Approximately
1-2% of the sun's radiation falling on Earth is converted to wind, as the uneven heating
of the Earth's surface causes the movement of large masses of air from one region to
another. The exploitation of this energy is done through wind turbines by
turning the kinetic energy of the wind into beneficial mechanical energy.
Due to the large variations in wind potential between the regions and the peculiarity of the ground, wind turbines of vertical axis have been developed, which rotate around a vertical axis towards the wind direction and are designed to exploit even the lowest wind speed. They can take advantage of the wind from all directions and their mechanical power is transferred through a vertical axis to the ground where an electricity generator is installed.
The vertical axis wind turbines (VAWT) that have been developed are of the Savonius and Darrieus types. The
difference of these two types, apart from their design, is that Savonius
type exploits winds with very low speed but at the same time it is not so efficient, while Darrieus type requires
moderate wind speed in order to operate and simultaneously it is very efficient. It is obvious that in case
we want to produce electricity for our home with a wind turbine that actually
has to operate mostly with low wind speeds, then we have to choose a wind
turbine of Savonius type. The advantages and disadvantages of Savonius wind
turbines are as follows:
Advantages:
• They exploit winds from all directions
• They produce less noise than other types of wind turbines
• Their construction is simple and low cost
• They can be placed almost anywhere due to their small size
• The electricity generator is mounted at the base of the system and is therefore easier to maintain
• They exploit winds from all directions
• They produce less noise than other types of wind turbines
• Their construction is simple and low cost
• They can be placed almost anywhere due to their small size
• The electricity generator is mounted at the base of the system and is therefore easier to maintain
Disadvantages:
• Low performance
• High starting torque which means low rotation speed
• Because of their small size, they cannot take advantage of high speed winds
• Low performance
• High starting torque which means low rotation speed
• Because of their small size, they cannot take advantage of high speed winds
Wind speeds vary in relation
with the relief of a region as well as
with time and day. In order for an area to be considered suitable for the use
of wind energy, the average annual wind speed, measured at a height of 10 m
above the ground, should be greater than 4 m/s.