Surrounded by national parks and significant wildlife areas, exposed granite boulders have been weathered over thousands of years leaving behind sandy soils. These soils drain freely, with low organic matter and reduced water holding capacity. However, Stanthorpe has a rich agricultural history with many fruit and vegetable crops grown in the region.
Average rainfall in the region is 700mm with low years experiencing on average 536mm. Rainfall over the last year has been well below average with most parts recording 150mm. Recent steady falls of 150mm over a two-week period has eclipsed last year’s total annual rainfall providing plenty of green grass. While it is bringing some welcome relief, farmers in the region are referring to it as a “green drought” as the area still requires successive rainfall events to fill the dams and provide water security.
During good rainfall years one of the Energy Savers audit farms in Stanthorpe typically produces 1000t of tomatoes and 240t of capsicums at a kWh benchmark of 18.69kWh/t. With the drought, the farm is having to adapt, and change crop management practices. Due to the low rainfall and water storage levels, the farm will not produce any capsicums and instead opt for well a managed tomato crop this year. The tomatoes are pruned from 6ft to 4ft seeing no significant loss of yield, resulting in a reduction of water and energy use. The cropping area is rotated to avoid disease and due to differing requirements of the paddocks, three centrifugal pumps are used on site. They are pumping more water than the irrigation system can deliver.
The farm had already implemented soil moisture probes with good results, prompting them to install additional probes onsite. This allows ease of use by monitoring and controlling the pumps from a mobile device providing exact amounts of water required by the plant due to the sandy soil.
To reduce the flow rate of the pump to match the requirement of the irrigation system, the owner is throttling the discharge valves increasing the friction head and consequently reducing the water flow rate. By throttling the valve, the amount of energy drawn by the pump is reduced but it is not the most efficient option to reduce the flow rate as it increases the kWh required for each ML pumped.
The audit showed that further reductions in energy use can be achieved by installing Variable Speed Drive (VSD) technology to the existing pumps onsite and replacing the main connection pipe to the dam. This may result in an average 1,545kWh in energy savings per pump, per year with a further 1,293kWh saved by replacing the connection pipe. Additional benefits include reductions in peak demand and the slow ramp up speeds of water pressure being delivered through the pipe. This reduces the incidence of irrigation pipes bursting and in the event of this occurring the pump will shut down saving precious water.
A total saving of 10,107kWh at a cost of $58,400 would be realised from implementing all the audit recommendations. Should the same 1,000t of tomatoes be produced this year, due to the capsicum crops being turned in, a new 13.07 kWh/t benchmark would be seen. When rain, and full production returns an overall reduction of 8.16kWh/t is a great result.
Through the audit process and the farms ingenuity, the overall kWh/t of production, crop stress, water requirements and labour inputs onsite have been reduced