Energy Resources (APES) — AP Environmental Science APES Study Guide

For: AP Environmental Science candidates sitting AP Environmental Science.

Covers: Classification of renewable and non-renewable energy, fossil fuel extraction methods and environmental impacts, nuclear fission mechanics and safety risks, and evidence-based energy conservation and efficiency strategies.

You should already know: Algebra 1, basic biology and chemistry.

A note on the practice questions: All worked questions in the "Practice Questions" section below are original problems written by us in the AP Environmental Science style for educational use. They are not reproductions of past College Board papers and may differ in wording, numerical values, or context. Use them to practise the technique; cross-check with official College Board mark schemes for grading conventions.

1. What Is Energy Resources (APES)?

Energy resources are natural or human-made sources of usable power that support all industrial, residential, agricultural, and ecological functions, and this unit makes up 10–15% of your total AP Environmental Science exam score per the 2024 College Board CED. Common synonyms include energy sources and power feedstocks; this topic overlaps heavily with Unit 7 (Atmospheric Pollution) and Unit 9 (Global Change) due to the cascading environmental impacts of energy production and consumption. Examiners frequently test this content in both multiple-choice and free-response sections, often asking you to evaluate tradeoffs between different energy sources for real-world communities.

2. Renewable vs non-renewable energy

The core classification system for energy resources relies on replenishment rate relative to human consumption:

• Non-renewable energy resources exist in fixed, finite quantities on Earth, forming over geologic timescales (millions of years) far slower than human consumption rates. Examples include coal, crude oil, natural gas, and uranium ore.
• Renewable energy resources are replenished naturally at rates equal to or faster than human consumption, typically on annual or shorter timescales. Examples include solar, wind, hydro, geothermal, sustainably harvested biomass, and tidal power.

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.

Worked Example

Global proven coal reserves are estimated at 1,074 billion short tons, with annual global consumption of 7.9 billion short tons. Calculate the R/P ratio for coal, and interpret the result.

1. Substitute values into the formula: $R/P=\frac{1074}{7.9}\approx 136$
2. Interpretation: At current consumption rates, global coal reserves will be exhausted in approximately 136 years.

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.

3. Fossil fuels — extraction and impacts

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:

1. 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.
2. 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 (e.g. 2010 Deepwater Horizon spill that killed 11 workers and contaminated 1,300 miles of Gulf Coast coastline), groundwater contamination from fracking chemicals, and induced seismic activity from wastewater injection.
3. 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.

Worked Example

A 1000 MW coal-fired power plant has an 80% capacity factor, and emits 2.2 lbs of CO₂ per kWh of electricity generated. If the plant is converted to run on natural gas, which emits 1.1 lbs of CO₂ per kWh and has an 85% capacity factor, calculate the annual percent reduction in CO₂ emissions.

1. Annual coal output: $1000\text{ MW}\times 0.8\times 365\text{ days}\times 24\text{ hours}=7,008,000\text{ MWh}=7.008\times 10^9\text{ kWh}$
2. Annual coal emissions: $7.008\times 10^9\times 2.2=1.54\times 10^{10}\text{ lbs CO₂}$
3. Annual gas output: $1000\times 0.85\times 365\times 24=7,446,000\text{ MWh}=7.446\times 10^9\text{ kWh}$
4. Annual gas emissions: $7.446\times 10^9\times 1.1=8.19\times 10^9\text{ lbs CO₂}$
5. Percent reduction: $\frac{1.54\times 10^{10}-8.19\times 10^9}{1.54\times 10^{10}}\times 100\approx 47\%$

4. Nuclear — fission, waste, safety

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: $${}_{92}^{235}\text{U}{+}_0^1\text{n}{\to }_{36}^{92}\text{Kr}{+}_{56}^{141}\text{Ba}+3_0^1\text{n}+\text{Heat Energy}$$ 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.

Waste classification

Nuclear waste is grouped by radioactivity level:

1. Low-level waste: Contaminated tools, clothing, and filters with low radioactivity and short half-lives, stored in shallow lined landfills.
2. Intermediate-level waste: Reactor components and chemical sludges with moderate radioactivity, stored in sealed steel and concrete containers above ground.
3. 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.

Safety

Nuclear power has one of the lowest per-kWh fatality rates of all energy sources (lower than coal, oil, and even rooftop solar), but high-profile accidents have driven public opposition:

• Three Mile Island (1979, US): Partial meltdown, no direct fatalities.
• Chernobyl (1986, USSR): Full meltdown, ~4,000 excess cancer deaths estimated by the WHO.
• Fukushima (2011, Japan): Meltdown triggered by a 9.0 magnitude earthquake and tsunami, no direct radiation fatalities, 100,000+ residents displaced.

Worked Example

A 1200 MW nuclear plant has a 93% capacity factor. How many tons of coal will it displace annually, if coal has an energy density of 24 MJ/kg and a coal-fired plant is 35% efficient?

1. Annual nuclear energy output: $1200\times 10^6\text{ W}\times 0.93\times 365\times 24\times 3600\text{ s}=3.52\times 10^{16}\text{ J}$
2. Mass of coal required: $\frac{3.52\times 10^{16}\text{ J}}{0.35\times 24\times 10^6\text{ J/kg}}\approx 4.19\times 10^9\text{ kg}=4.19\text{ million tons of coal per year}$

5. Energy conservation

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): $$EER=\frac{\text{Cooling output (BTU/h)}}{\text{Power input (W)}}$$ Higher EER values indicate more efficient appliances.

Proven conservation strategies include:

• Residential: LED light bulbs (75% less energy use than incandescents, 25x longer lifespan), programmable thermostats, wall and attic insulation, and Energy Star certified appliances.
• Industrial: Cogeneration (combined heat and power, CHP), which captures waste heat from electricity generation for space or water heating, reaching up to 90% efficiency vs 35% for conventional power plants.
• Transportation: Increased Corporate Average Fuel Economy (CAFE) standards, public transit expansion, electric vehicle adoption, and walkable/bikeable urban design.

Worked Example

A household replaces 10 60W incandescent bulbs with 10 12W LED bulbs that produce the same light output. The bulbs are used 4 hours per day, and electricity costs $0.15 per kWh. Calculate annual cost savings from the upgrade.

1. Total power saved: $10\times (60\text{W}-12\text{W})=480\text{W}=0.48\text{kW}$
2. Annual usage hours: $4\text{h/day}\times 365\text{ days}=1460\text{ h}$
3. Annual energy saved: $0.48\text{kW}\times 1460\text{ h}=700.8\text{ kWh}$
4. Annual cost savings: $700.8\text{ kWh}\times \$0.15/\text{kWh}=\$105.12$

Exam tip: Examiners frequently ask for payback period calculations for efficiency upgrades, calculated as: $$\text{Payback Period (years)}=\frac{\text{Upfront cost of upgrade}}{\text{Annual cost savings}}$$ A shorter payback period indicates a more economically viable investment.

6. Common Pitfalls (and how to avoid them)

• Wrong move: Confusing energy efficiency and energy conservation as identical concepts. Why it happens: The terms are used interchangeably in popular media. Correct move: Energy efficiency uses less energy to perform the same task (e.g. LED bulbs for equal light output), while energy conservation reduces use of the service entirely (e.g. turning off lights when leaving a room). Both count as demand reduction strategies.
• Wrong move: Claiming natural gas is a zero-emission "clean" energy source. Why it happens: Marketing often frames natural gas as clean relative to coal. Correct move: Natural gas produces 50% less CO₂ than coal when burned, but still emits sequestered carbon, and methane leaks make its lifecycle emissions far higher than true renewables. It is a transition fuel, not a long-term clean solution.
• Wrong move: Stating nuclear power produces greenhouse gas emissions during operation. Why it happens: Students confuse waste disposal and mining emissions with operational emissions. Correct move: Nuclear power produces zero GHG emissions during normal operation; lifecycle emissions (mining, construction, waste storage) are comparable to wind and solar.
• Wrong move: Adjusting R/P ratio calculations for projected consumption growth unless explicitly told to. Why it happens: Students assume they need to account for real-world demand increases. Correct move: APES exam conventions use constant current consumption for R/P ratio calculations unless the question specifies growth rates.
• Wrong move: Assuming all biomass is carbon-neutral. Why it happens: Textbooks state biomass is carbon-neutral as a general rule. Correct move: Biomass is only carbon-neutral if fuel crops are regrown at the same rate they are harvested. Cutting old-growth forests for biomass releases stored carbon that takes centuries to replenish, making it more carbon-intensive than coal in the short term.

7. Practice Questions (AP Environmental Science Style)

Question 1

A small town is considering replacing its 50 MW coal-fired power plant with either natural gas or nuclear power, using the data below:

1. Calculate the annual CO₂ emissions from the existing coal plant, in tons (1 ton = 2000 lbs).
2. Calculate the percent reduction in annual CO₂ emissions if the town switches to natural gas instead of coal.
3. The town’s annual power generation budget is $25 million. Can the town afford to switch to nuclear power? Show your work.

Solution

1. Annual coal output: $50\text{ MW}\times 0.7\times 365\times 24=306,600\text{ MWh}=3.066\times 10^8\text{ kWh}$ Annual emissions: $\frac{3.066\times 10^8\times 2.1}{2000}=321,930{\text{ tons of CO}}_2$
2. Annual gas output: $50\times 0.85\times 365\times 24=372,300\text{ MWh}=3.723\times 10^8\text{ kWh}$ Annual gas emissions: $\frac{3.723\times 10^8\times 1.0}{2000}=186,150\text{ tons}$ Percent reduction: $\frac{321930-186150}{321930}\times 100=42.2\%$
3. Annual nuclear output: $50\times 0.92\times 365\times 24=402,960\text{ MWh}=4.0296\times 10^8\text{ kWh}$ Annual nuclear cost: $4.0296\times 10^8\times 0.08=\$32,236,800$, which exceeds the $25 million budget. The town cannot afford the switch without additional funding.

Question 2

Fracking for natural gas has expanded 10x in the US since 2000.

1. Identify two environmental impacts of fracking unrelated to greenhouse gas emissions.
2. Describe one economic benefit and one economic cost of fracking for a local community.
3. Explain why switching from coal to natural gas reduces but does not eliminate contributions to global climate change.

Solution

1. Two valid impacts: (a) Groundwater contamination from toxic fracking chemicals that leak into drinking water aquifers; (b) Induced seismic activity (small earthquakes) from underground injection of fracking wastewater.
2. Economic benefit: Fracking creates local jobs in drilling, transport, and plant operation, increasing local tax revenue for schools and public services. Economic cost: Property values decline near drill sites, and increased public health costs from air and water pollution raise local government healthcare spending.
3. Natural gas produces ~50% less CO₂ per kWh than coal when burned, so switching reduces short-term greenhouse gas emissions. However, natural gas is still a fossil fuel, so burning it releases sequestered geologic carbon into the atmosphere, and methane leaks from infrastructure add potent greenhouse gas emissions, so it still contributes to climate change, just at a lower rate than coal.

Question 3

A household installs rooftop solar panels with an upfront cost of $18,000.Thepanelsproduce8000kWhofelectricityperyear,andthehouseholdcurrentlypays$0.20 per kWh for grid electricity.

1. Calculate the payback period for the installation, ignoring subsidies and maintenance costs.
2. Describe one government policy that would reduce the payback period for this household.
3. Explain why energy conservation upgrades often have shorter payback periods than renewable energy installations.

Solution

1. Annual savings: $8000\text{ kWh/year}\times \$0.20/\text{kWh}=\$1600/\text{year}$ Payback period: $\frac{\$18,000}{\$1600/\text{year}}=11.25\text{ years}$
2. Valid policy: The federal Investment Tax Credit (ITC) covers 30% of upfront solar installation costs, reducing the household’s upfront cost to $12,600 and cutting the payback period to 7.875 years.
3. Energy conservation upgrades have far lower upfront costs than renewable energy installations, while delivering comparable annual savings. For example, a $100LEDbulbupgradecandeliver$100 in annual savings, giving a 1-year payback period, far shorter than the 11+ year payback for solar panels, making conservation the most cost-effective first step for households to reduce energy costs.

8. Quick Reference Cheatsheet

9. What's Next

This unit on energy resources directly connects to three later units in the APES CED: Unit 7 (Atmospheric Pollution), where you will learn how fossil fuel combustion releases criteria pollutants like NOₓ, SO₂, and particulate matter that cause smog, acid rain, and respiratory illness; Unit 8 (Aquatic and Terrestrial Pollution), where you will explore the impacts of oil spills, acid mine drainage, and fracking chemical leaks on ecosystem health; and Unit 9 (Global Change), where you will calculate the contribution of different energy sources to anthropogenic climate change, and evaluate energy transition strategies to meet global net-zero targets. You will also see this content appear in FRQ 2 on the AP exam, which always asks you to analyze an environmental research problem or real-world intervention, often focused on energy systems.

To test your mastery of this topic further, try our full-length APES Unit 6 practice tests, which include multiple-choice and free-response questions aligned exactly to the College Board exam format. If you have questions about any concept, calculation, or exam strategy covered in this guide, you can ask Ollie, our AI tutor, at any time by visiting the homepage, where you can get personalized feedback, step-by-step problem solving help, and custom study plans tailored to your weak areas.