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 a 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.
||Solar Offset (kWh)
||Grid Import (kWh)
||Grid Export (kWh)
The audit showed that the 40kW solar system with a 30kW invertor to allow export was the optimal system for this site. Energy consumption would be reduced by 39.9 per cent, saving 43,151kWh, and costs of around $45,953p.a.
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 2021. The cost saving percentages shown are based on having to operate on 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
||Non-Obsolete Option +49% increase from current obsolete
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 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.
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