If there's one question that comes up more than any other from Zimbabwe homeowners considering solar, it's this: "Can I run my borehole pump?" The answer is yes — but it's not as simple as plugging it in. Borehole pumps are power-hungry on startup, and getting the setup wrong can trip your inverter or damage equipment. This guide covers motor types, inverter sizing, and the storage tank strategy that makes it all work.
Why Borehole Pumps Are Tricky
Borehole pumps are different from most household appliances in two important ways:
- High startup surge. When an electric motor starts, it draws 3-7 times its rated current for a few seconds. A pump rated at 1.5 kW can pull 5-8 kW during startup. Most household appliances don't have this kind of surge.
- Intermittent but heavy use. Your pump doesn't run all day — it runs for 1-3 hours, fills a tank, and shuts off. But while it's running, it's the single largest load in your house.
This combination — massive startup surge followed by sustained heavy draw — is what makes borehole pumps the most challenging load for residential solar systems.
Motor Types
The first thing to figure out is what kind of pump you have (or plan to install).
AC Submersible Pumps
This is the most common type in Zimbabwe. A standard AC submersible pump sits at the bottom of the borehole, powered by 220V AC from your house. It's reliable, widely available, and any borehole driller can install one.
The challenge: AC motors have the highest startup surge. Your inverter has to handle that surge, plus whatever else is running in the house at that moment.
| Pump Rating | Running Power | Startup Surge (Typical) |
|---|---|---|
| 0.75 kW | 750W | 3 – 5 kW |
| 1.1 kW | 1,100W | 4 – 6 kW |
| 1.5 kW | 1,500W | 5 – 8 kW |
| 2.2 kW | 2,200W | 7 – 12 kW |
DC Solar Pumps
Purpose-built solar pumps run directly on DC power from your panels, bypassing the inverter entirely. They use brushless DC motors with soft-start electronics that eliminate the surge problem. They're more efficient and can run without a battery, but cost 1.5-2x more, require a dedicated controller, and are single-purpose. Fewer local technicians are familiar with them.
AC Pumps with Variable Frequency Drives (VFDs)
A VFD sits between your inverter and the pump. It controls the motor speed electronically and provides a soft start, reducing the startup surge to 1.5-2x rated power instead of 5-7x. This is often the best retrofit option if you already have an AC pump and a solar system.
If you're buying a new borehole pump and already have a solar system, ask your borehole driller about a VFD-compatible pump. The VFD adds about $200-400 to the installation cost but dramatically reduces the inverter size you need.
Inverter Sizing for Borehole Pumps
This is where most people get it wrong. Your inverter needs to handle the surge, not just the running power.
The Rule of Thumb
For AC pumps without a VFD, your inverter's surge rating needs to be 3-5 times the pump's rated wattage. Note: this is the inverter's surge (or peak) rating, which is different from its continuous rating.
| Pump Rating | Minimum Inverter Surge Rating | Typical Inverter Size (Continuous) |
|---|---|---|
| 0.75 kW | 3.0 kW surge | 3 kVA inverter |
| 1.1 kW | 4.5 kW surge | 5 kVA inverter |
| 1.5 kW | 6.0 kW surge | 5 – 8 kVA inverter |
| 2.2 kW | 9.0 kW surge | 8 – 10 kVA inverter |
Most quality 5 kVA hybrid inverters can handle a surge of 10 kW for a few seconds, which covers pumps up to about 1.5 kW. But check your inverter's specification sheet — some budget inverters have poor surge capacity.
Never assume your inverter can handle the surge just because the pump's running wattage is within the inverter's continuous rating. A 1.5 kW pump on a 3 kVA inverter will trip the overload protection on startup every time. The surge is what matters.
With a VFD
A VFD reduces the startup surge to about 1.5-2x the pump's rated power. With a VFD:
| Pump Rating | Startup With VFD | Minimum Inverter Size |
|---|---|---|
| 0.75 kW | 1.1 – 1.5 kW | 3 kVA |
| 1.1 kW | 1.6 – 2.2 kW | 3 kVA |
| 1.5 kW | 2.2 – 3.0 kW | 5 kVA |
| 2.2 kW | 3.3 – 4.4 kW | 5 kVA |
This is a significant difference. A VFD can let you run a 1.5 kW pump on a 5 kVA inverter comfortably, where without it you'd be right on the edge.
The Storage Tank Strategy
Here's the approach that makes borehole pumps and solar work together beautifully: pump and store.
Instead of running your borehole pump on demand (whenever you open a tap), you pump water into an elevated storage tank during peak solar hours and gravity-feed the house from the tank.
How It Works
- Install a storage tank elevated above your house (on a stand, on a hill, or on the roof).
- Set a timer or float switch so the pump runs during peak solar hours (10 AM – 2 PM).
- The pump fills the tank using surplus solar power that would otherwise be wasted or sent to the grid.
- Gravity feeds the house 24 hours a day — no electricity needed for water pressure.
Tank Sizing
The goal is to pump enough water during 2-3 hours of peak sun to supply your household for 24 hours.
| Household Size | Daily Water Usage (Approx) | Recommended Tank Size |
|---|---|---|
| 2 – 3 people | 500 – 800 litres | 1,000 litres |
| 4 – 5 people | 800 – 1,200 litres | 2,500 litres |
| 6+ people | 1,200 – 2,000 litres | 5,000 litres |
| With garden irrigation | Add 500 – 2,000 litres | Size accordingly |
A 2,500-litre JoJo tank on a 2-metre stand gives you a full day's water supply for a typical family, with enough pressure to run taps and showers (gravity provides about 0.2 bar per metre of elevation).
A 2,500-litre tank at 2 metres elevation gives you roughly 0.4 bar of pressure. That's enough for taps and showers but won't power a sprinkler system. If you need more pressure, consider a small booster pump or a higher stand.
The Float Switch
Install a float switch at the top of the tank. When the tank is full, the switch cuts power to the pump. When the water level drops below a threshold, the pump restarts. This automates the whole system — you never need to think about it.
Combined with a timer that only allows pumping between 10 AM and 2 PM, you get a fully automated system that only draws power during peak solar production.
Cable Sizing: The Hidden Problem
Boreholes are often 50-100+ metres from the house. Long cable runs cause voltage drop — the voltage at the pump is lower than the voltage at the inverter. Too much voltage drop means the pump runs inefficiently, overheats, or refuses to start.
Calculating Voltage Drop
The rule of thumb is to keep voltage drop below 5% of the supply voltage (below 11V for a 220V system).
| Cable Run (One Way) | 0.75 kW Pump | 1.1 kW Pump | 1.5 kW Pump |
|---|---|---|---|
| 30 metres | 2.5 mm2 | 4.0 mm2 | 4.0 mm2 |
| 50 metres | 4.0 mm2 | 6.0 mm2 | 6.0 mm2 |
| 80 metres | 6.0 mm2 | 10.0 mm2 | 10.0 mm2 |
| 100 metres | 10.0 mm2 | 10.0 mm2 | 16.0 mm2 |
These are minimum cable sizes. Going one size up is always a good idea for long runs — the extra cost is minimal and it reduces losses and heat.
Undersized cables for borehole pumps are one of the most common installation problems in Zimbabwe. The cable heats up, insulation degrades over time, and eventually you get a fault. Spend the extra money on proper cable sizing. It's buried underground — you don't want to dig it up.
Sizing Example: Typical Zimbabwe Household
Let's put it all together for a common scenario:
The setup:
- 4-person household in Harare
- Existing 5 kVA hybrid inverter with 5 kW of panels
- 80-metre deep borehole, 50 metres from the house
- 1.1 kW submersible AC pump
The solution:
- Install a VFD on the pump (startup surge drops from ~5 kW to ~2 kW — well within the 5 kVA inverter's surge capacity)
- Install a 2,500-litre tank on a 2.5-metre stand near the house
- Set a timer for 10 AM – 1 PM pumping window (3 hours)
- At 3.5 m3/hour flow rate, the pump fills the tank in about 45 minutes
- Float switch cuts the pump once the tank is full
- Use 6.0 mm2 cable for the 50-metre run to the borehole
- Gravity-feed to the house — no electricity needed for water delivery
Daily energy cost: The pump runs for about 45-60 minutes during peak solar, drawing ~1.1 kW. That's roughly 1.0-1.1 kWh — easily covered by surplus solar production at midday.
Dedicated Solar Pump Systems
If you don't yet have a solar system and your primary need is water, a dedicated DC solar pump system may be more cost-effective. These wire 2-4 panels directly to a solar pump controller and a DC submersible pump — no inverter or battery needed. The pump runs when the sun shines (slower on cloudy days, faster on clear days). Pair it with a storage tank sized for 1-2 days and you'll always have water. These systems are popular for rural homesteads where grid electricity is unreliable.
Check Your System
Use SolMate's sizing calculator to see whether your system can handle a borehole pump. Enter your full appliance list including the pump, and the tool will recommend an appropriately sized inverter with enough surge capacity.
Size Your System
Calculate the right panels, batteries, and inverter for your home.
The equipment lookup tool shows each inverter's continuous and surge ratings — the two numbers you need to check before connecting a borehole pump.
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