Cutting The Energy Cost Of Delivering Irrigation Water

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Energy is a big cost for farmers, and Alberta Agriculture’s AgTech Centre has developed its On-Farm Energy Efficiency Program which was initially offered to dairy, beef and poultry operations.

It’s now turned its attention to irrigation. Project engineer Lawrence Papworth and his colleagues conducted an analysis of irrigation power use in southern Alberta to provide current baseline information.

“As always, it’s a case of the fundamental business principle: you can’t manage what you don’t measure,” says Papworth. “These projects have helped us to establish the fundamentals that will be important to developing a solid assessment program and related options for improving energy efficiency.”

Big range in energy use and cost

AgTech Centre staff used monitoring systems to collect information on 32 low-pressure, centre-pivot systems in southern Alberta, over the course of a full irrigation season.

Twenty-two of the systems used electric pumps, four were pressurized pipeline and six used natural gas. All the centre-pivot systems were electric drive and two used corner arms. All the electric units used centrifugal pumps except one, which used a turbine.

Pressurized pipeline systems had no pumps so the only energy used was to operate the centre pivot including the end gun. Energy use for the pressurized pipeline systems ranged from 0.8 to 1.8 kWh per acre inch with an average energy use of 1.2 kWh per acre inch. Based on applying 12 inches on a 130-acre field with electricity at 13 cents per kWh, the centre pivot operating costs ranged from $167 to $369 with an average of $233.

Energy use for the natural gas systems ranged from 0.22 to 0.41 GJ per acre inch with an average energy use of 0.30 GJ per acre inch. Based on applying 12 inches of water on a 130-acre field with natural gas at $4.50 per GJ, the irrigation pumping costs ranged from $1,524 to $2,895 with an average cost of $2,072. In addition, there is the electricity cost for operating the centre pivot, so the total irrigation cost for applying 12 inches of water on a 130-acre field averaged $2,305.

Energy use for the electric systems includes the electricity to power both the pump and the centre pivot, and ranged from 8.1 to 22.3 kWh per acre inch, with an average energy use of 14.6 kWh per acre inch. Based on applying 12 inches of water on a 130-acre field with electricity at 13 cents per kWh, the total irrigation cost ranged from $1,635 to $4,515 with an average cost of $2,963.

Potential to improve

For the project, 11 irrigation systems were selected for an energy assessment over a full irrigation season. Five systems used natural gas and six used electricity.

Among the five natural gas systems, three were standard quarter section pivots and two were wheel-line systems. Among the six electricity systems, three were standard quarter section pivots, one was a wheel-line system, one was a quarter section pivot with a corner arm and one was a section pivot with a corner arm.

One of the natural gas systems irrigated three pivots from the same pump site and the section pivot pumping system used two pumps in parallel.

The trials uncovered significant range variation coupled with overall evidence that there is lots of room to improve energy efficiency. Average overall efficiency for the four electric system types ranged from 57.7 per cent to 67.5 per cent, with an average of 61.8 per cent, compared to a potential overall efficiency of 74.3 per cent.

For the five natural gas systems, average overall efficiency was 14.6 per cent for the pivot systems and 15.7 per cent for the wheel-line systems, compared to a potential efficiency of 20 per cent.

When all system types are included, the trial identified opportunities to improve overall electric pumping unit efficiencies by 20 per cent and natural gas pumping unit efficiencies by 30 per cent. “Those are very significant opportunities,” says AgTech Centre engineer Darryl Slingerland.

Tune-up options

Engineer Gregg Dill, who worked with the AgTech Centre on the project, cited a number of possible causes for the lower efficiencies uncovered in the testing.

These included factors such as aging motors and pumps, as well as mismatched pumps on a parallel- pump system. Another key factor noted was water flow at a rate lower than the system design, which could be due to factors such as a restricted supply line to the pivot or plugged nozzles reducing flow. Other system-related potential issues acknowledged included inaccurate pressure gauges and inaccurate tachometers.

Dill says an option worth considering for some producers would be to install a variable-frequency drive (VFD) on a corner-arm system. The team is evaluating the cost effectiveness of this option.

Human factor key

Equipment and system issues are one thing, but the human element of management is just as important when it comes to efficient energy use. For example, Dill noted during the trial assessment that one potential issue was operating the pumping unit at lower than design speed.

“The importance of being knowledgeable about the equipment you’re using and making sure you’re running it in the right way, at the right levels, can’t be overstated,” says Slingerland. “You can have the best, most up-to- date equipment or systems, but without the right knowledge you’re still vulnerable to human error.”

Dill emphasizes the pitfall of operating under a flow rate that is lower than the system is designed for.

“Although, it is cheaper to operate a system with lower than design flow, in most cases, productivity will be limited which defeats the purpose of investing in irrigation to improve productivity,” he wrote. “This can also mask inefficiencies and system problems when compared to actual energy bills.”

The bottom line

In the trial assessment, the calculated average cost of applying an acre-foot of water with electricity was $31.35 and ranged from $22.90 to $39.92. In an ideal situation – i.e. theoretical maximum efficiencies – the average cost would be $25.94 with a range of $18.95 to $32.09. This places the potential saving from improving efficiencies at a range from $1.13 to $11.99 for individual systems.

The average savings per system per year, based on 12 inches, was $1,498 and ranged from $164 for a quarter section pivot to $4,625 for a section pivot.

The average cost of applying an acre-foot of water with natural gas was $19.60 and ranged from $13.91 to $43.50 for individual systems. That was compared to an ideal situation, where the average cost would be $14.11 with a range of $11.87 to $15.41. The average savings per system per year, based on 12 inches, was $607 with an average saving of $868 for a quarter section pivot and $345 for a wheel-line system.

More than the bills

Dill says that because it’s not common for irrigators to record irrigation hours, many of the problems identified in the trial assessment project would not be identified through an analysis of energy bills.

Even more importantly, although a comparison of energy bills to energy consumption may be useful in identifying an inefficient system, a more comprehensive assessment would be required to identify the specific opportunities to reduce energy consumption.”

That’s the drive toward the new irrigation component of the on-farm program, which is expected to come on stream in 2011.

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“Theimportanceofbeingknowledgeableabouttheequipmentyou’reusingandmakingsureyou’rerunningitintherightway,attherightlevels,can’tbeoverstated,”

DARRYL SLINGERLAND

AGTECH

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