WIND ENERGY BASICS
When you leave your home and feel the wind whip through your hair, you may view it as an annoyance, but the fact is wind is an important form of renewable energy. With the right equipment, the kinetic energy of moving air can be turned into electricity or usable mechanical energy.
WHAT CAUSES WIND?
There are a number of mechanisms that cause air movement around the earth. For example, when the surface of the earth absorbs heat from the sun, it does so at different rates. Land absorbs heat about eight times faster than water, and the warm air over the land rises, making room for the cool air over the water to move in. This moving air is wind. As the earth rotates and the sun "sets", the land looses its heat faster than the water, so the winds reverse themselves. Changes in the weather can also affect these cycles. The other major mechanism is related to latitudinal effect. The areas near the Equator obviously get more sunlight that the areas near the poles. This causes large scale air motions between the Equator and the poles. Mountains additionally affect the air currents.
HARNESSING THE WIND
The energy in the air molecules can be harvested by using electro-mechanical devices called wind power turbines (read more
about the turbines).
These machines have blades that can turn when exposed to the wind. The blades are connected to a drive shaft that spins an electromagnet or a permanent magnet. This motion produces rotating magnetic field. The variable magnetic field induces voltage in the armature of electric generator according to Faraday's law. In residential grade systems this voltage is not regulated. It has to be rectified and converted into stabilized 120VAC 60Hz by SMPS inverters
. Wind energy can also be converted to mechanical energy in windmills.
It is always available and cannot be used up. This fact makes it a fully renewable resource. The wind blows today, and it will blow again tomorrow regardless of whether or not we use its energy. The process of converting this renewable resource into electricity does not create greenhouse gases or air pollutants, which is important for our environment.
The initial monetary investment to put up a wind power plant is higher than fossil fueled options, because the machinery is quite expensive. Wind also is not as plentiful in all areas of the country. Unlike electricity from traditional fossil-based sources, the power flow from wind generators is erratic as winds rise and fall. The amount of wind can also vary from day to day, so those who use it off-grid must be able to store the electricity for days when the wind is not blowing, or have a supplementary source of power. The constant variability of the wind power presents challenges for the grid, which was designed to work with the relatively continuous power flow from the fossil-based plants.
There are concerns that the turbines can kill the bats and birds. Many residents do not like the way the windmills look. The rotor blades create noise which can be heard within a few hundred feet especially at night when background noise is low. This is a drawback in residential environments. Finally, some of the best sources of wind are in the country, away from the urban areas that use the most electricity. This means that the utility must find a cost-effective way to transport the electricity long distance to the areas where it is needed.
Prices of course vary widely due to many factors affecting installation. Currently the net cost of installation of a small wind system for a private home before rebates and incentives is about $4,000-6,000 per kilowatt. Such a system includes a turbine with a tower and a special grid-interactive DC-AC inverter. The so-called levelized cost of electricity produced on wind power plants is about $0.15-0.19 per kW-hour. This is about 50-100% higher than the cost of power generation from coal and natural gas. There is also the cost of getting the permit, which ranges from zero to $1,000 depending on the utility. Unlike photovoltaic electricity, the cost of wind energy kept growing during the last decade. However, in near future the prices may decrease as a result of imports of low-priced systems from China. For reference, in 2010 only about 0.7% of total energy consumed in US came from wind energy.