Environmental Science Energy Resources and Consumption 3 — Questions and Answers
Question 1: Which greenhouse gas has the highest global warming potential (GWP) over a 100-year timeframe among those listed?
- Carbon dioxide (CO2)
- Methane (CH4)
- Nitrous oxide (N2O)
- Sulfur hexafluoride (SF6) (Correct answer)
Correct answer: Sulfur hexafluoride (SF6)
SF6 has a GWP of approximately 23,500 over 100 years, far exceeding CO2 (1), CH4 (~28), and N2O (~265).
Global Warming Potential (GWP) measures how much heat a greenhouse gas traps relative to CO2 over a specified time period. Over 100 years: CO2 = 1 (reference), CH4 = 28-36, N2O = 265-298, SF6 = approximately 23,500. SF6 is used in electrical switchgear and circuit breakers; though emitted in tiny volumes, its extraordinary GWP makes leaks significant.
Question 2: Pumped-storage hydroelectricity is primarily used to:
- Generate base-load power from rivers continuously
- Store excess electricity by pumping water uphill and releasing it when demand peaks (Correct answer)
- Provide irrigation water to agricultural areas during dry seasons
- Filter drinking water using gravitational pressure
Correct answer: Store excess electricity by pumping water uphill and releasing it when demand peaks
Pumped storage is the largest form of grid-scale energy storage: excess electricity pumps water to an upper reservoir; releasing it generates power during peak demand.
Pumped-storage hydroelectricity accounts for over 90% of utility-scale energy storage worldwide. During low-demand periods, cheap surplus electricity pumps water from a lower to an upper reservoir. During peak demand, water is released through turbines to generate electricity. Round-trip efficiency is ~70-85%. It is critical for balancing grids with high proportions of variable renewables.
Question 3: Fracking (hydraulic fracturing) has raised environmental concerns primarily related to:
- Increased sea-level rise from coastal drilling platforms
- Groundwater contamination, induced seismicity, and methane leakage (Correct answer)
- Destruction of coral reefs from offshore waste disposal
- Ozone depletion from drilling chemicals
Correct answer: Groundwater contamination, induced seismicity, and methane leakage
Fracking injects high-pressure fluid into rock; concerns include well casing failures contaminating aquifers, disposal-well-induced earthquakes, and fugitive methane emissions.
Hydraulic fracturing injects water, sand, and chemicals at high pressure to crack shale rock and release natural gas or oil. Environmental concerns include: groundwater contamination from well casing failures or surface spills; induced seismicity from wastewater injection into deep disposal wells; fugitive methane emissions; habitat fragmentation from well pads and roads; and high water consumption in water-scarce regions.
Question 4: The capacity factor of a power plant refers to:
- The maximum output the plant can produce
- The ratio of actual energy produced to the maximum possible energy over a period (Correct answer)
- The efficiency of converting fuel to electricity
- The number of hours per day the plant operates at full load
Correct answer: The ratio of actual energy produced to the maximum possible energy over a period
Capacity factor = (actual energy output) / (maximum possible output at rated capacity) x 100%. It indicates how often a plant runs at full power.
Capacity factor measures the utilization of a generating facility over a period (usually a year). Nuclear plants typically achieve 90-93% capacity factors. Coal and natural gas combined-cycle plants: 50-80%. Wind: 25-45% depending on location. Solar PV: 10-25%. A low capacity factor doesn't necessarily mean the plant is inferior, but it affects economics and grid planning.
Question 5: What is the primary advantage of passive solar home design over active solar systems?
- Passive systems generate more electricity per square foot
- Passive design uses architectural features rather than mechanical equipment, reducing maintenance and cost (Correct answer)
- Passive systems work better in cloudy climates
- Passive solar panels are more efficient than photovoltaic panels
Correct answer: Passive design uses architectural features rather than mechanical equipment, reducing maintenance and cost
Passive solar design uses building orientation, insulation, thermal mass, and window placement to capture solar heat without pumps, fans, or electrical equipment.
Passive solar design integrates the building structure itself as the solar collection and storage system: south-facing windows (in Northern Hemisphere) admit winter sun, thermal mass (concrete, stone, tile) stores heat, overhangs shade summer sun, and insulation retains warmth. Unlike active solar systems (collectors with pumps and fans), passive systems have no mechanical components, require little maintenance, and add minimal construction cost when incorporated at design stage.
Question 6: Geothermal energy is most economically viable in regions:
- Near large coal deposits that heat underground water
- Located close to tectonic plate boundaries or volcanic hot spots (Correct answer)
- With high average annual solar radiation
- Adjacent to major river systems
Correct answer: Located close to tectonic plate boundaries or volcanic hot spots
High geothermal gradients near plate boundaries and volcanic areas (Iceland, Philippines, Kenya, western U.S.) bring heat close enough to the surface for economical extraction.
Geothermal energy taps heat from the Earth's interior. Where tectonic activity brings magma close to the surface - at divergent boundaries (Iceland), subduction zones (Philippines, Indonesia), and hot spots (Hawaii, Yellowstone) - high-temperature steam or hot water can be accessed at relatively shallow depths. Countries like Iceland, Kenya, and El Salvador generate substantial fractions of their electricity from geothermal sources.
Environmental Science Energy Resources and Consumption 3
Which greenhouse gas has the highest global warming potential (GWP) over a 100-year timeframe among those listed?