Free Unit Notes

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I. Renewable and Nonrenewable Resources (Topic 6.1)

  A. Resource replacement

1. Nonrenewable resources have limited supplies that cannot be replaced on a human time scale. Coal, petroleum, natural gas, and uranium are examples.

2. Renewable resources are replenished naturally at or near the rate of use. Examples include sunlight, wind, flowing water, geothermal heat, and sustainably harvested biomass.

3. Biomass is renewable only when new growth replaces what people harvest. Peat forms too slowly to be a practical renewable fuel.

4. Compare energy sources by availability, reliability, cost, pollution, land use, and effects throughout their life cycle, from extraction and manufacturing through disposal.

  B. Energy transformations

1. Kinetic energy is energy of motion. Potential energy is stored energy, such as water held above a turbine. Fuels store chemical energy.

2. The first law of thermodynamics states that energy changes form or location but is not created or destroyed.

3. The second law of thermodynamics explains why real energy conversions spread some energy into less useful forms, usually waste heat.

II. Global Energy Consumption (Topic 6.2)

  A. Consumption patterns

1. Fossil fuels supply most global primary energy, which is energy available in resources before conversion. Electricity is an energy carrier produced from other sources.

2. Industrialized countries generally use more energy per person. Many lower-income countries use less commercial energy and rely more on wood or charcoal.

3. Industrialization and population growth usually increase energy demand. Developing economies have often increased fossil fuel use as factories, transportation, and electricity access expand.

4. Per-capita energy use = total energy use ÷ population. Total use can rise even while use per person falls if population grows enough.

  B. Factors affecting energy choices

1. Availability, price, infrastructure, and government policies influence which sources people use. Climate, transportation systems, and efficiency also affect demand.

2. Imports provide access to resources but can expose countries to supply disruptions and price changes. Energy prices may exclude pollution and habitat damage costs.

3. When reading energy data, distinguish total energy from electricity, total use from per-capita use, and percentage share from absolute consumption.

III. Fuel Types and Uses (Topic 6.3)

  A. Wood, peat, and coal

1. Firewood and charcoal provide heat for cooking and buildings. Charcoal is made by heating wood with little oxygen. Both can create dangerous indoor smoke.

2. Peat is partly decomposed plant material that accumulates in waterlogged, oxygen-poor conditions. Burial, heat, and pressure over geologic time can turn plant material into coal.

3. Coal ranks generally increase in carbon content and energy per mass as burial conditions change.
   a. Lignite is moist, low-rank brown coal used mainly for electricity.
   b. Bituminous coal has more carbon and energy than lignite. It supplies electricity and industrial heat; suitable grades make coke for steel production.
   c. Anthracite is hard coal with high carbon content and relatively little volatile material. It is used for heating and specialized industry.

4. Coal impurities vary among deposits. Rank alone does not determine sulfur content or every pollutant released.

  B. Natural gas and petroleum

1. Natural gas is mostly methane, CH₄. It supplies heating, cooking, industrial energy, and electricity.

2. Natural gas generally releases less CO₂ per unit of energy than coal or oil when burned. It also produces much less sulfur dioxide and particulate matter than coal, but still releases CO₂ and nitrogen oxides.

3. Petroleum, or crude oil, is a mixture of hydrocarbons. Refining produces gasoline, diesel, jet fuel, and other products for different uses.

4. Oil sands, also called tar sands, contain sand, clay, water, and thick petroleum called bitumen. Recovering and processing it requires energy and water and can disturb extensive habitat.

  C. Cogeneration

1. Cogeneration, or combined heat and power, produces electricity and useful heat from one fuel source. A nearby building or factory uses heat that would otherwise be wasted.

2. Total useful efficiency includes both outputs. A plant supplying 35 MJ of electricity and 45 MJ of useful heat from 100 MJ of fuel is 80% efficient overall.

IV. Distribution of Natural Energy Resources (Topic 6.4)

  A. Uneven resource distribution

1. Fossil fuel deposits depend on geologic history. Coal commonly formed from ancient wetland plants; oil and gas commonly formed from buried aquatic microorganisms.

2. Petroleum and natural gas occur in large deposits in the Middle East. Canada has extensive oil sands; coal deposits occur in the United States, China, India, Russia, and Australia.

3. Uranium deposits occur where geologic processes concentrated uranium, including in Kazakhstan, Canada, and Australia.

4. A reserve is the known amount recoverable economically under current conditions. Prices, technology, and discoveries can change reserve estimates.

5. Strong winds favor wind power; abundant sunlight favors solar power; flowing water and elevation differences favor hydropower. Accessible underground heat favors geothermal power.

V. Fossil Fuels (Topic 6.5)

  A. Electricity generation

1. Combustion reacts fuel with oxygen and releases heat. Complete hydrocarbon combustion produces carbon dioxide and water: CH₄ + 2O₂ → CO₂ + 2H₂O + energy.

2. In a steam plant, fuel heats water in a boiler. Steam spins a turbine, which turns a generator to produce electricity. A condenser cools steam back into water for reuse.

3. A combined-cycle plant uses a gas turbine and then uses its hot exhaust to generate steam for another turbine. It makes more electricity from the same fuel.

4. Combined cycle produces additional electricity; cogeneration supplies useful heat as well as electricity. Both recover heat that would otherwise be wasted.

  B. Extraction and its effects

1. Surface coal mining removes overlying soil and rock. Strip mining and mountaintop removal destroy habitat, increase erosion, and can bury streams.

2. Underground mining reaches deeper coal but exposes workers to collapse, dust, and gases. Exposed sulfur-containing minerals can form acid mine drainage, lowering water pH and releasing dissolved metals.

3. Oil and gas wells extract fuel on land or offshore. Spills contaminate soil and water, poison organisms, and damage birds’ insulating feathers.

4. Hydraulic fracturing, or fracking, injects water, sand, and chemicals at high pressure to crack rock. Sand holds cracks open so oil or gas can reach the well.
   a. Water use and contaminated wastewater create disposal problems. Surface spills, damaged well casings, or poor waste handling can contaminate groundwater.
   b. Operations can release methane and volatile organic compounds (VOCs). VOCs contribute to ground-level ozone formation.
   c. Deep wastewater injection can trigger earthquakes; fracturing itself can also cause earthquakes in some locations.

  C. Combustion and cooling impacts

1. CO₂ warms the climate. Methane leaks also contribute to warming and can reduce natural gas’s climate advantage.

2. Sulfur dioxide and nitrogen oxides contribute to acid deposition. Nitrogen oxides also help form ground-level ozone; fine particles damage respiratory and cardiovascular health.

3. Incomplete combustion can produce poisonous carbon monoxide and soot. Coal can release mercury and leaves ash that requires safe disposal.

4. Scrubbers remove much of the sulfur dioxide; filters and electrostatic precipitators capture particles. These controls do not automatically remove CO₂.

5. Carbon capture and storage separates CO₂ for long-term storage, often underground. It requires additional energy and does not eliminate all fuel-related impacts.

6. Heated cooling-water discharge causes thermal pollution. Warmer water holds less dissolved oxygen and can stress aquatic life. Cooling towers reduce direct heat discharge but lose water through evaporation.

VI. Nuclear Power (Topic 6.6)

  A. Fission and electricity generation

1. Nuclear fission splits a heavy nucleus. A neutron striking uranium-235 can release heat and more neutrons, causing a chain reaction.

2. Fuel rods contain uranium fuel. Control rods absorb neutrons to regulate the reaction; a moderator slows neutrons, and coolant carries away heat.

3. Reactor heat produces steam, which turns a turbine and generator. In a pressurized-water reactor, reactor coolant transfers heat to a separate steam-producing water loop.

4. Nuclear power uses finite uranium and is nonrenewable. Fusion joins light nuclei and powers the Sun; it is different from the fission used in conventional nuclear plants.

  B. Benefits, waste, and accidents

1. Nuclear plants provide steady electricity from a small fuel mass without combustion emissions during operation. Mining, construction, and fuel processing still have environmental impacts.

2. Uranium mining disturbs land. Plants need cooling water and can cause thermal pollution. Construction, decommissioning, and waste management can be expensive.

3. Radioactivity is radiation released as unstable nuclei decay. Exposure can damage cells and increase cancer risk.

4. Spent fuel remains hot and radioactive. Cooling pools and later shielded dry containers provide storage; long-term isolation prevents exposure and contamination.

5. Loss of cooling can cause a meltdown. Radioactive decay continues producing heat after the chain reaction stops.
   a. Three Mile Island (1979): Equipment and operating failures caused a partial meltdown; containment limited the radioactive release.
   b. Chernobyl (1986): An unsafe test and reactor design problems caused explosions, fire, and widespread radioactive contamination.
   c. Fukushima Daiichi (2011): An earthquake and tsunami disabled power and cooling, causing core damage, hydrogen explosions, and radioactive releases.

  C. Half-life calculations

1. Half-life is the time required for half of an isotope’s undecayed nuclei to decay. Each half-life removes half of what remains, not half of the original amount.

2. Amount remaining = initial amount × (½)ⁿ, where n = elapsed time ÷ half-life. An 80 g sample becomes 40 g, 20 g, and 10 g after one, two, and three half-lives.

3. For one isotope, activity also falls by half each half-life. Daughter products may remain radioactive, so one isotope’s half-life does not establish when mixed waste is safe.

VII. Energy from Biomass (Topic 6.7)

  A. Sources and environmental effects

1. Biomass comes from recently living material, including wood, crop residues, and animal waste. Burning it provides heat directly or makes steam for electricity.

2. Decomposition without oxygen can produce methane-containing biogas, which can be captured and burned as fuel.

3. Biomass can be inexpensive and locally available, but burning it releases CO₂, carbon monoxide, nitrogen oxides, particles, and VOCs. Indoor smoke is a major health risk.

4. Overharvesting trees causes deforestation and erosion. Fuel crops can replace habitat and compete with food production for land and water.

  B. Ethanol and energy return

1. Ethanol is an alcohol fuel made by fermenting sugars from crops such as corn or sugarcane. It replaces some gasoline in suitable engines and blends.

2. Burning ethanol returns carbon recently absorbed by crops. Farming, processing, transportation, and land clearing can add emissions, so ethanol is not automatically carbon neutral.

3. Energy return on energy invested (EROI) = usable energy obtained ÷ energy used to obtain it. Some ethanol production pathways have low returns.

4. Obtaining 15 MJ of fuel while using 10 MJ gives an EROI of 1.5:1 and a net gain of 5 MJ. EROI differs from conversion efficiency.

VIII. Solar Energy (Topic 6.8)

  A. Solar technologies

1. Photovoltaic (PV) cells convert sunlight directly into electricity through a semiconductor. They do not require steam or turbines.

2. Active solar heating uses collectors and powered equipment to collect and transfer solar heat, often through a fluid. Heated water can be stored for later use.

3. Concentrating solar thermal plants use mirrors to focus sunlight, heat a fluid, and generate steam to turn a turbine.

4. Passive solar design uses building orientation, windows, shading, and materials to manage solar heat without powered collection equipment.
   a. In the Northern Hemisphere, south-facing windows can admit winter sunlight; overhangs can block higher summer sunlight.
   b. Thermal mass, such as a concrete floor, absorbs heat and releases it gradually. This is natural heat retention rather than an active collection system.

  B. Benefits and limitations

1. Solar systems avoid combustion during operation. Rooftop panels use existing space, while large ground installations can disturb desert habitat and other ecosystems.

2. Output depends on sunlight, clouds, shade, season, and location. PV produces no electricity at night; storage or other generation helps match supply to demand.

3. Installation can be expensive. Manufacturing requires energy and mined materials, and panels require proper recycling or disposal.

IX. Hydroelectric Power (Topic 6.9)

  A. Generating and storing electricity

1. A dam stores water in a reservoir. Water flows downhill through a penstock and spins a turbine connected to a generator.

2. The water’s gravitational potential energy becomes motion and then electricity. Greater flow and a larger vertical drop, or head, generally increase potential power output.

3. Run-of-river systems use flowing river water with little or no large reservoir. Tidal energy uses moving tidal water to turn turbines.

4. Pumped storage uses electricity to pump water uphill and generates electricity when water flows back down. It stores energy and returns less electricity than pumping used.

  B. Benefits and environmental costs

1. Hydropower generates electricity without combustion exhaust or fuel ash. Reservoirs may also provide water storage, recreation, and flood control.

2. Dams are expensive and flood habitat, sometimes displacing people. They can block fish migration and change downstream flow, temperature, and oxygen conditions.

3. Trapped sediment reduces reservoir capacity and the sediment reaching downstream floodplains and deltas. Fish ladders and managed releases reduce some impacts.

4. Drought limits generation. Decomposing flooded vegetation can release methane, especially in some warm reservoirs; hydropower is not impact-free.

X. Geothermal Energy (Topic 6.10)

  A. Using Earth’s heat

1. Geothermal energy comes from Earth’s internal heat. Wells bring hot water or steam toward the surface to supply heat or turn turbines for electricity.

2. Cooled water is often reinjected to maintain the reservoir. Accessible high-temperature resources are especially common near tectonically active areas.

3. Geothermal plants can provide steady power with low combustion emissions, but drilling is expensive and suitable locations are limited.

4. Fluids can contain salts and harmful gases such as hydrogen sulfide. Poor handling can contaminate water; some projects cause subsidence or induced earthquakes.

5. A ground-source heat pump uses electricity to move heat between a building and shallow ground. It heats or cools buildings but does not generate electricity.

XI. Hydrogen Fuel Cell (Topic 6.11)

  A. Electricity production

1. A hydrogen fuel cell combines hydrogen and oxygen to produce electricity, water, and heat: 2H₂ + O₂ → 2H₂O + electrical energy + heat.

2. In a common membrane fuel cell, hydrogen separates into ions and electrons at the anode. Electrons flow through an external circuit; ions cross the membrane and help form water at the cathode.

3. The cell supplies electricity while hydrogen and oxygen are supplied. It does not burn fuel and produces no CO₂ at the point of use.

  B. Hydrogen production and limitations

1. Hydrogen is an energy carrier that requires energy to produce. Electrolysis uses electricity to split water into hydrogen and oxygen.

2. Low-carbon electricity can make hydrogen with low production emissions. Fossil-fueled electricity or hydrogen production from natural gas can add substantial CO₂ emissions.

3. Fuel cells can power vehicles and provide stationary electricity, but cost, refueling infrastructure, storage, and production losses limit their use. Compressing or liquefying hydrogen also uses energy.

XII. Wind Energy (Topic 6.12)

  A. Generation and siting

1. Uneven solar heating helps create winds. Moving air turns turbine blades and a shaft connected to a generator, converting kinetic energy into electricity.

2. Open plains, ridges, and suitable coastal or offshore sites provide strong winds. Offshore construction, maintenance, and transmission can be expensive.

3. Wind produces no combustion emissions during operation and needs little operating water. Land between turbines can often support farming or grazing.

  B. Limitations and output

1. Wind varies, so output changes. Storage, transmission, flexible demand, and other generators help balance electricity supply.

2. Blades can kill birds and bats; roads and power lines can disturb habitat. Careful siting and targeted operating changes reduce harm. Noise and visual effects can affect nearby communities.

3. Capacity factor = actual energy generated ÷ (rated power × time). Multiply by 100 for a percentage. It measures use of rated capacity, not conversion efficiency.

4. A 2 MW turbine with a 35% annual capacity factor produces 2 × 8,760 × 0.35 = 6,132 MWh in a 365-day year.

XIII. Energy Conservation (Topic 6.13)

  A. Reducing energy demand

1. Energy conservation reduces use through behavior, such as turning off unused lights. Energy efficiency provides the same service with less energy, such as using an LED for the same light output.

2. Insulation and sealing air leaks reduce heat transfer. Adjusting thermostats reduces unnecessary heating and cooling; efficient appliances and lighting reduce electricity use.

3. Saving hot water reduces water-heating energy. Suitable shade trees reduce summer cooling demand, and windbreaks can reduce winter heat loss.

4. Green building design combines insulation, efficient systems, and passive solar features. Public transportation, walking, cycling, and compact development reduce driving.

5. Higher vehicle fuel economy reduces fuel used per mile. Hybrids combine engines and electric motors; battery electric vehicles have no tailpipe exhaust, but their life-cycle impacts depend on batteries and electricity sources.

6. Lower demand reduces fuel extraction, pollution, and costs. The rebound effect occurs when increased use partly offsets efficiency gains.

  B. Energy, power, and efficiency calculations

1. Power is the rate of energy use: 1 watt = 1 joule/second. Energy = power × time; watts × seconds gives joules, and kilowatts × hours gives kilowatt-hours.

2. Useful conversions are 1 kW = 1,000 W; 1 MW = 1,000 kW; 1 kWh = 3.6 MJ; and 1 Btu ≈ 1,055 J. A kilowatt-hour measures energy, not power.

3. Electricity cost = energy used in kWh × price per kWh. A 1.5 kW heater running for 4 hours uses 6 kWh; at an assumed $0.18/kWh, its energy charge is $1.08.

4. Efficiency (%) = useful energy output ÷ energy input × 100. A plant producing 120 MJ of electricity from 300 MJ of fuel is 40% efficient; most remaining energy leaves as waste heat.

5. Required energy input = useful output ÷ efficiency as a decimal. Use matching energy units before dividing.

  C. Savings and comparisons

1. Energy saved = reduction in power × operating time. Replacing a 60 W lamp with a 10 W LED saves 0.050 kW; at 5 hours daily, annual savings are 91.25 kWh.

2. Percent reduction = (original use − new use) ÷ original use × 100. The lamp replacement reduces electricity use by about 83% for the same operating time.

3. Simple payback time = extra upfront cost ÷ annual money savings. Compare technologies providing the same useful service and include relevant life-cycle effects.

4. To investigate savings, compare measured energy use over similar periods while keeping conditions such as room size and temperature comparable. Repeat measurements to check consistency.

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