Solar Irrigation System Double Check

[michaelbyrne00]

Hello, I am planning a new solar irrigation system and just wanted to see if I couldn't get some feedback. This is my first time designing a complicated irrigation system. OK here goes. The pump I am planning to use is a 1/2HP 1.5" discharge centrifugal pump capable of pushing 40GPM @ 40' of head. The maximum head in my system is around 25' or less, and the maximum demand for water in my system is 32.72 GPM. I calculate that I will need a system capable of producing 30 psi in order for the water to reach the furthest watering zone. The main line is 1.5" discharge lay flat hose, each watering zone reduces to 3/4" supply and drip tape with pressure regulators. Now the first thing that makes me nervous is that the pump seems to be more than capable. I will have a main pressure regulator and 12 psi drip regulators in the system to control pressure, but it's the flow I'm worried about. I've heard that these types of pumps are somewhat designed to self-regulate flow, but to what degree I am uncertain...I wouldn't want to tax the pump too much by constricting too much flow. I did find that 1.5" seems to be the minimum diameter main line I should use due to velocity and pressure loss seen over long distances. Additionally, the system will be controlled by an irrigation controller which will turn on the pump and supply valve via relays (Still need to find one for the pump).
This is a solar design, so here's what I was thinking.

• 100ah Deep Cycle Marine Battery
• 2000w continuous 4000w surge Power Inverter
• 90 watt Solar Charging Kit with 10 amp charge controller

This set up would allow me to water for 2 hours, leaving the battery @ 50% charge. The system uses higher flow drip tape (.67GPM), so after the 2 hours of watering, I should have applied what is equal to a half inch of rainfall. The battery could take 12 hours to charge...if there is a lot of cloudy weather, perhaps longer (thankfully irrigation is not typically needed on these days anyway). Planning to water every two to three days depending on the weather....I'll shoot for 1 - 1.5 inches of (rainfall)/wk, unless it is really hot and dry.

Well, what do you think? See any conflicts?

[Mike90250]

oh boy.

The 90w panel is nowhere near enough to run the pump, it can just barely recharge and keep the battery full.

My 1/2 hp pump, in real life, accounting for motor efficiency, Power Factor, and all losses, consumes 1,000 watts,
and generally runs 3 hours a day, consuming 3Kwh of power. To recharge the batteries at 80% efficiency, means i have to harvest at least 3,600 watt hours in a 5 hour solar day, needing at least 800w of panels to work in perfect weather.

the 12v 1000ah battery can hold at most, 1200watt hours, 50% of which are usable. You need at least 4 of those batteries, preferably wired in series (for an efficient 48V system) or parallel/series for 24V. 12V is a time bomb at the power you need.

[michaelbyrne00]

Thanks

Thanks for your input. I'm still a little confused. The amount of AMPs that this pump will draw will be akin to a hair dryer...right? That seems weird. I could imagine hooking up a hair dryer to an inverter on a 12v battery and powering it for a couple of hours...no? When I think about watts, what you're saying about the panel being too small makes sense. So, if I ran this system for 2 hours,...that would be around 2300watts. If the solar panel is a 90watt panel....that's 25.5hrs of SOLAR charging before the battery is restored, is that right? That's too slow. ...Back to the watts...So, if I think of the watts the way I think I was correctly thinking about amps...then I understand? Meaning, so not only can I discharge only 50% amps, but also watts..OK. So that would leave me with 500 - 600w per deep cycle battery.... 500 * 4 = 2000w. Well, that seriously boosts the investment cost... that's $1,400 in batteries!!! Out of curiosity...what kind of inverter would be used if this became a 48v system?

[Mike90250]

yes, well, your battery cannot run a hair dryer for an hour, and yes, you grasp the idea it will take several days to recharge it.

To scale this up, after the batteries (which you need anyways) a charge controller capable of 48V operation and just a 48v, 3000w inverter (depends on the starting requirement of the motor, if a 2Kw inverter can start it or what..

[Wy_White_Wolf]

Can you place a cistern at a higher elevation than what you're trying to irrigate?

If so then you may be able to do something closer to how I'm watering my orchard. I have a 350 tank as a cistern that I fill from the well solar direct (no batteries). I use a 120 watt panel feeding a Shurflo 9300 series pump. from there I use a battery powered timer so gravity can feed the orchard. Yo may need to change to a different drip emitter to avoid the 12psi of backpressure from them.

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