A central productivity issue for Australian farming
Lifting and distributing water is energy-intensive, particularly in water-efficient, pressurised systems. Approximately 65 percent of all bulk water in Australia is used by farms (ABS, 2010) and a majority of this water is pumped in some way. Generally, the more water efficient an irrigation systems is, the more energy it requires. The presents a dilemma to farmers facing water scarity, high water charges and high energy costs.
Irrigation farms typically move hundreds of megalitres (ML) of water, with application rates for different crops ranging from two to 10 ML per hectare (ABS, 2013). Audits of irrigation farms have found that energy used in irrigation can account for upwards of 50 percent of a total farm energy bill. Identifying and implementing energy efficiency measures in large irrigation systems could be regarded as a priority for both individual farmers and the national economy. Perverse outcomes of failing address energy efficiency in irrigation include farmers decommissioning water efficient systems and reverting to open furrow, gravity fed irrigation, or reverting to lower productivity dry land cropping systems.
Worthwhile but far smaller energy efficiency gains can be achieved in relation to stock and domestic water. All farms pump water for stock and domestic needs. While this is likely to be a small component of total farm energy use, there are worthwhile savings achievable and practical applications for renewable energy power sources.
Energy efficiency in irrigation has three key aspects.
- Needs analysis, design and planning. It is essential that farmers and their irrigation engineers consider and balance water-efficiency and energy-efficiency objectives when designing or modifying irrigation solutions.
- Optimising equipment. Ensure that pumps and control systems optimise return on energy inputs.
- Energy source. Electricity is more cost-efficient for pumping than diesel but not all farms are able to connect to the grid. Alternative energy sources, such as solar, may be a viable option in such cases.
Why create an irrigation plan?
Irrigation planners can help you determine the correct layout, pump sizes and configurations, as well as when and how long to run your irrigation systems to maximise profitability and energy efficiency.
Design and planning
If you have not already done so, engage a specialist irrigation engineer to review your irrigation system for both water and energy efficiency.
The key variables affecting energy efficiency when moving water are gravity, pressure and friction. When designing water distribution systems and specifying pumps, engineers consider the distance water has to be lifted and transferred, the depth below and height above sea level, and the friction caused within pipes and channels by layout, diameter and operating pressures. Further complications may arise from policy constraints on pump size, pipe diameter and allowable pumping hours.
A further consideration is the trade-off that may apply between water-efficiency and energy-efficiency aims. For example, forcing water through a drip irrigation network will use more energy that running it through channels and furrows, but this type of system will apply water more efficiently than a more energy-efficient centre pivot irrigation system.
Initial assessment and irrigation planning
While many irrigation systems are superbly designed, others may have evolved incrementally and without systematic engineering analysis. If you suspect that your system is not ideally configured, it may be time to consult a specialist irrigation engineer. A more efficient layout, for example, could enable lower specification pumps, shorter duty cycles and major energy savings.
An initial irrigation assessment is a good first step in understanding potential savings opportunities in an existing irrigation system set-up. A qualified irrigation planner may be able to identify opportunities for additional irrigation efficiencies and recommend alternative items to investigate.
If you are creating a new system, new technologies such as sensor networks, smart metering and automation can enable non-conventional approaches with gains in both water and energy efficiency.
The relationship between your system and upstream water delivery systems should also be considered, since matters such as timing, variability and flooding may all have bearing on system design.
Variable speed drives on pumps
Traditional pump motors have two speeds: on and off. To achieve maximum efficiency, a higher level of precision is useful. Variable speed drives (VSDs) provide a variety of speeds so that pumps can run at the optimal rate for the amount of water they are moving. The installation of VSDs on pumps is an important energy-saving measure, as lowering the speed of a motor by just 20 percent can produce an energy saving of up to 50 percent.
Refer to supplementary paper, VSDs in pumps.
Controls and smart systems
Sensors on irrigation systems help eliminate inefficiencies by providing feedback on key performance parameters. Soil moisture sensors, in conjunction with advanced controls, can stop a system from overwatering already damp ground. Bore sensors can alert controls on bore pumps to shut off automatically when water levels drop below a certain point. Timers and temperature sensors can help ensure that fields get irrigated at optimal times and under optimal conditions.
Refer to supplementary paper, Irrigation sensors and automation.
Correctly sized pumps
Oversized pumps use far more energy than is necessary, while undersized pumps cannot always provide the volume of water needed. To ensure that your pumps are properly sized, it is recommended that you consult with an irrigation engineer, who can help determine the correct total dynamic head (TDH) for your pumps and the proper layout of your irrigation system.
Refer to supplementary paper, Oversized pumps.
Pumps have a number of moving parts which deteriorate over time. It is common for efficiency losses of five to 15 percent to appear after 10 years of operation. This is due to dirt and particle build-up increasing friction, cavitation from high water pressures and other wear and tear. Regular maintenance not only extends pump life but ensures optimal energy efficiency for the age of the machine.
Refer to supplementary paper, Pump maintenance.
Pumps can be powered by diesel or electrical energy, with the latter supplied from the grid or from renewable energy sources. All farmers currently using diesel for pumping should consider the feasibility of switching from diesel to electric pumps.
Diesel versus electricity
Diesel is a versatile energy source that is ideal for use in remote locations and can be sourced from the farm’s general diesel supply. However, diesel pumps are less efficient than electric pumps and typically require more maintenance. Further, diesel is generally more expensive than electricity on a dollar-per-power basis.
Feasibility of switching depends on access to the electricity network and the cost of additional infrastructure for connecting pumps, which can be substantial.
Electric pumps also have the advantage that they can run on electricity generated by renewable technologies such as solar, wind and biomass. As these technologies mature, it may become cost-effective to supplement network power with power generated on farm.
Refer to supplementary paper, Diesel versus electric pumps.
NSW Farmers is researching the feasibility of solar energy solutions for pumping. The time-critical nature of irrigation and high power requirements of irrigation systems generally limits the potential of solar; however, hybrid solutions can be cost-effective in some situations.
Pure solar solutions may be feasible for low-volume and non-time-critical applications – for example, replenishing gravity tanks, or for stock and domestic applications.
Refer to supplementary paper, Solar PV pumping.
Wind mills driven pumps may always have a place on Australian farms. They are suitable for low energy demand pumping tasks
Technologies to watch
There are a number of emerging technologies relevant to irrigation and energy in agriculture. Some of these include:
- solar/diesel hybrid irrigation pumps,
- gas injection in diesel pumps,
- the use of recycled materials for enhanced water storage/reduction of evaporation, and
- sensor technology and digital control systems.
The effectiveness and affordability of such technologies is improving steadily. While the investment numbers might not yet make these attractive financial options, we encourage all farmers to keep a watching brief on these areas.
Farm Energy Innovation papers
- Oversized pumps - The importance of matching pump size to required pumping volume.
- Variable speed drives (VSDs) in pumps - Digital control systems can adapt pump engine speed continuously to pumping load, saving energy.
- Irrigation sensors and automation - Smart sensor networks coupled with automated control systems can fine-tune pumping duties to plant and stock water needs, minimising energy use and maximising water efficiency.
- Pump maintenance - Maintenance is essential if you’re to retain the rated operating efficiency of both diesel and electric pumps.
- Diesel versus electric pumps - Electric pumps are cheaper to power, cheaper to maintain and easier to control. The only problem is sourcing the electricity.
- Solar energy in irrigation - There is potential to use solar-generated power for all or some of your farm’s pumping duties.
ABS, 2010. Irrigation on Australian farms. [Online]
ABS, 2013. Water Use on Australian Farms 2011-12. [Online]
National program for sustainable irrigation, 2008. Irrigation in Australia: Facts and figures. [Online]
NSW Government Energy Savings Scheme, 2014. List of accredited certificate providers. [Online]