Unit 6 · Topic 6.12 Beta

Wind Energy

Wind turbines turn the kinetic energy of moving air into electricity with blades, a gearbox and a generator.

Practice 1: Concept ExplanationPractice 7: Environmental Solutions

Part 1 · Hook

Why this matters

On the plains of Iowa and Texas, rows of white turbines taller than a 30-story building turn slowly above fields of corn and cattle. In Iowa, wind now makes about two thirds of the state's electricity. It is free, clean while running and shares land with farming, but it stops when the air goes still.

Part 2 · Before you start

What this builds on

Part 3 · Prerequisite check

Quick check before you start

1. What drives the wind?

  1. Uneven heating of Earth's surface by the sun
  2. The moon's gravity
  3. Heat from Earth's core
  4. Ocean tides
Show the answer

Unequal heating makes air pressure differences, and air moves from high to low pressure.

  • Correct: Uneven heating of Earth's surface by the sun:
  • The moon's gravity:
  • Heat from Earth's core:
  • Ocean tides:

2. What does intermittency mean for an energy source?

  1. It is not available all the time
  2. It runs out
  3. It pollutes
  4. It needs fuel
Show the answer

An intermittent source, like solar at night, needs storage or backup.

  • Correct: It is not available all the time:
  • It runs out:
  • It pollutes:
  • It needs fuel:

Part 4 · See it

See it first

A wind turbine on a tall tower with three blades and a nacelle. Wind arrows push on the blades. A callout of the inside of the nacelle shows a shaft, a gearbox and a generator in a row: faster rotation, generator, electricity. An arrow at the base carries electricity to power lines. A list reads: no fuel and no emissions while running; land below can still be farmed or grazed; output varies with the wind (intermittent); blades can kill birds and bats.
A wind turbine: wind spins the blades, and the shaft, gearbox and generator in the nacelle turn that motion into electricity. LevlPrep original diagram.

Part 5 · Step by step

How it works, step by step

  1. The sun heats Earth unevenly, so air moves from high to low pressurewind carries kinetic energy across plains, coasts and seas
  2. Wind pushes on the turbine bladesthe rotor turns a shaft, a gearbox speeds it up and a generator makes electricity
  3. No fuel is burnedthere is no air pollution or carbon dioxide while running, and land below can still be farmed
  4. The wind slows or stopsoutput falls, so a grid with much wind needs storage, a wide network or backup

Part 6 · Key ideas

Key ideas

  • A wind turbine turns the kinetic energy of moving air into electricity. A wind farm is a group of turbines, on land or offshore.
  • Taller towers and offshore sites reach faster, steadier wind; output rises steeply with wind speed (about eight times for double the speed).
  • Advantages: no fuel, no emissions while running, very low life-cycle carbon dioxide, land shared with farming, income for landowners.
  • Drawbacks: intermittency, bird and bat deaths, noise and changed views, and new transmission lines from remote windy areas.

Part 7 · Misconception

A common mistake

The wrong idea: A wind farm takes a whole field out of use, the way a coal mine does.

What actually happens: The tower bases and access roads cover only a small share of a wind farm. Crops and cattle use most of the land between turbines, and the farmer earns lease payments too.

Part 8 · Check yourself

Check yourself

Exam-style questions. Anything you miss goes into your review queue.

1. How does a wind turbine make electricity?

  1. Wind cools a steam boiler, which then spins a turbine
  2. Sunlight on the blades makes an electric current flow
  3. Air pressure squeezes a battery inside the tall tower
  4. Wind spins the blades, which turn a generator
Show the answer

The kinetic energy of moving air pushes on the blades; the rotor turns a shaft (often through a gearbox) that spins a generator in the nacelle.

  • Wind cools a steam boiler, which then spins a turbine: There is no boiler or steam in a wind turbine.
  • Sunlight on the blades makes an electric current flow: Blades are not solar cells.
  • Air pressure squeezes a battery inside the tall tower: Turbines do not squeeze batteries.
  • Correct: Wind spins the blades, which turn a generator: Right: moving air, spinning blades, generator.

2. Which is an environmental drawback of wind farms?

  1. They produce radioactive waste each year
  2. Spinning blades can kill birds and bats
  3. They release carbon dioxide while turning
  4. They flood large areas of nearby farmland
Show the answer

Collisions kill birds and bats; careful siting and pausing turbines at low wind speeds reduce deaths. Turbines also make noise and change views.

  • They produce radioactive waste each year: Wind turbines make no radioactive waste.
  • Correct: Spinning blades can kill birds and bats: Right: bird and bat deaths.
  • They release carbon dioxide while turning: Turbines release nothing while running.
  • They flood large areas of nearby farmland: Wind farms do not flood land; that is a dam's impact.

3. A region gets a large share of its electricity from wind. What does it need to keep power steady on calm days?

  1. More turbines built in the same calm valley
  2. Taller blades that keep spinning without wind
  3. Turbines that run on sunlight stored in the tower
  4. Storage, a wide grid or backup power sources
Show the answer

Wind is intermittent. Batteries and pumped storage, grids that link windy and calm areas, and flexible backup plants keep supply steady.

  • More turbines built in the same calm valley: More turbines in a calm place still make nothing when there is no wind.
  • Taller blades that keep spinning without wind: Blades need wind to spin.
  • Turbines that run on sunlight stored in the tower: Turbines do not run on sunlight.
  • Correct: Storage, a wide grid or backup power sources: Right: storage, a wider grid or flexible backup.

Data

Electricity sources compared

Life-cycle carbon dioxide (from building, fuel and running, per kWh) and typical capacity factor (rounded values near published estimates; invented for practice)
SourceLife-cycle carbon dioxide (g per kWh)Capacity factor (%)
Coal82050
Natural gas49055
Nuclear1290
Solar (photovoltaic)4525
Wind (onshore)1135

4. Which two sources in the table release the least carbon dioxide over their full life cycle?

  1. Coal and solar
  2. Wind and nuclear
  3. Coal and natural gas
  4. Solar and natural gas
Show the answer

Wind (11) and nuclear (12) grams per kWh are the lowest. Solar is low too (45), and coal (820) is highest.

  • Coal and solar: Coal is the highest.
  • Correct: Wind and nuclear: Right: 11 and 12 g per kWh.
  • Coal and natural gas: These are the two highest.
  • Solar and natural gas: Natural gas is about 490 g per kWh.

5. A town replaces 50,000 MWh a year of coal electricity with wind. Using the life-cycle values, how many metric tons of carbon dioxide does it avoid each year? (1 MWh = 1,000 kWh; 1 metric ton = 1,000,000 g.)

Type a number, then its unit (metric tons). Scale words (2.5 million) and powers of ten (2.5 × 10^6) are read.

Show the answer

Saved per kWh: 820−11=809820 - 11 = 809 g. Total: 50,000×1,000kWh×809g/kWh÷1,000,000g/t50{,}000 \times 1{,}000\,\text{kWh} \times 809\,\text{g/kWh} \div 1{,}000{,}000\,\text{g/t}=40,450= 40{,}450 metric tons.

  • Answer: 40,450 metric tons

6. Wind's capacity factor (35%) is lower than nuclear's (90%). What does this mean?

  1. A wind farm releases more carbon dioxide than a nuclear plant
  2. Wind turbines are broken down 65 percent of the time
  3. A wind farm costs more to build than a nuclear plant
  4. A wind farm averages a smaller share of its maximum
Show the answer

Capacity factor is average output divided by maximum. Wind varies, so it averages about a third of its maximum; this is not breakdown time.

  • A wind farm releases more carbon dioxide than a nuclear plant: The table shows wind's life-cycle emissions slightly below nuclear's.
  • Wind turbines are broken down 65 percent of the time: Low output is mostly from light winds, not breakdowns.
  • A wind farm costs more to build than a nuclear plant: Capacity factor says nothing about building cost.
  • Correct: A wind farm averages a smaller share of its maximum: Right: lower average output relative to maximum.

Part 9 · Summary

Summary

Wind turbines turn the kinetic energy of moving air into electricity with blades, a gearbox and a generator. Wind is renewable, needs no fuel, releases no carbon dioxide while running and shares land with farming, so it has some of the lowest life-cycle emissions of any source. Its drawbacks are intermittency, which calls for storage or backup, harm to birds and bats, noise and views, and the need for new power lines.

Part 10 · Up next

What comes next

Part 11 · Connections

Connections

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