This guide explains the technology: MPPT, voltage limits and motor compatibility. For the buying checklist and application requirements, see How to Choose a Drive for Boreholes and Water Pumping.
A solar pump inverter lets an AC pump run directly from solar panels, without batteries. It is one of the simplest ways to move water on a farm, borehole or remote site, but it is not the same product as an ordinary variable speed drive, and choosing the wrong one is a common and expensive mistake.
This guide explains what a solar pump inverter does, how it works, and what the main specifications mean.
What Is a Solar Pump Inverter?
Browse our solar pump inverter collection for listed models. Final selection still depends on the motor, array and exact drive rating.
A solar pump inverter converts photovoltaic (PV) DC power into controlled AC power for a compatible pump motor. It adjusts motor speed as solar power changes. Pump delivery depends on both available power and the pump's hydraulic duty; below the speed needed to overcome the system head, little or no water may be delivered.
Many industrial versions drive three-phase motors, while some models support other motor types. Match the exact inverter to the motor, rather than assuming any AC pump is compatible. AC backup capability, automatic changeover and simultaneous AC/PV operation are separate features that must be confirmed for the supplied model.
How Is It Different From an Ordinary VSD?
An ordinary VSD is designed for a stable AC supply. A solar pump inverter is designed for a DC source that changes constantly. The differences include:
- DC input: it accepts a high-voltage DC input from the PV array, typically several hundred volts.
- MPPT: it continuously adjusts the load to extract as much power as the panels can deliver at that moment.
- Pump-specific protection: dry-run, low-speed and related functions may be available; confirm the model, sensors and commissioning requirements.
- Solar start and stop logic: it starts and stops the pump sensibly at sunrise, sunset and passing cloud.
An ordinary VSD can be fed from a DC source only if it is specifically designed for it. A standard AC drive should not be connected directly to a PV array.
What Is MPPT?
MPPT stands for maximum power point tracking. The power a panel array can deliver depends on the sunlight and the panel temperature, and the best operating point changes all day. An MPPT drive adjusts the pump speed so that the array works close to its maximum power point. This is what lets a pump run at the best speed the available sun allows.
DC Input Range
Three different voltage specifications matter. They are not interchangeable:
- Vmp: the array's voltage while producing power. It must meet the drive's operating and MPPT requirements, including when the panels are hot.
- Voc: the open-circuit voltage. Compare it with the manufacturer's recommended string-design guidance.
- Absolute maximum DC input: the limit that must never be exceeded. Calculate string Voc at the lowest design temperature, allowing for panel tolerances.
Series-connected panels add voltage; parallel strings add current. Check maximum PV power and current as well as voltage. A broad voltage range in a product title is not a string-design instruction. Use the complete model number and matching manual revision, and resolve conflicting documents before ordering.
Motor Voltage and Output
Solar pump inverters are built for a stated motor voltage class, commonly 380 V three-phase, and some ranges also offer 220 V versions with a lower DC window. The motor, the pump and the inverter output voltage must all match.
Protection Functions
Typical protections on a solar pump drive include overload, short circuit, over-temperature, under- and over-voltage, and pump-specific functions such as low-speed or dry-run detection. Exactly what is included depends on the model, so check the datasheet and do not assume.
Do You Need Batteries?
Direct solar pumping can operate without batteries. A tank or dam stores water for later use, provided its capacity and the downstream delivery arrangement suit the demand. If pumping must continue at night, grid or generator backup may be an option. A battery solution requires compatible conversion equipment and a separate design; batteries must not be connected directly to a pump drive unless the manufacturer explicitly permits that arrangement.
Sizing Considerations
A pump inverter is sized by the pump motor it drives, and the array is sized for that motor with some allowance. The key inputs are the motor kW and rated current, pump flow and head, the array configuration, and the site conditions. A full sizing walk-through is in our article on sizing a solar pump system for a borehole.
Communications and Monitoring
Related equipment is available in our PLC collection and routers and gateways collection. Check interface and software compatibility before ordering.
An RS-485 port may provide data through a protocol such as Modbus RTU. A compatible controller or gateway, register mapping, communications equipment and viewing software are needed to turn those values into remote monitoring. Confirm which values the exact model exposes. Estimated flow from a drive is not the same as measured water delivery.
Common Mistakes
- Using a standard AC drive on a PV array
- Forgetting the cold-weather Voc increase when sizing strings
- Mismatching the drive to the motor voltage
- Oversizing the array far beyond what the drive can use
- Forgetting DC isolation, surge protection and proper earthing
- Leaving out dry-run and tank-full protection
Technical Note
This article provides general information only. PV array design, electrical protection, earthing, pump selection and installation must be assessed for the specific site, in accordance with manufacturer documentation and applicable standards, and carried out by competent persons.
Related catalogue examples: Solar Pump Inverters | Custom Control Panels. For an equipment enquiry, contact Softcore Group Industrial Solutions at info@softcoregroup.co.za.
Technical Resources
- VEICHI SI23 manufacturer information
- VEICHI SI21 manufacturer information
- Slanvert Hope65-SPD manufacturer information
- Technical resources and manuals
Use the documentation for the exact supplied model and revision. Family documents can cover ratings and options that do not apply to every unit.
Related Articles
- How to Size a Solar Pump System for a Borehole
- Choosing a Solar Pump Inverter: Veichi SI23, Veichi SI21 and Slanvert Hope65
Selected Product Listings
- VEICHI SI23 2.2 kW listing — confirm the supplied model and ratings before selection.
- VEICHI SI21 2.2 kW listing — confirm the supplied model and ratings before selection.
- Slanvert Hope65 Solar 2.2 kW listing — confirm the supplied model and ratings before selection.