Wind Resource

Question 1

Where does wind come from?

Answer 1

Band of higher and lower pressure formed around the earth.

• high pressure produced bu cold dry air descending - adiabatic heating creates warm dry air at ground level
• low pressure areas experience rising air, which cools on expansion, creating rain

Question 2

In circulation about the earths atmosphere, how many cells are formed in each hemisphere?

Answer 2

Three

Question 3

What are the Coriolis effects?

Answer 3

• owing to the rotation of the earth, the trajectories of objects in the northern hemisphere will deflect to the right
• this causes prevailing westerly winds above 30N as air moves north from high to low pressure regions
• results in vorticity-cyclones (anti-clockwise rotation) around regions of low pressure

Question 4

Where does higher wind speed occur?

Answer 4

Around regions of lower pressure

Question 5

Wind speed measurement devices: Anemometers

Answer 5

• cup anemometers
• propeller anemometers
• drag devices (ERA gust anemometer)
• air-pressure devices (pitot tube)
• sonic devices
• doppler devices (LIDAR and SONAR)
• calibrated kites
• tatter flags

Question 6

Where are anemometers usually placed?

Answer 6

Towers form 10m to 200m
- at lower heights models of wind speed distribution can be used to determine speed at other heights (Prandlt / Power law modelling)

Question 7

Does the mean wind speed over a day give a good indication of the available energy in the wind?

Answer 7

No, periods of high wind speed and thus power are obscured when measuring a mean.

Question 8

What do is necessary to model the power in wind in a useful way?

Answer 8

A frequency distribution.

Question 9

What are two functions used to model the probability distribution of wind speed?

Answer 9

• Rayleigh function

- Weibull function

Question 10

Wind and energy peak at different speeds. What speeds should a turbine be designed for?

Answer 10

Design for greater than the average wind speed.