Savonius Wind Turbine : Darrieus Wind Turbine

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Two fundamental ways how wind turbines catch a passing wind

Many of the modern wind turbines used for both commercial and residential applications are based on the horizontal axis design. While these types of wind turbines can generate a lot of power when properly oriented into the wind, they require a lot of wind to orient them and start them spinning. This means they may not be the perfect solution in a residential setting where the wind is less consistent and tends to change directions often.

A new class of wind turbine construction has emerged for these residential settings based on a vertical axis design and these perform better in these residential settings. A vertical axis wind turbine is not a new concept and in fact all of the original windmills used centuries ago started as vertical axis designs. This type of wind turbine construction fell out of favor when windmills matured into generating electricity because of the lower output supplied by the vertical design.

The main advantage that a vertical axis wind turbine has over a horizontal design is that it does not need to orient itself to spin in response to a passing breeze. It can take full advantage of a wind arriving from any direction and immediately convert this wind into rotation and start generating electricity. This style of turbine is fast becoming the preferred DIY wind turbine design for many homeowners.

Wind turbine constructions following the Savonius and Darrieus concepts

There are two fundamental ways that a vertical axis wind turbine converts a passing wind into rotation and they are either being pushed by the wind, or using the lift the wind provides to turn. A good example of a vertical axis wind turbine that is pushed by the wind is the Savonius wind turbine. This style of vertical turbine uses a series of scoops to catch the passing wind and rotate its central shaft. A Savonius wind turbine is used in situations where reliability is essential since the design provides for a very consistent operation. Several models of recent turbine designs are based on the concepts first introduced with the Savonius wind turbine.

The other popular style of vertical wind turbine is based on lift and a good example of this is the Darrieus wind turbine design. Unlike the Savonius design that relies on blocking the wind to provide the energy for its rotation, the Darrieus wind turbine design uses the lift of the wind to provide rotation. Its blades are engineered to catch the upward thrust of a breeze and will spin in response to this lift.

The challenge with the Darrieus wind turbine design is that it is not a self-starting turbine. This means that it can't generate enough power to start rotating on its own and needs to have a little help getting started. Most of these styles of turbine use a small motor to start this rotation and then the Darrieus wind turbine will spin on it own as long as a breeze is blowing.

Some of the newer versions actually combine the two designs and use a small Savonius wind turbine mounted on the shaft of a Darrieus wind turbine to provide the initial spin and then the lift takes over from there. The advantage that the Darrieus wind turbine has over other models is that its blades can actually spin faster than the wind that is passing. This gives it a very high rotation and is perfect for generating power as a result.