APES
Unit 6 · 10–15% of exam

Energy Resources & Consumption

Fossil fuels, nuclear, renewables, energy efficiency. The most calculation-heavy unit. See the energy calculations priority page for worked dimensional analysis.

Must-know content

  • Nonrenewable: coal, oil, natural gas, nuclear. Fuel is finite.
  • Renewable: solar, wind, hydro, geothermal, biomass, tidal.
  • Coal types (low → high energy & cleanliness): lignite < sub-bituminous < bituminous < anthracite. Anthracite has highest carbon content, most energy per mass, lowest sulfur.
  • Oil: dominant transportation fuel. Spills devastate marine ecosystems (Exxon Valdez, Deepwater Horizon). Burning releases CO₂ and air pollutants.
  • Natural gas (CH₄): cleanest fossil fuel — least CO₂ per unit energy. Concerns: methane leaks (fracking), induced seismicity, groundwater contamination.
  • Nuclear (fission of U-235): near-zero operational CO₂. Drawbacks: radioactive waste needing 10,000+ year storage, meltdown risk (Chernobyl, Fukushima), uranium mining impacts, weapon proliferation.
  • Solar:
    • Active — photovoltaic (PV) cells convert sunlight directly to electricity.
    • Passive — building design (south-facing windows, thermal mass).
    • Concerns: intermittent, mining for rare-earth metals, panel disposal.
  • Wind: turbines convert kinetic wind energy to electricity. Bird/bat mortality, noise, intermittency.
  • Hydroelectric: dam stores potential energy → kinetic → electricity. Reliable but disrupts fish migration, sediment flow, displaces communities. Methane from reservoir decay.
  • Geothermal: uses Earth\'s internal heat. Reliable; minimal emissions. Limited to tectonically active regions.
  • Biomass: burning organic matter. Carbon-neutral if sustainably grown. Indoor air pollution risk in developing nations.
  • Energy efficiency: useful energy output / total input. Cogeneration captures waste heat → much higher overall efficiency.
  • Grid concepts: baseload (always-on, e.g., nuclear, coal) vs. peak power (turn on for high-demand periods, e.g., natural-gas turbines).

Example questions

MCQ Which fossil fuel produces the LEAST CO₂ per unit energy? (A) Lignite (B) Bituminous coal (C) Oil (D) Natural gas

Answer: D. Natural gas (CH₄) has the highest H:C ratio of any fossil fuel — more of its energy comes from H combustion (producing H₂O, not CO₂), so it emits less CO₂ per unit of useful energy.

FRQ A 1500 W hair dryer is used 0.25 hr per day for 365 days. Calculate the annual electricity use in kWh.

Answer:

Energy = Power × time

= 1500 W × (1 kW / 1000 W) × 0.25 hr/day × 365 day/yr
= 1.5 kW × 0.25 hr/day × 365 day/yr
= 136.875 kWh/yr ≈ 137 kWh/yr

Always carry units through every step. Without the kWh on the final answer, APES graders deduct.

MCQ A drawback of nuclear power compared to wind power is: (A) Higher CO₂ emissions during operation (B) Long-lived radioactive waste (C) Bird and bat mortality (D) Intermittency

Answer: B. Nuclear has near-zero CO₂ during operation but produces high-level radioactive waste that requires geological-scale storage. Wind has near-zero waste but suffers from intermittency and wildlife impacts.

Drill flashcards

Unit 6 Coal Tap / Space to flip
Unit 6 Most abundant fossil fuel. Highest CO₂ per unit energy. Releases SO₂, NOx, mercury, particulates. Mining damages land.
Unit 6 Petroleum (oil) Tap / Space to flip
Unit 6 Used for transportation. Spills devastate marine ecosystems. Releases CO₂ and air pollutants when burned.
Unit 6 Natural gas (CH₄) Tap / Space to flip
Unit 6 Cleanest fossil fuel — least CO₂ per unit energy. Methane leaks (fracking) are a major GHG concern.
Unit 6 Nuclear fission Tap / Space to flip
Unit 6 U-235 splits when struck by neutron, releasing energy + more neutrons (chain reaction). No CO₂ but radioactive waste.
Unit 6 Nuclear concerns Tap / Space to flip
Unit 6 Long-lived radioactive waste, risk of meltdown (Chernobyl, Fukushima), uranium mining impact, weapon proliferation.
Unit 6 Solar PV Tap / Space to flip
Unit 6 Photovoltaic cells convert sunlight directly into electricity. Intermittent (no sun at night). No emissions during operation.
Unit 6 Wind power Tap / Space to flip
Unit 6 Turbines convert kinetic wind energy to electricity. Concerns: bird/bat mortality, noise, landscape, intermittency.
Unit 6 Hydroelectric Tap / Space to flip
Unit 6 Dam stores potential energy → kinetic → electricity. Reliable but disrupts rivers, sediment, fish migration, methane from reservoirs.

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