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