Don’t cut corners on irrigation savings

Reducing water pressure when the corner arm isn’t needed can cut energy costs by 30 per cent or more

Producers with corner arm centre pivot irrigation systems can reduce their energy consumption by 30 to 40 per cent if a variable frequency drive (VFD) is added to the motor used to power the water pump, according to an Agricultural Technology Centre study.

“Corner arms on centre pivots swing out to water corners and are preferred by producers because the entire quarter section field can be farmed,” says Lawrence Papworth, a project engineer with the centre, located in Lethbridge.

“The water flow for the pivot varies from 700 to 1,200 gallons per minute (gpm) because the flow to the corner arm shuts off when not needed. Motor and pumps are sized to deliver the 1,200 gpm and when the flow is reduced the extra water pressure is wasted. A VFD slows the motor down to match the pressure and flow required by the system. This results in energy savings when the water flow to the corner arm is reduced or shut off.”

The study, conducted in 2012, looked at several variables to determine the energy savings of the system. The variables were rolling and level terrain, turbine and centrifugal pump, and location of the pressure sensor.

“Energy savings were 30 per cent on level land and 40 per cent on rolling terrain if the pressure sensor was located on the corner arm,” says Papworth.

Pressure sensors, typically located near the motor and connected with a wire, provided very low energy savings. A wireless system was used to connect pressure sensors located on the corner arm.

“Modern pivots use low-pressure nozzles so keeping the pressure low at the corner arm saves the most energy,” says Papworth. “There was no difference in energy savings between turbine and centrifugal pumps. These energy savings result in reduced costs of $2,200 per year on level land and $2,800 per year on rolling terrain based on applying 12 inches of water per year and a power cost of $0.16 per kWh.”

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