A wine grape producer located in Stanthorpe on 3.2ha of land produces around 16t of premium grapes per annum. With the current drought, the production forecast is well below expectations. 

The site currently draws water from a small DC pump located roughly 1km from the property. This pump is powered by two 5x75 watt solar panels that track the sunlight from a change in oil viscosity in a set of dampeners as the sun slowly increases their temperature. The water is pumped using a DC motor a kilometre from the creek through a 50mm mainline to a holding tank controlled by a float valve. Two types of soil moisture probes are used on-site including three G-Dots for visual clues, while two solar-powered Davis probes are connected to a weather station console by Wi-Fi, which engages the irrigation decisions. 

The grapevines are then irrigated from water in a holding tank using a 5.5kW AC pump through a network of drippers. The site consumes 12,382kWh at a cost of $3,670 per annum. A 7.2kW solar system covers the site load including the house and part of the 5.5kW load from the irrigation pump located in the shed.  

A recent energy audit highlighted that whilst the farm has previously implemented some efficient irrigation management practices, further improvements in energy efficiency could be achieved from the installation of a new pump and the ability to explore more energy efficiency options as the business moves into the future. The recommendation explored in the audit included:

• Replacement of the vine pump by a more efficient unit including Variable Speed Drive (VSD). 

Table 1. Energy and cost savings from audit recommendation

The grower has proceeded with the installation of the new pump with VSD. Actual savings will be updated once the measurement and verification process is complete.

By installing the recommendations in the audit, the business is expected to reduce energy consumption by 22% and costs by 25%, with carbon emission savings of 2.2 tCO_2-e per year.

Table 2. Pre and post audit energy consumption, costs, and irrigation efficiency improvements

After data logging with a flow meter and pressure gauge, the irrigation system efficiency was measured at 396-kilowatt hours per megalitre per metre of head (kWh/ML/m). The recommended replacement of the pump based on the current measured flow (m3/hr) and Head (m) as tested, has the potential to reduce energy consumption by 22%. The suggested centrifugal volute pump has a higher efficiency class and would reduce this metric to 156.70 kWh/ML/m, a 60% reduction. 

The site has been proactive and performed an irrigation audit which found some issues that have been rectified by: 

• The Vine pumps measured head and flow suggested a worn impeller; investigation discovered debris surrounding the impeller, reducing its performance, the debris was removed. 
• Replacing of all dripper and lateral lines was completed because the discharge variation of the emitters was very high at 76%;  
• Cyclic cleaning of the filtration system.  
• The DC motor has been replaced previously on occasion as a result of metal contraction caused by the extreme cold. Installing an insulated cover on the pump could fix further problems. 
• Flushing of the dripper lines and laterals annually to remove the debris build-up.  
• Implementing crop management practices including pruning the cordon arms to the first spur to reduce water transpiration from the vines, ultimately reducing pumping times and energy consumption. 

A more efficient pumping system will prevent over pumping to compensate for areas that require rectification. This also reduces crop water stress and improves yield uniformity. 

Moving forward, further improvements were highlighted in the energy audit process. The solar panels that operate the creek pump are showing signs of age. The browning discolouration is associated with aging and poor quality backing sheets. With the advances in solar and by replacing these there is potential to bypass the AC pump under optimal conditions and install batteries for night-time irrigation, should this prove feasible.  

With the help of a real–time energy meter, more HERE, the site is well informed to manually operate the pump when there is excessive solar generation to irrigate to field capacity. This requires monitoring of both the real-time energy meter and the soil moisture probes onsite. These measures can further assist to lower both energy and water consumption on site. 

An energy audit is a good investment 

An energy audit is a great way for a business to cut costs and boost productivity.  

An energy auditor will review your past energy bills, your equipment and the way your business operates. They’ll show you where you’re using excess energy and explain what you can do about it.  Find out about what’s involved in an energy audit HERE. 

See our range of agricultural energy efficiency case studies HERE and Subscribe to our bi-monthly energy e-news HERE  

If you have any energy efficiency related questions for the team get in touch at energysavers@qff.org.au. 

The Energy Savers Plus Extension Program is delivered by the Queensland Farmers Federation with support and funding from the Queensland Department of Energy and Public Works.