The farm is 150 ha and irrigated all year round, producing around 8 units per ha per year.

The annual energy consumption for the site during the 2018-2019 period was 48,500 kWh at a cost of $15,500, with a solar thermal system already implemented used to pre-heat water and a 5kW solar PV system used by the irrigation system. The energy consumption on the farm consists mainly of:

• Milk Cooling: plate cooler, cooling tower, vat cooling system.
• Milk harvesting and stalling: vacuum pump oil with a 7.5kW motor.
• Stock and Dairy water: two 37kW centrifugal pumps with Variable Speed Drives.

A recent energy audit showed how improving the current systems can lead to energy and cost savings. The audit recommendations are:

1. Install a plate heat exchanger: to pre-cool the milk before it enters the bulk milk vat, allowing to reduce 10-12 degrees of milk temperature, improving the efficiency of the cooling system.
2. Install a lobe vacuum pump with VSD and a 7.5kW motor: same size as the current system, which would reduce electricity consumption by 50%, improving the efficiency of the vacuum system. Additional savings of $500 per year are estimated as the vacuum pump oil is no longer used.
3. Reconsider milking machine wash program: using a warm wash (50-60 degrees) instead of the current hot cycle since the water heated by the solar system has been measured at 55 degrees. After the cleaning, the hot water system should be turned off.
4. Review electricity meters and tariff pricing: to rationalise the number of meters and their configuration, reducing the meter service charges and perhaps having access to lower tariff rates.
5. Investigate and fix pump: to improve performance of irrigation system that has been reducing from 2016.
6. Investigate and eliminate head losses in the Travelling Gun: to improve performance of irrigation system.
7. Replace 5ha of travelling gun irrigation with a solid set system: improve irrigation uniformity by around 35%, reducing in 45% the time required to meet the farm’s water requirements, with consequent labour and productivity gains estimated at $5,560 per year.
8. Install a 10-15 kW Solar PV system: on a west-facing roof to reduce afternoon demand.

Table 1. Costs and savings from audit recommendations.

The farmer replaced the travelling gun irrigator with a solid set system. The savings made have been measured in a Measurement and Verification (M&V) process, as outlined in Table 2.

Table 2. Estimated and Actual energy and cost savings.

The lower energy savings obtained from the M&V calculations compared to those estimated in the audit have been influenced by different assumptions on the use of water by the irrigation system. The audit used the same volume of water measured to estimate the energy savings of the proposed solution, while the M&V used a conservative calculation since the upgraded system requires less water to irrigate the same area (3.1 ML instead of 5.5 ML).

The increased watering efficiency has been caused by the increase in pump efficiency from 48% to 53.9% when changing the section from hard hose to solid set irrigation.

The production benefit from the irrigation system upgrade outweighs the cost of increased energy consumption with an increase in revenue. The travelling gun system had a Distribution Uniformity (DU) of 49%, which has improved to 81% with the implementation of the solid set system, increasing pasture production. Typical production levels for irrigation with low DU are 6-8 tonnes of dry matter per hectare per year (t DM/ha/year). With the improved uniformity, pasture production is expected to increase by 10-12 t DM/ha/year, to around 20 t DM/year for the 5ha irrigated, with a minimum estimated value of $5,000 (which has been included in the cost savings). These improvements haven’t been translated into increases in milk production.

From the implementation of recommendations in the audit, the farm has reduced total energy consumption by 1%, pump usage by 17%, and total costs by 37%, with Carbon emission savings of 0.4 t/CO₂-e per year.

Table 3. Pre and post implementation energy consumption, costs and energy productivity improvements.

This case study was developed as part of the Energy Savers Plus Extension Program, delivered by the Queensland Farmers Federation with support and funding from the Queensland Department of Energy and Public Works.