WIND ENERGY Wind are produced by disproportionate solar heating of the earth’s land and sea surfaces. –It forms about 2% of the solar energy –Small % of the 2% is exploited Worldwide installed capacity: 10,000 MW

Wind Energy Needs: Needs: Good winds Good winds Coastal areas, hilltops, E-W valleys Coastal areas, hilltops, E-W valleys Minimum average windspeed : Minimum average windspeed : 4.5 m/s at 10 metres 4.5 m/s at 10 metres 3 types of wind energy systems: 3 types of wind energy systems: central grid central grid isolated grid isolated grid off-grid off-grid 750 kW machine

WIND RESOURCES IN US

WIND RESOURCES IN THE WORLD

CONSTRAINTS TO THE APPLICATION OF WIND ENERGY Wind vary in speed, hence incident energy flux, during the day from season to season, and not necessarily in concert with demand for electricity. This non-dispatchable nature limits the portion of wind power in a utility’s generator mix, with provision for spinning and standby reserve and grid stability being important concerns. Other than the fortuitous proximity of pumped storage hydro installation, there is no sufficiently inexpensive way, at present, to store energy for future use. The best wind fields may not be in reasonable proximity to large population centers, which necessitates the construction of expensive high-voltage transmission systems and results in large line losses of the input energy

WIND POWER Power per unit area transported by fluid system is proportional to the cube of the fluid velocity.

SPECTRUM AVERAGE POWER Spectrum average power is of particular importance due to the variability of wind speed.

WEIBULL STATISTICS CONT. Generally, measured wind speed is fitted to weibull statistics. The two parameter weibull cumulative frequency distribution is given by;

WEIBULL STATISTICS CONT.

Weibull wind velocity frequency function for scale parameter c=1

Variation of wind speed with elevation For an idealized smooth plane surface, the average wind speed increases with height approximately as the 1/7 th power: Thus, wind turbine with a hub height of 50 m will experience about 7.6% rise in wind speed compared to one with a hub-height of 30 m and an increase in wind power of 24.5%

Factors Affecting Output of Wind turbine Topography and vegetation alter the wind field. Crest of treeless hills are advantageous; however, the flow above hills does not follow the 1/7 th power law In general, there is less fluctuation in air flow at greater heights Adjacent wind turbines interfere to reduce the energy flow field.

Air Density –The available power of fluid flow is directly proportional to the density. –At 15 o C and 1 atmosphere the value of ρ = kg/m 3 ; the value of the ρ at different temperature and pressure is estimated using the ideal gas relation –The density can also be estimated from ρ(1-0.1H s ) where H s the height above sea level –The value of ρ is also decrease by water vapor by a factor of T(in o C) Factors Affecting Output of Wind turbine

Maximum wind Turbine Efficiency Betz Ratio –From the Betz relation the maximum turbine efficiency is η max =0.593 –Well-design modern turbine can achieve a maximum efficiency of 50% –Net value of 40% after gearbox and electrical losses consideration –In addition to all the factor mentioned above the number turbine blades enhance the performance of the turbine. More blades mean higher torque and functionality at lower speed.

Wind Machinery and Generating Systems Figure 15.6

Wind Turbine Rating