Low Energy Spray Application (LESA) Irrigation
1/4/2013 6:08:57 PM by JackZ
Agricultural Sector. Growers of field crops with a slope of less than 1%.
LEPA has a water application efficiency of about 95% versus the 85% obtained with MESA. Use of the technology can save both water and energy. Irrigation predominately is used east of the Cascade Mountains in Washington and Oregon, plus in the states of Idaho and Montana.
Cooling Zone 2, Cooling Zone 3
The LEPA technology would have the "Agricultural--Irrigation" load shape (load factor =0.54, coincidence =0.33). Water applications and energy savings occur during the irrigation season which runs from April through September. The quantity of water applied is dependent upon type of crop and life stage, soil type, solar insolation, and rainfall. Peak irrigation requirements occur in July and August.
LEPA is a mature and highly efficient sprinkler technology, and few changes in performance are expected over the next 5 years. As LEPA systems have not been installed in the Northwest, efforts are underway to introduce and demonstrate the effectiveness of the technology.
No significant change is expected in the costs of this technology over the next 5 years.
Product Supply and Installation Risk:
No production shortages or manufacturing, distribution, or installation barriers are expected. Growers have time to modify their equipment during the fall and winter, so production is not impacted due to sprinkler system upgrading. Crop row spacing would have to be modified (possibly resulting in a slight decrease in crop size) and pumping plants would have to be modified to capture the energy savings potential given the reduced pressures required by the LEPA system. For deep well pumping systems, this means removing stages or use of an adjustable speed drive. For operating flexibility, some irrigation system designers include adjustable speed drive control for deep well turbine pumps (up to 700 hp).
Sprinkler systems can be categorized as "good, better, best" with respect to both energy consumption and water application efficiency. Irrigation systems include Mid-Elevation Spray Application (MESA—good) and Low Elevation Spray Application (LESA-better) and LEPA-best. LEPA provides improved application efficiency through eliminating high pressure spraying and applying the water directly to the ground with bubble emitters, drag socks or hoses.
The market segment for Low Energy Precision Application (LEPA) irrigation systems are growers of row crops (onions, potatoes, carrots, corn, and perhaps alfalfa) that currently use high, medium, or low pressure center pivots, lateral move or side roll systems, or Mid-Elevation Spray Application (MESA) systems. LEPA may be successfully applied in fields with a slope of less than 1%. Google Earth can be used to ascertain terrain slop and other features. Typically, a grower would identify the type of irrigation system desired. A system designer would verify field dimensions, design the circle, then acquire, modify, and install the irrigation equipment. Software tools are available to assist in mainline sizing, setting span lengths, nozzle sizing and spacing, and system design. Design practices size for lowest purchase price and operating cost.
LEPA sprinkler equipment would be sold through the existing network of irrigation equipment distributors and installers. These equipment suppliers can also handle installations and, in retrofit scenarios, provide pumping system modifications. While LEPA equipment has not been used in the northwest, equipment and design aids can readily be obtained from users. Many of the components, including pressure regulators, connectors (sledges), hose drops, sprinklers etc are common to MESA, LESA, and LEPA designs.
No regulations exist that dictate irrigation system selection. Irrigators are, however, awarded water rights which carry a "use it or lose it" aspect. Water that is "freed up" due to improved application efficiency may be used to grow additional crops (but at an improved metric of energy use per unit of production), transferred to junior water rights holders (if water is taken from an irrigation canal or river), or left in the river to provide additional instream flows that result in improved fish spawning and rearing habitat.
Other risks and barriers:
Growers are most interested in production (yield or quantity of crop per irrigated acre) and crop quality. The forthcoming BPA demonstration project will use soil moisture sensors to ensure that crops receive enough water, and document water application efficiency and yield, as well as providing for visual comparisons. Evaluations and sprinkler system design will ensure both water application uniformity and efficiency. Part of the demonstration project will involve the application of best management practices to mitigate LEPA runoff issues.One barrier is current design practice. Irrigation system designers like to provide 50-psig water to the circle. They cite a small "margin for error" in low pressure systems. Energy savings due to reduced operating pressures will only partially materialize if delivered pressures are maintained with nozzle pressures dictated by pressure regulators. Adjustable speed drives may have to be incorporated into pumping systems to provide growers with the confidence that water will be delivered as needed.
Basis of Savings:
The standard protocol for measuring energy savings is appropriate for center pivots or lateral move (side roll) systems using MESA and LEPA sprinkler technologies. Energy use is dictated by the input kilowatts to a pump drive motor and the pump run time. Input kilowatts is reduced when the required pumping flow rates and discharge pressure are reduced by using LEPA rather than MESA. It is assumed that pump run or irrigation times will remain constant, so energy savings can easily be documented through taking "before and after" power readings at the electrical panel serving the pump. One component of LEPA system optimization will be matching of new pumps to the modified load requirements or changing pump performance (through removal of stages in a multi-stage pump) to match pump output to sprinkler system requirements. This does not include any additional savings related to costs of water procurement.
The grower will apply water as needed to ensure that soil moisture requirements are met at the plant's root zone. Assuring uniformity of application and providing the needed amounts of water should ensure crop quality. Pumping savings will occur due to improved application efficiency and reduced pressure requirements. Energy savings would be determined through monitoring annual "before and after" energy use for pumps serving one or more center pivot or side roll sprinkler systems. Savings would vary with respect to crop type (due to varying irrigation requirements, uptake, and evapotranspiration) and before and after trends could be expressed as energy use per unit of production (of a particular crop). Water applications would vary depending upon rainfall that occurs during the irrigation season so the energy use data would have to be corrected to account for rainfall as well as temperature and humidity.
Texas A&M University, Economics of Irrigation Systems, December, 2001. http://itc.tamu.edu/documentsBradley King and Dennis Kincaid, "Optimal Performance from Center Pivot Sprinkler Systems", University of Idaho College of Agriculture, Bulletin 797, December, 1997. Texas Agricultural Extension Service, "Center Pivot Irrigation", Texas A&M University System, B-6096.USDA, Natural Resources Conservation Service, "Utilizing Center Pivot Sprinkler Irrigation Systems to Maximize Water Savings". Dick Stroh, BPA, Troy Peters, WSU IAREC, and Howard Neibling, Extension Irrigation Engineer, University of Idaho, "Multi-State LEPA Demonstration Project" Proposal to BPA, February, 2011.
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1/4/2013 6:08:57 PM by Jack Zeiger