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 .