Homework 13

Recently, national security issues have received increased attention in energy policy discussions. Although nuclear reactors are potential targets for terrorism, they do help diversify our energy portfolio and lessen our dependence on petroleum imports. The United States produces reactor fuel but also relies on imports of uranium oxide from abroad, particularly from Canada, Australia, Russia, Kazakhstan, Uzbekistan, South Africa, and Namibia.


How much uranium oxide did the United States produce in 2005?

5 million pounds


In what year did uranium oxide production peak in the United States?



What was the net amount of uranium imported into the United States in 2005?

45 million pounds


Describe the trends in uranium oxide domestic production from the peak production year to 2005.

Domestic production declined dramatically.


If current trends continue, the United States is likely to

decrease domestic production and increase imports and exports.


Of the new renewable energy alternatives, photovoltaic conversion of solar energy is one that most areas of the United States could adopt. The influx of solar radiation varies with time of day, time of year, and location, so all areas are not equally well suited. Today’s photovoltaic technology is approximately 10% efficient at converting the energy of sunlight into electricity, but new technologies under development may increase that efficiency to as much as 40%.


The red line shows the average per capita residential use of electricity in the United States in 2004. The blue line shows the average influx of solar radiation per square meter for Topeka, Kansas. The dashed lines represent the yearly average values for each.


Based on the yearly average values, calculate one person’s residential electricity needs for a year.

4,440 kWh per year


Based on the yearly average values, calculate the solar radiation per square meter for one year.

1,560 kWh per year


Assume that photovoltaic conversion of solar energy has 10% efficiency. Calculate how many square meters of photovoltaic cells would be needed to supply one person’s electricity for the year, based on the yearly average values.

28.5 m2


If efficiency of photovoltaic cells improves to 40%, how many square meters of photovoltaic cells would be needed for one person’s yearly electricity use?

7.12 m2


Commercially available household photovoltaic systems cost approximately $20,000. The average cost of electricity in the United States is approximately $0.09 per kilowatt hour. At these prices how long would it take for the photovoltaic system to generate $20,000 of electricity? Assume the system will produce enough kilowatt hours for a four-person household in Topeka, Kansas.

12.5 years


Approximately what percentage of overall U.S. energy consumption does bioenergy contribute?



Perpetually renewable sources include energy from the sun, wind, and Earth’s geothermal heat. These energy sources are often called “new renewables” because (1) they are just beginning to be used on a wide scale in our modern industrial society, (2) they are harnessed using technologies still in a rapid phase of development, and (3) they will likely play much larger roles in the future.

If solar, wind, and geothermal sources do play a larger role in U.S. electricity generation in the future, predict what graph (b) might look like in 2050. Select all that apply.

Solar, wind, and geothermal would make up a larger portion of the renewables bar; The renewable slice of the pie chart would get bigger.


Solar, wind, and geothermal would make up a larger portion of the renewables bar. The renewable slice of the pie chart would get bigger.



The United States generates more electricity from ________ than from any other renewable energy source.



Recently, how has Germany reduced its dependence on fossil fuels?

by utilizing the feed-in tariff system


by utilizing the feed-in tariff system



Click here to complete the graphing activity.

According to the data in Step 1, by how much would solar have to grow to match the current level of hydroelectric power?

about 60 times


According to the data in Step 2, which source represents 32% of renewables?

none of them


Which energy source’s annual growth rate is about four times greater than that of tidal power?



Assuming that renewable energy sources will contribute more and more to power generation in the future, do you expect the growth rates for these renewable energy sources to increase or decrease over the next 30-year period (2000 to 2030)?

These growth rates are relative to small absolute numbers. They will most likely decrease as the total contribution by renewables increases.


Which projection has nonrenewables comprising roughly 50% of our energy production in 2050?

Projection 2


Assume that the depletion of nonrenewables requires renewables to account for more than 30% of our energy production by 2040. What annual growth rate of renewables must be achieved in order to meet that goal?

at least 15% annual growth rate


Of the following, ________ represent proper ranking of the U.S. total primary energy consumed from the greatest to least used.

fossil fuels, nuclear, bioenergy, hydroelectric, new renewables


How is the sun’s energy production different from the process in which energy is produced in current nuclear power plants?

The sun releases energy through nuclear fusion, whereas our current nuclear power technology releases energy through nuclear fission.


Regarding photovoltaic (PV) cells, what is released from the “p-type” layer and transferred to the “n-type” layer, thus initiating an electrical current?



Which of the following is one of the three current major drawbacks of solar energy?

This resource is intermittent in nature.


Launch the Video

What happens to unused electricity generated by solar panels on a home? The extra electricity is __________.

sent back into the electrical grid for others to use


Where would you most likely find a solar thermal power plant in the United States?

in the southwestern states


The major problem impeding the widespread use of solar panels on residential buildings is the __________.

cost of solar panels


Massive solar thermal power plants generate electricity by __________.

using sunlight to boil water, generate steam, and turn the blades of a turbine


In the solar panel system presented in the video, which of the following was necessary to generate usable electrical current for a home?

DC power had to be converted to AC.


Which of the following best describes the energy conversion sequence in the solar panel system described in the video?

Photons, carrying energy from the sun, are used to create steam that turns turbines to generate electricity.


Which of the following would indicate that a home is using solar power to generate electricity and is NOT using batteries?

There are solar panels on the roof and no power lines going to the home.


If a home uses a large supply of solar panels to generate electricity, but has no battery system, surplus electricity that is produced is usually __________.

released into the power grid for others to use, generating a credit to the homeowner


Which of the following is a challenge to using solar-generated electricity in places not connected to a power grid?

the lack of efficient and inexpensive battery technology


Designing buildings to maximize absorption of sunlight during winter and to keep the interiors cool during summer is referred to as ________.

passive solar energy collection


Harnessing energy by designing buildings to maximize or minimize the absorption of incident solar radiation are ________.

passive solar energy collection


Which of these statements is NOT true of wind power?

Wind turbines take up large amounts of land that is then unsuitable for other purposes.


What sort of threat does wind energy pose to certain kinds of wildlife?

Flying creatures such as birds and bats are killed when they fly into wind turbine blades.


The ultimate source of energy that drives wind power is __________.

the sun


A typical wind farm in the United States consists of __________.

many very large wind turbines clustered in a region with a low human population


The year 2030 goal set by the US Department of Energy is to generate __________.

20% of electricity using wind-powered systems


Electricity in a wind turbine is generated __________.

when spinning magnets move past a coil of copper wire


Producing electricity using wind instead of fossil fuels __________.

generates no carbon dioxide in the process


________ built the first offshore wind farm in 1991



More and more wind farms are being located ________ because winds are stronger there.



What is the ultimate source for geothermal energy?

the radioactive decay of elements deep within Earth


Which of the following statements is NOT accurate regarding geothermal power?

Geothermal power generators are one of the true fully sustainable energy sources.


The form of energy delivered to an electrical generating turbine in a geothermal facility is in the form of ________.

hot water or steam


What is the process behind tidal energy?

the back and forth movement of the daily tidal cycle


The only energy source(s) from ocean water so far put into commercial production are ________.

tidal electrical generators


Hydropower uses the __________ energy of water to generate electricity.



Why is there little to no growth expected for hydropower?

Almost all rivers that can be dammed for power generation have been dammed already


________ strongly influences the amount of energy generated from hydropower.

The volume of water released and the height of the fall


________ leads the world in percentage of its electricity derived from hydropower



U.S. hydropower dam construction was greatest during the ________.

1930s to 1960s


Which of the following statements about ethanol is true?

Growing corn for ethanol requires substantial inputs of fossil fuel energy


How is cellulosic ethanol different from traditional corn-based ethanol?

It can be made from the nonfood portions of plants and from wood.


Worldwide, the most widely used renewable energy resource is ________.



The first stage in generating power from a hydrogen fuel cell is to ________.

split hydrogen atoms into hydrogen ions (H+) and electrons


Corn-based ethanol production has a number of drawbacks, including ________.

All: depletion of freshwater                                                                                                             increased use of pesticides                                                                                                       substantial inputs of fossil fuel energy                                                                                                increased use of fertilizers


Ethanol produced from bioenergy starts with ________ produced by ________.

starch; corn and sugar cane


Corn-produced ethanol ________.

results in higher food prices for corn and corn products


Bagasse and sugar cane-based ethanol are major items in the energy resources of ________.



The United States consumes 25% of the world’s petroleum. Most is used for transportation, and most of it is imported. In 1992, after the first Gulf War, the federal government passed the Energy Policy Act, whose goal was to replace transportation-related petroleum with alternative fuels. Biodiesel made from vegetable oil or animal fat is an economical alternative to petroleum-based fuels. It is safe, biodegradable, nontoxic, and has the highest energy balance of any liquid fuel. Unlike unrefined oils that can be burned directly as fuels, biodiesel can be used in conventional diesel engines without engine modification. It reduces wear without compromising performance, due to its high lubricity. It is renewable and emits far less air pollution when combusted as compared to petrodiesel. The raw material used to produce biodiesel exists in billions of gallons of vegetable oil used by restaurants each year, as well as in crops. Processing biodiesel yields an added benefit-its by-product, glycerine, is used to make soap. Although biodiesel burns well in pure form (B100), commonly it is blended with petrodiesel in mixtures such as B20 and B5, which reduce toxic air pollution proportional to their biodiesel content. Biodiesel is currently available at almost 500 filling stations nationwide. Demand is increasing due to federal and state tax incentives as well as the increased price and decreased availability of petrodiesel. More than 600 domestic fleets use biodiesel, including the military, NASA, Yellowstone National Park, and local governments. Many school districts use biodiesel-powered school buses. Musicians Neil Young, Bonnie Raitt, and Willie Nelson fuel their tour buses with biodiesel. Nelson, a lifelong supporter of American farmers, who benefit when their crops are used for fuel, sells his own brand, BioWillie Biodiesel, at many truck stops. Because biodiesel can be manufactured locally, fuel transportation costs are low, and dependence on foreign petroleum and the need for domestic oil exploration and development of sensitive wildlife areas, such as the Arctic National Wildlife Refuge, can be reduced when biodiesel is used as an alternative fuel. There is concern, however, that biodiesel from crops may not be sustainable in the long term. Crops which are potentially food for humans, such as rapeseed and soy, affect the price of foods and also require land, pesticides, fertilizers, and irrigation which may contribute to environmental degradation and stress on already limited resources.

Vegetable oil ________.

can be burned as fuel


B20 represents ________.

a ratio of biodiesel to petrodiesel in alternative vehicular fuels


What is the basis for the use of hydrogen fuel cells?

It is extremely energy-efficient.


What is electrolysis?

the splitting of water into component hydrogen and oxygen


Joan Ogden and Daniel Sperling view hydrogen as an ideal future fuel. Which of the following reasons do they discuss?

Several countries have committed billions of dollars in public funds to developing hydrogen energy.


Joan Ogden and Daniel Sperling view hydrogen as an ideal future fuel. Which of the following reasons do they discuss?

Several countries have committed billions of dollars in public funds to developing hydrogen energy


Ogden and Sperling also discuss the challenges of using hydrogen as our major fuel. Identify the statement that is one of the challenges.

Time is needed to develop mechanisms to store hydrogen on vehicles


In contrast to Ogden and Sperling, Joseph Romm views hydrogen fuel-cell cars as an “environmental dead end.” Which of the following statements from the pro-hydrogen essay would he dispute?

Most major automakers are developing hydrogen vehicles, investing hundreds of millions of their own dollars.


Ogden and Sperling argue that hydrogen is one of the only transportation fuels that can dramatically reduce greenhouse gas emissions. How might Romm respond to this statement?

No. Hydrogen cars are not a good use of renewable energy. We can achieve much greater greenhouse gas reductions by using renewable electricity to displace a future natural gas or coal power plant.


Use the information given by authors of both essays to select a strategy that achieves both short-term and long-term greenhouse gas emission reductions.

Invest in research and development for the hydrogen energy system (e.g., electrolyzers, hydrogen delivery infrastructures, etc.)


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