Definition

A Horizontal Axis Wind Turbine (HAWT) is a turbine that its axis of rotates parallel to the ground.

A Vertical Axis Wind Turbine (VAWT) is a turbine that its axis rotates vertically to the ground.

Background Information

• Vertical Axis Wind Turbines vs Horizontal Axis Wind Turbines [View Resource]
  
• Are Vertical Axis Turbines Better? [View Resource]
  
• Wind turbine - Wikipedia [View Resource]
  
• Vertical axis wind turbine [View Resource]
  
• horizontal-axis wind turbine (HAWT) [View Resource]
  
• Differences between Horizontal-Axis and Vertical-Axis Wind Turbines [View Resource]
  
• The main advantage of a vertical-axis wind turbine over a horizontal-axis wind turbine [View Resource]
  
• Vertical & Horizontal Axis Wind Turbines [View Resource]
  
• Vertical or Horizontal Axis Wind Turbines (VAWT or HAWT)? [View Resource]
  

  K-12 Experiments, Labs, Lesson Plans and Science Fair Projects

• Which is more efficient: a Horizontal Axis wind turbines or a Vertical Axis one? [View Experiment]
  
• Determine if multiple rotors will increase the torque of a horizontal axis windmill. [View Experiment]
  
• Determine the effect of the number of blades, pitch and the design of the blades on the electricity produced by a Darrieus-type vertical axis wind turbine at low, medium and high wind speeds. [View Experiment]
  
• Science Fair Wind Generators [View Experiment]
  
• How to Build a Wind Turbine for Your Science Fair? [View Experiment]
  
• Determine how much power a pinwheel generates at different orientations to a wind source. [View Experiment]
  

  College Experiments, Labs, Studies and Articles

• The Case for Vertical Axis Wind Turbines [View Experiment]
  
• Optimal Pitch for Untwisted Blade Horizontal Axis Wind Turbine [View Experiment]
  
• Performance Evaluation of Curved Blades Vertical Axis Wind Turbine [View Experiment]
  
• Yaw Dynamics of Horizontal Axis Wind Turbines: Final Report [View Experiment]
  
• The Mechanical Design, Analysis, and Testing of a Two-Bladed Wind Turbine Hub [View Experiment]
  

  Theses and Dissertations

• Optimization of a Savonius Rotor Vertical-Axis Wind Turbine for Use in Water Pumping Systems in Rural Honduras [View Thesis]
  
• Pitch Control of Horizontal Axis Wind Turbine [View Thesis]
  
• Experimental investigation of the performance of a diffuser-augmented vertical axis wind turbine [View Thesis]
  

  Patents

• Coupled vortex vertical axis wind turbine (US Patent 6784566, 2004) [View Patent]
  
• Vertical-axis wind turbine with a twisted blade configuration (US Patent 5405246, 1995) [View Patent]
  
• Modular wind energy device (US Patent 6481957, 2002) [View Patent]
  
• Vertical axis wind turbine with articulating rotor (US Patent 7677862, 2010) [View Patent]
  

  See Also

• Wind Turbine Design [View Experiment]
  
• Build Your Own Windmill [View Experiment]
  

HAWT advantages

• Blades are to the side of the turbine's center of gravity, helping stability.
• Ability to wing warp, which gives the turbine blades the best angle of attack. Allowing the angle of attack to be remotely adjusted gives greater control, so the turbine collects the maximum amount of wind energy for the time of day and season.
• Ability to pitch the rotor blades in a storm, to minimize damage.
• Tall tower allows access to stronger wind in sites with wind shear. In some wind shear sites, every ten meters up, the wind speed can increase by 20% and the power output by 34%.

HAWT disadvantages

• HAWTs have difficulty operating in near ground, turbulent winds.
• The tall towers and long blades up to 90 meters long are difficult to transport on the sea and on land. Transportation can now cost 20% of equipment costs.
• Tall HAWTs are difficult to install, needing very tall and expensive cranes and skilled operators.
• The FAA has raised concerns about tall HAWTs effects on radar near Air Force bases.
• Their height can create local opposition based on impacts to viewsheds.
• Downwind variants suffer from fatigue and structural failure caused by turbulence.

VAWT advantages

• Can be easier to maintain if the moving parts are located near the ground.
• As the rotor blades are vertical, a yaw device is not needed, reducing cost.
• VAWTs have a higher airfoil pitch angle, giving improved aerodynamics while decreasing drag at low and high pressures.
• Straight bladed VAWT designs with a square or rectangular crossection have a larger swept area for a given diameter than the circular swept area of HAWTs.
• Mesas, hilltops, ridgelines and passes can have faster winds near the ground because the wind is forced up a slope or funnelled into a pass and into the path of VAWTs situated close to the ground.
• Low height useful where laws do not permit structures to be placed high.
• Does not need a free standing tower so is much less expensive and stronger in high winds that are close to the ground.
• Usually have a lower Tip-Speed ratio so less likely to break in high winds.
• Does not need to turn to face the wind if the wind direction changes making them ideal in turbulent wind conditions.
• They can potentially be built to a far larger size than HAWT's , for instance floating VAWT's hundreds of meters in diameter where the entire vessel rotates , can eliminate the need for a large and expensive bearing.
• There may be a height limitation to how tall a vertical wind turbine can be built and how much sweep area it can have. However, this can be overcome by connecting a multiple number of turbines together in a triangular pattern with bracing across the top of the structure . Thus reducing the need for such strong vertical support, and allowing the turbine blades to be made much longer.

VAWT disadvantages

• Most VAWTs produce energy at only 50% of the efficiency of HAWTs in large part because of the additional drag that they have as their blades rotate into the wind. This can be overcome by using structures to funnel more and align the wind into the rotor (e.g. "stators" on early Windstar turbines) or the "vortex" effect of placing straight bladed VAWTs closely together (e.g. Patent # 6784566).
• Most VAWTS need to be installed on a relatively flat piece of land and some sites could be too steep for them but are still usable by HAWTs.
• Most VAWTs have low starting torque, and may require energy to start the turning.
• A VAWT that uses guy wires to hold it in place puts stress on the bottom bearing as all the weight of the rotor is on the bearing. Guy wires attached to the top bearing increase downward thrust in wind gusts. Solving this problem requires a superstructure to hold a top bearing in place to eliminate the downward thrusts of gust events in guy wired models.
• While VAWTs' parts are located on the ground, they are also located under the weight of the structure above it, which can make changing out parts near impossible without dismantling the structure if not designed properly.