The audit focused on a single electric pump at a pump station where there are 3 electric pumps and one diesel pump, with two of the electric pumps on one NMI. The pumps are all 26 inch centrifugal China pumps.

The audit found that the pump is operating well, with an efficiency of around 4.15 kWh/ML/m which is slightly above the target of 3.8 kWh/ML/m of head.

A challenge faced by the farm is the seasonality of electricity consumption, which is illustrated in the figure below, showing the monthly electricity consumption and demand for 2022 and 2023.

The auditor noted that the suction pipe would generally be considered to be too small at 660mm diameter, resulting in velocities that are too high, and he noted that he would generally recommend increasing the suction pipe to a 1050mm diameter pipe. He noted that in this case, however a larger pipe would actually reduce TDH but reduce the efficiency, because the lower TDH would mean pump moves down to a less efficient point on the pump curve. In this case, there is a flooded suction which is unlikely to lead to cavitation.

The audit suggested that to avoid peak demand charges, one of the electric motors could be replaced with a diesel engine.

A detailed analysis was conducted and found that If the pump is used for less than 3,550 hours per year (around 256.8 hours per month), it will be cheaper to use diesel. In this case, the higher use at a lower per-kWh tariff rate is enough to outweigh the high peak demand charge.

The graph below shows a comparison of annual operating costs (vertical axis) based on the time the pump is used (horizontal axis) over the course of the year.

The audit acknowledges that there are a range of variables that would impact on the comparison including:

• Whether the farm is a small or large electricity user and that the audit was based on 2023/24 energy prices at Ergon’s large customer Tariff 44.
• The difficulty in predicting annual or monthly operating hours
• Diesel price variability
• Capital expenditure for the diesel engine estimated at $150,000.

It should be noted that this cross-over point would be different for each pumpstation.

The audit assessed the feasibility of a 100kW Solar PV system for the site and found that it would not be feasible for the site due to the capital cost, the low utilisation because of the irregular pump use, and as the site is ineligible to receive a solar feed in tariff.

The case study is featured in a recorded QBEST webinar presented by the auditor Phil Szabo which is available to view on the Ag Energy Hub HERE.

Energy Audits. The farm had a Type 3 energy audit as a participant in the QBEST Ag program.

The program was delivered by the Queensland Farmers’ Federation and funded by the Queensland Government.