Solar Pump Inverters Explained: Keep Your Borehole Running Without Grid Power
Load shedding doesn't care whether your borehole, irrigation system or livestock trough needs water right now. If your pump only runs on mains power, every outage is a water outage too. A solar pump inverter solves that by letting the same pump run directly off a solar array during the day and switch to grid power automatically when it isn't — no batteries required. Here's how it works, and how to size one from UTC Industrial's VEICHI range.
What is a solar pump inverter?
A solar pump inverter is a variable frequency drive purpose-built to run a standard AC pump motor from a DC solar array, AC mains, or both. Unlike a general-purpose VSD, it's designed around two things a normal drive doesn't need to handle: converting DC solar input into the 3-phase AC output a pump motor expects, and automatically switching between solar and grid power as sunlight changes through the day — without you flipping a switch or the pump stopping and restarting.
The core piece of technology that makes this efficient is MPPT (Maximum Power Point Tracking) — the inverter continuously adjusts how it draws power from the solar array to extract the maximum available energy at any given light level, rather than just taking whatever the panels happen to be producing at a fixed voltage. That's the difference between a pump that struggles on a cloudy morning and one that keeps running at reduced but usable output.
How it keeps a pump running through load shedding
Because a hybrid solar pump inverter accepts both a DC array input and an AC mains input, the pump isn't dependent on either source alone:
- During daylight, it draws from the solar array — free running cost, no grid dependency.
- When sunlight drops (cloud cover, evening, load shedding on the grid side of things), it switches automatically to AC mains, if available, so the pump keeps running.
- Sleep/wake control lets the drive idle down in low-flow or low-light conditions and restart automatically once conditions recover, rather than tripping out and needing a manual reset.
- Dry-run protection stops the pump if the borehole or source runs low, protecting the motor from running dry — a common cause of premature pump failure on unattended sites.
For a borehole, irrigation block or livestock watering point that can't have someone on-site to reset equipment after every outage, that automatic handover is the actual value — not just the solar power itself.
The VEICHI range: Si21 and Si23
UTC Industrial stocks two VEICHI solar pump inverter series, sized differently for different jobs:
Si21 series — the higher-power range, from 1.5kW up to 7.5kW+, in 150–450VDC and 250–750VDC solar input variants (recommended array open-circuit voltage 360–430VDC), with 3-phase AC output up to 599Hz. Built for larger boreholes, bigger irrigation pumps, and sites with a substantial panel array already in place or planned.
Si23 series — the compact, cost-effective range, from 0.75kW up to 5.5kW, available in both a 220V single-phase-input/150–450VDC solar variant and a 380V three-phase-input/250–750VDC solar variant, with 3-phase AC output up to 320Hz. Suited to smaller domestic, livestock and market-garden pumping jobs where a lower-cost entry point matters more than headroom for future expansion.
Both series share the same core protections — dry-run, overload, over/under-voltage and phase-loss protection — so the choice between them comes down to motor size and available input voltage, not one being a "better built" option than the other.
Sizing one for your site
Three numbers decide which unit you need:
- Pump motor rating (kW) and rated current (A) — from the motor's own nameplate. The inverter's output current must be able to supply the motor's full-load current.
- Available input power — do you have single-phase or three-phase AC mains at the site (for the hybrid AC/DC switchover), and what's your solar array's open-circuit voltage?
- Application — irrigation and livestock watering can usually tolerate output dropping with the sun; a domestic supply pump feeding a tank generally can't, so mains backup availability matters more there.
If you're not sure which of these apply, send us the pump motor's nameplate details and what power sources are available on-site, and we'll confirm the right Si21 or Si23 unit before you order.
Common applications
- Agricultural irrigation, particularly on farms already running or planning a solar installation
- Livestock watering points in areas with unreliable or no grid connection
- Remote borehole pumping where running mains power to the site isn't practical
- Domestic and small-scale water supply pumps that need to keep running through load shedding
Quick FAQ
Do I need batteries for a solar pump inverter? No. Both the Si21 and Si23 series run directly off the solar array's DC output during the day and switch to AC mains when needed — no battery bank required, which keeps the system simpler and cheaper than a full solar-battery setup.
What happens at night or on a heavily overcast day? If AC mains is connected, the inverter switches over automatically and the pump keeps running on grid power. Where no mains connection exists, the pump runs only when there's sufficient solar input.
What's the difference between the Si21 and Si23 series? Mainly power range and output frequency: Si21 covers larger motors (1.5kW and up, output to 599Hz) while Si23 is the compact range (0.75kW–5.5kW, output to 320Hz) with a lower-cost entry point. Match the series to your motor's kW rating first.
Can I use my existing borehole pump and motor? In most cases, yes — the inverter is matched to the motor's kW rating and phase, not a specific pump brand. Send us the motor nameplate details to confirm before ordering.
Browse the full VEICHI Solar Pump Inverter range, in stock from our Pretoria East warehouse and shipped nationwide via The Courier Guy. Not sure which size or series fits your pump and solar setup? Contact us with your motor's nameplate details and your available power sources, and we'll confirm the right unit before you order.