Energy From Wind

What Energy From Wind covers

Energy From Wind is examined in Unit AS 1, The Earth's Capacity to Support Human Activity, a written examination. It covers horizontal and vertical axis wind turbines, kinetic energy, wind power and the Betz limit, power curves, rated output and energy losses, swept area, blade length and turbine mass, air density, hub height and turbine siting, power control, yawing and survival speed and choosing a location for a commercial wind farm.

The 7 subtopics

Each one has its own page. CCEA AS Environmental Technology students sit this topic in the first year.

• Horizontal and vertical axis wind turbinesHorizontal and vertical axis designs, Savonius and Darrieus rotors, upwind and downwind turbines, and the nacelle, gearbox, hub, blades, anemometer, wind vane, brake, transformer, tower and foundation.Open →
• Kinetic energy, wind power and the Betz limitThe kinetic energy of moving air, the power equation P = ½ρAv³ and why power rises with the cube of wind speed, worked rotor calculations, the Betz limit and the power coefficient of real turbines.Open →
• Power curves, rated output and energy lossesRotor collected energy against rated output and the losses between them, power curves, cut-in, rated and cut-out speeds, estimating annual output from site wind data, and capacity factor calculations.Open →
• Swept area, blade length and turbine massSwept area and its calculation, how power grows with blade length, why doubling blade length multiplies mass by about eight, glass and carbon fibre blades, stiffness and fatigue, and siting limits on blade size.Open →
• Air density, hub height and turbine sitingHow air density, temperature and altitude affect output, hub height and rotor diameter, why wind speed rises with height, wind resource assessment, terrain and visual impact, and cost–benefit decisions on tower height.Open →
• Power control, yawing and survival speedPitch control, passive and active stall, feathering, furling on small turbines, variable-speed operation, yawing and unwinding, and survival speed compared with cut-out speed.Open →
• Choosing a location for a commercial wind farmWind resource, grid connection and turbine spacing, development costs, birds and bats, upland peat, shadow flicker and noise, community acceptance and benefit funds, radar, environmental impact assessment, offshore sites and repowering.Open →

What you need to know

Answer each one before you reveal it.

Take Energy From Wind further

The same content, four other ways.

Commonly confused

Pairs that lose marks when they are blurred together.

• Horizontal axis wind turbine vs Vertical axis wind turbine

  Horizontal axis wind turbine: a machine whose rotor shaft points into the airflow, parallel to the ground. Vertical axis wind turbine: a machine whose rotor shaft stands upright and accepts airflow from any direction.

• Rotor collected energy vs Rated energy output

  Rotor collected energy: the kinetic share of moving air that the blades actually capture as shaft rotation. Rated energy output: the electrical power a machine is designed to deliver at its design wind speed.

• Pitch control vs Stall control

  Pitch control: turning each blade about its long axis to reduce lift in strong winds. Stall control: blades shaped so airflow separates from them, cutting lift in strong winds.

Questions from this topic

Each one with the model answer underneath.

1. 1

   What is the main difference between a horizontal axis and a vertical axis wind turbine?

   Model answer

   A horizontal axis wind turbine has its main rotor shaft parallel to the ground and pointing into the wind. A vertical axis wind turbine has its shaft standing upright, at right angles to the ground.

2. 2

   Why does a vertical axis wind turbine not need a yaw mechanism?

   Model answer

   A vertical axis turbine accepts wind from any direction without turning. The rotor works the same whichever way the wind blows.

3. 3

   Describe how a Savonius rotor extracts energy from the wind.

   Model answer

   A Savonius rotor has curved scoops, and drag on the hollow side of each scoop pushes the rotor round. The rotor turns slowly but with high starting torque.

4. 4

   How does a Darrieus rotor differ from a Savonius rotor?

   Model answer

   A Darrieus rotor has aerofoil blades that generate lift, so it spins faster and more efficiently. A Savonius rotor relies on drag and turns slowly.

5. 5

   Why is a Darrieus turbine often unable to start by itself?

   Model answer

   A Darrieus rotor produces little torque when stationary, because its aerofoils only generate useful lift once moving. Many designs need a motor or a small Savonius rotor to start them.

6. 6

   Give three advantages of a vertical axis wind turbine over a horizontal axis design.

   Model answer

   A vertical axis turbine needs no yaw system because it accepts wind from any direction. The gearbox and generator can sit at ground level, which makes maintenance easier. A vertical axis turbine also copes better with turbulent, gusty winds such as those around buildings.

What is inside Levo

Six ways to work the same material.

Energy From Wind revision questions

Is Energy From Wind examined at AS in CCEA Environmental Technology?

Yes. It sits in AS 1, which you take in the first year, so it is on the AS paper as well as counting towards the full A level.

What does Energy From Wind cover in CCEA AS-Level Environmental Technology?

7 subtopics: horizontal and vertical axis wind turbines, kinetic energy, wind power and the betz limit, power curves, rated output and energy losses, swept area, blade length and turbine mass, air density, hub height and turbine siting, power control, yawing and survival speed and choosing a location for a commercial wind farm. Each one has its own page with questions and model answers.

How is Energy From Wind organised?

By the CCEA 3930 specification, subtopic by subtopic, so it matches the order you are taught it in.