The site consists of three paddocks irrigated with solid set sprinklers. After talks with the farmer the audit focused on the smaller 4.4ha paddock as the current system is failing to deliver enough water for optimum irrigation. Catch can data from the Distribution Uniformity (DU) test showed a current of DU 14 per cent and a Co-efficient of Uniformity (CU) 44 per cent, with the target CU being 80 per cent.
The current system consists off a 500m 110mm mainline, five two inch PCV laterals spaced at 32m with 10mmx5mm jet sprinklers, set on 450mm risers at a spacing of 32.5m.
A flow rate of 9.3L/S was measured with 42m of head. Energy demand was 9.6kW and an assumed motor efficiency of 80 per cent was used to calculate the pump efficiency of 51 per cent. This results in an overall efficiency rating of 6.83kWh/ML/m which is slightly above the industry benchmark of 5kWh/ML/m and indicates improvements can be made.
The audit recommended to replace and relocate the pump with a new motor and Variable Speed Drive (VSD) to increase pressure delivery, while reducing the mainline length and replacing the sprinklers. Two separate pump and sprinkler options were explored, a breakdown of the cost for each system includes:
- Option 7025: Pump motor and VSD $8,000, .25m mainline $4,500 and sprinklers $7,500
- Option 8025: Larger pump, motor and VSD offers a higher pressure and flow $13,000, 25m mainline $6,000 and sprinklers $10,500
Irrigation options with potential energy and cost savings
|Recommendation and Savings
||7025 Option 18.5kW Motor
||8025 Option 30kW Motor
|Existing mainline shortened and new pump (Energy consumption kWh)
|New and shortened 150mm PVC mainline and new pump (Energy consumption kWh)
|Cost Savings including productivity gain minus increased energy costs ($)
|Optimum system payback period (Years)
The existing 110mm HDPE pipeline runs 500m to the 1st lateral. At the measured flow rate of 9.3 LPS, this has a friction loss of 7m. The new pump could be relocated reducing the distance to 150m, with a reduction of 5m of friction loss to 2m.
The table shows that the farm could save considerably with changes to the irrigation system from either option. Due to the higher flow rate in the 8025, pump run time is reduced by 127hrs though uses slightly more energy due to the motors larger size. This may lead to longer life expectancy of the pump and should be considered.
The system upgrade will result in energy consumption and costs roughly increasing by 1,200 kWh and $250 for the 7025, and 2,000 kWh and $450 for the 8025. The production benefit outweighs the cost of increased consumption with an increase in profit.
Typical levels of production for dry land farming can be 5-6 tonnes of dry matter (DM) per hectare per year (t DM/Ha/year). Typical levels of production with low DU can be 6- 8 tonnes DM/ Ha/ year. With improved uniformity and with careful management, production may increase to over 10-12t DM/Ha/year. Working on an increase of 4t/DM/Ha could result in an increase of 18 tDM/year for 4.4Ha. The value of this can be between $5- 10,000 depending on how it is utilised.
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