DC motor from a solar panel. The unit prevents stalling of the motor under less than full sun condition. The power of the sun is transformed to the motor running conditions so as the sun goes down the motor slows down instead of stalling. Conversely, or as the sun comes up the motor starts running much earlier instead of staying stalled for hours when it could be running. This translates into more running time of the motor where it spends a lot of time working instead of stalled doing no work.

There are pumps that have LCBs built in or as part of their controllers. Still does not give you 24x7 power for the pump, but very useful for filling a tank with a solar panel only powered pump (or running daytime fans, swamp cooler, etc.).

-Bill

Roadrunner

Re: Help needed with sprinkler system

Thank you Bill. But my question is, how will a reduction in panel current affect the output side parameters?
Will both the flow rate and discharge pressure get decreased, or only one of them? ( in reference to a centrifugal pump)

BB.

Re: Help needed with sprinkler system

Can be a fairly complex question... Centrifugal pumps use more power the higher the flow rate and the lower the pressure (think of a vacuum cleaner... If you block the air flow, the centrifugal blower motor increases RPM).

Also depends on the type of motor and controller... But for a DC motor, the RPM usually falls with lower current, and for a Centrifugal pump, both the pressure and the volume will fall too.

This website has pretty good information on pumps if you want to understand the details:

http://www.pumpfundamentals.com/centrifugal-pump-tips.htm

Or, something from Grundfos may be a little easier (since they map water output vs power input). See the PDF download here. Note that the 3-11 series pumps are Helical Rotor type (positive displacement pump) and the 16 through 60 are the centrifugal type pumps (the lines going 45 degrees across the page are different water based feet of head/pressure as seen by the pump).

-Bill