Aim for FiveEnvironmental Science

Analyze an environmental problem doing calculations

Planning a wind farm

  • Units 6 and 7
  • 10 points
  • About 24 minutes

You can use a calculator on this question, just like on exam day.

You work through an environmental scenario using numbers: set up and solve calculations (showing your work), then explain the science and propose solutions. Several of the 10 points come from the calculations, usually one for the setup and one for the answer. On the exam: Question 3 of 3 in the 70-minute free-response section (Section II is 40% of the exam score).

The question

A town of 12,000 homes currently buys all of its electricity from a coal-fired power plant. The average home uses 10,500 kWh of electricity per year. The town is considering building wind turbines. Each turbine has a maximum (rated) output of 3.0 megawatts (MW), but because wind speed varies, a turbine at this site produces on average 35% of its maximum output over a year. (1 MW = 1,000 kW; 1 year = 8,760 hours)

Suggested time: 24 minutes

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Part (a)

2 points

Calculate the amount of electricity, in kWh, that one turbine would generate in a year. Show your work.

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Part (b)

2 points

Calculate the number of turbines needed to supply all of the town's yearly electricity use. Show your work.

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Part (c)

2 points

The coal plant releases 0.98 kg of carbon dioxide (CO₂) for every kWh of electricity it generates. Calculate the mass of CO₂, in metric tons, that the town would avoid releasing each year if all of its electricity came from the wind turbines instead. Show your work. (1 metric ton = 1,000 kg)

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Part (d)

1 point

Explain why a wind turbine produces, on average, much less than its maximum output.

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Part (e)

1 point

Describe one environmental disadvantage of wind turbines.

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Part (f)

1 point

Identify one air pollutant, other than CO₂, released by the coal-fired power plant.

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Part (g)

1 point

Propose one realistic energy conservation measure the town's households could adopt that would reduce the number of turbines needed.

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