Wind-energy advocates say they will continue to push to ease restrictions on where wind turbines can be placed, undeterred by a stinging defeat this week in the Ohio General Assembly. The Ohio Senate supported the eased restrictions this week and …and more »
In contrast to the windmills common in the nineteenth century, a modern power generating wind turbine is designed to produce high quality, network frequency electricity whenever enough wind is available. Wind turbines can operate continuously, unattended and with low maintenance with some 120,000 hours of active operation in a design life of 20 years. By comparison, a typical car engine has a design lifetime of the order of 6,000 hours.
The rotors of modern wind turbines generally consist of three blades, with their speed and power controlled by either stall or pitch regulation. Stall regulation involves controlling the mechanical rotation of the blades, pitch regulation (now more commonly used) involves changing the angle of the blades themselves. Rotor blades are manufactured from composite materials using fibreglass and polyester or fibreglass and epoxy, sometimes in combination with wood and carbon.
Energy captured by the steadily rotating blades is transferred to an electrical generator via a gearbox and drive train. Alternatively, the generator can be coupled directly to the rotor in a direct drive`s arrangement. Turbines able to operate at varying speeds are increasingly common, a characteristic which improves compatibility with
the electricity grid. The gearbox, generator and other control equipment are housed within a protective nacelle.
Tubular towers supporting the nacelle and rotor are usually made of steel, and taper from their base to the top. The entire nacelle and rotor are designed to move round, or yaw, in order to face the prevailing wind.
Wind resources and monitoring
The wind resource is the fuel for a wind power station, and just small changes have large impact on the commercial value of a farm. Every time the average wind speed doubles, the
power in the wind increases by a factor of eight, so even small changes in average speed can produce large changes in performance. If the average wind speed at a given site increases from 6 metres per second (m/s) to 10 m/s, for example, the amount of energy produced by a wind farm will increase by over 130%. Detailed and reliable information about how strongly, from which direction and how regularly the wind blows, is therefore vital for any prospective development.
At a national and regional level, European wind atlases have been produced which record the wind speed to be expected in particular areas. For specific sites, more detailed assessment is required using data from nearby weather stations and specialist computer software to model the wind resource. Finally, site specific measurements are carried out using an anemometry mast on which a number of anemometers measure the wind speed and direction at different heights above ground.
Overall, the exploitable onshore wind resource for the European Union (EU-25) is conservatively estimated to be capable of generating an output of 600 Terawatt hours (TWh). The wind resource in offshore waters has been assessed at up to 3,000 TWh. This alone would exceed Europe`s entire current electricity consumption.
A number of constraints affect the siting of a cluster of wind turbines, usually described as a
wind farm or park. These include land ownership, positioning in relation to buildings and roads, and avoidance of sites of special environmental importance. Once these constraints have been determined, the layout of the wind turbines themselves can be planned. The overall aim is to maximise electricity production whilst minimizing infrastructure, operation and maintenance (O&M) costs, and environmental impacts. Specialist software has been developed to produce visualizations of how the turbines will appear in the landscape, enabling developers and planners to choose the best visual impact solutions before the project is constructed.
Apart from the turbines themselves, the other principal components of a wind farm are the foundations to support the turbine towers, access roads and the infrastructure to export the electrical output to the grid network. A 10 MW wind farm can easily be constructed within two months, producing enough power to meet the consumption of over 5,000 average European households.
Once operating, a wind farm can be monitored and controlled remotely. A mobile
team carries out maintenance work, with roughly two personnel for every 20 to 30 turbines. Typical maintenance time for a modern wind turbine is about 40 hours per year. Wind farms can vary in size from a few megawatts up to the largest so far – 300 MW in the western United States.
The advantages of wind power
� Low cost can be competitive with nuclear, coal and gas on a level
� playing field
� The fuel is free, abundant and inexhaustible
� Clean energy – no resulting carbon dioxide emissions
� Provides a hedge against fuel price volatility
� Security of supply – avoids reliance on imported fuels
� Modular and rapid to install
� Provides bulk power equivalent to conventional sources
� Land friendly – agricultural/industrial activity can continue around it.