|Published by||Tineke Iris|
|License||CC BY-SA 4.0|
|Automatic translations||Français, Español, 中文, العربية, Русский, Kiswahili and others|
|Cite as "CCAT solar irrigation for food forest". Appropedia. 2021. Retrieved 2021-08-3.|
This project seeks to install a low-impact irrigation system for a budding food forest and to provide clear information on the full process so that it can be replicated elsewhere. This irrigation system uses collected rainwater, a water pump powered by a photovoltaic panel, two 1000 liters collection tanks, and gravity to irrigate on-demand. The system uses drip irrigation for water distribution and is triggered by a programable automatic water timer. Planning and installation of the irrigation system was achieved within one semester at Humboldt State University. To approach the project we began by getting ourselves acclimated with what goes into a solar irrigation system and learning how to work closely with our clients. We conducted a detailed literature review on the different components of a solar-powered irrigation system. Once we gained a base-level amount of knowledge, we created a detailed plan of approach and had weekly contact with our clients at CCAT. We created a budget for the required components. A series of prototypes were made using the information we gathered from our clients to ensure our final system would be successful and met their desired criteria. Construction and testing were completed over a period of several weeks on site. As of May 2021, the completed irrigation system meets the client's criteria and is fully functional.
Background[edit | edit source]
The Campus Center for Appropriate Technology (CCAT) at Humboldt State University has established the grounds for a small food forest that is currently planted with a few saplings and covered in a layer of mulch. The vision is to provide a space for students and community members to harvest food throughout the years and to share knowledge about integrating landscapes that provide food security as an alternative to the lawns that currently dominate urban areas. This project was conceptualized in previous years by students and users of CCAT. Spring 2021 students have been assigned to create a solar powered irrigation system for the space provided for the food forest.
This project was an option of the Spring 2021 Engineering 305 class with instructor Lonny Grafman. The students undertaking this project are Luisa Close, Tineke Iris, Kyle Spears, and Samuel Killpatrick.
Problem statement[edit | edit source]
The area designated for the food forest is in need of an irrigation system to help the plants establish over the next decade. The objective is to create a low maintenance irrigation system for the food forest and provide a replicable template for other locations. Our plan is to use solar energy to pump water from a rainwater catchment tank (already installed) to the food forest area slightly down the hill from the water catchment location. The irrigation system will use rainwater collected in a nearby tank. We will use solar energy to reach a water flow adequate for the irrigation needs. The irrigation system will be used primarily during the summer months when there is seasonal drought in Humboldt county, and when not as many students are on campus to maintain the area.
Literature review[edit | edit source]
This is a review of some available literature pertinent to solar irrigation for food forest project.
Food forest aspects[edit | edit source]
Food forests are a means of cooperating with nature to address hunger and nutrition issues in both rural and urban areas. Even small gardens can incorporate forest aspects that nurture both the environment and the land stewards. Landscapes can be designed and planted in seven layers ultimately providing multiple functions. Taller trees can provide shade and mulch along with fruits or medicinal barks. Lower trees and shrubs can be planted in conjunction with other layers to fixate nitrogen in the soil and provide habitat for wildlife. Herbs and ground cover can also provide these functions as well as attracting pollinators. Root and vine layers can provide tubers to harvest or aesthetic pleasure for those who visit the space. When laying out the design for the food forest, the needs and purposes of end-users should be considered as well as the interrelationships between the plants as some form better companions and help each other thrive with others. Hardiness zones should also be considered when choosing the plants that will interact in this space.
Intercropping has been proven to increase yields and be more efficient on a land equivalent ratio. Despite the small space set aside for this project, the potentials for sustainable sustenance harvest and learning from this project is immense.
Solar basics[edit | edit source]
Photovoltaics have a history of experimentation and research that dates back to 1839 by a French physicist. Alexandre Edmond Becquerel discovered that conductance will increase with illumination while they were experimenting with metal electrodes and electrolytes. The first germanium solar cells were made in 1951 and Bell's Laboratories published results of a solar cell operating at 4.5% efficiency. The efficiency of solar cells grew to 20% by 1985.
Solar panels generate electricity by utilizing solar cells. Solar cells can convert sunlight into direct current electricity by using the photon energy of the incident light from sunlight using the photovoltaic effect of a solar cell. Solar cells generally have the same 5 components including; an anti-reflective coating which is typically placed over the bare silicon, front contacts to collect the current the cell generates, there is an emitter that absorbs the incoming photons and transports the energy to the excited state of charge, there is emitter at the base region which is joined at a junction with emitter region, lastly, there is a rear contact.
With solar arrays/panels there will be energy losses in the system which is often caused by shade and shadows on the panels. Some times and days are considered unfavorable, which is when the sun is at its lowest point in the sky. The most unfavorable day is different depending on which hemisphere the array is located in. The winter solstice, December 21st for the northern hemisphere and June 21st for the southern hemisphere, is considered the most inefficient day when it some to solar arrays. If the panels are angled incorrectly then there is the possibility that the best sunlight will pass over the top of the panel generating an inefficiency.
There is a growing demand for electricity to be supplied by sources that are not based on fossil fuels, and solar is helping with that need. There were an estimated 272,000 solar PV (photovoltaic) power generating systems a variety of sizes connected to the grid as of 2013. Roughly 4% of those were added in 2011, approximately 62,500 individual systems.
Irrigation specifics[edit | edit source]
Irrigation is essentially a man-made method for transporting water from a source location to a piece of land containing crops in need of water. Irrigation systems can come in a multitude of different forms but almost always use a pump to generate enough pressure to transport the water across the land to the crops. Systems have also been known to use gravity to assist water flow. Irrigation systems require energy to function and in this case, we plan to use solar energy and gravity to power our system. Irrigation systems can run underground, above ground, or both and are usually built to minimize both energy and water consumption. 
To be useful during the drier summer months, the system must be as efficient as possible and conserve as much water as possible as we will be working with a limited water supply (water is from the CCAT rainwater catchment system ). We must maximize crop yields while minimizing unnecessary water usage. The system could be susceptible to vandalism and solar damage. The system must also distribute water at a controlled rate to avoid drenching plant leaves (which can cause plant sunburns), and roots (which can lead to wilting). The water pressure must also be strong enough to reach the plants but not so strong that the water streams harm the plants. The system will have to factor in the pressure generated by the gravity pulling the water down from the catchment system to the food forest. The water will also have to be distributed according to how many plots the food forest has, so we will need to figure out how to get the water to flow evenly throughout each plot and multiple tubes simultaneously without the water favoring one tube over the other and using only one pump. It is integral that the water in the system is separated from the electrical parts of the system to avoid frying them. If any fertilizer is used or chemicals on the forest then the runoff must be contained to avoid pollution.
Our irrigation method of choice:
We believe that the type of irrigation best suited to our project is the drip irrigation system. Drip irrigation is a system that utilizes gravity and a slower form of water distribution to slowly drip water from the system to the plant's roots. It is considered one of the most efficient methods of irrigation. This system uses a collection of pipes, tubing, and emitters to effectively distribute water from the initial water source. This type of irrigation is extremely effective at saving water which can make it ideal for irrigation during long periods of drought. The drip technique limits evaporation by placing the water directly into the plant root area. It directly targets the plants. It has the potential to be extremely effective in a scenario like the one present in our project . That said, the tubes can be susceptible to sun damage and degradation as a result. Also clogging from the soil is common. The tubes will have to be above ground too which could impact the aesthetic if not desired.
Water pump specifics[edit | edit source]
The pump is used to create water pressure for the flow of water through the irrigation system. Flow rate is measured in gallons per minute (GPM). The pump converts electrical power to build pressure in the system. This pressure is measured in PSI or Head feet. Head feet are used because manufacturers don't know what the pump is intended to pump. Therefore the PSI will vary based on the liquid's properties being pumped. Selecting the right pump is important to obtain maximum efficiency. Using the most efficient pump will ensure the least amount of power is used and the maximum life will be had of the pump. Finding the amount of energy necessary for the pump can be by:
The hydraulic energy required (kWh/day)
=volume required (m³/day) x head (m) x water density x gravity / (3.6 x 106)
0.002725 x volume (m³/day) x head (m) []
A centrifugal pump will be best suited for the planned drip system as we will be pumping it up hill for gravity to feed the irrigation system. The vertical lift is ~16 feet to the top tank. The drip irrigation will be operating at ~35 PSI . This PSI is based on water pressure from the gravity fed tank.
Concerns with pumping
When using a pump some of the concerns are focused on efficiency and ability. This requires knowing the output needed for the project. Then selecting a pump that is right based on the Pump Chart from the manufacturer. Selecting a pump that is either too large or too small can result in shorter life expectancy and inefficient operating. Another concern is the maintenance of the pump. Making sure the pump is properly maintained to the manufacturer's specs is important to ensure maximum efficiency and life of your pump. Priming the pump is required on centrifugal pumps before startup. failure to do so will result in damage to the pump and the system failing to work. If the pump operates off of DC it can be hooked directly to our solar panel. However, if it requires AC the power would have to run from the solar panel through an inverter then to the pump. To keep the system as simple and inexpensive for budget as possible a pump operating off of our solar panel's power is preferred. To prevent having to use a battery or multiple panels. For this, we need a pump that operates on 24volts or less and a max of 135 watts (if the current solar panel works). This will help to keep the project on budget as well as keeping the system as user-friendly as possible. Having to do this may require moving the water tank lower on the hill as the pumps may not have as head lift potential.
Project Evaluation Criteria[edit | edit source]
The following criteria will be used to determine what are the most important aspects of the project. The ranking system is 1-5, with 5 being the highest. The rankings will help to focus efforts and budget of the solar irrigation build.
|Budget||Keep the budget at or below $600.|
|Durability||Needs to be able to function properly for at least 2 years with easy maintenance in case irrigation fails.|
|Days of autonomy||Must be able to work without sunlight for a maximum of about 3 days|
|Ease of use||Should be very simple to use and fix. Maintenance ought to be logical and intuitive. Must not interfere with walking paths while still being moderately easy to access for repairs.|
|Educational purpose||Important aspects, such as photovoltaics, should be visible for students and visitors of the food forest to understand their function and the project's reproducibility in other locations.|
Prototyping[edit | edit source]
The prototypes were created to represent the system to end users on paper or digital versions. Our prototyping was predominantly about having a way to visualize what the system looks like for visitors and the end-users.
One of the biggest issues was trying to decide on what we could use to indicate where irrigation lines were marked. There were many options that we went through before we finally decided on using large rocks. This can be seen in the farthest right image. The other two images present more developed versions of the eventual final poster set up for the poster.
Finally, we created a video with a 5 year old star actor (Max) to walk us through the current setup and indicate the changes that need to be implemented. The linked video provides a perspective what our prototype looked like as of April 2021.
Construction[edit | edit source]
It is important to note that much of the irrigation was already in place (see CCAT rainwater catchment drip irrigation system/OM) upon beginning construction and multiple improvements were required to make the system functional to the specification previously listed.
- The solar-powered water pump was installed to pump water from the lower tank to the top tank. The water pump is connected to the solar panel via 12 gauge red and black wire. The red wire is used to connect to the positive lead of the solar panel. This goes through a tethered float switch that will shut off power to the pump when a low water level is reached in the lower tank. A black wire is connected to the negative lead of the solar panel.
- The pump is connected to the lower tank through an outlet and the bottom of the tank and pumps water up to the tank at the top of the hill though PVC irrigation pipe.
- The top tank has a float that operates like a toilet tank float. Once the water level rises and lifts the float it closes off the connection between the lower tank and the upper tank. This allows the pump to build up back pressure to a PSI that will shut the pump off. Therefore no water is wasted by overflowing the top tank.
- We pulled up the irrigation lines to determine if there were any breaks in the lines. One break was found and we patched it up using quick connects and a hand torch to soften the two hose pieces.
- The automatic timer was connected to the PVC pipes bringing the water down from the top tank at a location adjacent to the solar panel.
- We dug new trenches for the irrigation lines and reburied the pipes along the walking paths in the food forest to avoid any potential tripping hazards. We aimed to make the trenches at least 3-4 inches deep to fully cover the exposed pipes.
- To indicate where these irrigation pipes were buried, we lined the irrigation pathway with ~10 inch rocks spray-painted white. Many rocks included a directional set of arrows to indicate the direction in which the pipes were buried underground. These stones are a display to visitors and our clients not to dig in these locations to avoid damaging the irrigation lines.
- We worked with a fellow HSU student, Jesse Beacham Grijalva de Prieto, to design the poster for for this project and ordered the sign to be installed by the the groundskeeper at CCAT.
Proposed timeline[edit | edit source]
The current proposed timeline for this project can be seen on the google sheet. The Rolling Thunder team intends to have the setup completed by mid-May 2021.
Costs[edit | edit source]
The following depicts the proposed budget for the supplies needed to fulfill this project at CCAT. The majority of the supplies, such as the solar panel and irrigation pipes, are already in place or available on site. The major expenses were the pump and the corrugated plastic information sign depicting the setup for visitors and future end-users. Funding for this projects is provided by CCAT and HSU.
|Quantity||Material||Source||Cost ($)||Total ($)|
|2||Quick connects||Ace Hardware||$3.00||$6.00|
|1||Automatic timer||Ace Hardware||$35.99||$33.99|
|1||Pump box supplies (lock/ wood)||Ace Hardware||$5.00||$5.00|
|1||Hardboard informational poster/ sign||Marketing Store||$120.00||$120.00|
|2||Spray paint||Ace Hardware||$4.00||$4.00|
|1||Masking tape||Ace Hardware||$7.00||$7.00|
Operation[edit | edit source]
- Water is collected from the roof and stored temporarily in the lower tank next to the solar panel. The lower tank has a tethered float switch inside of it that is connected to the solar panel and pump. When the water level drops to roughly 25 gallons, the float switch sinks to the off position where there is infinite resistance, hence no electrical current flowing through the component. Consequentially the pump will shut off automatically. This is so the pump is not dry pumping which leads to damaging the pump.
- The solar power harnesses energy from the sun providing power to the pump when there is direct sun on it. During the spring and summer months, the optimal time for the sun to fully hit the panel is between 2 and 4 pm. This is also the best time to verify that the pump is working as long as there is water in the lower tank.
- The pump pushes water in the lower tank up a hill into another holding tank. The top tank utilizes a float similar to that in a toilet tank. When the water gets to the maximum (roughly 275 gallons) capacity, the float rises to the top closing off the inlet valve. This allows the pump to use back pressure to build up to a PSI that shuts off the pump. This prevents overfill and water waste, and burning out the pump.
- The water then flows to the food forest by way of gravity if the outlet valve is opened allowing the water to flow downhill through to an automatic timer. The automatic timer can be set to regulate the water. 10-minute increments set for once or twice a week should provide enough water to keep the plants alive during months with little to no rain.
Maintenance[edit | edit source]
The amount of maintenance required aims to be as low as possible.
Clearing out the gutters which capture the rainwater periodically is important as these can become filled by leaves and pine needles over time. The system runs automatically due to the automatic timer, the setting on this can be modified according to the instructions on the automatic timer's user manual. The battery will need to be replaced annually in order to keep the automatic timer functioning (the timers screen shows battery health). The water tank should be cleaned periodically and the lid should be tightly secured to ensure there are no mosquitos breeding in the tank.
The rainwater catchment system needs to be cleaned periodically as well as the tanks. The system should be reviewed every semester to make sure all is functioning. The tanks obviously need water in them in order for the system to function. The pump will only function if the sun is shining directly on the solar panel. Pump maintenance can be found under the solar pump's user manual.
Schedule[edit | edit source]
Beginning and end of drought months
- Open the valve off the top tank to allow the water to flow down to the food forest.
- Set the automatic water timer to desired irrigation frequency. See: automatic timer's user manual
- During rainy months when irrigation is unnecessary, the valve at the top tank should be is closed as the system will be dormant
- Verify the water levels in the tanks to ensure availability of water storage
- Make informed decisions on water timer settings based on capacity and watering needs
- Clean out the gutters on the roof that collects the rain water
- Change the battery in the automatic timer
- Check the tanks for debris buildup and tight-fitting
- Check to make sure there are no irrigation breaks and that irrigation in the food forest drips are near the plants that need it.
- Every 2 years
- Reorganize the rocks that indicate where the irrigation lines are buried, clear out vegetation growth or buildup
- Clear out any overgrown plants around the pump or sign to ensure clear visibility and ability to service tanks, pumps, and irrigation lines
Instructions[edit | edit source]
Testing and operation instructions can be found in the video below
Conclusion[edit | edit source]
Testing results[edit | edit source]
Power to pump from PV panel
The solar panel and pump were tested for flow rate and power provided to the pump from the panel. When the solar panel was in full sun the pump was drawing an average of 4.42A at 17V which is 75.14 Watts(W=A*V). At the power, the water was flowing from the bottom tank to the top tank at a rate of 31.5L per minute. To test the amps the negative line was broken from the pump to the solar panel. Testing the voltage was done simultaneously with a second multi-meter. The negative lead from the multimeter was touched to the same break in line where the multimeter testing the amps was and the positive lead was touched to the positive connection from the solar panel to the pump.
Flow Rate Filling Top tank during pump activity
The flow rate was measured using a stopwatch. The stopwatch was running when the pump was in full power pumping water from the bottom tank to the top. The clock watch started at 200 liters and was timed until the tank reached 300 liters. This took roughly 9 minutes and 30 seconds, which is where the 31.5L per minute flow rate was measured.
Flow Rate irrigating the food forest
Measured using a stopwatch and measuring the amount of water that flowed through the drip irrigation in a 30-minute cycle. The outflow rate was ~ 5 liters per minute. During the 30 minute cycle, 150 liters of water flowed through the drip emitters into the food forest.
Discussion[edit | edit source]
After testing we have concluded that the system will work sufficiently to the requirements we wanted the system to meet. The testing results show that the panel provides more than sufficient power to move the water from the lower tank to the top tank. It should take approximately 95 minutes to transfer 1000 liters from the bottom tank to the top tank based on the flow rate with full power from the panel to the pump.
There are currently no leaks in the system. Our only major concern is that the water line breaks due to visitor's carelessness. Finding the leak may be a challenge for future users.
We recommend that the irrigation is set to water for 10 minutes every 3 days. This would release ~50 liters of water from the top tank per disbursement. That would allow for approximately 20 days total of releasing water. If spaced out every 3 days, this would allow one full tank to operate the irrigation system for ~6 weeks. This is subject to change depending on the clients' needs.
Lessons learned[edit | edit source]
Throughout this project, there were many lessons learned around issues we didn't anticipate being issues at the start of the project. These lessons will help us be better prepared for future projects of this nature.
One lesson learned was learning how to meet the needs of clients and how to professionally interact with them. Trying to balance what the needs of the end-users and clients are with what can feasibly be accomplished in one semester challenging. An example of this was figuring out how we can mark where irrigation lines underground. We had to go through many different possibilities that were inspired by nature, not fully permanent, but still easily visible. The option that we were most excited about did not meet the client's needs, thus requiring a complete rework. Making sure we communicated with the clients about proposals and prototypes was a vital part of the project. We also had to learn how to communicate the system with end-users, especially since CCAT has new staff every year. We needed to figure out a way to provide information and a variety of tools to the end-users in a way that was useful and does not lead to an overload of information.
We also needed to deal with the issue of sunlight given Humboldt county's fluctuating weather patterns. If we planned a day to test the solar panel, and it was forecasted to be sunny, there was always the possibility that it would be cloudy. Having to be flexible and prepare some cushion time in case it became cloudy was necessary for this project to have successful testing.
Learning to start the project with a clear understanding of the initial layout of the site and its layout before beginning the project was a hard lesson. Had we gone to the site before starting our brainstorming process and prototyping, we could have saved lots of energy and time. We would have known that much of the system was already in place, and the main issue we need to accomplish was fixing the system and figuring out ways to improve it.
Testing the voltage, current (Amps), and power (Watts) generated from a solar panel using a multimeter was a useful skill learned. Being able to measure the power (Watts= Amp x Volts) draw of the pump from a solar panel was also a useful lesson. There were also parts of the project that seemed like they would be simple or would not require much research, however, in practice these portions lead to some of the most thorough work. An example of this was during the research and purchasing of the pump. Initially, we had not thought it would take much work or research to find a pump that would fit our needs. However, there were many factors to consider (head, flow rate, etc.), but research into this was crucial to get the longest life out of the system. We also had to take into account getting a size that works the best for our system to ensure the pump will have the longest life.
Next steps[edit | edit source]
Beyond simply sticking to the maintenance schedule consistently to keep the system in working order, some possible next steps that could be taken in the future to improve the current design:
- Expansion of the solar food forest irrigation systems to include more plant beds and water a larger area as a result.
- Installation of some sort of system built to capture potential runoff, with an additional pump and irrigation lines that could be used to pump this water back up to the water tank.
- We noticed that a lot of the parts of the system already in place required repair. In particular, the rain gutter utilized for rainwater catchment, much of which is currently sitting out of line with the irrigation tubes leading to a lot of the rainwater it catches flowing out of the system and missing the pipe. As a next step, we could work to improve pieces of the irrigation system in need of repair to make it run smoother and more efficiently.
- To limit damage from the sun's rays all remaining irrigation tubes above ground could be buried and marked in the future.
- An additional tank could be placed at the top of the hill to capture more water during the rainy season.
Troubleshooting[edit | edit source]
More information on the initial setup for this project prepared by previous ENGR 305 students can be found at:
|Pump not running||-Check to make sure the solar panel is providing power
-Verify that all the wires are connected from the panel to the pump -Test the voltage and amps between panel and pump
|No water flow to the automatic timer||-Make sure the valve on the right-hand side from the top tank to the food forest is open
-Make sure there is enough water in the top tank
|Water draining from the top tank while the system is shut off|
|Emitter not delivering water
(where water drips out of irrigation lines)
Team[edit | edit source]
References[edit | edit source]
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