2. WIND ENERGY
The wind is a clean and plentiful source of energy.
A wind turbine is a machine that converts the
kinetic energy in wind into mechanical energy.
The mechanical energy is used directly by
machinery, such as a pump or grinding
stones, the machine is usually called a windmill.
The mechanical energy is then converted to
electricity, the machine is called a wind
generator, wind turbine, or wind energy converter
(WEC).
3. VARIETY OF WINDMILL SIZES
Large wind turbines- installed in clusters called
wind farms-generate large amounts of
electricity(MW).
Small wind turbines-generates 100 kW of
electricity-installed at homes, farms and small
businesses .
Used as a source of backup electricity, or to
offset use of utility power and reduce electricity
bills.
Very small wind turbines -20-500w- charge
batteries for sailboats and other recreational uses.
Applications
water pumping, telecommunications power
supply and irrigation.
5. OPERATION
A wind turbine converts kinetic energy in a
moving air stream to electric energy.
Mechanical torque created by aerodynamic lift
from the turbine blades is applied to a rotating
shaft.
An electrical generator on the same rotating
shaft produces an opposing electromagnetic
torque.
6. In steady operation, the magnitude of the
mechanical torque is equal to that of the
electromagnetic torque, so the rotational speed
remains constant, real power (the product of
rotational speed and torque) is delivered to the
grid.
Since the wind speed is not constant, a variety of
control mechanisms are employed to manage the
conversion process and protect the mechanical
and electrical equipment from conditions that
would result in failure or destruction.
7. WIND POWER
The formula used for calculating the power in the wind is
shown below:
Power = ½ .density of air. swept area.velocity^3
P = ½.ñ.A.V³
In practical
PM = ½.Cp.ñ.A.V³
Cp is the coefficient of performance of the wind machine
8. PRINCIPLES OF WIND ENERGY
CONVERSION
There are two primary physical principles of extraction:
Either lift or drag force or through a combination of the
two.
The difference between drag and lift is illustrated by the
difference between using a spinnaker sail, which fills like a
parachute and pulls a sailing boat with the wind, and a
Bermuda rig, the familiar triangular sail which deflects with
wind and allows a sailing boat to travel across the wind.
Drag forces provide the most obvious means of propulsion,
these being the forces felt by a person (or object) exposed
to the wind. Lift forces are the most efficient means of
propulsion but being more subtle than drag forces are not
so well understood.
10. BASIC FEATURES THAT CHARACTERIZE
LIFT & DRAG
Drag is in the direction of air flow .
Lift is perpendicular to the direction of air flow .
Generation of lift always causes a certain
amount of drag to be developed .
With a good aerofoil, the lift produced can be
more than thirty times greater than the drag.
Lift devices are generally more efficient than
drag devices Types and characteristics of rotors .
11. IMPORTANT WIND SPEEDS TO
CONSIDER
Start-up wind speed - the wind speed that will
turn an unloaded rotor.
Cut-in wind speed - the wind speed at which
the rotor can be loaded.
Rated wind speed - the windspeed at which the
machine is designed to run (this is at optimum
tip-speed ratio).
Furling wind speed - the windspeed at which
the machine will be turned out of the wind to
prevent damage.
Maximum design wind speed - the windspeed
above which damage could occur to the machine.
13. Two main families of windmachines:
vertical axis machines
Horizontal axis machines.
These can in turn use either lift or drag forces to
harness the wind.
The horizontal axis lift device is the type most
commonly used.
The tipspeed ratio :
It is defined as the ratio of the speed of the
extremities of a windmill rotor to the speed of the
free wind.
14. Drag devices-tipspeed ratios less than one -turn
slowly
Lift devices -high tip-speed ratios(up to 13:1)-
turn quickly relative to the wind.
The proportion of the power in the wind that the
rotor can extract is termed the coefficient of
performance (Cp) and its variation as a function
of tipspeed ratio is commonly used to characterise
different types of rotor.
As mentioned earlier there is an upper limit of Cp
= 59.3%
Although in practice real wind rotors have
maximum Cp values in the range of 25%-45%.
15.
16.
17. COMPONENTS OF WIND ENERGY
SYSTEMS
These basic components include:
A rotor
A gearbox
The smallest turbines (under 10 kW) usually do
not require a gearbox.
An enclosure which protects the gearbox,
generator and other components of the turbine
from the elements.
A tail vane or yaw system, which aligns the
turbine with the wind.
20. MAINTENANCE OF WIND TURBINE
It requires periodic maintenance - oiling and greasing,
and regular safety inspections. Check bolts and electrical
connections annually; tighten if necessary.
Once a year check wind turbines for corrosion and the
guy wires supporting the tower for proper tension.
If the turbine blades are wood, paint to protect from the
elements. Apply a durable leading edge tape to protect the
blades from abrasion due to dust and insects in the air.
If the paint cracks or the leading edge tape tears away,
the exposed wood will quickly erode. Moisture penetrating
into the wood causes the rotor become unbalanced,
stressing the wind generator. Inspect wooden blades
annually, and do any repairs immediately.
After 10 years, blades and bearings may need to be
completely replaced. With proper installation and
maintenance, wind turbine can last 20-30 years or longer.
Proper maintenance will also minimize the amount of
mechanical noise produced by your wind turbine
21. SAFETY CONCERNS
Internal brake and lock
To prevent maximum wind speed- survival
speed [they will not operate above].
Insulation
cold winter conditions, be prepared to de-ice
as required, and store batteries in an insulated
place.
Mounting turbines on rooftops is generally not
recommended
