APES - Unit 6: Energy Resources and Consumption

Renewable vs. Nonrenewable Energy Resources

• Renewable resources:

  • Can be replenished by natural processes (restocked).

  • Can continually regenerate themselves (e.g., trees regrowing).

  • Examples: biomass, solar, wind, and geothermal.

• Nonrenewable resources:

  • Cannot be replenished within a human timescale (processes take geologic time).

  • Present in a fixed amount; once used, they're gone.

  • Examples: fossil fuels (coal, oil, natural gas).

• Important distinction: Replenish vs. Reuse

  • Firewood example: It can be burned (used), but more trees can be grown to replenish it. Replenishing means restocking.

Global Energy Distribution and Consumption

• Uneven distribution: Depends on geologic history; some regions are energy "winners," others are "losers."

• Developed vs. Less Developed Countries:

  • Developed countries use energy at a much greater rate.

  • Analogous to the demographic transition model: industrialization increases energy demand.

• Factors influencing energy use: availability, price, and government policies.

• World energy consumption trends (measured in quadrillion British thermal units - BTU):

  • Natural gas use has generally increased and is projected to continue increasing.

  • Coal use has started to dip due to availability and price.

  • Nuclear energy use has remained relatively flat.

Coal: Pros and Cons

• Pros:

  • Plentiful and cheap.

  • Easy to extract, transport, and convert into electricity.

  • Most countries have some coal deposits (US, China, and Russia have large deposits).

• Cons:

  • Mining:

    • Habitat destruction (e.g., mountaintop removal).

  • Burning:

    • Releases carbon dioxide (a greenhouse gas).

    • Releases $SO_x$ gases (can form acid rain).

    • Releases heavy metals like mercury (a neurotoxin).

  • Waste Disposal:

    • Produces massive amounts of coal ash (hazardous waste).

Natural Gas: Pros and Cons

• Pros:

  • Abundant source with increasing accessibility.

  • Cleaner burning than coal.

  • Less mercury and sulfur impurities than coal.

• Cons:

  • Hydraulic Fracturing (Fracking):

    • Used to extract natural gas from shale rock.

    • Can contaminate groundwater with chemicals and water.

Electricity Generation from Coal and Natural Gas

• Basic Process (similar for both):

  • Burn fuel (coal or natural gas).

  • Combustion reaction: Hydrocarbon + Oxygen -> Carbon Dioxide + Water ($CO<em>2$ and $H</em>2O$ are greenhouse gases).

  • Heat water to create steam.

  • Steam turns a turbine.

  • Turbine powers a generator.

  • Electricity is transmitted via transmission lines.

• Cooling Tower:

  • Power plants located near water sources for cooling.

  • Water extraction for cooling can lead to thermal pollution if not cooled before returning to the environment.

• Coal Ash Disposal:

  • Hazardous waste due to heavy metals.

  • Ash ponds need liners to prevent contamination.

Nuclear Energy

• Non-renewable: Uranium-235 must be mined.

  • Habitat loss associated with mining.

• Electricity Generation:

  • Nuclear fission (splitting uranium atoms) generates heat.

    • $E=mc^2$: mass converted into large amount of energy

  • No combustion: Splits atoms to heat water and turn a turbine.

• Advantages:

  • No combustion = No direct emissions during electricity generation.

• Disadvantages:

  • Construction of plant requires lots of cement, generating $CO_2$ emissions.

  • Mining of uranium and transport of materials

Sample Problems

• Multiple Choice Example 1:

  • The major sources of commercial energy are coal, oil, and natural gas, with an increasing contribution from renewables.

• Multiple Choice Example 2: Advantage of Natural Gas over Coal

  • Natural gas produces less sulfur dioxide when burned.

  • Sulfur is an impurity in coal that leads to $SO_x$ gases when combusted which causes acid rain.

  • Even natural gas is cleaner than coal, its combustion still release greenhouse gas $CO_2$.

• Free Response Question 1: Nuclear Energy Claim

  • The claim: Nuclear energy is cleaner and more sustainable than fossil fuels.

  • Accept: Nuclear fission does not produce direct emissions like carbon dioxide (a greenhouse gas).

  • Reject: Nuclear fission generates radioactive hazardous waste that must be stored for long periods.

Half-Life Calculation

• Example: Cesium-137 near Chernobyl

  • Initial amount: 187 kilobecquerels (kBq).

  • Half-life: 30 years.

  • Calculate amount remaining after 90 years.

• Steps:

  1. Determine the number of half-lives elapsed: 90 years / 30 years = 3 half-lives.

  2. Calculate the remaining amount after each half-life:

     • After 1 half-life: 187 kBq / 2 = 93.5 kBq.

     • After 2 half-lives: 93.5 kBq / 2 = 46.75 kBq.

     • After 3 half-lives: 46.75 kBq / 2 = 23.375 kBq.

  3. Answer: 23.375 kBq of Cesium-137 will remain.

Renewable Energy Review

• Biomass:

  • Pros:

    • Renewable (if harvested sustainably).

    • Can be carbon neutral (if managed properly).

  • Cons:

    • Can lead to deforestation (major cause in developing countries).

• Solar Energy:

  • Pros:

    • Photovoltaic (PV) cells generate electricity directly.

    • Potential for small-scale solar photovoltaics.

  • Cons:

    • Lack of battery storage to address intermittency.

• Wind Energy:

  • Pros:

    • Turbines spin directly, eliminating mining and combustion.

  • Cons:

    • Potential impact on bird and bat populations (can be mitigated by siting).

• Geothermal Energy:

  • Pros:

    • Taps Earth's interior heat (not solar-related).

    • Can use heat to make steam without combustion.

  • Cons:

    • Can release hydrogen sulfide gas.

Carbon Neutrality of Biomass

• Fossil Fuels:

  • Formed from plants that took carbon out of the atmosphere millions of years ago.

  • Burning releases $CO_2$ that was sequestered underground.

• Biomass (e.g., Ethanol from corn):

  • Corn plants take $CO_2$ out of the atmosphere.

  • Burning ethanol returns the same $CO_2$ to the atmosphere.

  • This process is considered carbon neutral because it doesn't add new $CO_2$ to the carbon cycle.

Energy Conservation at Home

• Simple strategies:

  • Adjust thermostat.

  • Purchase ENERGY STAR appliances.

  • Use conservation landscaping (shade, evaporative cooling).

  • Passive solar energy (e.g. hang clothes on a line).

• Replace inefficient light bulbs with efficient ones.

Government Policies and Energy

• Governments influence energy use through:

  • Taxes: Disincentivize certain behaviors (e.g. taxing gasoline).

  • Incentives: Encourage other behaviors (e.g. carpool lanes).

  • Legislation: Fund electric vehicle charging stations, set fuel efficiency standards, subsidize industries.

Practice Calculation: Light Bulbs

• Scenario: Homeowner replaces incandescent bulbs with LED bulbs.

  • Data:

    • Incandescent: 73 watts.

    • LED: 9.9 watts.

    • Each bulb used 8 hours/day.

    • Electricity cost: 10.42 cents/kilowatt hour.

• Calculations:

  1. Calculate energy use (kilowatt hours per year) for each bulb:

     • Incandescent: 73 watts * (1 kilowatt/1000 watts) * 8 hours/day * 365 days/year = 213.26 kilowatt hours/year.

     • LED: 9.9 watts * (1 kilowatt/1000 watts) * 8 hours/day * 365 days/year = 28.9 kilowatt hours/year.

  2. Calculate cost savings (dollars per year):

     • Incandescent: 213.26 kilowatt hours/year * 10.42 cents/kilowatt hour * ($1/100$ cents) = $22.22/year.

     • LED: 28.9 kilowatt hours/year * 10.42 cents/kilowatt hour * ($1/100$ cents) = $3.01/year.

  3. Claim: The LED bulb is more energy efficient because it produces the same light intensity using less energy.

  4. Explain why:

     • The LED bulb is more efficient at converting electricity to light because less energy is converted to low-quality heat (2nd law of Thermodynamics).

Practice Problem: Offshore Wind Farm

• Scenario: Wind farm proposed to replace a coal plant.

• Location: 13 kilometers offshore, 10 meters deep.

  • Demand: $2*10^6$ megawatt hours per year.

• Calculate electricity (megawatt hours per year) the wind project must generate to provide 80% of demand -- $.8 * 2 <em>10^6 = 1.6</em>10^6$.

• Customer pay $0.2 per kilowatt hr. -- Calculate the revenue produced if produce 80%. --> 1.6 * 10^6 \frac{MWH}{yr} * 1000 \frac{KWH}{MWH} * \frac{$0.2}{KWH} = $320,000,000

• Environmental Benefit: Less coal burned, less habitat destruction from coal mining, reduced emission of carbon dioxide and $SO_x$.

• Unintended Consequence: Habitat fragmentation, death during migration period of birds and bats.

Key Takeaways:

• Distinguish between renewable and nonrenewable resources.

• Describe electricity generation from various resources.

• Calculate energy consumption and cost savings.

• Discuss the advantages, disadvantages, and unintended consequences of energy alternatives.