WIND ENERGY.pdf

WIND ENERGY
➢ It is the K. E associated with movement of large masses of air.
➢ Results in uneven heating of atm.by sun creating temp., density and pr.differences.
➢ Wind flows from high pr. to low pr.
❖Moderate to high speed winds (5m/s to 25m/s) are suitable for most wind turbines.
❖For small scale applications favorable winds are available on about 50% of the earth
➢ Advantages:
✓ Clean, cheap and pure form of energy
✓ No need of water, no pollution,
✓ Low payback period
➢ Disadvantages:
X Location specific
Source: Non conventional energy
sources by B. H. Khan

Harnessing Wind Energy:
❖Into Mechanical energy with the help of wind turbine
✓ Used locally to operate farm appliances
❖Into Electrical energy with the help of aero generator
✓ Used locally or fed to grid
Factors effecting winds:
♣ Pressure Gradient
♣ Rotation of earth
♣ Friction of Earth
Source: Non conventional energy sources by B. H. Khan

Types of winds:
✓Synoptic winds: caused by uneven heating of earth
✓Gradient winds: Coriolis acceleration and centripetal acceleration exactly
balance horizontal pr. force
✓ Prevailing Winds: blow constantly
in particular direction through out
the year.
✓ Geotropic Winds: wind in upper
atmosphere move parallel to the
isobars. These are the horizontal
winds

Types of winds:
➢ Planetary or permanent winds:
✓ also called PrevailingWINDS
✓ Blows from HPR to LPR and tries to deflect because of earth rotation.
➢ Two sets:
✓ Trade winds and westerlies

TRADEWINDS:
❖Originated from Latin word
‘TRADO’ means blowing
steadily in cont. dir.
❖50 to 300 north and south or
300N to 300S
❖ Result of Pr. Gradient b/w high tropical to low equatorial belt
❖ North East trade winds and south east trade winds
❖ Noted for steadiness and persistent in dir.

Westerlies:
❖between 35° and 60° North and South latitudes
❖From the Sub-Tropical High-Pressure Belts towards the Sub-Polar Low-
Pressure Belts.
❖These are on-shore winds on the west coasts and off-shore winds on their
east coasts.
❖The on-shore winds bring rainfall while the off-shore winds are lacking in it.
❖These winds are not as constant in strength and direction as theTradeWinds.

❖They are rather stormy and variable though the main direction remains from
west to east.
❖But as their general direction is from the west, they are called the “Westerlies”
or “Anti-Trade Winds”, because their movement is in the opposite direction from
that of theTradeWinds.
❖in the Southern Hemisphere,
between 40°S and 60°S, the
westerlies gain great strength
and persistence because of the
vast expanse of oceans in their
belt.

PolarWinds:
➢ The winds blowing in the Arctic and the Antarctic latitudes are known as the Polar
Winds.
➢ They have been termed the ‘Polar Easterlies’, as they blow from the Polar High
Pressure Centres towards the Sub-Polar Low-Pressure Belts.
➢ In the Northern Hemisphere, they blow in general from the north-east, and are called
the North-East PolarWinds
➢ In the Southern Hemisphere, they blow from the south-east and are called the South-
East PolarWinds.
➢ As these winds blow from the ice-capped landmass, they are extremely cold.
➢ They are more regular in the Southern Hemisphere than in the Northern Hemisphere.

Periodic Winds
1. See Breeze 2. Land Breeze 3. Monsoons
➢ Monsoon winds are seasonal winds.
➢ For six months they blow from land to sea, and for the other six months from
sea to land.
➢ The word ‘monsoon’ has been derived from the Arabic word ‘Mousim’, which
means ‘season’.

Meteorological Data:
❖ Every country has Meteorological services that record and publish weather related data
including wind speed and direction
❖Wind speed is measured byANEMOMETER
❖Wind direction is measured byWINDVANE
Swinging Vane anemometer cup anemometer

Sonic Anemometer

➢ Wind speed measurement should be made at an
effective height of 10m above ground.
➢ Frequency of measurement depends on usage of data.
➢ Graphical representation of wind data is called WIND
ROSE.
➢ It depicts the compass bearing from which the wind
comes along with average speed and duration in a year

Applications of Wind Energy
1. Mechanical power applications:
a. Wind pumps
b. Heating
c. Sea transport
2. As off Grid Electric source:
a. 40-1000W – space heating
b. >50kW –electric power for navigation signals, remote communications
c. 100-250kW- local usage
d. >250kW

WIND TURBINE SITING
➢ Power available in wind increases rapidly with wind speed.
➢ Therefore, main consideration for locating a wind power generation plant is the
availability of strong and persistent wind.
1. A suitable site should preferably have some of the following features:
2. No tall obstructions for some distance (about 3 km) in the upwind direction. (i.e. the
direction of incoming wind).
3. Open plain, open shoreline or offshore locations.
4. Top of smooth well-rounded hill with gentle slopes (about 1:3 or less) on a flat plain.
5. An island in a lake or the sea.
6. A narrow, mountain gap through which wind is channeled

➢ Based on axis of Rotation
✓ HAWT
✓ VAWT
➢ Based on Size:
✓ Small scale( up to 2KW),
✓ Medium (2-100KW),
✓ Large(>=100KW)
➢ Based on type of output power:
✓ DE output,
✓ AC output
➢ Based on Rotational Speed:
✓ Constant speed ,
✓ Nearly constant speed,
✓ Variable speed with fixed pitch blades
➢ Based on Utilization of output made:
✓ Battery storage,
✓ Direct connection,
✓ Grid connection
Source: Non conventional energy
sources by B. H. Khan
CLASSIFICATION OF WIND TURBINES:

TYPES OF WIND TURBINE
Turbines can be categorized into two overarching classes based on
the orientation of the rotor
Vertical Axis
Horizontal Axis

Horizontal Axis Wind Turbines (HAWTs)
➢This is the most common wind turbine design.
➢ In addition to being parallel to the ground, the axis of blade rotation is parallel to the
wind flow.
➢Some machines are designed to operate in an upwind mode, with the blades upwind
of the tower.
➢In this case, a tail vane is usually used to keep the blades facing into the wind. Other
designs operate in a downwind mode so that the
wind passes the tower before striking the blades.

Main Components of HAWT

Turbine Blades:
❖Made of High density wood or fibre glass or epoxy composites
❖Aerofoil type cross section
❖Blades are slightly twisted from outer tip to root to avoid stall
❖Should be capable of with standing different forces like centrifugal force, fatigue due
to continuous vibration and also forces arising from wind turbulence, gust and
gravitational force
❖All factors should be taken care off at design stage
❖The diameter of typical, MW range rotor may be of order 100m.
❖Two/Three blade rotor HAWT is also called Propeller type wind turbine

Number of Blades:
❖Most common design is the three-bladed turbine for stability.
❖A rotor with an even number of blades will give stability problems for a machine with a stiff
structure.
❖The reason is that at the very moment when the uppermost blade bends backwards, because
it gets the maximum power from the wind, the lowermost blade passes into the wind shade in
front of the tower.
Hub:
❖The central solid portion of rotor wheel
❖All blades are attached to the hub
❖The mechanism of pitch angle control is provided inside the hub

Yaw control mechanism:
❖ To adjust the nacelle around the vertical axis to keep it facing the wind
provided at the base of the nacelle
Nacelle:
❖means housing containing the engines of aircraft
❖Rotor is attached to nacelle and mounted at the top of the tower
❖Contains rotor brakes, gear box, generator, electrical switch gear and control
✓Breaks: to stop rotor when power is not desired
✓Gearbox: sets up shaft rpm to suit generator
✓Switch gear & control: Protection and control functions

Pitch Control System:
➢Pitch of blade is controlled by rotating its root to the hub
➢Pitch control mechanism is provided by a hydraulic jack in the nacelle
➢The control system continuously adjusts the pitch to obtain optimal
performance

Tower :
❖Supports nacelle and rotor
❖For medium and large sized turbines, the tower length is slightly higher than the
diameter of rotor
❖ For small turbines, the tower is much larger than the rotor dia.
❖ Both steel and concrete towers are used
❖The construction may be either tubular or lattice.

TYPES OF ROTORS
Based on no. of blades, wind speed and nature of application rotors are divided as follows

Teetering of rotor
Upwind and Downwind Machines

Advantages
# Blades are to the side of the turbine's center of gravity, helping stability
#The turbine collects the maximum amount of wind energy by allowing the angle of
attack to be remotely adjusted
#The ability to pitch the rotor blades in a storm so that damage is minimized
#The tall tower allows the access to stronger wind in sites with wind shear and placement
on uneven land or in offshore locations
# Most HAWTs are self-starting
#Can be cheaper because of higher production volume
Disadvantages
➢It has difficulties operating near the ground
➢The tall towers and long blades are hard to transport from one place to another and they
need a special installation procedure
➢They can cause a navigation problem when placed offshore

VERTICAL AXIS WIND TURBINE (VAWTs)
Vertical-axis wind turbines (VAWTs)are a type of wind turbine where the main rotor shaft is
set vertically.
Advantages
❖Easier access to maintenance
❖Smaller cost of production, installation, and transport
❖Turbine does not need to be pointed towards the wind in order to be effective
❖Suitable in places like hilltops, ridgelines and passes
❖Blades spin at a lower velocity, thus, lessening the chances of bird injury
❖Suitable for areas with extreme weather conditions like mountains
Disadvantages
➢Most of them are only half as efficient as HAWTs due to the dragging force
➢Air flow near the ground and other objects can create a turbulent flow, introducing issues
of vibration
➢ VAWTs may need guy wires to hold it up (guy wires are impractical and heavy in farm areas)

TYPES OF VERTICAL AXIS WIND TURBINE
1. Darrieus Turbine 2. Gyromill Turbine 3. Savonius Turbine
Darrieus Turbine:
The Darrieus wind turbine used to generate electricity from the energy carried in the
wind.
The main components of this turbine are as follows

❖Tower:
➢ A hollow vertical rotor shaft, rotates freely about vertical axis between top and bottom bearings
➢Upper part is supported by guy ropes
➢Height is about 100m
❖ Blades:
➢ Two or three thin curved blades shaped like egg beater in profile
➢ Blades are curved in a form that minimizes bending stress by centrifugal forces So called
TROPOSKIEN Profile
➢ Have “aerofoil” Cross section
➢ Dia of rotor slightly less than tower height
❖Support Structure:
➢provided at the ground to support the weight of rotor.
➢Gear box, brakes, electrical switch gear and controls are housed with in this structure

Gyromill Wind Turbine
➢A subtype of Darrieus turbine with straight, as opposed to
curved, blades.
➢The cyclo turbine variety has variable pitch to reduce the
torque pulsation and is self-starting.
Advantages of variable pitch:
♣ High starting torque
♣ Wide, relatively flat torque curve;
♣ Lower blade speed ratio;
♣ Higher coefficient of performance
♣ More efficient operation in turbulent winds
♣ Lower blade speed ratio which lowers blade bending
stresses.
♣ Straight, V, or curved blades may be used.

SAVONIUS WIND TURBINE
♠ Savonius turbines are one of the simplest
turbines.
♠ Aerodynamically, they are drag-type
devices, consisting of two or three scoops.
♠Looking down on the rotor from above, a
two-scoop machine would look like an "S"
shape in cross section.
♠ Because of the curvature, the scoops
experience less drag when moving against the
wind than when moving with the wind.
♠ The differential drag causes the Savonius
turbine to spin.

♠ Because they are drag-type devices,
Savonius turbines extract much less
of the wind's power than other
similarly-sized lift-type turbines.
♠ Much of the swept area of a
Savonius rotor may be near the
ground, if it has a small mount
♠ without an extended post, making
the overall energy extraction less
effective due to the lower wind speeds
found at lower heights.

PERFORMANCE CHARACTERISTICS OF WIND TURBINE

EFFECT OF PERTURBATION FACTOR ON POWER EXTRACTION

Relation between ‘a’ and power coefficient

Betz Criterion:
✓In practice all the KE of the wind cannot be converted to shaft
power since air must be able to flow away from the rotor area.
✓The Betz criterion derived from the principles of conservation of
momentum and conservation of energy suggests a maximum of
59%.

WIND ENERGY.pdf

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WIND ENERGY.pdf