Unit 6: Energy Resources and Consumption

Energy fundamentals: what energy is, how we measure it, and why efficiency matters

Energy issues in environmental science often look like debates about fuels and power plants, but underneath they’re really about energy transformations. Humans rarely “use up” energy; instead, we convert energy from one form into another (chemical to heat, kinetic to electrical, electrical to light, etc.). The environmental impacts largely come from how we make those conversions: what we extract from Earth, what we emit to the air and water, and what land we disturb.

The Sun is the source of energy for most life on Earth. It is heated to extremely high temperatures because nuclear fusion in its core converts nuclear energy into heat and radiant energy.

Forms of energy (know the vocabulary)

Environmental science questions often describe an energy system in words. Being fluent in the major forms helps you track what is being converted into what.

• Chemical energy is stored in bonds between atoms in a molecule.
• Electrical energy results from the motion of electrons.
• Electromagnetic energy travels by waves (radiant energy such as sunlight).
• Mechanical energy consists of potential and kinetic energy.
• Potential energy is stored energy in an object (position, configuration).
• Kinetic energy is energy of motion.
• Nuclear energy is stored in atomic nuclei and is released by splitting atoms (fission) or joining atoms (fusion).
• Thermal energy is the energy an object has due to the movement of its molecules.

What energy and power mean (and why the distinction matters)

Energy is the capacity to do work or produce heat. Power is the rate at which energy is transferred or used. This distinction shows up constantly in electricity questions: a device’s wattage tells you how fast it uses energy, while your electric bill charges you for the total energy used over time.

A core relationship is:

Power = \frac{Energy}{time}

Electricity use is commonly measured in kilowatt-hours (kWh), which is a unit of energy (not power). You can compute it with:

Energy(\mathrm{kWh}) = Power(\mathrm{kW}) \times time(\mathrm{h})

Example (electricity use): A 1.5 kW space heater runs for 4 hours.

Energy = 1.5 \times 4 = 6 \text{ kWh}

If electricity costs 0.15 dollars per kWh, then the cost is:

Cost = 6 \times 0.15 = 0.90

A common misconception is thinking “watts” are what you pay for. You pay for kWh, meaning how much energy you used over time.

Common units you may see

• British thermal unit (Btu) is the amount of heat required to raise the temperature of 1 pound of water by 1°F.
• Btu/hr is a power unit often used in heating/cooling; in many air-conditioning contexts, “a ton” refers to a cooling capacity expressed in Btu/hr.
• Horsepower (HP) is used in the automobile industry.

1\ \text{HP} = 746\ \text{watts}

Laws of thermodynamics (APES-level meaning)

• Zeroth Law of Thermodynamics: If body A is in thermal equilibrium with body B, and A is also in thermal equilibrium with body C, then B and C are in equilibrium with each other.
• First Law of Thermodynamics: The law of conservation of energy; energy cannot be created or destroyed.
• Second Law of Thermodynamics: In any energy conversion, the total useful work is always less than the heat supplied; some energy becomes less available to do useful work.

Energy quality and why “waste heat” is unavoidable

Not all energy is equally useful. High-quality energy is concentrated and can do lots of work (like electricity). Low-quality energy is dispersed, typically as low-temperature heat, and is harder to convert into work.

When you convert energy, some is almost always lost as heat to the surroundings. This is the APES takeaway from the Second Law of Thermodynamics: energy transformations increase disorder (entropy), and some energy becomes less available for useful work. You don’t need advanced thermodynamics math, but you do need the reasoning: every conversion has losses, so reducing the number of conversions and improving technology can reduce environmental impact.

Efficiency: the single most important “energy resource”

Energy efficiency describes how much of the input energy becomes useful output.

Efficiency = \frac{useful\ energy\ output}{total\ energy\ input}

Efficiency is often expressed as a percent by multiplying by 100.

Example (efficiency): A power plant uses 100 units of chemical energy from fuel and produces 35 units of electrical energy.

Efficiency = \frac{35}{100} = 0.35 = 35\%

Why this matters environmentally: higher efficiency typically means less fuel extraction for the same service, fewer air pollutants and greenhouse gas emissions, and (for thermal plants) less waste heat discharged to waterways.

It’s also important not to confuse efficiency with conservation. Efficient technology provides the same service using less energy; conservation is using less service (driving less, turning things off).

Exam Focus

• Typical question patterns
  • Calculate kWh from power and time; compare two appliances or behaviors.
  • Compute or interpret efficiency and link it to fuel use and emissions.
  • Explain why multiple energy conversions increase losses.
• Common mistakes
  • Treating kWh as power instead of energy.
  • Forgetting unit conversions (W to kW, minutes to hours).
  • Assuming 100% efficiency is possible in real energy systems.

Renewable and nonrenewable resources: what “renewable” does and doesn’t mean

Human civilization requires energy to function, and people obtain energy from fossil fuels, nuclear fuel, and renewable energy resources.

Renewable energy

Renewable energy is collected from resources that are naturally replenished on a human time scale. Renewable resources often exist over wide geographical areas, in contrast to some nonrenewable resources that are concentrated in fewer regions.

Nonrenewable energy

Nonrenewable energy sources are not sustainable on human time scales because they form over geologic time (typically millions of years). Fossil fuels are the main examples.

Why fossil fuels have been defended historically

Common arguments used to defend continued fossil fuel use include abundant supply (often lowering prices), concentrated fuel with a high net-energy yield, infrastructure already in place for extraction/processing/delivery, politics, and technology that already exists for their use.

Exam Focus

• Typical question patterns
  • Classify an energy source as renewable vs. nonrenewable and justify using formation/replenishment timescales.
  • Explain why a resource can be renewable but still environmentally damaging.
• Common mistakes
  • Treating “renewable” as synonymous with “no environmental impact.”
  • Mixing up “energy carrier” (electricity, hydrogen) with “energy source.”

How electricity is generated and delivered: from turbines to the grid

Electricity is not a primary energy source; it is an energy carrier. You generate electricity by converting other energy forms into electrical energy, then deliver it through a grid.

The basic mechanism: spinning a generator

Most large-scale electricity generation works like this:

1. Extract thermal energy from a fuel (or use a natural moving fluid) and create motion.
2. Convert that energy into kinetic energy in a turbine.
3. Use a rotary generator to convert the turbine’s mechanical energy into electrical energy.

Many systems specifically follow the classic thermal pathway: heat makes steam, steam spins a turbine, turbine spins a generator. The heat source can be burning fossil fuels, nuclear fission, geothermal heat, or concentrated solar thermal systems. Motion can also come directly from flowing water (hydroelectric) or wind (wind turbines).

Baseload vs. peaker power (reliability concepts)

Electric demand varies by time of day and season.

• Baseload demand is the minimum, steady level of electricity needed.
• Peak demand refers to higher-demand periods (hot afternoons with lots of air conditioning, for example).

Historically, large coal, nuclear, and some natural gas plants have provided baseload power because they can run continuously. Natural gas “peaker” plants can ramp up quickly to meet spikes. Variable renewables (wind and solar) generate when the resource is available, so they often require grid strategies like storage, transmission upgrades, and demand management.

Transmission, distribution, and losses

After electricity is generated, it moves through transmission lines (long-distance, high voltage) and distribution lines (local delivery). Some energy is lost as heat due to resistance in power lines, and additional losses occur at transformers and other equipment. Improving grid efficiency and siting generation closer to use can reduce losses.

Cogeneration (combined heat and power)

Many thermal power plants waste a lot of input energy as unused heat. Cogeneration, also called combined heat and power (CHP), captures some of that waste heat and uses it for industrial processes or building heating. Because it produces both electricity and useful heat from the same fuel input, cogeneration can significantly increase overall system efficiency.

Example (why cogeneration helps): If a plant would otherwise dump hot water/steam as waste, capturing that heat reduces the need to burn extra fuel in boilers elsewhere.

Exam Focus

• Typical question patterns
  • Describe how a turbine-generator system works for different energy sources.
  • Compare baseload and peak demand strategies; explain how renewables fit in.
  • Explain how cogeneration improves overall efficiency.
• Common mistakes
  • Calling electricity an “energy source” instead of an energy carrier.
  • Assuming transmission is lossless.
  • Confusing baseload (demand concept) with “baseload power plants” as a fixed list.

Fossil fuels: fuel types, why they dominate, and why they cause major environmental impacts

Fossil fuels (coal, oil, natural gas) are energy-rich materials formed from ancient organic matter over geologic time. They are nonrenewable on human time scales because they take extremely long periods to form.

They have dominated historically because they are energy dense, portable and storable, and supported by extensive infrastructure. However, they create major environmental problems because their energy comes from combustion, which produces air pollutants and greenhouse gases.

Fuel types you should recognize

• Burning wood fuel produces by-products including carbon dioxide, heat, steam, water vapor, and wood ash.
• Peat is an accumulation of partially decayed vegetation or organic matter (often wetland vegetation like mosses, sedges, and shrubs) that forms in acidic and anaerobic conditions.
• Coal forms when dead plant matter decays into peat and is converted into coal by heat and pressure of deep burial over millions of years.
• Natural gas is composed mostly of methane and is often found with oil deposits; it formed from ancient organic matter under heat and pressure.
• Oil (petroleum) is a liquid fossil fuel formed from deeply buried organic material under high temperatures and pressure over millions of years.

A common framing for origins is that coal is primarily associated with land vegetation, while oil and natural gas are often associated with marine organisms whose remains became buried, transformed, and trapped in sediments and rock.

Other nonrenewable fossil-fuel resources (know the names)

• Methane hydrates (clathrates) are methane trapped in an ice-like structure at low temperature and high pressure. They occur in permafrost regions, beneath the ocean floor, and on continental shelves.
• Oil shale is an organic-rich, fine-grained sedimentary rock containing kerogen from which shale oil can be produced.
• Synfuels are fuels produced from coal, natural gas, or biomass through chemical conversion.
• Tar sands (also called oil sands) contain bitumen, a semi-solid form of oil that does not flow. They can be mined (including strip-mining approaches) or extracted in situ using steam.

Combustion and emissions: what comes out and why

Combustion of fossil fuels generally follows the pattern of hydrocarbon combustion:

C_xH_y + O_2 \rightarrow CO_2 + H_2O + energy

Carbon dioxide produced during fossil fuel combustion for heat and electricity is a major contributor to global CO_2 emissions and is associated with global warming due to the greenhouse effect.

More complete combustion tends to produce more CO_2 and H_2O. Incomplete combustion and impurities produce additional pollutants.

Key emission categories (APES-relevant):

• Greenhouse gases: especially CO_2; methane leakage is important for natural gas systems.
• Air pollutants: particulate matter, nitrogen oxides, sulfur dioxide (especially with sulfur-containing coal and oil), volatile organic compounds.
• Toxic metals: coal can contain mercury and other trace metals that can be released.

Extraction impacts: the “front end” of fossil fuels

Environmental impacts are not just from burning fuel. Extraction and processing can cause habitat destruction, land disturbance, and water pollution from runoff, spills, and wastes. A useful APES habit is life-cycle thinking: extraction → processing → transport → combustion → waste/cleanup.

Economics vocabulary sometimes paired with energy: supply and demand

• Law of Supply: all else equal, as the price of a good/service increases, the quantity suppliers offer increases (and vice versa). Suppliers try to maximize profit by increasing quantity offered as price rises.
• Law of Demand: all else equal, the quantity purchased is inversely related to price.

These ideas show up in energy policy and resource questions because price shifts can change consumption patterns, extraction rates, and incentives for alternatives.

Exam Focus

• Typical question patterns
  • Trace environmental impacts across a fossil fuel’s life cycle.
  • Compare air pollutants vs. greenhouse gases from combustion.
  • Explain how supply/demand incentives can influence extraction and consumption.
• Common mistakes
  • Treating all fossil fuels as identical in impacts (they differ).
  • Ignoring extraction and transport impacts and focusing only on combustion.
  • Confusing climate change (greenhouse gases) with smog/acid rain (criteria pollutants).

Coal: formation, coal types, mining methods, and pollution tradeoffs

Coal is a carbon-rich solid fossil fuel used primarily for electricity generation and some industrial processes. It has been historically abundant and relatively inexpensive, but it has high environmental and health costs.

Coal types (rank and common uses)

Coal forms over time as plant material is buried and transformed. Major ranks you may see include:

• Lignite (“brown coal”) is generally lower-energy and higher in impurities. It is used widely for electric power generation and is associated with significant human health impacts due to pollutant emissions.
• Bituminous coal is used primarily as fuel in steam-electric power generation.
• Anthracite is higher-carbon coal used primarily for residential and commercial space heating.

How coal is extracted: surface mining vs. subsurface mining

Two broad categories:

• Surface mining removes soil and rock to access near-surface seams (e.g., strip mining and mountaintop removal). It tends to create large immediate land disturbance.
• Subsurface mining uses tunnels and shafts to reach deeper seams. It often creates less surface disruption per area but has higher worker safety risks.

Environmental impacts of coal mining can include habitat loss, increased erosion and sedimentation in streams, and acid mine drainage. Acid mine drainage occurs when sulfide minerals exposed by mining react with water and oxygen to produce sulfuric acid; the acidic water can dissolve and mobilize metals, harming aquatic life.

A common misconception is that reclamation fully restores ecosystems. Regrading and replanting can reduce erosion and improve appearance, but soil structure, native biodiversity, and stream systems often remain altered.

Coal-fired electricity and pollution controls

Coal plants burn coal to boil water into steam that spins a turbine. Because heat-to-electric conversion has large losses, improving plant efficiency reduces coal required per kWh.

Coal combustion produces several major pollutant streams:

• Air pollutants (SOx, NOx, particulates)
• Toxic metals (including mercury)
• Coal ash, which can contain toxic metals and requires careful disposal
• Greenhouse gases (especially CO_2)

Scrubbers (flue-gas desulfurization) can reduce sulfur dioxide, and particulate controls can reduce soot/ash in the air. However, traditional controls do not eliminate CO_2 unless combined with carbon capture technologies.

“Clean coal” and carbon capture and storage (CCS)

“Clean coal” refers to technologies that attempt to mitigate emissions of CO_2 and other pollutants arising from coal burning.

Carbon capture and storage (CCS) captures CO_2 from emissions and stores it underground. In principle, this could reduce climate impacts, but CCS adds cost and energy use (an “energy penalty”), and long-term storage integrity is a key concern.

Technologies used to remove pollutants from flue gases

APES may ask you to match a pollution-control technology to the pollutant it reduces.

• Baghouse filters are fabric filters used to reduce particulates.
• Cyclone separators remove particulates using rotational (spinning) effects and gravity.
• Electrostatic precipitators remove fine particles (dust, smoke) from flowing gas using an electrostatic charge.
• Scrubbers inject chemicals into dirty exhaust to “wash out” acidic gases; they can reduce SOx and also help reduce particulates.
• Sorbents (activated charcoal, calcium compounds, silicates) convert gaseous pollutants into compounds that other devices (baghouses, precipitators, scrubbers) can collect.
• Burning pulverized coal at lower temperatures involves crushing coal into a fine powder and injecting it into a firebox; operational choices like temperature can influence certain emissions.
• Fluidized-bed combustion burns coal with far more air than conventional burners and can reduce NOx, SOx, and particulates.
• Coal gasification converts coal (and other carbon-based fuels) into “syngas.” Impurities can be removed from syngas before it is combusted, lowering emissions of sulfur dioxide, particulates, and mercury.

Exam Focus

• Typical question patterns
  • Compare surface and subsurface mining impacts.
  • Explain acid mine drainage and its effects on waterways.
  • Identify major coal-related pollutants and what technologies reduce them.
• Common mistakes
  • Assuming scrubbers remove all pollution (they target specific pollutants).
  • Forgetting coal ash as a waste stream with toxicity concerns.
  • Treating CCS as “free” with no tradeoffs.

Oil (petroleum): extraction, refining, transportation, and spill risks

Oil (petroleum) is a liquid fossil fuel used heavily in transportation (gasoline, diesel, jet fuel) and as a feedstock for many petrochemicals (plastics, solvents, lubricants). Its liquid form makes it easy to transport and energy-dense for vehicles.

How oil is obtained and processed

Oil production typically involves exploration and drilling (on land or offshore), extraction (pumping; sometimes enhanced recovery), transport (pipelines, ships, rail), and refining into fuels and other products.

Refining separates hydrocarbons into fractions with different boiling ranges and uses additional processing to meet fuel standards.

Environmental risks across the oil life cycle

Key concerns include oil spills (drilling/shipping/pipelines), habitat disruption from infrastructure, and air pollution plus CO_2 from combustion.

Oil spills matter because oil can coat feathers and fur (reducing insulation and buoyancy), smother intertidal habitats and marshes, and persist in sediments and food webs depending on conditions. Cleanup is difficult because oil spreads and can become trapped in complex coastlines. Methods like booms, skimmers, dispersants, and controlled burns have tradeoffs and are not universally effective.

Oil sands, tar sands, and heavy oil (high-impact sources)

Some petroleum resources such as tar sands/oil sands (bitumen) require more energy and processing to produce usable fuels. This tends to increase land disturbance, water use, and greenhouse gas emissions per unit of fuel compared with conventional oil. Extraction can involve mining (including strip-mining approaches) or in situ steam-based methods.

Exam Focus

• Typical question patterns
  • Describe environmental impacts of oil extraction, transport, and spills.
  • Compare conventional oil with higher-impact sources (like oil/tar sands) conceptually.
  • Link oil combustion to air pollution and climate change.
• Common mistakes
  • Focusing only on spills and ignoring routine impacts (habitat fragmentation, emissions).
  • Assuming dispersants “solve” spills without ecological tradeoffs.
  • Confusing oil (transportation focus) with coal (electricity focus) as primary uses.

Natural gas: combustion benefits, methane leakage, and hydraulic fracturing

Natural gas is a fossil fuel composed mostly of methane. It is widely used for electricity generation, heating, and industrial processes.

Why natural gas expanded so quickly

Natural gas is often promoted as “cleaner” than coal because, when burned, it generally emits less sulfur dioxide and particulate matter than coal and less CO_2 per unit energy (because methane has a higher hydrogen-to-carbon ratio). It also works well with modern turbines and can ramp output quickly, which helps meet peak demand.

The big caveat: methane leakage

Methane is a potent greenhouse gas. If methane leaks during extraction, processing, and transport, it can significantly increase the climate impact of natural gas systems.

APES expects this reasoning:

• Burning natural gas produces CO_2.
• Leaks release methane directly.
• Lower CO_2 at the smokestack does not automatically mean low climate impact if leakage is substantial.

Hydraulic fracturing (fracking): what it is and what it changes

Hydraulic fracturing (fracking) is an oil and gas well development process that injects water, sand, and chemicals under high pressure into bedrock via a well. The goal is to create new fractures and expand/connect existing fractures, increasing oil/gas flow to the well. It is commonly used in low-permeability rocks like shale, sandstone, and some coal beds.

Potential environmental concerns include high water use in some regions, wastewater handling (salts, chemicals, naturally occurring substances), groundwater contamination risk pathways if well casings fail, and increased seismic activity in some areas (especially linked to wastewater injection).

Exam Focus

• Typical question patterns
  • Compare natural gas to coal in terms of air pollutants and CO_2 per unit energy.
  • Explain why methane leakage changes the climate calculus.
  • Describe fracking steps and identify environmental concerns.
• Common mistakes
  • Saying “natural gas has no emissions” (it still produces CO_2 when burned).
  • Confusing fracking (creating fractures) with wastewater injection (often linked to induced seismicity).
  • Treating groundwater contamination as guaranteed rather than as a risk dependent on well integrity and management.

Nuclear power: fission electricity with low air pollution and difficult waste tradeoffs

In APES, nuclear energy typically means electricity generated from nuclear fission, where the nucleus of a heavy atom splits into smaller nuclei and releases energy.

How nuclear fission becomes electricity

In a typical nuclear plant:

1. Fission reactions release heat.
2. Heat produces steam.
3. Steam spins a turbine.
4. The turbine drives a generator.

So nuclear plants share the same basic turbine-generator structure as coal plants; the difference is the heat source.

Nuclear fission, meltdowns, and control

During nuclear fission, an atom splits into two (or smaller) nuclei along with by-product particles, releasing heat. If controlled, that heat is used to generate electricity. If not controlled, a severe accident can occur.

A nuclear meltdown is a severe nuclear reactor accident that results in core damage from overheating.

Nuclear fuels and isotopes (key facts)

• U-235 is less than 1% of naturally occurring uranium. Reactors typically use enriched uranium (increased concentration of U-235).
• Critical mass is the minimum amount of U-235 required for a sustained chain reaction.
• U-238 is the most common uranium isotope and has a half-life of 4.5 billion years. When hit by a neutron, it can eventually decay into Pu-239.
• Pu-239 has a half-life of 24,000 years and can be produced in breeder reactors from U-238. Its fission provides about one-third of the total energy produced in a typical commercial nuclear power plant.

A useful comparison fact: the fission of an atom of uranium produces about 10 million times the energy produced by the combustion of an atom of carbon from coal.

Major reactor components (recognize the roles)

• Core contains up to 50,000 fuel rods.
• Fuel rods contain stacked fuel pellets (commonly enriched U-235).
• Control rods move in and out of the core to absorb neutrons and slow the reaction.
• Moderator reduces the speed of fast neutrons, enabling a sustainable chain reaction.
• Coolant removes heat and produces steam used to generate electricity.

Benefits and drawbacks

Benefits: During routine operation, nuclear plants emit very little sulfur dioxide, nitrogen oxides, particulate matter, or CO_2 compared with fossil fuel plants.

Drawbacks/risks: Accident risk (rare but potentially high consequence), uranium mining and processing impacts, and radioactive waste that remains hazardous for long periods and requires secure containment and long-term monitoring. Nuclear plants can also create thermal pollution and have high cooling-water demand; warmer discharge water can lower dissolved oxygen and stress aquatic organisms.

A common misconception is that nuclear waste is a large-volume problem like household trash. It is typically smaller in volume than many fossil waste streams, but uniquely challenging due to longevity and hazard.

Exam Focus

• Typical question patterns
  • Explain how fission power plants generate electricity (heat to steam to turbine).
  • Identify roles of control rods, moderators, coolants, and the core.
  • Compare nuclear and fossil fuels on air pollution and climate impacts.
  • Identify major nuclear drawbacks: waste storage, accident risk, thermal pollution.
• Common mistakes
  • Confusing fission (used in power plants) with fusion (experimental).
  • Claiming nuclear power has “no environmental impact” (mining, waste, water use matter).
  • Overstating waste volume rather than focusing on hazard and storage time.

Solar energy: photovoltaic electricity, solar thermal, and passive/active design

Solar energy consists of collecting and harnessing radiant energy from the Sun to provide heat and/or electricity. Electricity and heat can be generated at homes, industrial sites, or at central solar-thermal plants.

Photovoltaics (PV): sunlight directly to electricity

Photovoltaic (PV) cells convert sunlight into electricity using semiconducting materials. PV systems produce no direct emissions during operation, but generation is intermittent (day/night and weather). PV can be deployed at many scales, from rooftops to utility-scale arrays.

Environmental considerations include land use for large installations, mining/manufacturing impacts (life-cycle impacts), and end-of-life handling and recycling of panels.

Concentrated solar power (CSP): sunlight to heat to electricity

Concentrated solar power (CSP) uses mirrors to concentrate sunlight to heat a fluid, producing steam to spin a turbine. Like other thermal plants, CSP can involve water use for cooling depending on design. Some CSP systems include thermal storage (such as hot molten salts), allowing electricity generation after sunset.

Passive solar heating

Passive solar heating uses building features (orientation, windows, insulation, shading, and thermal mass) to absorb heat and release it slowly, maintaining indoor temperature without a mechanical heating device.

Active solar heating

Active solar heating generally generates more heat than passive systems and relies on three components: (1) a solar collector to absorb solar energy, (2) a solar storage system, and (3) a heat transfer system.

Residential photovoltaic system components

A typical residential PV setup includes solar panels, a solar inverter to convert DC to AC, and (in many designs) battery storage and backup.

Exam Focus

• Typical question patterns
  • Compare PV and CSP mechanisms and tradeoffs (direct electric vs. thermal generation).
  • Explain intermittency and how storage or grid strategies can help.
  • Identify passive vs. active solar features and connect them to reduced energy demand.
• Common mistakes
  • Treating PV and solar thermal as the same technology.
  • Assuming solar is “100% clean” without life-cycle thinking.
  • Assuming passive solar means “solar panels on a roof.”

Wind energy: converting moving air into electricity and managing variability

Wind turbines use wind to make electricity (the reverse of how a fan uses electricity to make wind). Wind turns turbine blades, and that motion powers generators. Turbines clustered together are called wind farms.

Variability and grid integration

Wind is variable, so power output fluctuates with wind speed. Wind works best with geographic diversity (turbines spread across regions), strong transmission connections, complementary generation (hydropower or natural gas), and/or storage.

Environmental and social considerations

Key tradeoffs are place-based: bird and bat mortality (reduced through careful siting and improved technology), land use (the turbine footprint is often smaller than the total farm boundary and land between turbines can often remain in agriculture), and noise/aesthetics affecting community acceptance.

Scale and trends (commonly cited figures)

• Wind supplies about 6% of U.S. electrical demand.
• Current U.S. wind capacity powers approximately 20 million homes.
• Offshore wind represents a major opportunity to supply power to densely populated coastal cities.
• The largest turbines can harness enough energy to power roughly 600 American homes.
• China has the largest installed wind capacity, followed by the United States.
• Wind turbine use has increased substantially in the last decade (often reported around a 25% increase), though wind still provides only a small fraction of total world energy.
• A commonly cited estimate is that 1 megawatt of wind capacity can offset on the order of thousands of tons of CO_2, but the exact value depends on what fossil generation it displaces and how the grid operates.

Exam Focus

• Typical question patterns
  • Explain why wind is variable and how grids manage variability.
  • Identify major wind impacts and mitigation approaches (especially siting).
  • Compare wind’s operational emissions with fossil fuels.
• Common mistakes
  • Claiming wind is dispatchable like a gas plant without storage.
  • Overgeneralizing wildlife impacts without noting siting and mitigation.
  • Ignoring transmission needs from windy regions to demand centers.

Hydroelectric power: low air pollution, major ecosystem tradeoffs

Hydroelectric power uses flowing water to spin turbines. Dams trap water in a reservoir, then release and channel water through turbines that generate electricity. Hydropower is renewable because the water cycle replenishes flows, but output depends on precipitation, snowpack, and water management.

Hydroelectric generation accounts for approximately 44% of renewable electricity generation and about 6.5% of total electricity generation in the United States. There are about 75,000 dams in the United States that block roughly 600,000 miles (about 1 million km) of what had once been free-flowing rivers.

Advantages

Hydropower often has low operating and maintenance costs and long life spans, can provide moderate to high net-useful energy, produces very low operational air pollution, and can provide water storage for municipal and agricultural use. Reservoirs may also provide flood control and recreation.

Disadvantages and ecological impacts

Hydropower is not impact-free. Dams can flood upstream habitats, displace people, destroy wild river ecosystems, block fish migration, reduce land available for agriculture around reservoirs, trap sediment (sometimes requiring dredging), and alter downstream temperature and dissolved oxygen. Sediment trapping can also starve downstream habitats and deltas.

Flooding: contributing causes you may be asked to identify

Floods can be caused or worsened by failures of dams, levees, and pumps; fast snowmelt; increased impervious surfaces (asphalt, concrete); natural hazards such as wildfires that reduce vegetation that absorbs rainfall; prolonged heavy rainfall; severe winds over water; tsunamis; and unusually high tides and storm surges.

Exam Focus

• Typical question patterns
  • Explain how hydropower generates electricity and why dams change river ecosystems.
  • Identify hydropower tradeoffs: fish migration, sediment trapping, altered flow regimes, habitat flooding, displacement.
  • Reason about drought and variability affecting hydropower output.
• Common mistakes
  • Assuming hydropower is always renewable at constant output (drought matters).
  • Ignoring downstream impacts (sediment starvation, altered flooding).
  • Treating low air emissions as proof of “no environmental impact.”

Geothermal energy: steady renewable power with geographic limits

Geothermal energy uses heat contained in underground rock and fluids from magma, hot dry-rock zones, and warm-rock reservoirs. Underground steam and hot water can be used to drive turbines and generate electricity, and geothermal heat can also be used directly for heating.

Advantages include low operational emissions and steady, baseload-like power where resources are strong. Concerns include site-specific availability, possible release of gases or dissolved minerals from underground fluids, and induced seismicity in some engineered systems.

Exam Focus

• Typical question patterns
  • Describe how geothermal electricity generation works (steam/hot fluids drive turbines).
  • Explain why geothermal is geographically limited.
• Common mistakes
  • Treating geothermal as universally available rather than site-dependent.
  • Ignoring potential fluid chemistry or seismicity concerns.

Biomass and biofuels: renewable in principle, complicated in practice

Biomass is biological material derived from living or recently living organisms that can be burned (often to make steam for electricity). Biomass can sometimes be grown on marginal land not suitable for agriculture, but sustainability depends on local conditions.

Why biomass is appealing

Biomass can be stored and used on demand (unlike wind/solar), can sometimes use existing combustion/fuel infrastructure, and can turn waste streams into energy (manure digesters, landfill methane capture).

The central issue: carbon neutrality is not automatic

Biomass is sometimes described as “carbon neutral” because plants absorb CO_2 as they grow. The more accurate APES reasoning is:

• Burning biomass releases CO_2 now.
• Regrowth can reabsorb CO_2 over time.
• Net climate impact depends on land use, regrowth speed, the ecosystem that existed before, and what would have happened to the biomass otherwise.

If forests are cut faster than they regrow, or if high-carbon ecosystems are converted to fuel crops, biomass can increase atmospheric CO_2 for long periods.

Anaerobic digestion (biogas)

Anaerobic digestion is a set of processes in which microorganisms break down biodegradable material in the absence of oxygen to produce methane gas, which is then burned to produce energy.

Potential benefits include reducing reliance on coal and oil, reducing land disturbance impacts associated with coal mining, and reducing methane emissions from landfills that would otherwise contribute strongly to global warming.

Biofuels: ethanol and biodiesel

A biofuel is a liquid fuel produced from living organisms. Biofuels are biodegradable and can be converted into bioethanol (ethanol) or biodiesel to power vehicles. They can often be produced in many places, unlike fossil fuels, and are considered renewable when feedstocks are managed sustainably.

Key tradeoffs include land competition (fuel vs. food vs. habitat), water and fertilizer use (runoff and eutrophication), and life-cycle energy/emissions costs of processing.

Waste-to-energy and methane capture

Capturing methane from landfills or anaerobic digesters can reduce greenhouse impacts because methane that would have vented is combusted to CO_2 (still a greenhouse gas, but generally less warming than methane over relevant time horizons). This is a strong example of systems thinking: sometimes the best option is the one that prevents a worse emission.

Exam Focus

• Typical question patterns
  • Evaluate whether a biomass option is sustainable using land use, regrowth, and life-cycle reasoning.
  • Compare biofuels’ potential benefits with agricultural impacts (fertilizer runoff, habitat conversion).
  • Explain why capturing methane from waste can reduce overall climate impact.
• Common mistakes
  • Stating all biomass is carbon neutral without conditions.
  • Ignoring fertilizer and water impacts of fuel crops.
  • Treating waste-to-energy as “zero impact” rather than a tradeoff-based strategy.

Hydrogen fuel cells: an energy carrier that produces electricity and water

A hydrogen fuel cell operates similarly to a battery with two electrodes: oxygen passes over one electrode and hydrogen passes over the other.

• Hydrogen reacts with a catalyst to form negatively charged electrons and positively charged hydrogen ions (H+).
• The electrons flow out of the cell to be used as electrical energy.
• The hydrogen ions move through a membrane and combine with oxygen and electrons to produce water.

Unlike batteries, fuel cells do not “run out” in the same way; as long as hydrogen and oxygen are supplied, the electrochemical reactions can continue.

Exam Focus

• Typical question patterns
  • Distinguish hydrogen (an energy carrier) from primary energy sources (fossil, nuclear, renewable).
  • Describe the basic outputs of a hydrogen fuel cell (electricity and water) and the need for a hydrogen supply.
• Common mistakes
  • Treating hydrogen as a naturally occurring “free” fuel rather than something that must be produced using energy.

Comparing energy resources: renewability, energy density, externalities, and life-cycle thinking

When asked to compare energy resources, the goal is not to memorize “best” and “worst,” but to reason using criteria and recognize tradeoffs.

Key comparison criteria (how to think like an APES evaluator)

1. Renewability: Does the source replenish on human timescales?
2. Operational emissions: What is emitted during electricity generation or fuel use?
3. Life-cycle impacts: What happens during extraction, manufacturing, transport, and waste disposal?
4. Land and water use: How much area is required? How does it affect ecosystems and water resources?
5. Reliability and variability: Can it supply power on demand? If not, what infrastructure is needed?
6. Cost and access: What are the economic barriers? Who benefits and who bears costs?

Externalities: the hidden costs that shape energy decisions

An externality is a cost or benefit of an activity that is not reflected in its market price. For example, coal electricity can look cheap at the meter while imposing health costs from air pollution, and oil prices may not fully capture spill risk or climate damages. Policies (like pollution limits or carbon pricing) attempt to internalize externalities.

Comparison table (use as a reasoning scaffold, not a memorization list)

Exam Focus

• Typical question patterns
  • Compare two energy options using at least three criteria (emissions, land use, reliability, cost).
  • Identify an externality in a scenario and propose a policy/technology to address it.
  • Use life-cycle reasoning to critique a simplistic “clean/dirty” claim.
• Common mistakes
  • Choosing an energy source based on a single criterion (usually CO_2) and ignoring others.
  • Mixing up operational emissions with life-cycle emissions.
  • Treating “renewable” as synonymous with “no environmental impact.”

Reducing energy use: conservation, efficiency, and smarter systems

The fastest way to reduce pollution from energy is often to reduce energy demand through behavior changes (conservation) and better technology/design (efficiency).

Conservation vs. efficiency (and why APES cares)

• Conservation reduces energy use by reducing or changing an activity (drive fewer miles, turn devices off).
• Efficiency provides the same service using less energy (LED bulbs instead of incandescent, efficient heat pumps).

Efficiency gains can be partially offset by the rebound effect, where cheaper operation leads to increased use.

Buildings: heating/cooling leverage points (plus concrete actions)

Because heating and cooling are major energy uses, strategies like insulation, air sealing, passive solar, smart shading, and efficient HVAC can have big impacts.

Practical conservation/efficiency steps include:

• Add extra insulation and seal air leaks. Improving attic insulation and sealing air leaks can save 10% or more on annual energy bills.
• Use a programmable HVAC thermostat. A programmable thermostat can save as much as 15% on heating and cooling costs.

Lighting: a major efficiency win (worked example + key facts)

Switching lighting technology is a classic kWh question.

Worked example: comparing two lighting choices
Suppose you need the same brightness for 1,000 hours.

• Incandescent: 60 W
• LED: 10 W

Convert to kW:

• 60 W = 0.060 kW
• 10 W = 0.010 kW

Energy used:

E_{inc} = 0.060 \times 1000 = 60 \text{ kWh}

E_{LED} = 0.010 \times 1000 = 10 \text{ kWh}

The LED uses 50 kWh less for the same service. If your electricity comes from fossil fuels, that directly reduces upstream fuel combustion and emissions.

Additional LED note: LED lights do not contain mercury and can be disposed of with regular household trash.

Phantom loads

A phantom load is the energy an appliance or electronic device consumes when it is not actually turned on. A commonly cited figure is that a large share of electricity used to power home electronics can be consumed while products are turned off (often quoted around 75%), which is why unplugging devices or using power strips can matter.

Transportation: why fuel economy and electrification matter

Transportation relies heavily on oil-derived fuels. Reducing impacts involves fuel-economy improvements, public transportation and urban design that reduce vehicle miles traveled, and electric vehicles powered by cleaner grids. Electric vehicles have no tailpipe emissions, but the electricity generation mix determines upstream emissions.

Industrial efficiency and cogeneration

Industry can reduce energy use through efficient motors, process improvements, heat recovery, and cogeneration (CHP).

Exam Focus

• Typical question patterns
  • Distinguish conservation from efficiency with examples.
  • Use kWh calculations to quantify savings from an efficiency upgrade.
  • Explain how building design, phantom loads, and transportation choices affect energy consumption.
• Common mistakes
  • Calling any reduction “efficiency” even when it’s conservation.
  • Forgetting that electrification benefits depend on grid energy sources.
  • Ignoring rebound effects when interpreting efficiency improvements.

Energy policy and decision-making: incentives, regulation, and choosing among tradeoffs

Energy transitions are not just technological; they’re political and economic. APES expects you to reason about how policies change behavior by changing costs, benefits, and constraints.

Why policy is necessary (link to externalities)

Because many energy harms are externalities, markets alone may underinvest in cleaner technologies. Policies can limit pollution (regulation), encourage cleaner options (subsidies, tax credits), discourage harmful options (pollution fees, carbon pricing), and improve information (efficiency labels).

Common policy tools (conceptual)

• Regulatory standards: emissions limits, fuel economy standards, renewable energy mandates.
• Market-based approaches: fees, taxes, cap-and-trade.
• Public investment: research and development, grid upgrades, public transit.

Environmental justice and energy systems

Energy extraction, generation, and waste disposal often affect communities unevenly. Power plants, refineries, and waste sites have historically been more common near lower-income communities and communities of color in many places. An APES-level evaluation asks who gets benefits (jobs, electricity, profits), who bears costs (pollution exposure, health risks, land loss), and whether affected communities are included in decision-making.

Putting it together: choosing an energy path for a region

A realistic plan to reduce emissions while maintaining reliability often combines demand reduction (efficiency and conservation), cleaner supply (renewables, possibly nuclear, and in some contexts lower-leakage natural gas), and grid upgrades (transmission, storage, demand response). The APES skill is building an argument that acknowledges constraints and tradeoffs rather than picking a single “perfect” source.

Exam Focus

• Typical question patterns
  • Propose a policy to reduce a specific pollutant and justify how it works.
  • Identify externalities in an energy scenario and explain who pays without policy.
  • Evaluate energy choices through an environmental justice lens.
• Common mistakes
  • Proposing a technology without a mechanism for adoption (cost, incentives, infrastructure).
  • Treating policy as purely environmental and ignoring economic and social outcomes.
  • Writing one-sided arguments that ignore a major tradeoff (land use, reliability, waste, cost).

Related study reference: Chapter 7: Atmospheric Pollution (often paired with Unit 6 air-pollutant questions).