Solar Drive vs Variable Speed Drive

Solar Drive vs VSD

AC pumps are usually used for high volumes of water supply and require well-regulated AC power (usually 3-Phase). Using a Variable Speed Drive (VSD), pump motor efficiency can be increased, and electricity use can be decreased (saving costs). The amount of energy a VSD can save however depends on the average load of the motor and the number of hours per day it is turned on etc. While average energy savings vary, it is safe to say that most AC motors do not need to be running at full capacity for most hours of their use, making VSDs very beneficial with short payback periods.

Free power from the sun is however the obvious choice for many pumping applications. Solar Drives are essentially designed to make use of this free power from the sun, as well as combining it with the benefits of using a VSD. Solar Drives are environmentally friendly, with a long lifetime and low maintenance costs with no need for expensive electrical connections in remote areas. It is independent from the grid (with no need for batteries) and produces no pollution or noise.

Solar Drives are designed so that DC from the PV array can be supplied directly into the DC Bus inside the Solar Drive (VSDs typically convert the AC power supply to DC and back to AC again, adjusting the voltage and frequency as required). As the sun rises and PV voltage and current increases, the Solar Drive accepts the input (when the power is high enough) and will start the pump (PV array must be large enough to provide enough power).

Solar Drives thus use VSD capabilities to drive AC submersible and surface mount pumps, using PV Solar as a power source (with the option of AC input as a backup).

Solar Drives are thus essentially basic VSDs (subset of features) with specific additional features and functionality applicable to Solar Water Pumping Systems, providing complete protection to the pump and controlling its functions. These solar specific and pump control functions typically include:

  • Maximum power point tracking (MPPT) for optimising PV array power output;
  • Going dormant (switching off) when radiation is too low;
  • Waking up (switching on) when radiation is high enough;
  • Going dormant (switching off) or Waking up (switching on) when high or low water level has been reached;
  • Under-load pre-warning (Dry run protection);
  • Auto-switch to grid supply (if available);
  • Other control and protection functions.

Choosing and sizing the correct pump can however be a challenge as levels of solar radiation fluctuate during the day, with none in the evening. A Solar Water Pumping System thus needs to be designed to pump daily water requirements within these energy limitations (unless there is an AC power source as backup as well). The size of the Solar Water Pumping System is determined by the amount of water that needs to be moved and by how far and to what elevation this water must be moved. Once these performance parameters have been specified, a custom solution can be designed to suit the specific needs.

In summary, Solar Drives are thus modified VSDs, designed as fully automated Solar Water Pumping Solutions to provide water at an affordable cost in areas with limited or no access to electricity. Typical applications include irrigation, community water supply, fish farming and agriculture.

For more information regarding Solar Drives (for Water Pumps), please refer to the following related blog posts:

For more information regarding VSDs, please refer to the following related blog posts:

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