There are a variety of wind turbines of vertical and
horizontal axis types. Arrays of large turbines, known as wind farms, are
becoming an increasingly important source of renewable energy and are used by
many countries as part of a strategy to reduce their reliance on fossil fuels.
Wind turbines can rotate about either a horizontal or a
vertical axis, the former being both older and more common. They can also
include blades (transparent or not)[20] or be bladeless.
Horizontal axis
wind turbines
Horizontal-axis wind turbines (HAWT) have the main rotor
shaft and electrical generator at the top of a tower, and must be pointed into
the wind. Small turbines are pointed by a simple wind vane, while large
turbines generally use a wind sensor coupled with a servo motor. Most have a
gearbox, which turns the slow rotation of the blades into a quicker rotation
that is more suitable to drive an electrical generator. Since a tower produces
turbulence behind it, the turbine is usually positioned upwind of its
supporting tower.
Vertical-axis
wind turbines
Vertical-axis wind turbines (or VAWTs) have the main
rotor shaft arranged vertically. One advantage of this arrangement is that the
turbine does not need to be pointed into the wind to be effective, which is an
advantage on a site where the wind direction is highly variable. There are
several sub-types.
This postcard shows a wind
farm - but there is no indication on this card of where this farm is located. This
postcard from Michael (4 September 2015) Postcrossing is an advertising card of
the Danish company NEG Micon which is no longer operating under this name. The
company has since merged with another Danish wind turbine manufacturer, Vestas,
in 2004, and it is now operating under that name.
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