Solar Garden Irrigation

Cal Poly UNIV 392 Explores: Solar-Powered Irrigation

As initially conceived in the UNIV 391 Fall 2015 class, we are interested in creating a solar-powered irrigation technology for farmers in developing countries. This intermediate technology will be affordable and tailored to the unique resources and needs of the target population.

As illustrated in Figure 1 by GapMinder , Ghana’s GDP is largely dependent on agriculture as a source of GDP, especially in comparison to other countries. Additionally, Ghana ranks very low in relation to income per capita among the rest of the world’s nations. This highlights an interesting truth about Ghana: agriculture stands at the heart of the macro-economy, yet the current agricultural infrastructure is not contributing to the economic well-being on an individual level.

Given this national context, our group sees a large potential for the appropriate technology of solar-powered water pumps and gravity fed irrigation systems to maximize the efficiency and profit of individual agricultural efforts in Agbokpa, Ghana.

Figure 1: Association between agriculture as a percentage of GDP and income per capita within various countries. Source: Gapminder. (2011). Retrieved March 10, 2016.

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Exploring the impact of a Solar-Powered Community Garden in Agbokpa, Ghana

Problem Definition: Insufficient water harnessing resources leave a lakeside village in Ghana, Agbokpa , with no efficient way to sustain water-intensive crops during the dry season which is approximately half a year long. Agbokpa is primarily comprised of farmers who make a living by selling their surplus crops [crops not used to feed their families] at nearby markets. Therefore, for approximately half of the year, the majority of the village is not able to earn a sufficient salary due to the influence of water scarcity on crop production.

Figure 2: Current water gathering methods in Agbokpa, Ghana

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As illustrated in Figure 2 above, the Agbokpa villagers currently harness their water directly from the lake using buckets. It is not feasible to harness all the necessary water to sustain a farm during the dry season which forces them to look toward alternative forms of income during this time; primarily charcoal production. This brings up another potential benefit of the solar-powered garden: it could potentially lessen the need for charcoal producing which has a negative effect on the global environment. Nevertheless, we must also take into consideration the cultural and social implications that such a switch might have.

Figure 3: Diagram of the Fall 2015 proposal

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2016 Concept Progress

While initially we planned on creating a scaled prototype of the irrigation as it would be implemented in Ghana, but after a few iterations and refinements, we have altered our project and design to fit our resources and time. After gaining a lot of insight from Dylan Robertson from the Student Experimental Farm (SEF) and Polyponics, we realized we wanted to do something that demonstrated the concept of using solar pumps for irrigation, but we also wanted to do something that would benefit the SEF and Polyponics in the long run and potentially inspire future projects.
Using solar energy as the power source for the water pump, we will take advantage of the SEF aquaponics system and harness the water from the fish tank to irrigate the crops. It’s a win-win situation: the fish will get an unlimited oxygenated water supply and the crops will have fertilized water with rich nutrients from the fish’s waste. The concept design is illustrated below in Figure 4:

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2016 Progress Update

Irrigation Pivot: After further consideration of the limitations of design and the need to unite various third parties for the irrigation concept, we have pivoted to a more simplistic design. Once we reconsulted Dylan from the SEF, we have agreed to create a “water battery” to help aerate the biodiversity tank and safeguard the fish living there. A constant drip from the water battery will prevent the death of the fish in event of a crash of the electrical grid (two tragedies have occurred thus far towards this end).

The design involves an elevated tank that the water pump will continuously fill and drip during the day while the sun is out. However, to keep this system effective at night, we will design the tank to release steady drips to last through the morning when the solar panel will kick the pump back on and fill the tank. We will need to figure out flow rate into the elevated tank, create an appropriate drip rate out of the tank, figure out the amount of water we will need to last 12 hours without power, and build a strong enough tank and base to hold the water. We will be using a solar pump to demonstrate the technology for aeration, but note how it is easily and commonly applied for methods of drip irrigation.

Figure 5: Diagram of the current design


Similar designs have been developed to ours. More information and illustration can be found here.

Our short-term goal is to modify the design to suit the Cal Poly Student Experimental Farm, which can be found at the following link for more exploration: Poly Student Experimental Farm Wikipage

In order to determine the size of the tank we needed, we calculated the drip rate to be:


Table 1: Design Matrix

Criteria Cost of building Cost of Use Enviorenmental impact Services provided Feasibility Time to build Maintenance Learning experience Consistent w my values Impress others Total Out of a perfect score
Solar energy 6 8 10 8 7 5 6 8 7 7 72 100
Human labor 10 10 10 0 0 10 10 0 0 0 50 100
Electricity 4 6 4 9 9 4 5 8 6 5 60 100
Rain 10 10 10 0 0 10 10 0 0 0 50 100
No electricity 0 10 10 10 10 10 0 10 10 10 80 100
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Figure 6: A Digital sketch for the final modification for SEF
Figure 7: Final product set up at SEF

The biggest challenge we had to overcome in this last design iteration deals with maintaining a constant drop rate into the biodiversity tank. We ended up making our own “overflow valve” in which a cone, our glue cap, is attached to a piece of styrofoam that will float as the water fills up in the tuna can to cut off the flow of water from the larger tank. When enough of the water drains from the tuna can, the styrofoam piece will drop bad down, allowing water to drip back into the tuna can. This mechanism gives us that control over the drip rate that we’ve been trying to solve.

A few things changed in the final implementation of this mechanism:
1. The string anchor became two plastic chopsticks glued to the bottom of the can. We found that string allowed too much rotation and misalignment back into the hole, which defeated the whole purpose of having a stopper.
2. Originally we tried gluing the cap to the styrofoam piece, but the glues we tried kept eating away at the styrofoam. Instead, we attached the cap with a paperclip, with a piece of it extending out through the hole. This is important because it allows us to be able to manually unclog or re-clog the hole if something goes wrong.

Figure 8: The Valve System Inside the Can

Discussion and Conclusion: Where will this project go?
Future innovators that adopt this project design should attempt to fulfill the initial proposals we had in mind. Instead of just a water battery, the solar-powered drip system may be adapted to water plots next to the biodiversity tank. This will double the functionality of our design as we conserve the manual labor and/or electrical power that currently fulfills that objective.

Improvements on the design of this system can be made for future efforts to push our SEF adaptation:
1. Stronger solar panel with better access to the sun through the SEF greenhouse covering.
2. A non-plastic container for the elevated tank. The plastic is good because its long lasting, but not necessarily for this project because of the weight it needs to hold. Too much water in the tank causes it to warp and bend a bit, which in the long-term would probably be bad. We would need to take a look into a more stable material that is also not toxic to the fish and plants, can support all of that water weight, and tolerates water.
3. More permanent support system. The system is currently balanced on concrete blocks so the tuna can is suspended over the tank. The tank at full capacity may not hold, the tank may need to be moved to a different location around the biodiversity tank that might require more or less support.
4. Drill a second hole into the top of the tank to thread the aquarium tubing through so it’s not just resting on top of the tank and can slip out or off.

Meet our team

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Left to right: Michael, Brian, Kat, and Jolie.

Michael Zamora: Fourth year Political Science major with an interest in public policy and law. His passions involve learning more about himself through others, innovative idea generating, and ethical discussions about the use of new technologies.

Brian: Third year Mechanical Engineering major. He enjoys learning more about new innovations that are made to better the lives of others.

Kat Tran: Third year Molecular Biology. Growing up in Vietnam with little to no technology, she is fascinated with how things are the way they are. Her passion is learning so that she can help her community and better herself.

Jolie Leung: Fourth year Landscape Architecture with a minor in Real Property Development. A dream of hers is to explore the social power of landscape architecture and expand its place in humanitarian work.