A Fan Spun By Water
A water turbine is a fan that gets spun by water instead of air.
Aim moving water at curved blades and they rotate. Connect them to a generator, and out comes electricity. Scientists say the turbine converts the kinetic energy of moving water (the energy of motion) into mechanical energy, which is a fancy name for spinning, and the generator converts that into electric energy.
Open up a small hydro turbine and the basic components include the same pieces every time. Here is what each one does.
The Parts Of A Water Turbine At A Glance
| Part | What it does | Where you find it |
|---|---|---|
| Nozzle | Squeezes water into a fast jet | Impulse turbines (Pelton, Turgo, cross-flow) |
| Wicket gates | A ring of vanes that sets how much water gets in | Reaction turbines (Francis, Kaplan) |
| Runner | The spinning wheel with blades, buckets or vanes | Every turbine |
| Shaft | Carries the spin from the runner to the generator | Every turbine |
| Bearings | Let the shaft spin smoothly and stay in line | Every turbine |
| Generator | Turns spinning into electric energy | Every hydro system |
| Casing | Holds the water in and protects the moving parts | Splash guard on impulse, sealed shell on reaction |
| Draft tube | A widening pipe after the runner that wins back energy | Reaction turbines |
| Load controller | Keeps the speed and voltage steady | Most micro hydro systems |
Where The Water Comes In: Nozzle And Wicket Gates
Water arrives from your stream or river through a pipe called the penstock. What happens next depends on the turbine design.
In an impulse turbine, the pipe ends in a nozzle. It turns slow water under pressure into a fast jet, like your thumb over a garden hose.
A reaction turbine has no jet. The water flow is channeled through a curly scroll case and then through wicket gates, a ring of little vanes around the runner. They set the amount of water that gets in. On a Kaplan, the gates and the blades can both adjust, so it copes with a river that changes through the year.
→ The full story of intakes, pipes, and what feeds the turbine
The Turbine Runner
The runner is the spinning wheel inside the turbine, the heart of the whole machine.
A Pelton wheel carries metal cups called buckets, a Kaplan looks like a ship's propeller, and a Francis has a ring of fixed, curved blades, usually nine or more.
In an impulse turbine, the jet slams directly into each bucket and the push makes the runner rotate. Think of a kid blasting a paddleboat with a garden hose.
In a reaction turbine, the runner sits fully under water, and the flow and pressure push on the blades together to make it rotate.
To compare every shape side by side, see the types of water turbines and when each one fits.
The Shaft And The Bearings
The shaft is the metal rod that carries the spin from the runner to the generator. It has to turn perfectly straight for years, because a wobble wears out the bearings.
Bearings are rings of small steel balls or rollers that the rod rides on. Picture a skateboard wheel: the bearings inside let it continue rolling after you push off.
Giant turbines in a hydroelectric power plant float their heavy spindles on a film of oil instead, while small home turbines use ball or roller bearings that need grease.
In a home system, the bearings are what usually wears out first. Check them during the yearly service, and replace them when they whine or grind.
→ What yearly maintenance actually looks like
The Hydroelectric Generator
A generator is a magnet spinning inside a coil of wire. In 1831 Michael Faraday found that moving a magnet near a wire makes electricity flow in it, and every generator still uses that trick, from a car alternator to the giant machines inside dams.
The rod from the runner turns the magnet, directly or through a belt. The faster it spins, the higher the voltage it can produce, so the speed has to stay steady.
The Casing And The Draft Tube
The casing is the metal shell around these components.
On a Pelton the casing is mostly a splash guard, because the jet hits the buckets in open air.
A Francis or Kaplan is different. Its casing has to be sealed, because the water inside is under pressure. Behind the runner sits a draft tube, a pipe that gets wider as it goes down. It slows the leaving water and wins back energy that would otherwise be lost. Impulse turbines do not need one.
Keeping The Speed Steady: Governor Or Load Controller
When you switch off the lights, your generator suddenly has less work to do, so it would speed up.
Big hydropower stations use a governor that opens and closes the gates to match the water flow to the power people need.
Most micro hydro systems do it the other way around. The same volume of water keeps flowing directly through the turbine, and an electronic load controller sends any spare power to a ballast load, usually an electric heater in water or air. When your house needs less, the heater gets more, and the turbine never notices. People call that a dump load, and it can provide free warm water.
Micro Hydro Power: From Turbine To House
Coming out of the generator are the output wires. A battery-based system often sends the power into a battery bank as a buffer, and then through an inverter, a translator box that changes the battery's DC into the AC your appliances expect.
By the time it reaches your light switch, the fridge has no idea a river made it.
Micro hydro means systems smaller than 100 kilowatts, which covers almost every home hydro turbine you could install. Still deciding on size? Compare micro hydro vs pico hydro.
How Much Electricity Can I Generate From A Water Turbine?
It depends on two factors: head, the height the water falls, and flow, the volume of water passing each second. More of either means more power, and the third factor is efficiency.
The rough rule is 9.8 × head in meters × flow in liters per second × efficiency gives you watts. Most micro hydro systems reach 50 to 70 percent efficiency once you count the pipe, turbine, generator and wires, so the output you get is always less than the energy available in the stream. Run your own numbers with the hydro power calculation guide.
Why The Design Matters
A well-made Pelton can turn about 90 percent of the water's energy into spinning, even at micro hydro size. Put the wrong runner on your stream, though, and it will produce much less.
That is why your location decides the design, not the other way around. One kind wants a big drop and little water, while a Kaplan wants a low drop and lots of water. Match the wheel to the water available, and every part in this article gets to do its job.
→ How hydro compares to solar and wind → Back to the full hydro overview
Sources
- Wikipedia, Water turbine
- US Department of Energy, Types of Hydropower Turbines
- US Department of Energy, How Hydropower Works
- Wikipedia, Electromagnetic induction
- Wikipedia, Draft tube
- energypedia, Control Equipment, Hydropower
- energypedia, Micro Hydro Power Plant, Turbine Types
- Government of Ontario, Micro-hydro systems
- US Department of Energy, Planning a Microhydropower System
- Wikipedia, Hydroelectricity
- Renewables First, Pelton and Turgo turbines
Hard Words
| Term | What it means |
|---|---|
| Rotor | Another name for the runner, the spinning wheel inside the turbine. |
| Blade | The curved piece on the runner that catches the water. Its shape depends on the stream. |
| Shaft | The metal rod that carries mechanical energy from the runner to the generator. |
| Bearings | Rings of small steel balls or rollers that let the rod spin without wobbling. The most common wear part. |
| Impulse turbine | A turbine where a fast jet from a nozzle hits the buckets, like a Pelton wheel. |
| Reaction turbine | A turbine sitting fully in water, pushed by flow and pressure together. Francis and Kaplan are reaction turbines. |
| Generator | A magnet spinning inside a coil of wire, the effect Michael Faraday found in 1831. |
| Governor | A device that adjusts the water going into the turbine to keep its speed steady. |
| Casing | The metal shell around the turbine. A splash guard on impulse turbines, a sealed shell on reaction turbines. |
| Inverter | A box that changes DC from the battery into the AC power your appliances expect. |
Common Questions
What are the main parts of a water turbine?
The nozzle or wicket gates that let water in, the runner with its blades, the rod and bearings, the generator, the casing, a draft tube on reaction turbines, and a load controller.
What's the difference between impulse and reaction turbines?
An impulse turbine is hit by a fast jet in open air. A reaction turbine sits fully under water in a sealed casing and is pushed by flow and pressure together.
Why does the blade shape matter so much?
A good runner matched to the stream can turn about 90 percent of the water's energy into spinning. The wrong one lets much of it slip past.
How does a magnet make electricity?
Moving a magnet near a wire makes electricity flow in it, as Faraday found in 1831.
What wears out first?
Almost always the bearings. Replace them when they whine or grind.
What does a load controller do?
It keeps the generator's speed and voltage steady by sending power your house does not need to a heater, called a dump load.
What does the casing do?
It holds everything in and protects the moving parts: a splash guard on impulse turbines, a sealed shell on reaction ones.