An irrigated cotton farm in the Emerald region could benefit from a recent Energy Savers Audit. The farm predominately grows cotton, with peanuts, gritting corn, wheat, and mung beans grown in a winter rotation. Water is pumped to two centre pivots through 360m of 10inch PVC to the first pivot, and then flows through 700m of 6inch PVC to the second centre pivot.
A total 39,948kWh of energy was used for pumping resulting in emissions of 36.7t/CO2-e, costing $8,497 per annum. Using the known energy consumption at the pump, the unit of power consumption per mega-litre per metre of head (kWh/ML/m) is calculated to assess and benchmark the pump.
Main, and Boost Pumps Measured Performance
| Irrigation Used | Main Pump kWh/ML/m | Boost Pump kWh/ML/m |
| One Pivot | 4.57 | 4.64 |
| Both Pivots | 4.98 | 4.53 |
The audit noted that both pumps are operating below the manufacturers pump curve. The energy audit recommended the farm consider either the refurbishment or replacement of the two pumps and the installation of a 30Kw solar PV system to address the inefficiency and reduce energy consumption onsite.
Recommendations and Savings from the Energy Audit
| Recommendation | Energy savings (kWh) | Cost Savings ($) | Payback Period (Years) | Emissions (t/CO2-e) |
| Option 1: Refurbish Pumps | 5,208
|
1,399
|
2.1 | 4.8 |
| Option 2: Replace Pumps | 10.7 | |||
| 30kW Solar PV | 25,495 | 8,851 | 3.3 | 23.5 |
| Total | 30,703 | 10,250 | N/A | 28.3 |
The farm has two options. They could replace the impeller, shaft, and bearings, costing roughly $800 and $2000 in labour to perform on both pumps. Or replace the two pumps, costing $15,000 for both pump sites. The refurbishment or replacement of both pumps would increase 30 minute energy demand from 15.8kW to 18.8kW with both pumps operating, and 12.6kW to 15.1kW when the main pump is operating alone.
There is a subsequent increase in water flow rate from 39.3L/s to 53.8L/s with both pumps operating and 38.9L/s to 51.2L/s with the main pump operating alone. The refurbishment or pump replacement poses the same energy savings though differing paybacks reflecting the different costs. It was recommended to inspect the impeller, shaft, bearings, and volute casing due to the shorter payback before replacing the pump. Both recommendations will reduce electricity consumption by 13 per cent or 5,208.38kWh, while pumping the equivalent quantity of water.
Installation of a 30kW solar system would reduce electricity consumption by 63.8 per cent and costs by 80.5 per cent, including solar feed-in.
Pre and Post Audit Metrics
| Metric | Pre-Audit | Post Audit | Reduction (%) |
| Energy Consumption | 39,948 | 9,245 | 76 |
| Energy Costs | 8,497 | -1,753 | 120 |
| Emissions (t/CO2–e) | 36.7 | 8.4 | 77 |
An energy audit is a great first step in moving a business towards a more efficient future by reducing energy use, costs, and carbon emissions onsite. See some other Energy Savers Case studies HERE. Find out about what’s involved in an energy audit HERE.
If you have any energy efficiency related questions for the team get in touch at energysavers@qff.org.au.