Variable Speed Drives

optimal energy utilization from a pumping point of view.

The Solution

A solar photovoltaic( PV) system was installed which makes use of 200 solar panels that are capable of generating 51kW of peak power during the day. This solar DC power source was connected to the existing pumps located on the Berg River using a 300m underground cable.

Each of the pumps were fitted with new variable speed drive control panels( VSD). Two additional control panels were installed. The first one is for managing the AC and DC supply and the

second is to manage the 2 x 22kW pumps so as to allow either single or parallel operation, depending upon operations. This provided additional flexibility to the operations. The motor control panels are linked to both the AC Eskom grid as well as the DC solar power source- thus providing the option of power from either source.

The electrical design of the system is carried out in such a manner that the DC source would always have precedence over the AC source. A typical daily power curve is shown below demonstrating the operation of the system over a 24 hour period

As the sun rises and DC solar PV energy is generated, power consumed from the AC grid source is reduced. The opposite is true as sunset takes place: with more AC power being absorbed from the grid while less DC power is being generated by the solar PV system.

Three levels of power savings are achieved with the benefits provided by this specific system –

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Variation in system flow takes place from one day to the next due to the irrigation dynamics on the farm. By adopting constant pressure PID control through the variable speed drives( VSDs), they unlock energy savings as the pumps’ speed is adjusted to meet the required flow at the selected pressure.

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The VSD motor control panels have been equipped with multiple pressure set points

allowing for an optimum operating pressure to be selected while irrigating the various blocks. This also plays a significant role in unlocking energy savings.

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The installation of the Solar PV system has unlocked further energy savings.

In conclusion, the use of variable speed drives in applications that are partially powered by Solar PV while remaining grid tied presents a great opportunity to unlock significant energy savings.

This type of system can be adopted on a modular basis and expanded on as operations expand and finances allow. Contact Irri-Gator Products or Ren Energy for further information on our Solar assist and full Solar pumping solutions.

www. irrigator. co. za or www. renenergy. co. za.