30 Apr

Building a solar pump irrigation system

A part of this land had been terraced decades ago, perhaps even more than a century. The terraces have mature citrus trees, some olives, figs and many grapevines. Three wells are located on these terraces including one large well next to which we installed this irrigation system.

Objectives

To build an autonomous, solar-powered irrigation system that pumps water from an old agricultural well and delivers it to young citrus trees and grapevines on a terrace several meters above the well. The mature citrus in this area is different kinds of oranges, so we planted lemon, lime, tangerine and grapefruit.

Here is the well next to which we built the irrigation system as we found it, ahem, a bit overgrown:

agricultural well

Here you can see the completed housing, and the whole area around the well, a bit tidier:

agricultural well solar pump irrigation

Construction

Overall this is a much smaller system than the siphon irrigation in the main orchard. We built another brick and cement housing with metal door to contain the pump, filter, valve, battery and charge controller. It was built next to an existing water tank, which we can also fill with this system. I imagine that sometime in the future we can fill this tank with excess solar energy during peak daylight hours, and then gravity feed to one of the terraces below. Here’s the basic idea:

solar pump irrigation system

irrigation system intake filterTo minimize dry operation of the pump (most pumps don’t like it), its important that the pump is near (or in) the water source. In this case the pump has to draw from between 1-3 meters below, depending on the level of the well. Submersible pumps can be used as well, but they tend to cost a lot more.

The water is filtered at the intake (left) to prevent large particles, frogs and critters to be sucked in, which is similar to the one we built for the siphon, a window-screen covered end-section of the pipe drilled with holes, secured with plastic wire-ties. In this case we used 20mm PE pipe. It is also suspended off the bottom with a rock and float.

Another finer-mesh filter is installed before the pump to catch smaller particles. The pump is a Shurflo 8000, which runs on 12V DC, 7 amps, and pumps at a rate of about 6 liters per minute.

Irrigation is timed by the same Gardena valve with integrated timer  that we use in the siphon system. It’s program starts and stops the watering cycle. The pump starts and stops via an integrated pressure switch, so when the valve opens and pressure drops, the switch activates the pump until the valve closes again, which quickly causes a pressure buildup that triggers the pressure switch to shut the pump off. This works very well as long as there are NO AIR LEAKS in the system. Here is the setup in the housing in an almost-finished state:

solar pump irrigation system in portugal

20mm PE irrigation pipe fitted with driplines completes the system. However, here we use higher-flow adjustable flow drippers because of the pump’s relatively high throughput rate. The 4-8 liter per hour drippers that work well on a gravity feed system are not suitable in this setup because their throughput cannot keep up with the pump’s capacity, thus causing a pressure buildup in the system that causes the pump to switch on and off during the watering cycle. This isn’t necessarily a big problem, but to protect the pump and have things run smoothly, we want to avoid the start/stop. If enough of the slow-flow drippers are part of your system, then you’re fine. The point here is to balance the total output of all drippers with the pump’s performance.

Here’s a quick video to show the system in operation.. it’s a placeholder for a more thorough one to come soon:

The solar module is hidden in a thicket of ferns nearby to lessen the risk of theft. The cable, like the irrigation pipes, are buried in the ground. Since this is open land, and we are not there all the time, we want to hide things as much as possible.

Materials & Costs

Shurflo 8080 Pump + Filter€105
80W Solar Panel + Cable€167
Battery and Charge Controller€78
1 Gardena Timer-Valve€55
Manual valves, fittings and water volume counter€40
Irrigation system pipes, drippers€60
Housing material + door€130
Total cost of system€635

Time to install: 5 days (2 persons)

Most of these components were supplied by the very helpful people at MareSolar.

Considerations & Learnings

It’s essential that the system around the pump has no leaks. All fittings must be completely tight, so get yer teflon tape out and wrap those threads well. The pressure switch on the pump is a bit touchy, so even a slow leak can cause the pressure to drop and the pump to switch on when it shouldn’t. If some air gets into the system the pressure switch may not turn the pump off again, and it may burn itself out. The pump we use here is meant for intermittent use, so we actually can’t run it for more then about 25 minutes at a time. Shurflo has many pumps though and a number of them are designed for continuous use.

The system’s battery is virtually always full. It takes only a few minutes of direct sunlight to top it off. It’s clear that there is a massive amount of excess energy that an 80W panel produces, which I’m sure we will find a way to use at some point.

It’s very handy to have the water counter installed to measure what the system takes from the well. Over time, this will tell us a lot about what we can take from the well in a season, and how well water level correlates with annual rainfall.

After a few years of use of these solar-powered pump systems I have come to the conclusion that they are great for small gardens and intermittent use but that they do not stand up well to the kind of application we have here. Trees needs lots of water to thrive in the dry summer here and a system like this struggles to meet the demand. I have, on average, burned out one pump per season. After 50-100 tons of water, the pumps simply wear out, and also sometimes damage themselves when they run dry because of a small leak in the system.

My conclusion is that gravity rules! If you can gravity feed to where you need the water, then that is far more reliable and maintenance-free. Larger-scale irrigation systems will be the subject of some upcoming posts, so look here again soon, or subscribe to updates.

One thought on “Building a solar pump irrigation system

  1. I do a lot of landscape work over a wide range of territory. This actually might be something that would work well for me for irrigating some of my trees. I love that it is solar powered, and it would make perfect sense to hide the solar module in order to lesson the risk of theft. Thanks for posting this!

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