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Dalby Cotton Farm - Queensland Farmers' Federation
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Energy Savers
Darling Downs

Dalby Cotton Farm

Proposed
40
Energy Savings
35
Savings
45,953
Industry
Cotton
Irrigation
Centre Pivot
Pumps
Bore
Technology
Solar Photovoltaic
Capital Cost
$52,720

Farm Profile

220ha irrigated cotton farm near Dalby which also produces corn, barley, wheat and chickpeas could save electricity by implementing the recommendations from their Energy Savers audit. Three pumps lift water from the creek to three separate centre pivots and consume nearly 110,000 kWh at a cost of $23,000. Four potential solar systems were compared with the best payback chosen to reduce consumption from the grid below 100,000kWh.  

As consumption is just over 100MW p.a. both small and large customer tariffs were considered, and a comprehensive analysis shown to minimise operating costs by implementing the recommendations in the audit. 

The audit initially investigated the pumping and irrigation system. The assessment determined the electric motor efficiency is at 85 per cent, but should be 94.7 per cent according to the electric motor specification plate. This is due to the heat generation within the bell housing, reducing air flow for heat exchange across the electric motor.

Pivot 1 has a nozzle setup for 90L/s, pivot 2 45L/s and pivot 3 70L/s. Pivot 1 requires a centre tower pressure of 217kPa with the assessment recording 296kPa.

Pivot 2 and 3 pressures are currently unknown and are assumed to be similar to pivot 1 with pivot 3 recording centre tower pressure of 310kPa. When irrigating through pivot 2 and 3, pivot 2’s tower pressure was 131kPa and pivot 3’s was 145kPa. The over pressurising of the system causes drift due to over atomisation of the irrigation water, reducing distribution uniformity. To confirm pivot pressures, a functioning pressure gauge and Nelson controller valve are used to ensure the system is operating as required. 

Four ground mount solar options including a 10kW, 20kW, 30kW and 40kW systems were assessed to determine the most suitable, summarised in table 1. With grid connect solar systems, it is important to size for optimal utilisation and export which will minimise your payback period and maximise your return on investment. See our article on getting the most from solar PV on Farm HERE. 

A general cost assumption of $1.85 per watt has been used to calculate the cost of a proposed solar system minus the price of small scale technology certificates which are kept up to date HERE. 

Table 1. Solar systems recommended for site. 

System Size  Cost ($)  Solar Offset (kWh)  Grid Import (kWh)  Grid Export (kWh)  Payback (Years) 
10kW Solar  13,180  13,856  94,331  1,435  0.36 
20kW Solar  26,360  25,179  83,089  5,404  0.66 
30kW Solar  39,540  35,018  73,169  10,855  0.92 
40kW Solar  52,720  43,151  65,036  18,014  1.1 

 

The audit showed that the 40kW solar system with 30kW invertor to allow export was the optimal system for this site with a capital cost of $52,720. Energy consumption would be reduced by 40 per centsaving 43,151kWh and costs of $45,953p.a., with CO2 savings of 35 tonnes per year.

A comprehensive tariff analysis undertaken in the audit shows the need to select the correct tariff for your site to keep operating costs to a minimum. Currently on obsolete Tariff 66, the farm will need to consider alternative options and transition by 2021The cost saving percentages shown are based on having to operaton T50 as without installation of solar which would be the lowest cost option as outlined below in table 2. 

Table 2. Current tariff opportunities and savings with no solar installed. 

Small Asset Customer  Large Asset Customer 
Tariff  Cost ($)  Change (%)  Tariff  Cost ($)  Change (%) 
66  41,688  Current  44  95,771  53 
20  29,576  -52  45  90,632  45 
22A  31,274  -50  46  175,633  180 
24  76,511  22  50  62,520  Non-Obsolete Option +49% increase from current obsolete 
41  63,401  1.4     

 

The table shows that under current operating practices a 52 per cent reduction could be achieved immediately by simply changing tariffs. As the site is over the 100,000kWh than this change is currently unavailable. Upon installation of the solar system this tariff would be available with energy costs reduced by 71.2 per cent from $62,520 to around $17,980 on tariff 20 as costs savings would be further reduced from exporting to the grid. 

An energy audit also details benchmark indicators used to measure pump performance, which was the focus of this audit. 

The first, measures the electricity consumption (kWh) per megalitre (ML) of water pumped (kWh/ML). This is useful for growers to compare individual pump performance from season to season. However, it does not consider the total dynamic head which can be expressed as electricity consumption (kWh) per megalitre of water (ML), per metre of head (kWh/ML/m head). This figure provides a benchmark for pump and system efficiency and can be used to compare any pumping system across any industry.  

The audit showed the centre pivot pump site has an electricity usage of 4.20kWh/ML/m head irrigating through pivot 1 and 4.39kWh/ML/m head for pivot 3. Irrigating through pivot 2 and 3 electricity usage is 5.67kWh/ML/m head, operation with the bore pump usage improves to 5.33kWh/ML/m head. A typical benchmark for efficiency in industry is 5kWh/ML/m indicating there could be further efficiency gains for the site.  

An energy audit is a good investment 

An energy audit is a great way for a business to cut costs and boost productivity. Find out about what’s involved in an energy audit HERE and subscribe to our bi-monthly energy e-news HERE.

If you have any energy efficiency related questions for the team get in touch at energysavers@qff.org.au.

 

The Energy Savers Plus Extension Program is delivered in by the Queensland Farmers Federation with support and funding from the Queensland Department of Energy and Public Works.

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