Wind Energy PPQ Flashcards
Describe two differences between Vertical Axis Wind Turbines (VAWT) and Horizontal Axis Wind Turbines (HAWT)
Any 2 of VAWT can opreate with any wind direction HAWT has to face the wind, VAWT can operate at very low windspeeds whereas HAWT cannot, VAWT has a lower RPM than a HAWT, VAWT is quieter than a HAWT.
Calculate the wind speed required to produce 17,280 joules of energy from 540 kg of air
K.E = 0.5mv^2 17280 = 0.5 x 540 x v^2 v^2 = 17280/ 0.5 x 540 v^2 = 64 v = 8m/s
Define what is meant by the term Betz Limit when applied to a wind turbine and explain how it is related to power efficiencies achievable by wind turbines in the real world
The maximum a mount of the winds kinetic energy that a HAWT can convert to mechanical energy turning a rotor. Betz calculated this at 59.3% of the kinetic energy from the wind.
Most modern turbines can convert 35 - 45% of the winds energy to electricity. This is because of the losses of energy to heat and sound throughout the system.
Explain the relationship between Power output and swept area for a HAWT
Power output is directly proportional to the swept area
Explain the relationship between Power output and wind speed for a HAWT
The power output increases with wind speed as power out is directly proportional to v^3
Describe how the power output of a wind turbine is affected by the air density and temperature
When air density is lower the power output is less or when air density is higher the power output increases
When temperature is lower the turbine power output is greater or when temperature is higher the turbine power output reduces
A turbine has a mas of 10 tonnes, if the blade length is doubled how is the new mass 80 tonnes
Existing mass (10 tonnes) is proportional to R^3, If the blade length to 2R then the new mass is proportional to 8R^3. If R corrisponds with 10 tonnes then 2R corrisponds with a mass of 80 tonnes.
Describe the purpose of the Yaw mechanism
It ensures the rotor faces the wind at all times and maximum energy extraction
