wind power power available from the wind performance of a hawt design procedures
Post on 22-Dec-2015
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WIND POWER
• POWER AVAILABLE FROM THE WIND
• PERFORMANCE OF A HAWT
• DESIGN PROCEDURES
ANNUAL WIND ENERGY AVAILABLEAT 50m, IN MWh/m2
LIFTING DEVICELIKE AN AIRCRAFTWING OR HELIPCOPTERROTOR.PRESSURE DIFFERENCEPRODUCES A FORCEA COMPONENT OFTHE FORCE ACTS TOPRODUCE ROTATIONAND THE OTHERCOMPONENT ACTS ONTHE TOWER.
SIMPLE WIND TURBINE THEORY
• POWER COMES FROM KE OF WIND
• THERE IS AN OPTIMUM POWER EXTRACTION RATE
• CAN ESTIMATE FROM APPLICATION OF CONSERVATION PRINCIPLES
• FORCE-MOMENTUM & BERNOULLI
CONTROL VOLUME FOR SIMPLE ANALYSISOF WIND TURBINE PERFORMANCE
ACTUAL PERFORMANCE
• CANNOT TAKE ALL POWER OUT OF WIND SINCE THIS WOULD SHROUD THE TURBINE IN STILL AIR
• THEORETICAL MAX POWER IS 59%
• PRACTICAL VALUE IS 45%
• eg V = 10m/s, (Force 5)
• Power = 270 W/m2
EFFECT OF TIP-SPEED RATIO
• OPTIMUM T/S DEPENDS ON WIDTH & NUMBER OF BLADES – SOLIDITY
• BLADES NEED TO INTERACT WITH AS MUCH AIR AS POSSIBLE & FILL UP THE SWEPT AREA
• MANY BLADES – HIGH SOLIDITY – LOW TIP SPEED
• FEW BLADES – LOW SOLIDITY – HIGH TIP SPEED
• UPPER LIMIT OF TIP SPEED -COMPRESSIBILTY
TIP-SPEED RATIO
• TOO LOW A SPEED - WIND GETS THROUGH WITH NO CONTACT
• TOO HIGH A SPEED – BLADES OFFER TOO MUCH RESISTANCE – WIND GOES ROUND THE TURBINE
• Eg 2 BLADED ROTOR HAS T/S 1/3rd HIGHER THAN A 3 BLADED ROTOR
• OPTIMUM T/S BETWEEN 6 & 20
BLADES
• TOO MANY BLADES – INTERFERENCE- SO HIGH SOLIDITY TURBINES LESS EFFICIENT
• 3 BLADES TEND TO BE BEST• GENERATORS RUN AT HIGH SPEED
SO NEED A GEARBOX• SO LOW SOLIDITY GOOD BECAUSE
THEY RUN AT HIGH SPEED
RPM
• MUST BE CONSTANT WHATEVER V
• DEPENDS ON NUMBER OF POLES IN ELECTROMAGNET
• N = CONSTANT = 6000/POLES
• POLES = 6, 8 ETC
• TURBINE MAY HAVE 2 OPERATING VALUES OF N, DEPENDING ON V
POWER OUTPUT FROM A HAWT
• SEE “WINDTURB” IN RESOURCE FILE
• POWER IN WIND VS WINDSPEED
• WINDSPEED FREQUENCY DISTRIBUTION
• POWER CURVE OF TURBINE
• ANNUAL POWER OUTPUT
• EFFICIENCY VS WINDSPEED
302
1VAP T
POWER OUTPUT CURVEFOR A TURBINE
6.5 m/s = 15mph = Force 4A moderate wind
RAYLEIGH FREQUENCY DISTBN
FMEAN WIND SPEED
22
)4
exp(2 MM V
V
V
V
MV
F IS THE FRACTION OF 8760 HOURS WHEN THE WIND IS ATSPEED V. MEAN WIND SPEED IS 5 m/s.
EFFECT OF Vm ON RAYLEIGH DISTRBN
EFFICIENCY = POWER OUTPUT/POWER IN WIND
FORCES ON TURBINES
• VERTICAL WIND SHEAR
• HORIZONTAL WIND SHEAR
• WIND GUSTS
• GRAVITY
• TOWER SHADOW
CONCLUSIONS
• A DILUTE FORM OF ENERGY• NEED TO PROCESS LARGE VOLUMES• NOT ECONOMIC UNLESS USE NFFO• NOT THE ANSWER TO GROWING
ENERGY CRISIS• NEEDS ENERGY STORAGE SYSTEM• CAN DISPLACE UP TO 10% OF
ELECTRICAL SUPPLIES