Solar Drip Irrigation Solutions

Problem Statement
Many communities in Ghana rely on hand watering, hand pumping, and other physically laborious irrigation techniques for their agricultural needs. On top of this, some of the water that they use for irrigation is lost through evaporation, or is an inadequate quantity for healthy crop production. Our goal is to design an easy to install and maintain, cost effective solar pump drip irrigation system that farmers in Ghana will be interested in implementing. To accomplish this, the system must be within a starting price range that the farmers can afford, and it must increase crop yield and financial gain within the foreseeable future.

We are involved in a project, working with a community in Ghana called Agbokpa. It is fairly difficult to find on a map which causes problems with distribution and shipping, but is in the southeastern region of Ghana near a small lake.

General location of Agbokpa, marked by the Google Maps pin
General location of Agbokpa, marked by the Google Maps pin

This is a shot of our target community Agbokpa, and it is not on the average map. This map was provided by the Appropriate Technology Class.
The important piece of information is their proximity to the lake, which is called lake Volta and where they get all of their agricultural water.
We have a community in need of year round irrigation supply to allow for a steady income from agricultural farming. Currently for half of the year the farms are abandoned in the dry season due to lack of access to water from reservoirs, and the rest of the year the process of obtaining water is arduous. Many farmers gather the water by hand, or use their children to help out and pump water from reservoirs using cheap treadle pumps that require a lot of unnecessary physical activity. Our goal is to find a simple and affordable technological solution tor bringing water up from the reservoirs and into the farms using renewable solar energy.

treadle pump.JPG
Typical treadle pump utilized by Ghanaian farmers

Work has already been done towards determining the optimal type of system and the requirements, as well as an estimate on pricing. Initial testing was performed on the performance of a small pump (experiment described later) to get an idea of how the application of this project would actually work, outside of theory and assumptions.

We already have a prototype for a storage tank if necessary that was provided by Brown University. The next step is to figure out if the drip irrigation system would work best from the gravity storage tank, or whether we could just attach the drip system directly to the solar pump. A direct connection would eliminate an intermediate step, but gravity will be constant day and night whereas solar intensity will not, meaning it may affect our drip rate. We also must take into consideration what times of day we need to be irrigating and how this changes through the seasons.

Basic System
basic system 1.PNGbasic system 2.PNG

We have been in contact with a team in the appropriate technology class who is currently modeling an irrigation system, and we are helping to determine how the solar pump would be integrated.
Their official website-Design Website
Their Class Website- Appropriate Technology Class

Brown University worked on a storage tank prototype last year and created a foldable stand alone tank that could be built on site, which would lower shipping costs while still retaining its integrity. This prototype was great, although is somewhat difficult to build. The appropriate technology class will be trying to recreate the build to understand how effective this approach is.
Brown’s Work- Brown University

Burro aims to provide advanced technologies at low prices for places that are either underdeveloped or impoverished. They provide tools for agriculture cooking and cheap sustainable energy solutions for those in need. They work in obscure places such as Ghana to try and make the costs of these technologies cheaper.

We are in contact with Nathan Heston,(Nathan’s Wikispace)
who has an understanding of product sourcing and the difficulties of transporting supplies to these remote places in Ghana.

Demographic Information for Ghana (compared with US):
Sources: CIA World Factbook, Freedom House

Ghana US
Population 26,900,000 323,995,528
Growth Rate 2.18% 0.81%
Urbanization 54% 81.6%
Infant mortality 36/1000 5.8/1000
Life Expectancy 66.6 years 79.8 years
Drinking water access 88.7% 99.2%
Sanitation access 14.9% 100%
Literacy 76.6% 98%
Freedom House Score 1,2 (Free) 1,1 (Free)
GDP PPP per capita $4,400 $57,300
GDP growth rate 3.3% 1.6%
% labor in agriculture 44.7% 0.7%
GINI index 42.3% 45%
Electricity production 13 billion kWh per year 4.1 trillion kWh per year
Electricity per capita 483.3 kWh per year 12,654 kWh per year
Fossil fuel percentage 45.4% 73.5%

Ghana is not a wealthy nation, but it is gradually progressing to becoming a developed country. While it is lacking in many areas, such as literacy, sanitation access, and life expectancy, it has one of the most democratic governments in Africa. For many other African nations, kleptocratic governments or militias hinder any efforts at charity and development.
Ghana’s electricity production is also relatively low. The United States produces about 26 times the electricity of Ghana per capita. However, Ghana is somewhat unique in its low use of fossil fuels. Less than half of the electricity produced comes from fossil fuels. Most of the remainder, however, is hydroelectric power, which has environmental concerns of its own. Large scale hydroelectric power can displace a large amount of land, especially if the hydroelectric plant is built on flat land, since these lands could be forests or potential agricultural lands. The plants can have direct effects on the environment, like turbine blades harming organisms such as fish and other aquatic animals. The accumulation of water in the reservoir can dry out rivers downstream, so it must be accounted for to prevent dramatic problems for the ecosystem. Also of importance, greenhouse gases can also be emitted after flooding causes decomposition of plants in the area. If these effects can be minimized, the ecosystem in the area can improve further. Environmental Impacts of Hydroelectric Power

A large portion of Ghana’s population work in agriculture. As a result, improving irrigation methods can have a major effect on the Ghanaian economy and the quality of life of its residents. Additionally, the opportunity to introduce solar-powered irrigation equipment can help ensure that Ghana remains sustainable as it further develops.

One of our research goals has been to find out about the photovoltaic pump technology available and to find viable pumps that could be implemented in our project. We found several sites that promote solar pumps without controllers that simply work when the sun is out and do not, when the sun is down. Simple PV Pump. This would be the most ideal system, though the price may be higher than a pump that is not solar power specific. If we could pair this with the gravity storage tank, the irrigation flow could be regulated manually and the solar pump would simply fill the tank when the sun shines requiring little to no technical maintenance by the farmers.

We are finding that the pumps can be used without a controller, except the long term effects of this causes the pump to burn out over time, which would defeat the purpose of designing a long lasting system. Burning out essentially occurs during times of low sunlight, when the solar panels fail to provide ample electrical current to the pump to overcome the force of gravity on the water. The pump then stalls and is damaged. To overcome this, a linear current booster may need to be purchased, though this only adds to the full cost by about $100-$200. Another option would be to educate the farmers on how to manually turn on and off the pumps for use. Essentially, in the morning once the sun is rising, the farmer would unlock the pump and solar panels, set them up and connect the pump to the piping leading to his farm, and turn on the pump only if there is enough solar power being provided to the pump to supply water to the piping. Although the farmers would have to monitor the system constantly, this would still reduce the physical strain on them, and allow for a more effective irrigation system.
Controller Warning

Current Physics:
This project has deep complexities based in poverty and politics, but we are physicists and so the only logical thing we could do to start this project was rough calculations. We started with a basis pump power of P Watts. We multiply this by the daily use which we assume to be 8 hours due the the average sunlight hours in Agbokpa found here. If we then multiply this by the number of use days a year which we have assumed to be 250 although we have done other day use estimates for sensitivity analysis but get a result of:

E_{daily} = P*Watts * 8 hours = 0.008*P frac{kWh}{day}
E_{yearly} = 0.008*P frac{kWh}{day} * 250 days = 2*P frac{kWh}{year}

This is the power consumption of our crude solar pump. Assuming this pump does not burn out, it will provide water during the daylight hours to a storage tank that will use a gravity drip irrigation system. The main problem then becomes finding affordable pumps, drip tape, and controllers to match our requirements.

Our function is to work with the resources we have, which is the lake and gravity. Currently we are trying to thwart gravity, and we also need to use it for our advantage. Our project goal has been to create this system using the resources at hand, but a more realistic goal would be to produce the means necessary for the system and wait until the technology is cheap and viable. We are very close, but the reality is that we need a solar panel and a pump that will not burn out, which will cost us money regardless of shipping price.

Water Requirements
Understanding Water Units
Estimating Water Needs
Irrigation of Crops – Statistics and Estimations
Crop Water Requirements
Drip Irrigation for Small Plots
Drip Irrigation Design Guidelines

Crops require a certain amount of water per day, on average. This is generally expressed in acre-inches (one inch of water over an entire acre) which is equivalent to 27,000 gallons. Most crops require around 0.2-0.4 acre-inches per day during the peak season. We will assume that our crop is corn, which requires 0.4 acre-inches per day but has a relatively high yield, giving it a good water use efficiency. We will assume that the system pumps for eight hours during the day, and irrigates the field at night. Evapotransition will not be a big factor, since the water is absorbed at night.

Additionally, the weather around Agbokpa can also be a factor. In April, May, Jun, July, September, and October, the rainfall exceeds 100mm, or about 4 inches. The graph below was taken from the worldbank website. June has the greatest amount of rainfall, at 172 mm, or 6.8 inches. This equates to an average of 0.23 inches of rainfall per day. This would mean that, on average, we would still need to pump water to the fields.

Agbokpa rainfall.png

Water_{daily} = 0.4 frac{acre-inch}{day} * 27,000 frac{gallon}{acre-inch} = 10,800 frac{gallons}{acre}
P_{pump} = frac{10,800 gallons}{480 minutes} = 22.8 frac{gallons}{minute}

For 1/4 acre, we would need 2,700 gallons and a pump power of 5.7 gpm. The height of the storage tank will need to be enough to provide the pressure required to reach the entire field. This will mean that the pump needs to be powerful enough to push the water up the required height as well as transport it from the lake to the farm. For each foot of height, water gains 0.43 psi of pressure. For a tank elevated at 10 feet, we would have 4.3 psi of pressure.

According to the University of Maryland, a water velocity of 4 feet per second is a safe speed for transporting the water. For a flow rate of 5.7 gpm and a water velocity of 4 feet per second, a pipe of size 0.75″ would be desired. link Based on sprinklerwarehouse, prices can be found for PVC pipes of varying sizes. For 100 meters of pipe, it would cost about $66.

Overhead Irrigation vs Drip Irrigation
Micro vs Overhead Irrigation
Overhead/sprinkler irrigation techniques reach an average of 70-75% efficiency, while trickle/drip irrigation reach an average of 90-95% efficiency, due to a decrease in water evaporation. Drip irrigation distributes water directly to the base of the plants, while sprinkler irrigation sprays water directly onto the leaves of the plants or soil around the plants where the potential for evaporation is greatest. This means that a lower flow rate and therefore lower price pump can be used, decreasing the overall cost for the irrigation system.

Possible Pump Systems
Solar Water Pump
Electric Pump

In general, it seems like larger pumps are cheaper in terms of $/GPM. It also means less total installation costs, less controllers needed, etc. This may mean that a larger, community water system could be an overall better approach, as long as there are multiple neighboring farmers that wish to purchase a joint system.

Because it would likely be cheapest to have local sources for equipment, we have tried looking for pump systems in Ghana that can meet our needs. This is very difficult, as we cannot easily find information about pumps sold in Ghana. A submersible pump we found was about $270 and can supply up to about 21 gpm. It, and some other pumps, was found here.

Storage Tank
A gravity fed system would likely be preferable to a direct pump to irrigation lines technique, because it would be easier to regulate and distribute pressure evenly throughout every line. That being said, a gravity fed system requires a significant amount of pressure in order for the water to flow throughout the irrigation lines effectively.

Solar Panels
The size of our solar panels will be determined by the power requirements of our pump. For a mass of 3.8 kg/gallon, a height H, the potential energy can be calculated as
E = (3.8 frac{kg}{Gallon} * 9.8 frac{m}{s^2} * H = 37.2 * H frac{Joule}{gallon}

At a flow rate of F gpm, the power needed by the pump is
P = E * F * frac{60 second}{minute} = 0.62 * H * F Watts

For example, if we had a flow of 5 gpm and a tank at 3 meters, we would need a minimum power of 9.3 Watts.

However, in order to operate correctly, the pump needs to receive constant power. A single panel will vary its output sinusoidally as the angle of the sun changes across the sky. There are two ways to fix this:

1. Use a sun tracker system with the solar panel. This will orient the panel so that it is perpendicular to the sun at all times, and the power stays mostly constant while the sun is above the horizon. 2. Arrange multiple panels at different angles so that they collect energy effectively during the entire day. The simplest version of this would be two panels arranged like a tent, one which would be pointed east and another west. We can find the angle of the tent that gives the best power over the entire day.
SolarDiagram1.png SolarDiagram2.png

Which system we use depends on whether the cost and reliability of a sun-tracking frame (single vs dual axis, active vs passive) is greater than or less than the cost of an additional panel. Ultimately, our goal is to run the pump for as long as possible each day, so we need to ensure that steady power is provided as long as possible.

x = Sun angle (relative to east horizon)
I(x) = Direct (perpendicular to Sun) intensity – changes due to atmospheric thickness. Due to the complexity of atmospheric absorption, this is going to be an approximation. Below is Hotter’s clear-day model. (figure 2.1.2)
I(x) = (frac{1353 W}{m^2}) * [a0 + a1*e^(frac{-k}{sin(x) } )]
a0 = 0.4237 - 0.00821(6 - A)^2
a1 = 0.5055 + 0.00595(6.5 - A)^2
k = 0.2711 + 0.01858(2.5 - A)^2

A = elevation in km

Our community is at an elevation of around 250 m, so the constants become:
a0 = 0.1522
a1 = 0.7379
k = 0.3652
I(x) = (frac{1353 W}{m^2}) * [0.1522 + 0.7379*e^(frac{-0.3652}{sin(x) } )]

A = area of solar panel
a = angle of panel relative to surface

Sun tracker:
P = I(x)*A
E_{daily} = frac{43200}{pi} * int^b_a I(x)*A dx
E_{daily} = frac{43200}{pi} * 2215.11 * A = 3.06*10^7 frac{J}{m^2}

P = I(x)*A*MAX(0, cos(a-x)) + I(x)*A*MAX(0, -cos(x+a))
– the “MAX” functions ensure that the function does not produce “negative” power when the sun is below the plane of the panel. In the total energy calculation, I just set the integration limits for each panel to avoid this.
E_{daily} = frac{43200}{pi} * ( int^{frac{pi}{2}+a_0} I(x)(A*cos(a-x),dx - int^pi_{frac{pi}{2}-a} I(x)*A*cos(x+a),dx )

Note: the 43200/pi constant converts angle (radians) into seconds, assuming an even 12 hour day/night cycle. This allows us to calculate daily energy in Joules.

The below graphs show how power output changes as the angle of the Sun changes across the sky. Note that the axes are different for each case, and that the “tent” configuration has a total panel area of 2*A while the Sun tracker has an area of A. We want to minimize the amount of wasted energy and maximize the amount of time the pump runs each day. The pump will only kick in at a power Pmin, and will only be able to use power up to Pmax. During the mornings and evenings, P < Pmin, and the pump will not run. The linear current booster will help the pump run for longer during these periods by reducing Pmin. Otherwise, the energy produced at these times is wasted. At the Sun’s peak, if P > Pmax, the excess energy is also wasted. If we can find a way to divert that power to other activities, then it’s not as big of a concern.

Angle Edaily
Sun tracker 3.06E7 J
90 1.71E7 J
60 2.92E7 J
45 3.49E7 J
30 3.97E7 J
0 4.44E7 J


Drip Irrigation Requirements
Our contacts in Ghana tell us that numerous samples of soil around Agbokpa has been seen to be clay or sandy loam, which we can estimate as medium soil, between slightly coarse and fine. With this assumption, the Drip Emitter Spacing should be every 1 meter. For a 900 square meter plot (~1/4 acre), and the cost of drip tape estimated to be around $0.20/meter in USD, the tape would cost around $180. For a full acre plot, this would be 4 times as much money, at $720. This is much more expensive than we had previously considered, as drip tape was one of the last components we had expected to be pricey.

Other Functions:
We have also seen a need for water transport in the Navajo Nation and would hope to apply our findings to their community as applicable. They are currently working on electricity for the Navajo nation, but we can use their contacts in the Navajo nation to help out. Unfortunately, the Navajo Electricity group has not focused on water transport, so we have not been able to directly apply our findings to the Navajo Nation. However, our calculations can be used as guidelines for any future groups that are planning to work on providing water to the Navajo Nation.
Navajo Electricity

Looking at DigDeep’s website and mission, we see that filtration is a large aspect of the health of the Navajo Nation.

Solar Panel and Pump Test
We have been working closely with the appropriate technology class, and have been able to do some tests on a small scale solar pump. The pump is a 24V pump that draws on average 15V from the solar panels. We used the solar panels from the Bio Resource lab on campus and set up a pump system with a volt meter and pressure gauge to measure our experiment. We wanted to get the voltage and amps to figure out the actual power we were getting from the pump. We also wanted to measure head height potential using pressure.
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We only used a single panel that was 25V. In order to measure the flow rate we filled a graduated cylinder to 2000ml and tracked the time it took to fill at different pressures and power situations. We can see in the scatterplot, that the flow rate obviously increases with power. The three low flow rates are due to an increased pressure that we induced.
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With the Pressure we were able to calculate head height of our model using h = 2.31 p / SG where SG is the specific gravity of water, which is simply 1 and h is height in feet and p is pressure in psi.
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These figures are provided to give a relevant understanding of our setup. We originally started with the bucket on the ground and then we moved it to the table and had the pump moving water to the same height. This eliminated any siphoning or error due to random height, and we simply used the pressure gauge to see head height.
The solar power generated was determined by the physical weather provided and we took qualitative readings of the cloud cover during the experiment, but this is accurately measured in the power provided by the panel.
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Final Package

  • Pump – about $270
  • Solar panel – around 200 W. Assume $0.40/W – $80
  • Storage unit – Current brown system is $100
  • Drip tape – $180 for ¼ acre to $720 for 1 acre
  • PVC Piping – 4 feet per second velocity for safety. For ¼ acre plot, at 5.7 gpm, requires 0.75” pipes. For 1 acre plot, at 20 gpm, requires 1.5” pipes. Assume around 100m for pump distance. At about $0.20 per foot of 0.75” pipe, $66. At about $0.54 per foot of 1.5” pipe, $177
  • Total – $ 700 (¼ acre), $1300 (1 acre)

Selling Point
Our contacts in Ghana tell us that a typical farmer in Ghana would be hard pressed to invest in a system for more than $200 up front, which is much less than our estimate system costs. One possible option is to introduce a payment plan over the course of a few years, or a small loan. Because Ghanaian farmers typically have reduced crop yields during dry seasons and the costs of crops increase during those times, the increase in yields from the pumped irrigation system would offset their costs considerably. The only additional issue here is that we do not know how much money the farmers would be making in the charcoal mines during dry growing seasons, and if growing during those times would offset those profits. Alternatively, if the farmers could educate their children or family members on how to operate the pump and solar panels, they could continue to work in the charcoal mines while the farms is worked as normal. This would increase the income of the farmers considerably, and more than offset the added startup cost from the system.

Looking Forward:
After all of our efforts and experimentation, we have key take-aways. One is that the expense of the system at the current standard of living, we will have pumps that are out of the farmers feasible price range. The solar panels are cheap enough to work on the project as well as the drip tape. With this conclusion we think going forward, it may be a good idea to try and form a community aggregate form of water supply. This would allow the high pump cost to be mitigated. We believe the next step is determining the layout and feasibility of this setup. They could have a powerful pump and try to share this pump between 10 people, or there could be a large container that the water would be pumped to where the farmers could tap into and use gravity to feed the drip system. We believe the issue with this is the low pressure that is provided by gravity as we expressed earlier. There are opportunities to make small water towers with galvanized pipe that is fairly cheap and affordable.

TJ Tamura, Stuart Slavin, Joe Long, William Xiong, Ian Stone

William Xiong – I am a fourth year Electrical Engineering major at Cal Poly San Luis Obispo with a focus on power electronics. I’ve always been a big supporter of sustainable technologies, whether for environmental or economic reasons, so learning more about it in this class has been a great opportunity for me. I hope that the knowledge that I have obtained here at Cal Poly will help me contribute more to these technologies.

Joe Long- Energy and physics enthusiast by heart, Economist by trade. I have a passion for learning and would hope to be paid to learn instead of pay to learn at some point, but that economy does not exist yet. I enjoy knowing things a mile wide an inch deep and believe this class embodies that. Beyond that I appreciate the proximity to nature that SLO provides and believe it encourages sustainability here at Poly. I am a Senior at Poly and will be graduating this quarter and pursuing a Master’s at Poly in Quantitative Economics.

TJ Tamura – I am a third year Environmental Engineering student at Cal Poly, with a passion for reducing waste and increasing efficiency in modern technologies and processes. This Physics of Energy class is satisfying a technical elective for me, and giving me an opportunity to understand how energy sources and electricity generation relate to sustainable technologies for people around the world. This drip irrigation project is particularly exciting for me because I can implement designs from my hydraulics classes for an efficient irrigation technique.

Stuart Slavin – I am a fourth year physics major. I have a passion for studying materials and their thermal properties. I believe that a wide mixture of technologies will be needed to sustain our society into the future, and I’d like to play some small role in that. I am especially interested in providing water to the developing world, and hope to create a system which can be implemented across the world.

Future Goals

1. Reach out to Burro and find out what they need from us to create a package to sell. Get a quote from them and design an affordable payment plan for the farmers
2. Find more accurate information about prices in Ghana
3. Look into the possibility of a large, community system more carefully
4. Create and run a small-scale system for several days

– please assume a 1/4 acre plot and estimate the amount of water you need to pump. Then pick a rise in height. You will not have 12 hours of sunlight/day.

-I request that you consider a different implementation model: The system needs to be built in Ghana by local people. How are we going to do that? There is lots available in the cities there as it is. We can ask for exact merchandise numbers, but we can assume for now that if it’s simple, there will be a reasonable analogue in Ghana. Please consider and price out other options. I read the controller warning, but I think that in the end, we would be better off getting more solar panels because they are getting cheaper and cheaper. If you can’t find an inexpensive control box, I think you should design one that won’t power the pump up until there is sufficient power available. Please look deeper into this… or is the LCB very inexpensive. Please outline the problem… the problem is that when there is insufficient power, the motor can stall and burn out because of arcing… why is it arcing?

-this seems way high-end and is likely expensive. Please price out a simple electric pump and a solar panel. Both these things are likely available in Ghanian cities.

-I would like to see more research about the community. I can ask the direct questions that you need to answer, but I think you can guess what important things are. Now I see that this information is below. I recommend that you provide demographic information closer to the beginning or at least provide an introduction to the community up front.

-link? reference? what environmental “concerns” (rather than “issues”) does it present?

-which you will calculate.

-this is a good start. There are other options that are cheaper. You could just have a cut off and put more solar panels in. You could have a capacitor or small battery, which would probably be more expensive because it would require a charge controller. Please explain this in the body of the website and price out different options.

-please communicate with them directly

Maybe something about each of you?

-You have a good start, but this page needs to be better organized. Additionally there seems to be a communication of frustration. Please figure out what you are going to do, and do your best. Please speak with me if my suggestions are not understood or not what you want to do.