Solar Drip Irrigation [RE-wrenches]

[Windy Dankoff]

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Ray

Array-direct pressure pumping isn't appropriate. It will often supply  
below-peak flow and lead to very uneven distribution of water, always  
favoring the same (lower, closer) emitters. There needs to be a  
battery, but it can be quite small in relation to the load, because  
it will be drawn upon mostly during dry (sunny) weather.

If they need little enough flow to have used the Slowpump, they can  
simply use Slowpump on a battery system. If it's the larger (2507)  
model, then they can select the "Low Speed" model Flowlight Booster  
Pump which is made of the same components but comes with pressurizing  
accessories.

Warning however (clear in the specs) is that water must be filtered  
crystal clear. That is probably not feasible with a rain catch system  
in our dusty climate. You might look at another pump. For low flows,  
centrifugal pumps are not efficient. You'll probably use 1/3 the  
energy with another type of positive displacement pump. All I know of  
is Shurflo or similar diaphragm pump. They can tolerate fine silt.  
Likely, the only acceptable longevity results from using a 24V one of  
the largest model, and running it at 12V (half the rated flow). -- IF  
that doesn't produce enough flow, you can plumb two pumps in  
parallel, but wait ... Look at the Sunpumps Quad diaphragm  
submersible (the original Solarjack company). It's long lasting and  
saves you potential freeze problems. It's 24V and can run 1/2 speed  
at 12V.

Love,
Windy

> Date: Mon, 18 Dec 2006 10:06:06 -0700
> From: Ray Walters <walters at taosnet.com>
>
> Hi All;
>
> I've been contacted by a local high school wanting to do a  
> demonstration
> project. They're installing rain catch cisterns, and want to use solar
> power to run the pressure pump to the drip irrigation system. I'm
> picking up after another wrench who had to leave the area, his plan  
> was
> to use a Dankoff Slow Pump array direct. It seemed that would not
> provide consistent pressure or flow rate for the system's emitters. I
> was considering adding a large pressure tank to the design, or going
> with a Grundfos MQ booster pump (similar to the SQE: no surge, no P
> tank, constant pressure) .  The irrigation guy says the MQs are way
> better for drip systems due to the constant pressure.  The problem  
> with
> that approach, is we're back to a battery and inverter based  
> system.  I
> believe the MQ can run on mod sine but I'm not positive about that  
> either.
> Any advice or experience  that the group has had will be as always
> invaluable and greatly appreciated.
>
> Thanks in Advance,
>
> Ray Walters


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