Evaluating Other Energy Sources
Answer Key
1. What factors are important to consider in deciding the fuel source to use for generating electricity?
Important factors to consider when deciding which fuel source to use for generating electricity
are: Is the fuel renewable? How much space is needed for generation? How much will it affect
natural habitats? How much water does it use? Is there potential for contamination of the
environment? How many greenhouse gases are emitted? How much waste material is created,
and how will that waste be treated?
2. Which fuel source has provided most of the electricity since 1949?
coal
3. How did the generation of renewable energy change from 1949 to 2011? (Renewable energy
includes hydroelectric power, wind, solar, geothermal, and biofuels.)
Between 1949 and 2001, renewable energy generation increased. It almost doubled, but it still
remains a very small part of electricity generation in the United States.
4. What areas of the country have the best solar resources? (Check all that apply.) (See slide 1.)
Southwest
6. What areas of the country have the best geothermal resources?
(Check all that apply.) (See slide 4.)
Southwest
Northwest
7. What areas of the country have the highest concentration of nuclear resources?
(Check all that apply.) (See slide 10.)
Northeast
Southwest
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5. What areas of the country have the best wind resources? (See slides 2 and 3.)
The middle section of the country has good wind resources. This extends from North Dakota
south to Texas. The coasts also have good wind resources, mainly the Atlantic Coast from
Maine to Georgia, the Gulf Coast along Texas and Louisiana, the Pacific Coast of the contiguous
United States (Washington, Oregon, California) and all coasts of Hawaii, particularly the
southern-most coast.
Evaluating Other Energy Sources
Answer Key, continued
8. What areas of the country have the most fossil fuel (natural gas and coal) resources?
(See slides 7, 8, and 9.)
The most fossil fuels are found in the Northeast, Midwest, Gulf Coast area, and middle section
of the country, basically everywhere but Florida and the West Coast.
9. What energy sources are most abundant in your area of the country?
Student answers will vary. Check the maps for the resource availability in your location.
10. Which fuel source used to generate electricity emits the most carbon dioxide?
coal
11. Which fuel source used to generate electricity emits the most methane?
natural gas
12. Earth’s climate system consists of greenhouse gases, incoming solar radiation, and outgoing
infrared (heat) radiation. Describe how fossil fuel usage affects Earth’s climate system.
Fossil fuel usage increases the amount of carbon dioxide being emitted into the atmosphere.
Carbon dioxide is a greenhouse gas. Greenhouse gases trap heat in the atmosphere. Therefore
fossil fuel usage leads to increasing temperatures as carbon dioxide traps heat in the atmosphere.
14. Explain your answer.
Hydropower doesn’t add any contaminants to the water. The quality of the water may be affected
by being dammed up, but it will not be contaminated with heavy metals by being dammed up.
Wind and solar may contaminate water supplies just because the manufacturing process uses
rare and/or toxic materials. Geothermal probably doesn’t have much of an effect on water quality,
unless the pipes in the ground leak into an aquifer. Biomass also probably doesn’t have much of
an effect on water quality. Water is used to grow crops for fuel, so it might be contaminated with
residues from pesticides, if they were used in growing the crops. Natural gas will only contaminate
water if there is a leak, but leaks sometimes happen. Coal can contaminate the water directly with
runoff from mines, or it can contaminate the water with particulate emissions after it’s burned.
Nuclear also has a low potential for water contamination unless there is a leak, which has not
happened in this country but has happened in other areas of the world.
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13. Which energy source used to generate electricity has the lowest environmental impact
on water quality?
hydropower
Evaluating Other Energy Sources
Answer Key, continued
15. All energy sources have an ecological impact. Why is it important to consider land use when
thinking about renewable energy sources?
It is important to think about land use, particularly when thinking about renewable energy sources,
because renewable energy sources take up a lot of space. Solar farms and wind farms take up
vast areas and can cause fragmentation or destruction of natural habitats.
16. Which energy source has the largest ecological impact on its surroundings?
hydropower
17. Explain your answer.
Hydropower has a large ecological impact on its surroundings. Rivers are dammed up preventing
the free migration of fish species up- and downstream. Currents are destroyed by the damming,
messing up the cues that migratory fish use to navigate the river. The animals that prey on the
fish are affected by the disrupted flow. Sediments aren’t carried downstream, leading to the
depletion of river deltas. The land that used to surround the river is put underwater, displacing
thousands of acres of natural habitat for organisms. The water is deeper and therefore colder
than it would otherwise be. This disrupts the habitats of animals that live in the water.
Nuclear has a low impact on the environment aside from issues directly at the mining sites,
where runoff can affect local aquifers, and nuclear accidents, which affect the area around the
nuclear plant. Nuclear plants also discharge heated water into streams and lakes that can kill
fish by depleting the level of oxygen in the water.
Geothermal has a very low impact on the ecosystem. There is some disruption as wells are
drilled, but unless there are leaks from the wells, there is very low effect on local habitats.
Wind and solar both take vast areas of land, which can disrupt local ecosystems. The noise
from wind turbines can disrupt animal communications, and animals can fly into the turbines
and be hurt or killed.
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Fossil fuels have a lower impact than hydropower. Extracting the fossil fuels can have a local
environmental impact, but those impacts can be managed with careful planning. Burning fossil
fuels has an impact on air quality, which can affect ecosystems nearby and far away as the
wind moves pollutants through the air.
Evaluating Other Energy Sources
Answer Key, continued
18. Why is it beneficial to have many different sources for electricity generation, even though some
sources are quite inefficient in some respects (as biofuels)?
Relying on many different options is better for Earth than relying on a single option for electricity
generation. Spreading out the risk over several different sources means that at least one source
will be available any time. If you rely on a single source, it can easily be depleted, and then you’re
stuck trying to develop new sources while having no electricity in the present. If you have multiple
sources, you can develop more environmentally-friendly ways of extracting the fuel as opposed
to having to get the fuel in whatever way necessary because it’s the only fuel source. Even an
inefficient fuel source is better than using a more efficient fuel source in a way that’s hazardous
to local ecosystems.
19. Which energy source used to generate electricity in the United States is most efficient?
hydropower
21. How certain are you about your claim based on your explanation?
Student answers will vary.
22. Explain what influenced your certainty rating.
Student answers will vary. Scientific evidence includes specific reference to numbers in the
table. Students may state that they don’t know whether to measure efficiency in terms of MWh
per unit land or dollars per MWh.
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20. Explain your answer.
Hydropower is the most efficient power source. The cost per unit of electricity is the lowest for
hydropower (starting at $59 per MWh). The cost is a measure of the efficiency. Once the dam is
built and the turbines installed, there is very little cost to generating more electricity. The water
does not have to be mined and transported to the plant; it flows there automatically. Measured by
energy per square meter, natural gas is the most efficient. There is a lot of natural gas, and it is in
the same price range per MWh as hydropower. It just depends on how you measure efficiency.