One of the finest applications of solar photovoltaic panels is in powering drip irrigation systems for farmers in hot, sunny, poor parts of the world. You don’t even need to store the electricity. The pumping is mainly needed when the sun is shining.
To gauge the remarkable benefits of such systems, start with this peer-reviewed study of solar irrigation projects in Africa’s dry zone led by Jennifer Burney of the University of California, San Diego, and Stanford: “Solar-powered drip irrigation enhances food security in the Sudano–Sahel.”
One of the challenges, as with many solar systems, is cost.
Now, Paul Polak, a veteran developer of simply designed products that can benefit the world’s poor (particularly farmers), is trying to raise $50,000 using Indiegogo to produce what he and some volunteer engineers say will be a 2,000-watt solar pumping system that is affordable for farmers who make $3 to $5 a day. (There are three weeks and around $35,000 to go.)
The initial focus is to establish something of a water hub in a village in India. As Polak explains, “When two or more of these pumps are in the same vicinity it creates a micro-market for excess water, creating opportunity for the poorer farmers.”
There’s much more background on the proposal here and in this video:
I sent some background on the technology to Professor Burney and sent her questions to Polak. Read on for the discussion (I’ve cleaned up some e-mail shorthand):
Jennifer Burney:
This is fantastic to see. Paul Polak and Bob Yoder have been working for a while now on low-cost solar pumping and I’ve heard rumors of different designs / approaches over the years. It’s hard to know exactly what the design is based on the video and description… but I’m looking forward to finding out more….
Again, not knowing any details, the biggest question mark for me is on well drilling costs and depth/flow limits.
(1) Borewells are really expensive (unless they’re through soft material and can be done by hand). I am very curious to know what they are exploring on that front
(2) Irrigating 1 hectare [just under 2.5 acres] in dry climates requires quite a bit of water, which means reasonably high flow rates, which…implies depth limits. I’d love to know what specifications they are designing for.
Paul Polak:
Jen raised some very good questions!
First of all, Jack Keller, who has written the classic texts on drip and sprinkler irrigation [some of his work is here] and who Jen probably also knows, is also an active participant in the design team.
The breakthrough in affordability is based on a total systems design approach, in which the cost of the photovoltaic electricity generation system is an important component. Many of the affordability breakthroughs are based on other parts of the system- the controller, the inverter, the motor, the pump, the water conveyance from the well to the crop, the water application system, the selection of high value diversified crops to be grown, and optimization of farmer production methods and access to market. For example, we can provide a drip irrigation system that costs $1,400 for one hectare, less than half the cost of conventional systems. Replacing earth channels by lay-flat hose and conventional surface irrigation by low cost drip at least doubles crop/drop efficiency. Fine tuning impellers to the exact vertical lift improves efficiency by as much as 40 percent.
This project is market driven. There are approximately 20 million diesel pumps producing irrigation water just in India now. Most of them are 5 horsepower with vertical lifts in the suction range. We are designing a radically affordable 2 kilowatt solar pumping system capable of drip irrigating one hectare of high value diversified off-season fruits, vegetables and spices at a retail price 80 percent lower than the existing price of $7,000 for an installed 2 kilowatt solar pumping system in India today. To irrigate 1 hectare (2.5 acres), Jack’s calculations assume we need to apply 5mm/day, which we will deliver through a low cost drip irrigation system. Since it is capable of irrigating 1 hectare of land, this system will be attractive for a very large population of farmers, first in India and then in other developing countries.
Since PV is costly, we start by lowering the cost of the PV system through the use of concentrators. The basic idea is that its cheaper to build flat plate mirrors with a simple tracking devices than it is to invest in larger solar panels. With an efficiency of about 70 percent in mirror-reflected light, our pilot tests with miniaturized models indicate we can obtain an output of about seven suns from 10 mirrors on which 10 suns of light fall when the sunlight is concentrated on a solar panel. This means that in full scale models, we should be able to get approximately 2000 watts output from a 300 watt panel on which 10 mirrors concentrate light.
The problem of overheating of the panels is addressed by attaching a simple water based heat exchanger to the back of the panel through which a small portion of the groundwater we are lifting is pumped. We are using flat plate mirrors because they are one-third the cost of parabolic mirrors, and because flat plate mirrors can be obtained just about anywhere comparatively cheaply in rural areas in developing countries.
This is an example of the options that are being considered. In the end each of the system components will be designed or selected to provide the most cost effective solution that optimizes total system performance to create attractive profit generating opportunities for farmers. The systems approach will minimize the energy required to accomplish what a conventional 5 horsepower diesel pump does. So we economize on the use of water by using low cost drip irrigation application systems, and creating breakthroughs in lowering filter friction, pipe friction, and pump energy losses through a system design approach in which each component contributes optimally to the efficiency and affordability of the total system.
Since our initial business strategy is to directly compete in the marketplace with installed 5 horsepower diesel pumpsets, we bypass the problem of drilling costs — the farmers we will sell to initially already have tubewells that deliver the required amount of water. We also have a good deal of experience in affordable drilling of boreholes when in the future we start marketing to farmers ready to drill new wells. Fortunately in India there is already a lot of experience with low-cost drilling. Even wells with 4-inch casings suitable for engine pumps are being made at low cost. This is in the Himalayan outwash plain that covers much of eastern India. A large percentage of the 20+ million engine pump wells in operation in India were drilled manually and pump from shallow aquifers that are refilled each monsoon.