What Is the Most Efficient Design for a Small Vertical Axis Windmill?

Wind is one of the most cost-effective, renewable energy sources. The majority of windmills used have a horizontal axis, yet vertical axis designs are also possible. They typically have lower operating costs and ease of maintenance, which makes them more suitable for household use. There are many vertical axis designs available. Choosing the most efficient design will ensure maximum benefits.

Vertical Axis

• Vertical axis windmills operate via either the wind lift or wind drag principle. They are unaffected by wind direction as the blades rotate according to whichever direction the wind is blowing. They are also able to withstand turbulence. These properties allow vertical axis windmills to be built smaller and closer to the ground.

Drawbacks

• A number of vertical axis windmills are unable to self-start due to a low start-up torque. Also, in most vertical axis windmills, the blade needs to be dragged back through the wind with each half rotation. This decreases its efficiency when compared to a horizontal axis windmill. Despite its residential suitability, vertical axis windmills are not readily available for home purchase, hence its popularity as a do-it-yourself project.

Less Efficient Designs

• The Darrieus design, also called the eggbeater windmill contains two or three C-shaped blades. It has a high speed but a low torque, which is undesirable as it requires a manual or mechanical start. The Savonius design has a higher torque, but its blades rotate considerably slower than approaching wind speeds, making it less efficient at producing electricity.

More Efficient Designs

• Several optimized windmills have been developed using the same principle of the Darrieus design. In the helical blade design, helical blades are used as a replacement, which reduces main bearing failure by limiting the pulsating torque. The cycloturbine design has blades that rotate at varied angles, which minimizes the blade drag. Although complex, this design is most efficient and is also capable of self-starting.