How do Solar Drives (for Water Pumps) Work?

How do Solar Drives Work?

Solar Inverters

All solar powered systems require a Solar Inverter to operate AC powered equipment and appliances. A Solar Inverter is a device that converts direct current (DC) generated by solar panels (or other alternative sources, such as batteries), into alternating current (AC) for use in industrial, commercial, and residential use.

Pure Sine Wave vs Modified Sine Wave vs Square Wave

Key technical aspects differentiating Solar Inverters include the following:

• Pure Sine Wave Inverters: The power from a Pure Sine Wave Inverter is similar to that supplied by the power grid and enables devices such as microwave ovens, fans and fluorescent lights to run quietly without distortion or disturbance. Pure Sine Wave Inverters also ensure that computers run smoothly and without overheating. These inverters are typically a must for anything that has a screen e.g. TV, PC etc.
• Modified Sine Wave Inverters: Modified Sine Wave Inverters have higher efficiencies at lower cost per watt, but do not necessarily work for all applications. For instance, laser printers and certain types of fluorescent lights do not function as well as they would with Pure Sine Wave Inverters, as do certain power tools and battery chargers for cordless power tools. Modified Sine Wave Inverters can also interfere with the proper functioning of televisions sets and digital clock radios, as well as important medical equipment.
• Square Wave Inverters: There are very few, but the cheapest inverters are Square Wave Inverters. A Square Wave Inverter will run simple things like tools with universal motors without a problem, but not much else. Square Wave Inverters are seldom seen anymore.

Grid-Tied vs Off-Grid vs Hybrid

Besides the abovementioned technical aspects differentiating Solar Inverters, there are also other aspects used to differentiate between the different types of Solar Inverters in the market, these include:

• Grid-Tied: Grid-Tied Inverters use PV Panels to generate DC power which in turn gets inverted to AC power. These inverters require a stable Grid power source (synchronise to the Grid) to operate (disconnects if the Grid goes down). These Grid-Tied Inverters use the power generated by the PV Panels and then meet any additional power requirements that may arise by using power from the Grid power source.
• Off-Grid: Off-Grid Inverters requires batteries. Power from PV Panels charge the Batteries directly and then the battery power is inverted to AC (from DC). These are typically used in situations where no Grid power source is available.
• Hybrid: Hybrid Inverters are the best of both ‘worlds’ mentioned above. Not only does Hybrid Inverters have all the features of an Off-Grid Inverter, but it also works well for those who want to fall back to the grid if and when required. More importantly, these Hybrid Inverters can use all the energy sources (‘blending’ the energy) in the most efficient way to power the load (it essentially allows the optimal mix of PV Panel, Battery and Grid power available in order to power a system at any given moment).

Solar Drives

Solar Drives (for Water Pumps) on the other hand are unique when compared to these Solar Inverter types and applicable for more specific applications. Solar Drives are essentially basic Variable Speed Drives (VSDs) with a subset of VSD features, but with specific additional features and functionality applicable to Solar Water Pumping Systems, providing complete protection to the pump and controlling its functions. Solar Drives are thus essentially designed to make use of the free power from the sun, as well as combining it with the benefits of using a VSD.

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 Modified Sine Wave AC power again, adjusting the voltage and frequency as required – please see How do VSDs Work? for more info). 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 are thus used independent from the grid (with no need or option for batteries, but with the option of AC input as a backup). Since VSDs (and therefore Solar Drives) provide Modified Sine Wave power, these Solar Drives are not suitable for applications such as powering home appliances (such as TVs and Computers for example).

Solar Drive 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.

In summary, Solar Drives are modified VSDs, designed as fully automated Solar Water Pumping Solutions, in order 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:

• What is a Solar Drive (for Water Pumps)?
• Advantages of Solar Drives (for Water Pumps)
• Variable Speed Drive vs Solar Drive (for Water Pumps)
• EMHEATER VSD and Solar Drive Fault Diagnosis – Errors
• Solar Drive (Solar VSD) – PV Array Design