Generation of electricity from wind is now one of the fastest growing sources of renewable energy.
Wind energy has been harnessed for over 6000 years, first for powering boats, windmills and wind pumps, and now for generating electricity. Modern wind equipment ranges from small water pumps and chargers (used to charge batteries at remote locations) to large multi-megawatt wind turbines arranged in wind farms that supply power to the electricity grid.
World-wide, there over 25,000MW of installed capacity, mostly in Europe and the USA.
Wind power equipment has been developed to provide a range of power outputs, from under 100W up to 3MW. The overall reliability of wind turbines is high – 97-99% availability is standard for modern turbines – and modern machines are designed to have a useful life of about 25 years. Turbines can have fixed or variable speed rotors, can be pitch or stall regulated, or in the case of small turbines can have furling rotor blades. When used for electricity generation, turbines can generate either direct or alternating current. The flexibility of design of individual turbine components means that machines can be matched to areas with high, medium or low average wind speeds, from the Arctic to the Sahara, and from mountain tops to locations out to sea.
Within the design parameters necessary for conditions at any individual site, the size of turbine required will depend on the type of application:
Large-scale, grid-connected electricity generation
This requires a number of large turbines grouped together on one site to form a wind farm or wind park, either on- or off-shore. The power from the individual turbines is aggregated at a central point before it is fed through a power line to the point where it connects with the national grid. It usually passes through a transformer at the central point to match the voltage to that of the grid. The central point usually doubles as a command point, where computerized equipment can be installed to allow the remote control of the wind farm. This is particularly important for remote and off-shore wind farms, where adverse weather may prevent access for long periods of time.
Small-scale, grid-connected electricity generation
Where electricity grids are unable to accommodate large amounts of generation, typically in remote areas, it is still possible to deploy individual turbines or small clusters of turbines of varying sizes. Frequently the grids in these areas are at relatively low voltage in which case the installations are designed to connect directly into the grid with little or no additional voltage transformation. Where the grid is an isolated grid (not connected to the main national or regional grid), the wind turbines are usually run in conjunction with another form of generation, typically diesel (see hybrid systems below).
Applications for standalone wind power are more varied. They may be as small as a charger used to charge the batteries on an ocean-going yacht, or megawatt-size turbines used for powering a desalination plant on an arid coastline. The use of solitary wind pumps feeding water tanks has been a familiar sight in much of the world for over 150 years.
Wind power is also very suitable for incorporation into hybrid systems. These offer flexibility, because they can provide power even when the wind is not blowing. Wind-diesel combinations are common, but more recent developments include wind-photovoltaic units, a hybrid option which offers power generation from 100% renewable sources.