Wind energy is a source of renewable energy (naturally replenished). It is caused by the movement of wind due to the uneven heating of the atmosphere, irregularities of the earth’s surface and the rotation of the earth.
Wind is usually measured by its speed and direction. The speed is measured by an anemometer and the direction by the vanes. After measuring wind data for at least one year, the mean annual wind speed can be calculated. Wind statistics show the best sites to locate wind farms per the best wind resources. They also provide further information on how the turbines should be positioned in relation to each other and what should be the distance between the turbines.
The simplest way to think about this is to imagine that a wind turbine works in exact opposite manner to the way a fan works. Instead of using electricity to make wind, as in the case of a fan, turbines uses wind to make electricity. Almost all wind turbines producing electricity consist of rotor blades which rotate around a horizontal hub. The hub is connected to a gearbox and generator, which are located inside the nacelle. The nacelle is the large part at the top of the tower where all the electrical components are located.
Most wind turbines have three blades which face into the wind; the wind turns the blades round, this spins the shaft, which connects to the generator. Then the generator converts mechanical energy into electrical energy, as opposed to an electric motor which does the opposite.
Wind turbines are available in a variety of sizes, and power ratings. Each turbines production capacity ranges from a few kilowatts (kW) to 7.5MW. Typical commercial wind facilities are 1.5 MW. These are modular and quick to install hence they can be rapidly deployed. A 10 MW wind farm may take only 2 months to be built. The commercial operation of the first wind turbine was of 15 meters diameter in the 1980s, and the average size of wind turbines has grown by 10-fold in the last 30 years. It is nearly 152m today and the new extra large turbines could approach 305m in diameter soon.
It generates different outputs dependent on the wind speed. A modern wind turbine produces electricity 70-85% of the time.
A wind turbine typically lasts around 20 years.
There are two basic kinds of wind turbines: Horizontal Axis Wind Turbine (HAWT) and Vertical Axis Wind Turbine (VAWT). HAWT are most common types of wind turbines built across the world and are more frequently used than the VAWT as they are more effective.
Preventive checkups are required 2-3 times per year.
The major components of any wind turbine, irrespective of their size are: hub, blade, shaft, gear box, and electrical generator. On large turbines, additional speed-controllers and drive motors are added to ensure proper positioning of machine for optimal capture of the wind.
The theoretical maximum energy which a wind turbine can extract from the wind blowing across it is approximately 59.3%, known as the Betz limit. For good turbines it is in the range of 35-45%.
The optimum number of blades for a wind turbine depends on the job the turbine has to do. Turbines for generating electricity need to operate at high speeds, but do not need much torque or turning force. These machines generally have two or three blades.
Generally, five times increase in height of the tower results in two fold increase in the wind energy output or power. In fact turbulence due to ground clutter decreases as we go up, hence the wind speed increases with height and in turn wind energy output is more.
A typical wind farm of about 20 turbines extends over an area of about 1-2 square kilometers. But only a small fraction of this land, about 1-2 per cent, is occupied by the turbines and access tracks. The bulk of the land is unaffected and can continue to be used for agriculture, grazing, etc.
Wind power plants, like all other energy technologies, have some environmental impacts. There is some concern over the noise produced by the rotor blades, aesthetic impacts, and bird and bat mortality. Wind turbines have moving parts but the sound they make is virtually undetectable from a distance. Noise is not a problem with modern wind turbines. A wind turbine a quarter of a mile away is no noisier than a kitchen refrigerator.
Wind farms can occasionally disrupt TV and radio signals, but any problems should be identified during the planning phase and can be solved with suitable repeater equipment or TV aerial modifications. Planning authorities can ensure that developers should provide the necessary equipment as part of the planning permission process.
Modern wind turbines have special features which are designed to handle excessively high winds. Wind turbines have a wind cut-out speed. If the wind speed exceeds the cut-out speed than the turbine will take action to prevent damages to the turbine. There are numbers of technical solution in hands. In some machines an automatic brake is activated by a wind speed sensor. Some machines twist or “pitch” the blades to spill the wind. Still others use “spoilers,” drag flaps mounted on the blades or the hub which are automatically activated by high rotor rpm’s, or mechanically activated by a spring loaded device which turns the machine sideways to the wind stream. Normal wind turbine operation usually resumes when the wind drops back to a safe level.
As a general rule wind turbines should not be mounted on homes because the vibration from the turbine could be transferred to the building and damage both the mounting and the building. In addition most turbines need to be mounted higher than the typical roof in order to get good wind speed and avoid turbulence.
Cold air is denser than hot air. Thus, wind turbines are able to generate about 5% more power at any given wind speed in the winter than they are during the hot days of summer.
It is one of the cleanest forms of renewable energy and it is currently used by many leading developed and developing countries to fulfill their demand for energy. It does not produce any harmful waterborne emissions or toxic solid wastes, thus it doesn’t pollute the environment. Wind energy will exist as long as the sun exists. It offsets the emissions of other energy sources, reducing our contribution to global climate change.
Wind energy entirely avoids carbon costs, geo-political risk associated with supply and infrastructure constraints, and energy dependence on other countries. Distributed generation is less vulnerable to disruption than large, centralized power plants. It is compatible with other land uses such as agriculture and it can serve as a boost for rural economic development. It also generates revenues for local communities as it creates alternative revenues for farmers who lease their land.
When the wind stops blowing, electricity continues to be provided by other forms of generation in an isolated system (e.g. batteries, diesel generator), and by the grid in a grid-connected system.
Wind resource analysis and mapping allows the wind developers to estimate when and how much wind energy is available, with a high degree of certainty. When the wind blows, it can displace fossil-fueled generation such as oil and gas. Studies have shown that when a utility diversifies its power portfolio with the addition of wind energy, it can meet energy demands more effectively.