These turbines are not only used to provide electricity to an electrical grid, there are also smaller ones available for households. The most commonly used home turbines are the horizontal axis types. They are either mounted on a tower or onto the roof. This provides a good way for households to lower their carbon footprint and electricity bills. It is also possible to sell excess electricity to an electrical grid in some countries.
The horizontal axis types are the most common and probably the most familiar to people. They have a propeller that rotates on a horizontal axis. As a winds speed is higher at altitude, the propeller is placed on a very high tower along with the generator. The propeller is movable so it is always facing the winds direction, and is mostly used in an area where the winds direction is fairly consistent.
The advantages of the horizontal axis types are that they can produce more energy. The disadvantage is that they are more difficult to maintain due to their height. Also a lot of pressure is placed on the propeller particularly during very high winds, so they are more prone to failure.
Vertical axis models are less common. They have vertical blades with a generator at the bottom. As the winds hit the turbine's blades, the whole unit spins. These models are much shorter than the horizontal type and are often placed on top of buildings, or in an area where a wind tunnel is present.
Vertical axis turbines have two subtypes. These are called Darrieus and Savonius. The eggbeater-shaped Darrieus turbine produces more energy than its Savonius counterpart; however they require energy to begin rotating. The Darrieus models tend to be used where winds are less reliable. The Savonius models have two scoops on either side, which catch air currents, making the unit rotate. They do not produce as much electricity, but do not require any energy to get going. Savonius turbines are usually used where there are less turbulent winds.
The vertical Axis types can be grouped much closer together in a wind farm and take up less space. They are easier to maintain as the generator and main parts are close to the ground. They also do not require a turning mechanism, as they do not have to face the direction of the air flow. They are unable to produce as much energy as the horizontal types of wind turbines, but they can be placed at locations where a horizontal axis turbine cannot.
