You've seen them before. Tall metal towers with spinning blades, standing alone in the middle of a dry Karoo farm. They look simple. Almost boring, even.
But here's the thing — that spinning metal tower is solving one of the hardest problems in rural South Africa: how do you get water out of the ground when there's no electricity for 100 kilometres?
The answer is a windmill. And it's a lot cleverer than it looks.
Step 1: The Wind Pushes the Blades
Wind is just air moving from one place to another. Simple, right? But when that moving air hits the blades of a windmill, something interesting happens.
The blades aren't flat — they're angled. And that angle changes everything. Instead of the wind just pushing the blade backwards and stopping, the angled blade gets pushed in a circular motion. It spins.
Windmill blades are shaped almost exactly like aeroplane wings. Hold your hand out of a moving car window — flat, then angled. Feel the difference? That's exactly what makes both planes fly AND windmills spin.
The force that makes angled surfaces move through air is called aerodynamic lift. The angle of a surface relative to the airflow — called the angle of attack — determines how much lift is generated. Windmill blades are shaped as aerofoils to maximise this effect.
Step 2: Spinning Gets Turned Into Pumping
So the blades spin. Great. But spinning blades alone don't pump water. This is where the real magic happens.
At the top of the windmill, the spinning is connected to something called a crankshaft. Think of a bicycle pedal — your legs go in circles, but the wheel moves forward. The crankshaft takes the round-and-round spinning and turns it into an up-and-down motion.
That up-and-down movement travels all the way down a long rod — sometimes 40 metres underground — to where the water is hiding.
A crankshaft converts rotational motion into linear reciprocating motion — turning continuous circular movement into a back-and-forth pumping action. This mechanism appears in car engines, steam trains, and thousands of other machines.
Step 3: The Valve Does the Work
At the bottom of that long rod, deep underground, is a pump with a clever little door called a valve.
When the rod moves up — the valve opens. Water rushes in.
When the rod moves down — the valve closes. The water gets pushed upwards.
Up. Down. Up. Down. And slowly, water climbs all the way from underground to the surface.
South Africa has over 250,000 windmills still in active use. Many are decades old and still pumping perfectly. The most common — the Climax windmill — is manufactured right here in SA, designed for our deep boreholes and dry conditions.
The pump uses a check valve — a one-way valve allowing fluid to flow in only one direction. On the upstroke, low pressure opens the valve and water enters. On the downstroke, high pressure closes it and forces water upward. This is called a positive displacement pump.
The Clever Bit: The Water Tank
A windmill only pumps when the wind blows. So what happens on still days?
Next to almost every windmill is a large water tank. On windy days, the windmill pumps extra water into the tank. On still days, the farmer uses stored water. The windmill and tank work together as a system.
The big idea: The water tank is the windmill's battery. It stores energy — not as electricity, but as water. This is called potential energy storage, and it's one of the oldest and most reliable energy storage systems ever invented.
From Farm Windmill to Wind Turbine
Those giant wind turbines generating electricity near the coast? Same basic idea. Wind spins blades. Blades turn a shaft. The shaft drives something useful — a pump in 1890, a generator in 2026. The physics hasn't changed in over 150 years.
Hold your hand flat out of a moving car window. Feel the air push it back. Now tilt your hand at an angle — feel how it wants to rise or dip? That angle is exactly what makes windmill blades spin. You just felt aerodynamic lift with your own hand.
Now Build One Yourself
The first InventZA Engineering Box features a real working windmill mechanism — a crank, a valve, and a pump. Register your interest to be first to know when it launches.
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