Solar Irrigation System (Need help!)

[KOgrowsfood]

Hi all, I need help planning out an off grid irrigation system. I work at a school and we just got a property donated to us and it is 100% off-grid. We are going to start a large school garden that is about 100’ x 100’ plot.

We have mapped out 30 40’ garden beds. We would like to use drip irrigation. We have a 1,600 gallon water tank. There will be two 3/4” main lines coming out of the water tank that will run perpendicular to the garden beds and then two 1/4” spaghetti drip lines coming off the main line going down each bed with 1 gal/hr emitters every 12”.

How do I figure out how big of a pump I need and what kind of solar setup I need to run it? I’d like to water for at least 15 mins everyday for seedlings.

Thank you so much for your help!
Kyle

 

[SeaGal]

Welcome. I have no idea about regulations in the USA, but in the UK we have quite strict 'health and safety at work' regulations that will cover use of electricity in public places; which would include schools, gyms, clubs, holiday camps, campsites etc.

Whilst DIY solar is permitted for own use, you enter into a whole minefield of regulation if you are deploying such systems for money or where others may come into contact with your DIY work.

As you are asking basic questions such as "how big a pump" and "what kind of solar setup", I am assuming you are not electrically qualified. I suspect that there will be specific rules regarding grounding of equipment, RCD protection of live circuits, routing of wires and fuses that will all need to be complied with.

Sorry if I am sounding too negative and, maybe the regulation in the USA are quite different to the UK , but first I'd suggest you check out the legal/regulation/permit side of things before the technical how-to. It may be the case that you can design the system and then have a qualified electrician install everything for you.

 

[BentleyJ]

Agree with SeaGal regarding regulations, this needs to be investigated further.

To explore the technical side of the question. Perhaps it would be possible to use a 48V DC pump connected directly to a battery pack via a switch or controller and then just use solar to charge the batteries. Avoid the inverter and 240V all together. I believe this would be considered a low voltage system and may not require the Ground Fault protection (RCD).

At the very least, you would need to estimate the flow rate required, then size the pump and make sure it is rated for the proper duty cycle for the application.

 

[hwy17]

What fills the 1600 gallon tank?

 

[KOgrowsfood]

Thanks all. I’m hoping it is going to be a pretty low tech system using a 24v pump. Indeed, I am a beginner in this world but ultimately just need to crunch the numbers I listed in terms of: pump power to fill the amount of lines listed and a solar setup to power said pump.

We will fill the tank via water truck at this time because there is not current rain water catchment opportunity. Land is flat and has no current or planned structures at this time.

Anyone have experience running a similar system or way to crunch those numbers and the source the correct items? Thanks for your help!!

 

[seneysolar]

What fills the 1600 gallon tank?

This.

Start with the pump (voltage, startup current, and running load) and determine how often it runs.

 

[sunshine_eggo]

First, I suspect that you might not be able to run the entire system at once. You may need to break it up into sections. Our robust 75psi water pressure can't handle running our small backyard irrigation all at once (back when we used to run it). It's split into two separate "circuits."

IMHO, you need to start with your irrigation requirements.

# of emitters, E

gpm = E * 1gal/h/60min/h

Then figure your friction losses:

Friction Loss Explained

Friction Loss Explained Friction loss is the loss of pressure in the tubing or pipe caused by friction between water and the inner walls of the tubing. The factors that influence friction loss in irrigation tubing include: flow rate, the mate...

help.dripdepot.com

Break the system into suitable "circuits"

Find a pump that can deliver sufficient gpm and pressure.

Find that pump's power requirements.

Determine your needed runtime.

Determine your daily energy requirements.

Design your off-grid power power system.

 

[hwy17]

Sounds like a bad plan to grow anything on trucked water.

 

[Mattb4]

Hi all, I need help planning out an off grid irrigation system. I work at a school and we just got a property donated to us and it is 100% off-grid. We are going to start a large school garden that is about 100’ x 100’ plot.

We have mapped out 30 40’ garden beds. We would like to use drip irrigation. We have a 1,600 gallon water tank. There will be two 3/4” main lines coming out of the water tank that will run perpendicular to the garden beds and then two 1/4” spaghetti drip lines coming off the main line going down each bed with 1 gal/hr emitters every 12”.

How do I figure out how big of a pump I need and what kind of solar setup I need to run it? I’d like to water for at least 15 mins everyday for seedlings.

Thank you so much for your help!
Kyle

Looking over what you gave for 1gph emitters for every 12 inch of drip tube. The 40 ft run length and 30 beds it would seem you would have 1200gph (1gph/ft X 40ft/bed X 30 beds) pump requirement. Or 20gpm

 

[Mattb4]

BTW: Nothing says you can not use multiple small pumps in parallel to equal a large one in terms of flow. Without looking stuff up myself for any DC 12v pumps amps rating it would be a simple manner of adding up the total and having a sufficient battery capacity to cover running them the 15 minutes. The solar and SCC would be than sized to recharge the battery over a normal day.

1 cook might have a hard time cooking for 100 but 10 cooks* make it a bit easier. Divide and Conquer!

*I tried using this concept for why I needed more than one lady friend but somehow they don't work out in parallel like the math would suggest.

 

[marionw]

Or , elevate the tank and use gravity to feed the drip irrigation

 

[wme]

5 ft of head would give you 2 psi. Make up a simple test rig, say 5 gal of water, 5 ft head and 5 emitters. See how long it takes to leak out all of the water. In real life just use 12v valves to turn on the flow, a simple timer would control things. If this would work it will require a lot less solar and batteries

 

[Bluedog225]

Or , elevate the tank and use gravity to feed the drip irrigation

This. Bring in a load of dirt or two. Put the tank on the dirt. Pump water from truck to tank. Use gravity from there.

 

[marionw]

Keep in mind that most big box store drip irrigations systems rate the emitters gal/hour based on 25 psi. The system uses a 25 psi regulator with a vacuum break. Each foot of elevation of the water tank provides 0.433 psi. Price the cost of a 15ft tower made from readily available lumber to the cost for a solar powered system. At 15ft you would have 6.495 psi. Using battery powered electronic water timers you could calculate how many hours per day (or every other day) you would need to water to achieve the required soil saturation for whatever you are growing. With mulitple timers and manifolds you could make it work

 

[onrbikes]

I pump from a holding tank to a 4000l header that's 5m high. Total head about 20m.
I only use an old car battery hooked up to 180 solar panel using a 12v sureflo pump. I might pump 1000l once per week. Takes about 3 hours. Real low tech

This is for my offgrid house and is worked for over 20 years. I occasionally get another used battery.
The main thing is to use as large a pipe in and out. The large pipe is less resistance and the water is easily pumped. The pump is located next to the holding tank.

I use 1.5"poly pipe. More than enough pressure for the house.