Climate and energy systems

A planet's average albedo increases while incoming solar power stays the same. What is the most direct initial effect?

1. A

   Less incoming energy is reflected

2. B

   More incoming energy is reflected, so less is absorbed

3. C

   The planet stops emitting infrared radiation

4. D

   All greenhouse gases disappear

1. a

   Select and explain Select the best response and explain how the change affects the energy balance before feedbacks occur.

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   Correct choiceB

   1. 1

      Selects option B: a higher albedo reflects more incoming energy, so less is absorbed.

   2. 2

      States that a higher albedo means a greater fraction of incoming radiation is reflected.

   3. 3

      Concludes that absorbed solar power initially decreases, tending to lower equilibrium temperature if other factors remain fixed.

A community compares two 1.0 MW electricity projects. Use 8760 hours in one year and annual energy = rated power × capacity factor × time.

1. a

   Calculate Calculate the annual electrical energy from each project in MWh.

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   1. 1

      Uses 1.0 MW × 0.30 × 8760 h for wind.

   2. 2

      Obtains 2628 MWh for wind.

   3. 3

      Uses 1.0 MW × 0.18 × 8760 h for solar.

   4. 4

      Obtains 1576.8 MWh, or about 1577 MWh, for solar.

2. b

   Compare Use the table and your calculations to state two evidence-based advantages of wind in this comparison.

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   1. 1

      States that wind produces more annual energy at the same rated power.

   2. 2

      States that wind has lower listed lifecycle emissions per kWh.

3. c

   State State why the table is not enough to make a final community decision.

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   1. 1

      Identifies missing evidence such as cost, storage or grid needs, habitat surveys, land ownership, reliability, noise, construction impacts, or stakeholder priorities.

A combined heat-and-power plant receives 100 MJ of fuel energy. It supplies 35 MJ of electrical energy, rejects 65 MJ as thermal energy, and can deliver 40 MJ of that thermal energy to nearby buildings in winter. An advertisement calls the plant ‘100% efficient because no energy is destroyed.’

1. a

   Calculate Calculate the electrical efficiency and the winter useful-energy efficiency.

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   1. 1

      Calculates electrical efficiency = 35 ÷ 100 = 35%.

   2. 2

      Adds useful outputs: 35 MJ + 40 MJ = 75 MJ.

   3. 3

      Calculates winter useful-energy efficiency = 75 ÷ 100 = 75%.

2. b

   Explain Explain why conservation of energy does not make every device 100% efficient.

   2
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   1. 1

      States that total energy is conserved.

   2. 2

      Explains that some energy becomes less useful or is transferred to unwanted surroundings, so useful output is smaller than input.

3. c

   Evaluate Evaluate the advertisement and the plant's value across a full year.

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   1. 1

      Rejects the 100% claim as a confusion between conservation and useful-energy efficiency.

   2. 2

      Recognises that 75% depends on a real demand for the recovered heat, which may fall in warm seasons or at distant buildings.

   3. 3

      Gives a balanced conclusion: heat recovery can substantially improve resource use, but performance must be reported for actual demand and system boundaries.