From the energy audit and discussions with the local pump shop, and electrician, the best efficiency and production outcomes for the site included:
- Installing a smaller pump and motor, and adding a Variable Speed Drive (VSD) with remote pressure sensors.
- Adding a 40kW solar system with a 30kW inverter to cover pump load power, with possible export.
- A 7.5kW solar system for the farm shed.
- Retrofit existing lighting with LEDs on the farm shed
- A change in strategy to day-time pumping using energy produced from solar on-site, with a change to Tariff 20.
Table 1. Audit recommendations comparing savings between tariffs.
||Capital Cost ($)
||Energy Savings T62 (kWh)
||Energy Savings T20 (kWh)
||Cost Savings T62 ($)
||Cost Savings T20 ($)
||Payback period T62 (Years)
||Payback Period T20 (Years)
|40kW Solar System
|Pump replacement and VSD
|7.5 kW Solar System
|Retrofit lighting with LEDs
A 55kW pump was removed and downsized to 45kW. The pump, which supplies a small centre pivot and a large travelling irrigator was positioned lower to the water reducing suction lift and improving efficiency. To overcome the slope as the irrigator moves across the paddock a Variable Speed Drive (VSD) was installed on the electric motor, controlling the motor speed to improve the irrigation system efficiency.
Additionally, a new radio link has been established between the lateral irrigator, centre pivot, and pump. This measures the pressure available at the irrigator or pivot sending the data back to the VSD, ensuring the correct water pressure is maintained. The pump will run slower using less power at the bottom of the paddock increasing up the slopes maintaining perfect pressure and even water distribution. Further, the radio link will allow remote starting, and should the pump stop or there is a fault with the pivot or irrigator then the pump will not operate.
The solar system will cover most of the load required by the new pump. A 39.6 kW solar array with 30kW inverter capacity has been installed arranged in an East/West configuration. As the irrigators run for long periods, the panels facing East will get to maximum capacity earlier in the morning with the panels facing West producing maximum power in the afternoon.
As the inverter capacity is no larger than 30kW the installation was treated as a micro embedded generating unit keeping the connection process simple and meaning the farm is still able to export during times of no irrigation. Maintaining grid connection allows the irrigator to draw grid power when required.
The savings made have been measured in a Measurement and Verification (M&V) process, as outlined in Table 2.
Table 2. Estimated and Actual annual energy and cost savings.
|Energy Savings including exports (kWh)
|Cost Savings including exports revenue ($)
*Extrapolated based on 3 months of measured data.
The lower cost savings measured compared to the estimated have been affected by the high amount of energy exported to the grid and the low 2020 feed-in tariff. From the annual solar generation, only 26,500 kWh are being used onsite valued at $6,163 and 33,176 kWh valued at $2,608 are being exported to the grid. However, if the farm was able to adjust energy usage to offset all the energy consumption from the grid, it would lead to further cost savings as the revenue from feeding into the grid is lower than the cost of using energy from the grid.
By implementing the recommendations in the audit, the farm has reduced energy consumption by 46%, including the energy exported to the grid, and costs by 33%, including feed-in revenue, with total Carbon emission savings of 48.3 tCO2-e per year.
Table 3. Pre and post implementation energy, costs, and energy productivity improvements.
|Energy Consumption (kWh)
|Energy Productivity (kWh/ton)
With the reductions in energy consumption and, if possible, maximising the use of solar energy onsite through changes in the operation of the irrigation system, the farm is likely to reduce their consumption below 100,000kWh per annum and access the small business tariffs, removing any possible demand charges.
In the future should the farm implement changes at the shed the savings from the irrigation changes will cover any potential difference.
An energy audit is a good investment
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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.