CCAT solar irrigation for food forest

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Food Forest before irrigation set up

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 mulch. The vision is to provide a space for students and community members to harvest food throughout the year 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.

The Rolling Thunder team in the Spring 2021 Engineering 305 class with professor Lonny Grafman undertaking this project is composed of 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 following years. The objective of this project is to create an irrigation system, solar array, and pump for the food forest. 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 [1]. 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 esthetical 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 in relation to others [2]. 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 [3]. Despite the small space set aside for this project, the potentials for sustainable sustenance harvest and learning from this project are 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. [4]

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. [4]

With solar arrays/panels, there will be energy losses in the system which is often caused by shade and shadows on the panels. There are times and days that are considered unfavorable, which is when the sun is at its lowest point in the sky during noon. 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 wrongly then there is the possibility that the best sunlight will pass over the top of the panel and hit right below the next. [5]

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 plants of all sizes connected to the grid as of 2013. Of the number, about 4% of those plants were added in 2011, that’s around 62,500 plants that were added. [6]

Irrigation specifics[edit | edit source]

Irrigation Basics:

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 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 to power our system. Irrigation systems can run underground, above ground, or both and are usually built to minimize both energy and water consumption.[7] and [8]

Irrigation Concerns:

In order 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[9]. We must identify the best solution to find a compromise between system durability/longevity and system preventability. 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 downward from the catchment system to 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[10]. This system uses a collection of pipes, tubing, and emitters to effectively distribute water from the initial water source[11]. 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 [9]. That said, the tubes can be susceptible to sun damage and degradation as a result. Also clogging from soil is common. The tubes will have to be above ground too which could impact the aesthetic if not desired [12].

Water pump specifics[edit | edit source]

Pump Basics:

The pump is used to create water pressure for flow of water through the irrigation system, flow rate is measured in gallons per minute (GPM)[13]. The pump converts electrical power to build pressure in the system. This pressure is measured in PSI or Head feet. Head feet is used because manufactures don’t know what the pump is intended to pump. So, 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) [[14]]

A centrifugal pump will be best suited for the planned drip system. As drip systems require a pump to provide 30 PSI[15]. This will be achievable with the centrifugal pump requiring no vertical lift, as the rainwater catchment system is on ground level (water is from the CCAT rainwater catchment system ).

Concerns with pumping

When using a pump some of the concerns are focused around efficiency and ability. This requires knowing the output needed for the project[16]. Then selecting a pump that is right based on the Pump Chart from the manufacturer[16]. Selecting a pump that is either to large or to small can result in shorter life expectancy and inefficient operating. Another concern is maintenance of the pump. Making sure the pump is properly maintained to the manufacturers 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[17]. If the pump operates off of DC current it can be hooked directly to our solar panel. However, if it requires AC current the power would have to run from the solar panel through an inverter then to the pump.

References[edit | edit source]

  1. Mansourian, Stephanie, Christoph Wildburger, and Bhaskar Vira. Forests and Food: Addressing Hunger and Nutrition across Sustainable Landscapes. Cambridge: Open Book Publishers, 2015. DOI 10.11647/OBP.0085
  2. Hemenway, Toby. Gaias Garden a Guide to Home-scale Permaculture. White River Junction: Chelsea Green Publishing, 2009.
  3. Sun, Tao, Cai Zhao, Xiaomin Feng, Wen Yin, Zhiwen Gou, Rattan Lal, Aixing Deng, Qiang Chai, Zhenwei Song, and Weijian Zhang. "Maize‐based Intercropping Systems Achieve Higher Productivity and Profitability with Lesser Environmental Footprint in a Water‐scarce Region of Northwest China." Food and Energy Security 10, no. 1 (2020). doi:10.1002/fes3.260.
  4. 4.0 4.1 Zaidi, Beddiaf. Solar Panels and Photovoltaic Materials. London: IntechOpen, 2018.
  5. Calise, Francesco, Massimo Dentice DAccadia, Andrea Lanzini, Domenico Ferrero, and Massimo Gian Luka Santarelli. Solar Hydrogen Production: Processes, Systems and Technologies. London: Academic Press, an Imprint of Elsevier, 2020.
  6. Gibson, Bob. "What's Next for Solar." The Electricity Journal 26, no. 2 (March 2013): 51-57. Accessed February 28, 2021.
  7. National Geographic Society. “Irrigation.” National Geographic Society, October 9, 2012.
  8. Melby, Pete. Simplified Irrigation Design, 2nd Edition. 2nd ed. John Wiley & Sons, 1995.
  9. 9.0 9.1 Kourik, Robert. Drip Irrigation: for Every Landscape and All Climates. 2nd ed. Occidental, CA: Metamorphic Press, 2009.
  10. Martinez, J, and J Reca. “Water Use Efficiency of Surface Drip Irrigation versus an Alternative Subsurface Drip Irrigation Method.” Journal of Irrigation and Drainage Engineering 140, no. 10 (May 12, 2014).
  11. Jackson, Afton. “Sprinkler Systems vs. Drip Irrigation, Pros and Cons.” Gardening Channel, December 4, 2020.
  12. Sharaf, Bidisha. “Bidisha Sharaf.” CIvil Today. Accessed February 28, 2021.
  13. Irrigation Tutorials. 2021. Basic Pump System Hydraulics - Irrigation Tutorials. [online] Available at: <https://www.irrigationtutorials.com/basic-pump-system-hydraulics/> [Accessed 28 February 2021].
  14. Solar (PV) water-pumping#SOLAR .28PHOTOVOLTAIC.29 WATER PUMPING
  15. Pushard, D., 2011. Rainwater Catchment System Pump Sizing. Harvest H20, [online] Available at: <http://www.harvesth2o.com/pump-sizing.shtml> [Accessed 28 February 2021].
  16. 16.0 16.1 Scherer, T., 2017. Irrigation water pumps. North Dakota State University.
  17. 1959. SCS national engineering handbook, section 15. Washington, D.C.: U.S. Department of Agriculture, SCS.