As a result of skyrocketing oil prices , and a several energy crises , the intrest in new and more cheaper energy sources arose again. One of the most common is wind power.
Wind power is not a new idea. For millennia, it has been put to a variety of uses, including pumping water, powering mills and propelling sailing vessels. Today, modern wind turbines are seen in many countries. Currently at about 7.6 gigawatts (GW) accumulated installed capacity (about 35,500 units world wide).
However, 0.1 percent of electricity used in the world comes from wind. Germany, with rather moderate wind resources, now has the greatest installed capacity. A number of countries with good wind resources have virtually no installations.
The costs of generating electricity from wind depends mostly on the average wind speed of the site and the capital cost of the installation. Between 1980 and 1995, the real cost of wind-generated electricity fell by 10 percent per year. For Europe, wind generation costs are mostly in the range of 4 to 8 US cents per kilowatt hour ($c/kWh). This is competitive price to new nuclear and clean coal plants, but is not competitive with Combined Cycle Gas Turbines. The wind energy market is currently dependent on government support or other stimulation programes.
European manufacturers of wind turbine generators accounted for over 90 percent of world sales in 1997, with Danish manufacturers taking almost 60 percent. Off-shore wind farms represent a new market sector. Several near-shore projects exist (Denmark, Sweden, Netherlands). True off-shore projects (more than 5 km from shore and in less than 20m of water) provide better wind qualities and a vast increase in the exploitable resource.
In principle, wind power is harnessed for electricity by means of windmills. The modern equivalent, known as a wind turbine, works on the same principle.
The performance of a wind turbine depends on two factors: the strength of the wind and the size of the blades. The power output of the turbine is proportional to the cube of the wind speed.
The typical design of modern wind turbines has evolved since the 1970s, from mainly Danish origins. The visual aspect is a tall, slender tower, supporting a nacelle with a propeller-like, three-bladed rotor on a horizontal axis . The nacelle contains all the rotating parts, and allows access for maintenance and inspection. Electronic control equipment sits in the tower base. A comprehensive supervisory control and data acquisition system with remote operation is becoming standard. Also standard is a twenty-year life span, although many turbines are designed to last for longer.
Design drivers are maximisation of electricity production, technical availability of equipment, minimisation of intervention, and (especially for offshore) safe access to installations. Fatigue loads on the system are the main limiting factor on design life and availability, and many variations on the basic turbine model have been developed to address these issues.
The generating capacity of a wind turbine is the nameplate rating of the generator. The capacity factor for a wind turbine is the energy delivered over a year as a percentage of the potential generating capacity.
Technical risks are generally well manageable, with an emerging support industry aware of typical wind power requirements. Future developments in wind turbines strive towards cost reduction by decreased material use, increased generating capacity, and increased reliability. Offshore turbines will grow in capacity, to reduce impact of overhead costs like foundations and maintenance.
The perfect site for a wind turbine is windy, has a lw level of turbulence, is cose to a grid connection or anher back-up supply, rmote from habitation and bird migration routes, wll accessible for construction and maintenance, ds the wind predominantly blowing from one direction, or directions at 180 degrees to one another.
The most important of all benefits is the avoidance of emissions of pollutants. Emissions from renewable energy sources are negligible compared with conventional sources of energy, even taking account of the emissions associated with construction.
While wind farms are spread across large areas, the actual land that they use is low. The turbine footings use a fraction of 1 percent of the land. Most of the remaining land area is physically available for use as before. There is no evidence that installed turbines interfere with normal arable or livestock farming.
But wind farms are highly visible. Reactions to this are subjective. The reactions to visual aspects depend strongly on the geographical location and population density. Manufacturers have attempted to improve the appearance of their machines and developers take account of visual amenity in the siting and design of their projects.
Modern wind turbines are quiet and becoming quieter. Their noise is a function of rotor speed and design, 2 bladed rotors are noisier than 3 bladed, because they rotate faster than three bladed rotors for the same energy efficiency. The sound level at 40 m from a typical modern turbine is 50 - 60 dB(A), about the same level as conversational speech. Nonetheless, the noise levels affecting neighbouring houses is an important factor in wind farm siting and design.
Birds often collide with structures they have difficulty seeing. In absolute terms, wind turbines are only a minor cause of bird deaths. Radar studies show that birds in flight deliberately avoid wind turbines during the day or night. Nonetheless industry practice is to avoid sites that are critical to birds (habitats, migration routes).
