Solar for Boreholes and Pumping Machines in Nigeria

Almost every system we are called out to fix has the same story attached. Everything works, until somebody turns on the pump.

The lights are fine. The freezer is fine. Then the borehole starts and the whole house drops out, on a battery that is showing three quarters full.

There is one idea behind all of it, and once you have it, everything about pumps and solar makes sense.

A motor does not start gently

Your pump might be rated 1.5 horsepower, which is a bit over a kilowatt. That is what it draws while running, and it is the number on the label.

But starting is different. To get a stationary motor and a column of water moving, it pulls a surge that can be three to seven times its running figure, for a second or two. So a pump that runs at 1.1kW can demand five or six kilowatts at the instant it kicks in.

Your battery has that energy. The question is whether your inverter can deliver it that fast, and if it cannot, it protects itself and drops the load. Which looks, from inside the house, exactly like a flat battery.

Why the battery gets blamed

This is the misdiagnosis that costs people money.

The system trips, somebody says the battery is weak, and a perfectly healthy battery gets replaced. Then it happens again with the new one, because the battery was never the problem.

So the test is simple. If it trips the instant the pump starts, and the battery is showing plenty, that is surge and the inverter is too small for it. If it runs the pump fine but the battery is empty by morning, that is capacity, and it is a different conversation. The difference shows up on the display, which is why our post on what your inverter is telling you is worth reading alongside this.

What actually sizes a system with a pump

Three numbers, and only one of them comes from your meter.

The surge sets the inverter. Take the pump’s running wattage, multiply by four as a working assumption, and that is the floor for what the inverter must handle instantaneously.

The run time sets the daily energy. A pump filling a tank for forty minutes a day uses far less than people fear, because it is the surge that hurts, not the running.

The tank is the part nobody mentions, and it is the cheapest lever you have. A bigger overhead tank means the pump runs less often, which means less starting, which is where all the stress is.

Run it in daylight, if you possibly can

Here is the trick that changes the economics of this entirely.

Pump during the day and the panels carry most of it directly. The surge still goes through the inverter, so that still has to be sized properly, but the energy comes from the sun rather than out of the battery you were saving for the night.

Filling the tank between ten and three costs you almost nothing. Filling it at nine in the evening comes straight out of your night. Same water, very different system.

Soft starters, and when they earn their place

A soft starter ramps a motor up instead of throwing it straight to full power. It cuts the surge substantially, and on a big pump it can be the difference between needing a much larger inverter and not.

On a small household pump it is usually cheaper to size the inverter properly. On a farm borehole, or anything three phase, it is often the sensible answer. Which one applies to you depends on the pump, and anybody who recommends one without asking what you have is guessing.

Farms and businesses are a different scale, not a different problem

We have put systems on farms where the borehole is the single biggest load on the property, well past anything a house would run.

The arithmetic does not change. Surge sizes the inverter, run time sizes the energy, storage smooths it out. What changes is that the cost of the pump not running is much higher, so the design has to be more conservative. Our webinar on why solar disappoints people here covers what undersizing looks like from the inside, and the replay is free.

Tell us the pump, not the house

If you are getting quoted for a system with a borehole on it, the first question out of the installer should be about the pump. Its rating, whether it is single or three phase, whether it is submersible or surface, how long it runs, and what size tank it fills.

If nobody asks any of that, they are sizing your house and hoping the pump fits. It will not.

So when you message us, lead with the pump. Send us the plate details on WhatsApp on +234 809 988 9885, or a photo of the label, and we will tell you what it takes to run it before we talk about anything else in your house.