Cotton farm uses solar energy to boost pumping efficiency

John Mulligan with the new solar photovoltaic array that now helps power the irrigation system at DP Ag.
John Mulligan with the new solar photovoltaic array that now helps power the irrigation system at DP Ag.
NSW Office of Environment & Heritage (OEH)

“We replaced our old diesel-guzzling irrigation system with a much more efficient and reliable solar-diesel hybrid that uses less than half the diesel of our old system,” says John Mulligan, Director of DP Ag. “We’ve reduced our diesel consumption by 60 percent, saving us more than $46,000 a year.”

About DP Ag

We are a family-run farming business producing fine-grade cotton from a 200-hectare site in Moree, NSW. We’ve been growing cotton there since 1978, producing around 400 tonnes of top-quality lint a year. We market our cotton to merchants in Australia who then on-sell overseas, mainly to China and Vietnam.

Our situation

Cotton is a desert plant that is drought- and heat-tolerant. It uses about the same amount of water as other summer crops, and less water than that required for rice, maize, soybeans and many vegetable crops.

At our farm, rainfall is supplemented by irrigation. We have a diesel irrigation pump which operates whenever rainfall is low, and around the clock during the hot, dry months between October and February. The pump uses more than 67,500 litres of diesel fuel per year and, because of the high cost of diesel, we had to look at ways to reduce the cost.

The irrigation system at DP Ag, a cotton-farming enterprise near Moree.
The irrigation system at DP Ag, a cotton-farming enterprise near Moree.
NSW Office of Environment & Heritage (OEH)

What we did

We decided to upgrade our traditional diesel engine irrigation pumping system to an off-grid solar-diesel hybrid power plant. This means that during the day, when it’s sunny, the pump is powered by solar energy, and at nights and when it’s cloudy it’s fuelled by diesel.

The system consists of a new diesel generator, a new pump motor and a 70-kilowatt solar power system. The solar power system is a ground-mounted solar array located in the optimum location on the farm for maximum solar gathering.

The upgrade also included an energy-management control system with a variable speed drive (VSD) to better regulate the pump motor’s power needs, particularly outside of peak periods, ensuring that it doesn’t run at full speed when the demand is low. The control system manages the diesel generator, solar power system, VSD output and the fuel supply.

We were assisted by energy consultants YellowDot Energy, with the NSW Office of Environment and Heritage (OEH) contributing $10,000 as part of its technical support package for businesses undertaking energy-efficiency projects.

The results

The new pumping system is saving us, on average, more than 40,000 litres of diesel annually, representing a 60 percent saving. This equates to around $46,500 in savings per year.

The system gives us energy savings even when we are pumping water 24-7 in the peak use season between October and February.  And the multiple sensors and computer modem communications let us monitor and control it remotely, meaning we don’t have to go to the site in the middle of cold nights or on wet days.

We also use water more efficiently now. The system lets us extract water more consistently over the course of the year, reducing water-level drawdown during dry periods when demand for water is at its peak.

John Mulligan, Director of DP Ag: “We’ve reduced our diesel consumption by 60 percent, saving us more than $46,000 a year.”
John Mulligan, Director of DP Ag: “We’ve reduced our diesel consumption by 60 percent, saving us more than $46,000 a year.”
NSW Office of Environment & Heritage (OEH)

By the numbers

Cost of upgrade:                       $180,589

Estimated cost savings:           $46,468 a year

Fuel savings:                            40,761 litres of diesel (60% of existing annual consumption)

Simple payback:                       3 years 11 months

The technology

Solar-diesel (standalone) power systems for water pumping

Solar power systems that convert sunlight into energy can be integrated with existing diesel-powered systems to operate irrigation pumping motors. Also known as photovoltaics (PV), these electronically-controlled systems can operate around the clock in ‘hybrid’ mode, and in ‘solar-only’ mode during the day. These systems can be controlled and monitored remotely.

Integration of solar PV can reduce the cost pressures from rising energy costs in the mid to long term and make a positive contribution to the environment. The Office of Environment & Heritage (OEH) has information on solar power financing options for businesses.


Variable speed drive (VSD) on irrigation pumps

When a single pump is required to operate over a range of flow rates and pressures, such as in irrigation, standard procedure is to design the pump to meet the greatest output demand of both flow and pressure. For this reason, pumps are often oversized and thus operate inefficiently over a range of duties.

This common situation presents an opportunity to reduce energy requirements by using control methods such as variable speed drives (VSDs) A VSD fitted to an irrigation motor regulates the frequency of the electrical power supplied to the pump to match the volume or pressure requirements of the irrigation system, thus reducing energy use.

Taking action

To find out how you can save on your business’ energy costs, visit the Energy Efficient Business team section of the NSW OEH website, email the team via energy.saver@environment.nsw.gov.au, or phone 1 300 361 967 and ask for the Energy Efficient Business team.

Energy

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