Solar-powered irrigation

Tofts Sand, a Queensland farm in the Childers area, grows a number of different crops including sugarcane and peanuts and utilises a mains-powered pump to irrigate them. With increasing operating costs and competition, it sought help to see what options were available.

Project scope

Tofts Sand wanted to reduce its production costs by running a pump from solar energy, allowing it to avoid using the mains supply when possible. The mains supply would therefore only be required at night or when there was not sufficient solar power available during the day.

The 22 kW 415 V pump moves water out of a dam along a 400 m underground pipe to a centre pivot that moves around the field for crop irrigation.

Solution

Based on current and expected future requirements, Control Logic recommended and supplied a 22 kW ABB ACSM1 Solar VSD, which was then implemented by Betts Electrical. The ACSM1 Solar VSD has solar-specific firmware to provide maximum power point tracking (MPPT). It is also capable of taking DC directly from the PV array.

Betts Electrical installed the VSD into a cabinet that had the incoming mains supply connected to it, as well as installing DC from a 30 kW PV array. Given that both supplies were connected to the VSD at the same time, blocking diodes were connected in series on the plus and minus coming from the PV array and the VSD DC bus connection. This prevented current flowing back into the PV array.

For the irrigation system to function correctly, a constant pressure must be maintained in the pipes. A pressure transmitter was connected to a PLC, which performed PID control to maintain a pressure setpoint. The PLC varied the speed reference to the VSD, as well as starting and stopping it.

PLC communication between pivot and pump is now possible via a controller on the centre pivot and, using a radio signal, the pump is run only when the centre pivot is ready.

Benefits

In agriculture applications, irrigation is one of the major costs of daily operation and implementation of the new system will see many of these costs dramatically reduced.

The proportion of power coming from the mains or from the PV array will now depend on the amount of solar power available. Because irrigation at Tofts Sand mainly takes place during the spring and summer months, solar power supply availability should be favourable, saving costs and reducing carbon emissions.

On a clear sunny day, all power would be completely derived from the PV array. This means the mains would only be utilised at night or partly during the day, depending on cloud cover. This substantial cost saving will enable Tofts Sand to irrigate 24/7, yet still reduce production costs.

Another benefit of having the pump VSD controlled, rather than being directly connected to the mains supply, is the elimination of ‘water hammer’. By smoothly ramping the pump up and down, knocking noises from the water pipe, which occur when a tap is quickly turned off, are eliminated.

 

“Concerned and frustrated by increasing costs for irrigation, especially for electricity to grow our sugarcane and peanut crops, we decided to investigate alternative ways to defray costs,” said John and Deb Russo, Tofts Sand.