AP (APES) : Energy Resources — Environmental Science
1. Classification of Renewable vs Non-Renewable Energy ★★☆☆☆ ⏱ 3 min
The core classification system for energy resources relies on replenishment rate relative to human consumption. This is one of the most commonly tested foundational concepts on the APES exam, often paired with tradeoff evaluation questions.
A key metric for comparing non-renewable resource longevity is the reserve-to-production (R/P) ratio, calculated as:
R/P = \frac{\text{Total proven reserves of resource}}{\text{Annual global consumption rate}}
This value gives the number of years the resource will remain available at current constant consumption rates, excluding future demand growth or new reserve discoveries.
Exam tip: Examiners often ask you to compare lifecycle carbon intensity: non-renewables have 10–100x higher CO₂ emissions per kWh than most renewables, except unsustainably harvested biomass.
2. Fossil Fuels: Extraction and Environmental Impacts ★★★☆☆ ⏱ 5 min
Fossil fuels are formed from the compressed, partially decomposed remains of ancient marine and terrestrial organisms, and supply ~80% of global primary energy as of 2024. Extraction methods and associated impacts vary by fuel type.
- **Coal**: Shallow deposits are extracted via surface mining (strip mining, mountaintop removal), while deep deposits use subsurface underground mining. Impacts include habitat destruction from surface mining, acid mine drainage (sulfuric acid leaching from exposed pyrite rock that contaminates waterways), particulate air pollution, and high worker risk of black lung disease and mine collapses.
- **Crude oil**: Conventional drilling extracts oil from porous underground reservoirs, while hydraulic fracturing (fracking) injects high-pressure water, sand, and toxic chemicals into tight shale rock to release trapped oil. Impacts include catastrophic oil spills, groundwater contamination from fracking chemicals, and induced seismic activity from wastewater injection.
- **Natural gas**: Extracted via conventional drilling and fracking, it has the lowest carbon intensity of all fossil fuels. However, methane (a greenhouse gas 28x more potent than CO₂ over a 100-year timeframe) leaks from extraction and transport infrastructure, so its lifecycle emissions are 30–50% higher than direct combustion-only estimates.
3. Nuclear Energy: Fission, Waste, and Safety ★★★☆☆ ⏱ 4 min
Nuclear power supplies ~10% of global electricity, and generates power via controlled nuclear fission, where heavy uranium-235 (U-235) isotopes are bombarded with neutrons, splitting into smaller atoms and releasing large amounts of heat that boils water to drive steam turbines.
A simplified fission reaction is:
^{235}_{92}\text{U} + ^1_0\text{n} \rightarrow ^{92}_{36}\text{Kr} + ^{141}_{56}\text{Ba} + 3^1_0\text{n} + \text{Heat Energy}
The extra neutrons produced trigger a controlled chain reaction, regulated by neutron-absorbing control rods (made of boron or cadmium) that are inserted or removed to adjust reaction speed.
Nuclear waste is grouped by radioactivity level for storage:
- **Low-level waste**: Contaminated tools, clothing, and filters with low radioactivity and short half-lives, stored in shallow lined landfills.
- **Intermediate-level waste**: Reactor components and chemical sludges with moderate radioactivity, stored in sealed steel and concrete containers above ground.
- **High-level waste**: Spent fuel rods with extremely high radioactivity and half-lives up to millions of years. No permanent long-term storage facility is operational globally; most waste is stored in on-site dry cask storage at nuclear plants.
Nuclear power has one of the lowest per-kWh fatality rates of all energy sources, but high-profile accidents have driven public opposition, including Three Mile Island (1979, US, partial meltdown, no direct fatalities), Chernobyl (1986, USSR, full meltdown, ~4,000 excess cancer deaths), and Fukushima (2011, Japan, tsunami-triggered meltdown, no direct radiation fatalities, 100,000+ displaced).
4. Energy Conservation and Efficiency ★★☆☆☆ ⏱ 4 min
Energy conservation is the reduction of energy use via efficiency improvements or behavioral changes, and is the lowest-cost, lowest-impact strategy to reduce greenhouse gas emissions, with a higher return on investment than building new power generation capacity.
A key metric for appliance efficiency is the Energy Efficiency Ratio (EER), calculated as:
EER = \frac{\text{Cooling output (BTU/h)}}{\text{Power input (W)}}
Higher EER values indicate more efficient appliances. Examiners also frequently test payback period calculations for energy efficiency upgrades:
\text{Payback Period (years)} = \frac{\text{Upfront cost of upgrade}}{\text{Annual cost savings}}
A shorter payback period indicates a more economically viable investment. Proven conservation strategies span residential, industrial, and transportation sectors:
- **Residential**: LED light bulbs (75% less energy use than incandescents, 25x longer lifespan), programmable thermostats, insulation, and Energy Star certified appliances.
- **Industrial**: Cogeneration (combined heat and power, CHP), which captures waste heat from electricity generation for heating, reaching up to 90% efficiency vs 35% for conventional power plants.
- **Transportation**: Increased fuel economy standards, public transit expansion, electric vehicle adoption, and walkable urban design.
Exam tip: Payback period questions are extremely common on APES FRQs, always remember to divide upfront cost by annual savings, not the reverse.
Common Pitfalls
Why: The terms are used interchangeably in popular media.
Why: Marketing often frames natural gas as clean relative to coal.
Why: Students confuse waste disposal and mining emissions with operational emissions.
Why: Students assume they need to account for real-world demand increases.
Why: Textbooks state biomass is carbon-neutral as a general rule.