Nearly every wind turbine in the world looks like an airplane propeller stuck on a pole. But there's a second family that looks nothing like that, and it is almost a hundred years old.
A vertical axis wind turbine, or VAWT, looks more like an egg beater or a giant whisk standing up. The blades wrap around an upright pole and spin like a merry-go-round, so wind from any direction turns it the same way. It doesn't need to orient itself into the wind first.
They're the underdog of wind power. But in the right spot, especially where wind is messy, a vertical axis turbine is the smarter design.
What Is A Vertical Axis Wind Turbine?
It's a wind turbine whose main shaft stands straight up instead of lying on its side. The wings are fixed to the top and the bottom of that vertical rotor, and the whole machine spins with it.
Compare that with the propeller kind, which engineers call horizontal axis wind turbines (HAWTs). They spin on a sideways shaft high up on a pole, the way a fan does. Nearly all working wind turbines today are horizontal axis machines.
So a vertical axis wind turbine is the same idea, turned on its end, and it works without having to face the wind.
How A VAWT Turns Wind Into Power
As the blades swing around, the wind pushes on them. Half the rotor is moving with the wind and getting shoved forward, while the other half is coming back against it. The push on one side beats the push on the other, and that keeps the rotation going.
That rotation is mechanical energy, the same kind as a bike wheel turning. The vertical shaft carries it down to a generator, which converts mechanical energy into electricity. Inside, copper wire spins through a magnetic field, and electricity flows out.
On a propeller turbine, the generator, gearbox and brake sit in a box called the nacelle, high up on top. To fix them, someone climbs. On a vertical axis wind turbine, the heavy parts can sit at the base, at ground level. That lowers the centre of gravity and makes maintenance a ground level job.
A VAWT has the same core parts as any wind turbine: a rotor that spins, a shaft down to the generator, a control system that watches rotor speed and slows or stops the rotor in a storm, and a support structure. The wings pull and push in turns, so the structure has to handle sideways forces, not just weight.
What Are The Different Types Of Vertical Wind Turbines?
There are two main designs, and each catches wind its own way.
Darrieus wind turbines look like a giant two-bladed egg beater. The curved wings arc out from the top and bottom of the pole. French engineer Georges Darrieus filed his patent in the 1920s, and he got the US patent in 1931. The blades have an aerodynamic shape, like bird wings, so they use lift: air flowing over a curved blade pulls it forward, like a plane wing. That makes a Darrieus the efficient one. Its weak spot is getting going: at low rotor speed the wings create very little turning force, so it often needs help.
Savonius wind turbines look like a barrel cut in half lengthwise, with the two halves shifted apart. Finnish engineer Sigurd Savonius patented his rotor in the 1920s too. A Savonius uses drag: the wind simply shoves the cupped side harder than the rounded side, like wind catching an open umbrella. Savonius claimed it "starts under load from any position", which is its big trick. The cost is efficiency, because drag pulls less power out of the wind than lift.
So what do engineers do? They combine them. A hybrid design puts a small Savonius in the middle to get things spinning, with Darrieus blades outside to produce the power.
How Do Vertical And Horizontal Axis Turbines Differ?
The big difference is the pole. A vertical axis turbine spins on an upright pole and takes wind from any direction, while a horizontal axis turbine spins on a sideways axle and has to turn to face the wind. Here's how that plays out.
| Vertical axis (VAWT) | Horizontal axis (HAWT) | |
|---|---|---|
| Shaft | Stands up | Lies sideways, high up |
| Wind direction | Any direction, no turning needed | A yaw drive turns it to face the wind |
| Generator | Can sit at the base | In the nacelle on top |
| Turbulence | Less sensitive | More sensitive |
| Efficiency | Lower | Higher |
| How common | Very few in use | Nearly all turbines |
The honest truth: a HAWT pulls more energy out of the same wind. One review puts the best aerodynamic efficiency of VAWTs some 15 to 25% below the best HAWTs, and that's why wind farms use propellers. The rotor of a VAWT also gets pushed and pulled on every rotation, and that repeated wobble tires the mechanical parts over time.
But VAWTs win where wind is messy. In urban areas, wind bounces off every building, swirls and keeps changing direction. That's called turbulence. A propeller turbine has to keep turning to chase it, while a VAWT just keeps spinning. Easy repairs and messy-wind skills are the main advantages. The fuller list is on our page about the advantages of vertical axis wind turbines.
Where VAWTs Get Used
Most applications are small machines close to people, where a big propeller would not fit.
Rooftops and cities. In 2015, two vertical axis turbines went up on the Eiffel Tower, about 400 feet above the ground, where they catch wind from any direction. They ran almost silently, right next to a restaurant.
Hybrid setups. In off-grid applications, paired with solar panels and a battery bank, a small VAWT can add power at night and on stormy days when the panels are resting. More examples are on our page about vertical axis wind turbine applications.
Is A Vertical Axis Wind Turbine Right For Your Home?
It can be, if your site gets steady wind and you have a clear spot for it. Small VAWTs typically make modest amounts of power, so check three things before you buy.
Wind. Even a VAWT needs wind. A propeller turbine's controller typically lets it start at a wind speed of about 7 to 11 miles per hour, so below that there is no power at all. And a UK study found turbines on town and suburban houses made no more than 200 kWh a year. That's a tiny output. Check your site across a full year with is there enough wind on my site, then work out what size wind turbine you need.
Site. A free-standing spot away from obstacles is more suitable than a roof, and higher is better.
Rules. Many towns require a permit and limit height, noise and how close a turbine may stand to the property line, so check before installation. Our guide to vertical axis wind turbine installation walks through it.
To see what a turbine could add up to over a year, try the yearly kWh calculator.
Where VAWTs Are Heading
The crazy part is that the biggest plans for VAWTs are out at sea. Sandia National Laboratories, which has studied them since the 1970s, is designing floating VAWTs as one of its solutions for deep water. With the heavy parts low down, the whole machine sits more steadily on the water.
Others are working on smarter blade designs, including hybrid blades that need no push to get going. See where it's going in the future of vertical axis wind turbines.
VAWTs won't take over wind power for home or anywhere else. But anywhere the wind is messy and changes direction around you, they're a good choice.
Sources
- US Energy Information Administration, Types of wind turbines
- US Department of Energy, How a wind turbine works (text version)
- US Department of Energy, Sandia work to reduce the cost of deep-water offshore wind
- Sandia National Laboratories, Vertical-axis wind turbines for offshore wind energy
- Google Patents, US1835018A, Darrieus turbine with transverse rotating shaft
- Google Patents, US1697574A, Savonius rotor adapted to be driven by wind or flowing water
- Celik et al. 2023, Hybrid blade design and self-starting of an H-type Darrieus wind turbine
- Wind-Works, Market, cost and technical analysis of vertical and horizontal axis wind turbines
- ASME, The Eiffel Tower goes green
- University of Southampton, UK's best locations for domestic wind turbines (Energy Saving Trust study)
Hard Words
| Term | What it means |
|---|---|
| VAWT | Vertical Axis Wind Turbine. An egg-beater-shaped turbine that spins around an upright pole. |
| HAWT | Horizontal Axis Wind Turbine. The propeller kind, spinning on a sideways shaft high up. |
| Darrieus turbine | A VAWT with curved, wing-shaped blades. Efficient, but needs help to get going. |
| Savonius turbine | A VAWT shaped like a barrel cut lengthwise. Catches wind by drag and starts on its own. |
| Drag | Wind pushing directly against a surface. How a Savonius captures energy. |
| Lift | The pull on a wing-shaped surface as air flows over it. How a Darrieus captures energy. |
| Nacelle | The box on top of a propeller turbine that holds the generator, gearbox and brake. |
| Yaw drive | The motor system that turns a propeller turbine to face the wind. A VAWT doesn't need one. |
| Turbulence | The messy, swirling wind in towns and near obstacles. Hard on HAWTs, easier on VAWTs. |
Common Questions
What is a vertical axis wind turbine?
A wind turbine whose main shaft stands straight up. The blades wrap around that upright pole and spin like a merry-go-round, so wind from any direction turns it.
What's the difference between Darrieus and Savonius?
A Darrieus has curved, wing-shaped blades and uses lift. It is efficient but slow to get going. A Savonius is barrel-shaped and uses drag. It starts on its own but pulls less power from the wind. Hybrids combine both.
Is a vertical axis wind turbine good for a home?
It can be, if your site has enough wind across the year. Turbines on houses in towns often make very little power, so a free-standing spot clear of obstacles is better.
How big of a wind turbine is needed to power a house?
It depends on how much electricity your home uses and how windy your site is, so there is no single answer. Start with your yearly use, then use our wind turbine sizing guide.