the extraction of kinetic energy from
wind
has been used for centuries to propel
sailing boats
and used to pump water and milling
grains in windmills
let's look at how the energy from wind
is harnessed
to generate electricity by exploring how
wind turbines work
we will explore the fundamental science
of wind how
energy is extracted from the wind
aerodynamics of the blades
and key components with their function
in modern wind turbines as well as
different types of wind turbines
before exploring how wind turbines work
let's get an understanding of the main
enabler for wind turbines
simply put wind is the motion of air
molecules which consist
of 78 nitrogen 21 oxygen
between one and four percent water vapor
and other trace elements let's zoom out
from a molecular level
to see how air is manipulated on a large
scale to create wind the energy that
drives wind
originates with the sun which heats the
earth unevenly
creating warm and cool spots for example
a sea breeze occurs when inland areas
heat up on a sunny afternoon
the air is warmed and expands leading to
a lower density
causing it to rise and creating less
pressure cooler heavier air
at a higher pressure rushes in from the
ocean to take its place
and wind is created because of the
pressure difference
the topography of an area has a major
effect on the wind climate
more wind is experienced on the tops of
hills and mountains
compared to sheltered valleys obstacles
such as trees or buildings
significantly reduce wind speeds the
amount of energy in wind depends on
three factors
the volume of air velocity of air
and mass of air the power output from a
wind turbine is given by the expression
p equals half cp times rho
times a times u cubed where cp
is the power coefficient and we will
talk about this in a bit
rho is the air density a is the swept
area of the rotor
and u is the velocity of the wind there
exists a theoretical maximum
of the power coefficient known as beta's
limit
beta's limit is 59.3
and is derived from the principles of
conservation of mass
and momentum of the airstream flowing
through an
idealized actuator disk that extracts
energy from the windstream
a higher efficiency is not possible due
to the fluid mechanical nature of wind
power that requires the continuous flow
of air in motion historically power
output of a wind turbine has increased
with the hub height and rotor diameters
but there are some engineering
limitations the limit of the size of
wind turbines
at present is determined by the problems
in transporting
the large blades and pillar components
the size of the cranes required to erect
the turbines
and the cost associated with this a
solution to some of these problems is to
build the blades and pillars offshore
similar to oil rigs modern turbines use
sophisticated aerodynamic principles
to capture the wind's energy most
effectively
turbine blades are shaped a lot like
airplane wings
or propeller blades using an airfoil
design
blowing air passes around both sides of
the blade
because of uneven air pressure
distribution pressure is higher on one
side of the blade and lower on the other
and a lift force is generated which acts
perpendicular to the direction of the
wind
and causes the blades to rotate starting
the energy generation process
now that we know how energy is extracted
to the wind turbine
let's look at how individual components
function
to ensure the operation of a wind
turbine
a wind turbine consists of a tower
a nacelle mounted on top of the tower
and a turbine rotor
within the nacelle are several
components responsible for converting
the wind energy
into electrical energy the components
inside the nacelle
includes a gearbox
generator
transformer
and control systems
the rotor converts the kinetic energy in
the wind
into mechanical energy
the rotor contains a hub and blades
which is connected with mechanical
joints
the router hub is manufactured with
casting and made from spheroidal
graphite iron
modern wind turbines mostly have three
blades
the ideal material for blade
construction must be low density
possess high strength fatigue resistance
stiffness and damage tolerance with a
low cost
materials used for the shell of wind
turbine blades
are typically made of glass fiber
reinforced polyester
combined with a resin matrix to produce
a composite
the upper and lower shell are supported
by shear webs
and bonded on the leading and trailing
edges with adhesives
modern blades taper from the root to tip
to reduce drag at the faster moving tip
and have a high aspect ratio the blades
also twist from the root to tip to
improve the aerodynamic efficiency
mechanical power from the rotor is
transmitted
to the generator through a transmission
system which typically consists
of the rotor shaft mechanical brake and
a gearbox
the gearbox of a wind turbine converts
the slow
high torque rotation of the aerodynamic
rotor
into a much faster rotation of the
generator shaft
the low speed rotor shaft connects to
the gearbox
to step up to a speed that's suitable
for standard induction generators
the low speed shafts are rotating at
speeds between 48
and 12 rpm and gear ratios between
1 to 31 and 1 to 125
are generally required a mechanical
break is located on the high speed
shaft which connects the gearbox to the
generator
mechanical brakes are applied as a
backup method
of keeping the turbine stationary for
maintenance or in the case of emergency
situations such as extreme wind gusts or
excessive rotational speed
the high speed shaft connects to the
generator which is an electromechanical
component
that converts the mechanical power into
electrical power
generators typically have a stator a
stationary housing
with coils of wire mounted in a certain
pattern
and a router the rotating part of the
generator
when the high speed shaft rotates
electricity is generated
due to electromagnetic induction
because the wind's direction and speed
are ever changing
a control system is necessary to ensure
the optimal operation of wind turbines
control systems in wind turbines are
used when store
occurs on the router blades when the
wind speed exceeds a certain critical
level
to maximize power production and reduce
structural loads
on the mechanical components pitch
control allows for the rotation of each
blade
about its own axis active pitch control
means blades can be quickly turned away
or into the wind
as the power output becomes too high or
too low
when the wind exceeds a certain
threshold the blades rotate to a
specific
angle of attack and stall occurs
eliminating the force of lift and
decreasing
the speed of the blades pitch bearings
are interposed between
each blade and the hub to allow the
blade to be rotated
about its axis a your controlled wind
turbine has a your drive
which is constantly rotating the nacelle
to get as much air through the router
disk
as possible in order to apply the
correct control movement the wind
parameters
must be measured an anemoscope and a
wind vane
are used to detect immediate wind status
when the operating status changes the
anemoscope
and wind vane send a signal the signal
is diagnosed
processed and an output signal is sent
to the yawing system pitch control
system and
the mechanical brake which changes the
operating status of the wind turbine
accordingly the tower and foundation
mainly provides support and height to
the electric
power generating nacelle and router with
the tower
raising the nacelle and the router to a
position
where the wind has higher speeds special
consideration
must be given to buckling
and the first mode natural frequency to
avoid
the excitation of resonant tower
oscillations
caused by router thrust fluctuations
the vast majority of wind turbine towers
are constructed from steel and towers
have a very modest taper
slab multi-pile and mono-pile
foundations
are used to provide support vertical
axis
wind turbines has the advantage of
generating power
from wind that comes from any direction
generally
they are not efficient enough to compete
with horizontal axis wind turbines
both in terms of power generation and
economic feasibility
offshore wind turbines are becoming more
popular
as offshore mean wind speeds are higher
wind turbulence is low
and large areas are available for wind
farm development with limited
environmental impact
general electric's halide x offshore 12
megawatt wind turbines are the most
powerful offshore turbines
siemens gamesa is a newly launched 14
megawatt offshore wind turbine
aiming to conquer the halyard eggs
winter turbines are a clean and
sustainable source of energy
with relatively small amounts of
greenhouse gas emissions
caused mostly because of the
manufacturing and transport of the
turbines and plates
the intermittency of wind noise
pollution and the initial cost of
setting up wind farms
are the major drawbacks nevertheless
wind is a renewable energy source
that can be utilized in conjunction with
other renewable energy sources
to move towards a greener planet