This guide focuses on buying and specifying a solar pump drive for an application. For the underlying technology and DC voltage terminology, see How Solar Pump Inverters Work.
Solar pump inverters are designed to operate electric pumps from photovoltaic power while controlling the motor in a way that suits changing solar conditions. They are commonly used for boreholes, irrigation, livestock watering, reservoir filling and remote water systems where extending a conventional electrical supply can be difficult or expensive.
A solar pump inverter is not selected from motor kilowatts alone. The motor rated current, motor voltage, PV array voltage, inverter input range, pump duty, available solar resource and control requirements all need to work together.
What Does a Solar Pump Inverter Do?
A solar pump inverter takes DC power from a PV array and converts it into controlled AC output for a compatible pump motor. The inverter adjusts motor speed and operating frequency according to the available solar energy and the control strategy.
Many solar pump drives include functions intended specifically for water pumping, such as MPPT, dry-run protection inputs, tank-full control, automatic restart and sensor-based operation. The exact feature set varies by manufacturer and model, so the specific datasheet must always be checked.
What Is MPPT?
MPPT means Maximum Power Point Tracking. Solar panel voltage and current change with sunlight, temperature and operating conditions. MPPT allows the inverter to operate the PV array near its most useful power point so that the available solar energy can be used effectively.
For pumping applications, this helps the system adapt as available sunlight changes through the day. It does not remove the need to size the PV array and inverter correctly.
Motor kW Is Only the Starting Point
When selecting a solar pump inverter, obtain the motor nameplate information. At minimum, confirm rated power, voltage, full-load current, frequency, phase and speed. The inverter output current must be suitable for the actual motor and duty.
Two motors with the same kW rating can have different current requirements. The pump load, starting conditions, cable length, site temperature and altitude can also affect drive selection.
Match the Motor Voltage
The inverter output voltage must suit the motor. A three-phase 380 or 400 V motor requires a compatible drive output. Smaller systems may use other motor voltages depending on the pump and inverter family.
Do not assume that any solar pump inverter can operate any pump motor simply because the kW rating looks correct.
PV Array Voltage Matters
Solar pump inverters operate within specified DC input voltage limits. The PV array must be designed so that its operating voltage sits within the inverter's usable MPPT range while its maximum open-circuit voltage remains below the inverter's permitted DC input limit under the coldest expected site conditions.
This means panel quantity and string arrangement cannot be chosen from total wattage alone. Panel Voc, Vmp, Isc, Imp, temperature coefficients and the inverter DC limits all matter.
How Much Solar Capacity Is Needed?
The required PV array depends on the motor power, pump duty, solar conditions, operating hours and inverter requirements. In practice the PV array is normally designed with sufficient capacity to operate the pump across the intended solar window and account for real-world losses.
The correct oversizing ratio is system-specific and should follow the inverter manufacturer's recommendations and the site's solar design calculations.
What Happens in Weak Sunlight?
As solar energy decreases, the inverter may reduce pump speed if the system supports variable-speed operation. Below the minimum usable power or DC voltage, the drive can stop the pump and restart when adequate solar power returns.
This makes solar pumping well suited to applications where water can be stored in a reservoir or tank during daylight rather than requiring constant electrical energy storage.
Do You Need Batteries?
Many solar pumping systems are designed without batteries. Instead of storing electrical energy, they store water in a tank or reservoir and pump when solar energy is available.
Batteries may be appropriate for some projects, but they add cost, maintenance and system complexity. Whether battery storage is required depends on the water demand profile and the required operating philosophy.
Hybrid Solar and AC Operation
Some solar pump inverter systems support a combination of solar and an AC source such as grid or generator power. Hybrid operation can be useful where pumping must continue outside the available solar window or where the solar contribution is intended to reduce grid consumption.
Hybrid capability is model-specific. Confirm the permitted AC and DC input arrangement, changeover philosophy and protection requirements before selecting equipment.
Borehole Pumping
Solar pump inverters are widely used on boreholes. The system may pump directly into a reservoir or elevated tank and stop automatically when the destination is full.
Important borehole considerations include motor current, borehole yield, pump setting depth, total dynamic head, cable length, dry-run protection and the required daily water volume.
Reservoir and Tank Filling
A simple reservoir filling system can use level switches or a level transmitter to start and stop pumping according to the destination level. More advanced systems can use a PLC or telemetry system where several pumps, reservoirs or remote sites must be coordinated.
Control logic should also consider the source water level so that a full destination tank or an empty source can stop pumping safely.
Dry-Run Protection
Running a pump without adequate water can damage the pump and motor. Dry-run protection may use a level probe, float switch, pressure or flow feedback, dedicated dry-run sensor or logic built into the drive.
The appropriate method depends on the type of pump, borehole conditions and available instrumentation.
Long Motor Cables
Borehole motors can be located a significant distance from the inverter. Long motor cables can introduce voltage drop and high-frequency effects from PWM drive output.
Cable size, shielding, earthing and the possible need for an output reactor, dV/dt filter or sine filter should be assessed using the motor and inverter manufacturers' guidance.
Outdoor Installation
The inverter's own enclosure rating may not be sufficient for every outdoor installation. Consider direct sunlight, heat, rain, dust, insects, condensation, corrosion and access for maintenance.
Where a separate enclosure is used, it must provide suitable environmental protection without trapping excessive heat around the drive.
Protection and Isolation
A solar pump system requires appropriate DC and AC protection and isolation. Depending on the design, this can include PV string protection, DC isolators, surge protection, AC protection, motor protection, earthing and lightning protection.
The exact protection scheme must be designed for the specific installation and applicable standards.
Instrumentation and Remote Monitoring
A solar pumping installation can be expanded with pressure, level and flow instrumentation, PLC or RTU control, industrial routers and remote monitoring. This is useful for farms, municipal infrastructure and distributed water systems where operators need to see pump status, reservoir level, alarms or runtime information remotely.
VEICHI SI23 Solar Pump Inverters
Softcore Group Industrial Solutions currently lists VEICHI SI23 solar pump inverter configurations for three-phase water pumping applications. Available models should be selected from the actual motor current, supply arrangement and PV design rather than choosing only the nearest kW value.
For project-specific sizing, provide the complete motor nameplate and PV information so that the appropriate configuration can be checked.
A Practical Planning Checklist
- Motor manufacturer and model
- Motor kW
- Motor rated voltage
- Motor full-load current
- Single-phase or three-phase motor
- Pump type and application
- Borehole depth and pump setting depth where relevant
- Required flow and total dynamic head where known
- Existing PV panel make and model if already purchased
- Panel Voc, Vmp, Isc and Imp
- Number of panels and proposed string arrangement
- Whether AC backup or hybrid operation is required
- Tank or reservoir control requirements
- Dry-run protection requirements
- Approximate motor cable length
- Site location and environmental conditions
Where a project requires PV design, hydraulic calculations, electrical engineering, programming, installation or commissioning, those activities should be completed or verified by appropriately qualified professionals.
Technical Note
This article provides general purchasing and specification guidance. Final inverter selection, PV array design, electrical protection, cable sizing, hydraulic design and installation must be based on the specific equipment, manufacturer requirements, applicable standards and site conditions.
Related catalogue examples: Solar Pump Inverters | Custom Control Panels. For an equipment enquiry, contact Softcore Group Industrial Solutions at info@softcoregroup.co.za.