MAIL: Solar Drip-Irrigation

Beginner

In 2009, we bought an acre of land in Homestead, Florida, 35 minutes south of Miami. Since the parcel had no electricity and no structure to accommodate a large PV array and the related inverters and water pump for a full-scale sprinkler system, I settled for a PV-powered drip irrigation system.

I wanted it to be as simple as possible with the least demand for equipment. The solution was to use a 275-gallon plastic tank ($60 used), and a 2-inch electric valve ($100) to release the water controlled by a timer ($12). Electricity is supplied by a Unisolar PV136 module ($125). The water pump is a 4-inch, 24 V, 1.6-gallon-per-minute well pump ($145) at the bottom of the shallow well. The battery storage is two marine batteries ($58 each). The water tank has a 2-inch manual valve that goes to the electric valve control and then to 2-inch PVC main pipes, which branch into 3/4-inch flexible plastic tubes.

I have about 82 trees. Each tree is fed by a 1/4-inch drip tube coming from the 3/4-inch secondary tubes. All this is accomplished by gravity, and in 10 minutes each tree gets about 1.5 gallons of water—more than enough. It then takes the pump 11/2 hours to replenish the tank.

The battery bank never drops below 85%, and it gets recharged 100% before noon. The single module provides more than enough energy for the task.

Chunin Martinez • Miami, Florida

Comments (3)

Chunin Martinez's picture

The kind of solar panel does not matter. You can use any type as long as it is 24V. The one I used was a Unisolar136W 24V flexible panel. I would have used standard poly type but since I did not have a shed on which to install it I went for the flexible one just laying on the ground surrounded by a small mulch wall to conceal it. The area is safe but did not want to attract too much attention to it. The well is not deep and is only about 20 feet as here in Miami the water table is very high. You can find water just by digging as little as 10 feet in most cases. The specs on the pump says that it has a lift of 230 feet and max immersion of 100 ft so it might be enough for your use. If not you could always use a different pump. Remember that water flow and pressure reduces as you go deeper. Use the minimum depth and tube length for your use to make as efficient as possible. A floating switch takes care of keeping the water tank full. When the water is released by the timer the water pump kicks in until it is full to the floater lever switch. The floater swich is less than $10 on Amazon. Remember that you have to use a relay to activate the pump as the amperage of the switch is low. The most important point is that you have to use an electronic release valve that can operate with zero pressure as the irrigation switches that you find at your local hardware store are meant for use where there is water pressure. That is why the zero pressure switches are more expensive. I got it off Ebay. Just select the size for your project. Mine was 2 inch because the water tank had a 2 inch outlet. And so the main pvc distribution tube was also 2 inch. The branching tubes were the black flexible type as they are cheaper, easier to use and move. Now I have added 1/2 inch tubes coming from the 3/4 inch ones in order to grow vegetable. Seeing that the system supply enough electricity and water I have harvested Chinese winter melon, squash and pepper. I have also added moringa trees in between the fruit trees. I'm also starting to grow melons at the base of some trees in order to take advantage of the existing water lines. Because of this extra water usage I have programed the timer to release water two times a day, in the morning and evening as the sun is too hot during the afternoon. The good thing about the system is that you can adjust it in anyway you want for your needs. If it is a small garden you could use a 55 gallon drum and maybe like a 1 inch tube and valve which would be less than half the price of the bigger 2 inch valve. Flexible tubes allow you to puncture the connecting 1/4 inch outlets for each plant anywhere you want. And if your water usage is high then could put more panels and maybe even a 110V well pump with an inverter. You can make the system they way you need and spend as much or as little you want. My water tank as at ground level as I did not want to built a base for it as it would be more work and expense. But if you put it higher then you will have better water pressure and faster water flow. That is also the reason I only use about half the tank in each watering period in order to preserve a good water flow. I will try to post pictures of the system. Just checking where or how I can host them.

Isaias Dambe's picture

Thank you very much for the useful information. I would have liked it if I got a few more exact details about the type of solar plates (amorphous or crystalline) the wattage, the depth of the well etc. Otherwise thanks for the tips.

How and where can we get this equipment, especially if we are to import for Africa where I live?

Ed Eaglehouse's picture

Thanks for telling us about your project. The type of components you used and their cost is very helpful. I was considering something like this, but your project is simpler and cheaper than what I had dreamed up. Nice job!

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