Solar irrigation system. (Photos: John Pincince)
John Pincince
For some years, my wife, Lucy, and I used a small gasoline generator to run a well pump for irrigation. This was not in keeping with our desire to reduce our consumption of fossil fuels. So, we looked into a photovoltaic (PV) system. Serendipitously, the Natural Resource Conservation Service was offering grants for alternative, low carbon footprint projects. We sized our system and included the amount of drip tape and accessories needed then applied and received a grant to cover a fair percentage of the cost.
Control panel.
Now our solar-powered Grundfos deep-well pump supplies all the irrigation water we need for our 26-foot by 48-foot hoop house and our over half acre of mixed annual vegetables, asparagus, fruit trees, strawberries, elderberry bushes and perennial flowers.
The pump is powered by four 250-watt solar panels connected to a general duty safety switch, a small Grundfos digital control panel, a 100-psi pressure tank then through underground conduit directly to the well head and down to the pump. We used two-flow reduction valves at the spigot because there was so much pressure it was blowing the end caps off the drip tape system we use. It is critical to have the correct pressure tank control switch so the tank does not go over the pressure that it is rated for.
We also have a lot of iron in the well water. The microscopic particles of iron were beginning to clog the drip tape, so we placed two in-line water filters to absorb some iron.
The PV panels are mounted on structures we built using mostly repurposed materials. Old 3/4-inch galvanized pipe from an apartment house, southern yellow pine and galvanized steel from a set of school bleachers and other odds and ends from different projects. We used the steel pieces to make two supports for each of the two support structures. We drilled three 3/4-inch holes in each support arm to allow for seasonal adjustment of the panels but found that there is plenty of energy produced without adjustments. For our latitude location in Maine, which is 44.28, we leave the panels at 45 degrees.
Electric Hook-up.
The winds blow quite strongly in this exposed location so to secure the two mounting structures holding the four panels we used 3/16-inch galvanized cables fastened to 18 inch long cork screw type ground anchors. They have been in place for three years now without too much of a problem. The supports did move off the concrete blocks they were set on. I decided to let them sit on the ground. I’ll use cardboard as a weed barrier under the panels and use some crushed rock under the legs of the support structures to allow for drainage. This winter a very high northwest wind caused a set of two panels to flip forward onto the ground because, on one side, the stainless-steel bolt and nut that kept the adjustable arm in place had come undone. Wind vibration then caused the other arm to slip off. Thankfully no damage was done because the panels are joined together across the underside and then are attached to the frame of the structure with heavy galvanized strap hinges which we used because we thought we would need to adjust the angle during the growing season.
No wires pulled out because there was enough slack – good planning and good luck.
There are more permanent types of structures used to mount panels, but we like the idea of using what is at hand and avoid using any pressure treated wood, as this is a certified organic farm.
To irrigate, we run four garden hoses from a multi-faucet attachment to the header pipes for each major crop type. One supplies all the drip tapes for the annual vegetables in the hoop house. One connects to the field vegetables and asparagus, one to the fruit trees, and one to the strawberries. This way we can control each at the faucet. We also have shutoffs in some of the drip tapes so we can stop irrigating crop rows that may need less water than others. Keep in mind that until the plants are well established the drip tape needs to be secured with ground staples. You can make your own with 12-gauge galvanized wire or purchase them from FEDCO in Maine.
Pressure tank.
The drip tape system is very efficient. The water goes directly onto and into the ground near the seeds, seedlings and maturing plants. Very little is lost to evaporation and aside from the spring laying out and autumn retrieval and storage, very little of my time is needed to irrigate. The downside is that the drip tape is plastic. We have used the same drip for tape five years or more. Still, it is plastic and we wish we could use it for ten years at least.
The beauty of it all is that when the sun is out, the system is working, except when there is enough water in the ground, then we turn it off. When it is raining, we obviously don’t need it and even if the system is still switched on, it is not getting any sun so it is not pumping.
To install the solar system, we had expert help from a friend who is an electrician and between my wife and I we had enough basic plumbing skills to plumb the system. We set the well pump into the well and hooked up the pressure tank, but we did need advice regarding the pressure switch. It needs to be matched to the pressure tank and able to work with direct current. The tank is rated to 100 psi. Ours is a 60/40 switch. When the pressure reaches 60, the switch shuts off. When the pressure goes below 40, the switch turns on.
We always disconnect the well pipe at the well head and at the pressure tank before the heavy freezes signal the approach of winter. To store the 25 fifty-foot lengths of drip tape for winter, we keep each strip at full length, bunch them together and stretch them on the ground on the north side of the hoop house with some weight on them. They are out of the sun and won’t blow away. Although despite our best efforts, well maybe they could be better, the wind sometimes causes the tapes to cross over one another, but we’re able to deal with that pretty easily. Doing it alone however is not recommended!
It is possible to use these panels along with storage batteries to provide lighting to extend our cool season crops in the hoop-house. We would also supply a little heat with fresh horse manure. Water -filled black painted barrels could help moderate temperature in the hoop-house, too. Maybe someday!
John Pincince lives with his wife and cat in West Penobscot Bay in Lincolnville, ME. They grow their own food and have an Airbnb apartment on their beautiful land. John is active in ways to protect the nature of Maine by collecting signatures and writing letters regarding the proposed CMP corridor and to prevent a massive pier from desecrating the shoreline that is so dear to all the generations that have walked, kayaked, canoed or sailed along it.
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