14-05-2013, 12:02 PM
Savonius vertical axis wind turbine
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Advantages of vertical axis wind turbines
VAWTs offer a number of advantages over traditional horizontal-axis wind turbines (HAWTs). They can be packed closer together in wind farms, allowing more in a given space. This is not because they are smaller, but rather due to the slowing effect on the air that HAWTs have, forcing designers to separate them by ten times their width.
VAWTs are rugged, quiet, omni-directional, and they do not create as much stress on the support structure. They do not require as much wind to generate power, thus allowing them to be closer to the ground. By being closer to the ground they are easily maintained and can be installed on chimneys and similar tall structures.
Research at Cal Tech has also shown that carefully designing wind farms using VAWTs can result in power output ten times as great as a HAWT wind farm the same size.
However most of the above claims are considered debatable by people with experience of wind engineering. There is very little history of successful VAWT operation, despite their very long history. During this history they have repeatedly been portrayed as innovative, more efficient, quieter, more bird-friendly, more cost-effective etc whereas there is no factual evidence for any of these claims.
Disadvantages of vertical axis wind turbines
Some disadvantages that the VAWTs possess are that they have a tendency to stall under gusty winds. VAWTs have very low starting torque, as well as dynamic stability problems. The VAWTs are sensitive to off-design conditions and have a low installation height limiting operation to lower wind speed environments.
The blades of a VAWT are prone to fatigue as the blade spins around the central axis. The vertically oriented blades used in early models twisted and bent as they rotated in the wind. This caused the blades to flex and crack. Over time the blades broke apart and sometimes leading to catastrophic failure. Because of these problems, VAWTs have proven less reliable thanHAWTs.
Research programmes (in 2011) have sought to overcome the inefficiencies associated with VAWTs by reconfiguration of turbine placement within wind farms. It is thought that, despite the lower wind-speed environment at low elevations, "the scaling of the physical forces involved predicts that [VAWT] wind farms can be built using less expensive materials, manufacturing processes, and maintenance than is possible with current wind turbines".
Savonius vertical axis wind turbine
Although with less efficiency compared with three-bladed wind turbines, the savonius vertical axis wind turbine
has the advantage of being compact, economical and aesthetic.
This allows it to be easily integrated into buildings.