Ron Sheffield, Girouard, Ernest
Most agricultural producers are using older diesel power units and old wells where upgrading to newer wells and diesel or electric motors need to be technically and economically evaluated. Over the summer of 2008, the radio and television were all abuzz with the record-high costs of gasoline and diesel fuel as well as the high cost of food in the United States and worldwide. These higher fuel costs dramatically increased the cost of irrigating crops in Louisiana.
Irrigators need a mechanism by which to evaluate the state of their pumping systems. With the current high diesel cost, this information is crucial in determining the profitability of switching to an electric motor or investigating in rebuilding existing diesel power plants. Additionally, producers need such analyses when applying for federal grant funds from RC&D or NRCS to assist them with electrical infrastructure or well replacements, respectively.
How is pumping efficiency determined?
A pumping system’s efficiency is calculated by comparing the amount of fuel used with the amount of water pumped. This efficiency will change due to the depth of water being pulled from a well, the condition of an engine and the rate at which the motor is turning. The calculated performance is then compared with the performance of the motor under perfect, laboratory standards. Typically, electric pumping systems will have a 75-85% overall efficiency, and diesel-powered pumps will have between 18-35% efficiency, depending on the age and care of the engine.
To calculate a system’s pumping efficiency, several pieces of information are needed. If this information is not able to be collected, assumptions can be made to estimate the efficiency. However, great care needs to be taken to make appropriate assumptions to prevent a gross over- or underestimation of the system’s performance.
In the spring of 2009, NRCS and extension specialists from Texas A&M University and the LSU AgCenter evaluated several diesel and electric pumping plants in southwest and northeast Louisiana. These tests were conducted to quantify the average operational costs and to evaluate if there is a need for further irrigation pumping-plant efficiency tests in Louisiana.
In southwest Louisiana, diesel-powered pumping systems on wells with water depths of 70-130 feet were found to have an average efficiency of 15.9 ± 0.02% with a 25% potential standard efficiency. The cost of irrigating an acre-inch, assuming $2/gallon for fuel, was found to be $2.93 ± $0.31 and an hourly cost of $11.51 ± $2.03 per pumping unit. Through proper operation, maintenance or replacement of system components, that can average $1.23 ± $0.28 per acre-inch irrigated or $9,258 ± $2,260 over a typical 2,000-hour pumping season. In a third of the units tested, nearly $16,000 per year could be saved through making appropriate changes to the farm's irrigation pumping systems. With the price fluctuations seen during the summer of 2008, the cost savings per pumping plant will only become more evident.
Electric pumping systems on wells were found to have an average efficiency of 40.1 ± 0.04% with a potential standard efficiency of 65.1 ± 0.01%. The cost of irrigating, assuming $0.06/kWh, was found to be $1.31 ± $0.13 per acre-inch irrigated and an hourly cost of $6.40 ± $1.05 per pumping unit. It is estimate that through proper operation, maintenance or replacement of system components, that can average $1.52 ± $0.14 per acre-inch irrigated or $5,144 ± $1,558 over a typical 2,000-hour pumping season.
With an average potential savings of over $9,000 per year for diesel pumping units, the need for pumping-plant efficiency testing is greatly needed, even at the cost of $2 per gallon for diesel fuel. The LSU AgCenter and NRCS are developing programs to conduct irrigation audits in Louisiana. It is hoped that statewide audits can be conducted for interested producers by spring 2010.