Renewable Energy - Wind (Part 2)

Wind energy basically involves converting airflow into electricity by using wind turbines. A wind turbine is a device that converts kinetic energy from the wind into mechanical energy and the mechanical energy is used to produce electricity. There are two types of wind turbines, based on their rotation axis; wind turbines can rotate about either a horizontal or a vertical axis. Interestingly, wind power always been integrated with solar power in hybrid renewable energy system due to the both system simplicity and operation independent.

1) Horizontal Axis

Horizontal-axis wind turbines (HAWT) have the main rotor shaft and electrical generator at the top of a tower, and must be pointed into the wind. Small turbines are pointed by a simple wind vane, while large turbines generally use a wind sensor coupled with a servo motor. Most have a gearbox, which turns the slow rotation of the blades into a quicker rotation that is more suitable to drive an electrical generator.

Since a tower produces turbulence behind it, the turbine is usually positioned upwind of its supporting tower. Turbine blades are made stiff to prevent the blades from being pushed into the tower by high winds. Additionally, the blades are placed in a distance in front of the tower and are sometimes tilted forward into the wind a little. Most HAWTs are of upwind design and most commonly used between the two types.

2) Vertical Axis

Vertical-axis wind turbines (VAWT) have the main rotor shaft arranged vertically. Key advantages of this arrangement are that the turbine does not need to be pointed into the wind to be effective. This is an advantage on sites where the wind direction is highly variable. The key disadvantages of VAWT include the low rotational speed, the inherently lower power coefficient, the pulsating torque generated and the difficulty of modelling the wind flow accurately.

In VAWT configuration, the generator and gearbox can be placed near the ground, using a direct drive from the rotor assembly to the ground-based gearbox, hence improving accessibility for maintenance. When this turbine is mounted on a rooftop, the building generally redirects wind over the roof and these can double the wind speed at the turbine. This type of wind turbine is suitable in urban areas because wind speeds within the built environment are generally much lower than at exposed rural sites.

Other than wind, maybe we can directly harness the electricity from the skies, lightning...

... maybe not, but still, it's a good possibility... (if we can find a way to harness 1.21 gigawatts from a lightning bolt that is 5 times hotter than the surface of the sun!)