Basic Questions
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Multiple Choice
1/1 point (graded)
This a multiple-choice problem. You will choose just one response, receiving credit for
the right answer.
Select a vowel from the list below.
A
...
Basic Questions
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Multiple Choice
1/1 point (graded)
This a multiple-choice problem. You will choose just one response, receiving credit for
the right answer.
Select a vowel from the list below.
A correct
B
C
D
E
Submit
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the Submit button.
Hint Show Answer
Dropdown
1/1 point (graded)
This is a dropdown problem. It's basically identical to a multiple-choice problem, it just
displays things in a different way. Dropdown problems only ever have one correct
answer.
Which of these numbers is a prime number?
correct
Submit
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the Submit button.
Hint Show Answer
Checkboxes
1/1 point (graded)
This a checkbox problem, also known as a "check all that apply" problem. You will
choose ALL of the correct responses, receiving full credit only if you select all of them
and none of the incorrect answers.
17
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This problem also allows for partial credit! It uses a scheme called "Every Decision
Counts," which is the standard scheme in this course. Each choice is worth an equal
amount of the total credit (20% in this case). Try answering the question different ways
to see how partial credit works!
Which of the following are vowels? Select all that apply.
A
B
C
D
E
Complex Questions
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Numerical Input
1/1 point (graded)
Some problems require a numerical input. Your answer will be marked correct if it is
within a certain range of the right answer (usually about 5%, though it varies from
problem to problem).
If you need a calculator, you can find an icon in the bottom right-hand corner of your
window that will show one for you. Click the (i) button to learn how to use it. You can
also find many good calculators online, from Google's push-button calculator to Wolfram
Alpha.
Enter the approximate value of the mathematical constant π (pi):
correct
3.14
Submit
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the Submit button.
Show Answer
Exponential Input
1/1 point (graded)
Very large or very small numbers are best input with exponential notation. For instance,
the number 8,000,000 (eight million) is equal to 8×106. In this course, you can enter
3.14
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that as either 8 * 10 ^ 6 or as 8e6 in these problems. Try out exponential notation in the
question below.
One gigajoule is equal to 947817 British thermal units. Enter this number below in
exponential notation. The tolerance on this question is 5%.
BTU correct
9.47×105
Submit
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the Submit button.
Show Answer
Formatting Numbers
While there is a 5% tolerance for most of the problems in this course, you must also be
sure to enter your numbers in the right format. If you type "9.48e5" in the answer box
above, the computer knows how to interpret that. Similarly, it knows how to interpret
"9.48*10^5" or"9.48 * 10 ^ 5" (with spaces).
What it doesn't know how to do is handle "9.48 x 10 ^ 5" with an "x" instead of a star.
That little change throws things off. You need to use exactlythe right formatting.
This is one of the most common errors made by people who are new to edX. If you are
working on a numerical problem, you should double-check your formatting before
entering each answer.
Also - did you look at the answer to the last problem? It contains extra information about
partial credit in numerical problems! Go take a look if you didn't see it before.
Matching
1.0/1 point (graded)
This is a matching exercise. Drag the elements on the left into the ones on the right to
create a match. Click on the [-] to remove the match. You can match items with more
than one other item, but you should choose the best match if you can. Click on the
individual items for a better view if you need it.
This problem type gives partial credit! Each correct assignment is worth one point; each
error takes a point away. Play around with different matches to see how it works.
9.47e5
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Syllabus Quiz, Part 1
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Now that you know how to answer edX questions, it's time for your first quiz. Below are
some quick questions to make sure you understood the most important highlights from
our syllabus. This should be very easy - all of the information can be found on
the Syllabus, the Schedule page, and in the introductory videos in this section.
A syllabus quiz might seem a little silly, but reading the syllabus carefully will improve
your course experience. Also, our course staff often spend a substantial amount of time
answering questions where the answer is in the syllabus. We're always happy to help,
but hopefully this quiz will help you know the most important information before starting
the course.
Unlike the practice problems, this quiz is graded, so do your best! This quiz appears
as Work01 on your Progress page.
Annotate
Collaboration
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1/1 point (graded)
Select all that apply.
Which of the following are acceptable ways to collaborate?
Working jointly to develop an overall approach to an assignment
Taking someone else’s formulas and plugging in your numbers to get the final
answer
Posting answers to a problem before the deadline
Getting hints from peers or course staff if you’re stuck
correct
Submit
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the Submit button.
Show Answer
Graded Assignments
1/1 point (graded)
Select all that apply.
Which of the following types of graded assignments appear in this course?
Quizzes
Practice
Exams
Coursework
Peer-graded Essays
correct
Submit
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the Submit button.
Show Answer
Course Content
1/1 point (graded)
In this course you’ll learn... (Select all that apply.)
Details of solar and nuclear power
Details of wind power and biofuels
Environmental impacts including climate change, air pollution, and land use
The flow of energy through modern economies, including costs
Details of end uses of energy (tranportation, industry, etc.)
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Lots of theory, e.g. electrodynamics as a foundation for understanding solar panels
Lots of details about real world devices, e.g. the performance and cost of modern
commercial solar panels
How to critically compare energy options, using good references and combining
quantitative and qualitative analysis
correct
Submit
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the Submit button.
Show Answer
Deep Dives
1/1 point (graded)
In this course, deep dives are...
Underwater explorations
Our recommended resources for learning more about a topic correct
Required readings
Submit
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Navigating from Page to Page
1.0/1.0 point (graded)
EdX courses have many parts to them. You can find page links at the top of the site,
sections and subsections in the course overview, and the Contact Us button on the far
left of your window.
Some subsections (like this one) also have multiple pages. Where can you find the links
that take you to these pages?
Select all that apply.
Via the buttons in the "ribbon" at the top of the page.
Via the left-right arrows in the "ribbon" at the top of the page.
Via the left-right arrows at the bottom of the page.
Via links in the course that take you to a specific page.
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Syllabus Quiz, Part 2
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Certificates
1/1 point (graded)
If you pass this course and pay for a verified certificate, where will you get your
certificate?
This course does not give certificates
In e-mail
In your edX dashboard correct
In the mail
Submit
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the Submit button.
Show Answer
Grades
1/1 point (graded)
Where can you find your grades?
On the Progress page correct
By e-mailing edX
On the Discussion page
This course is ungraded
Submit
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Show Answer
Deadlines
1/1 point (graded)
When are the deadlines for your work in this course?
There are no assignments in this course.
Every Sunday night at 23:30 UTC.
As long as we get it done before the last day it's ok. correct
Submit
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Where to Learn More
1/1 point (graded)
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Where can you go for more information on this course and its topics?
Select all that apply.
I can visit the discussion boards.
I can read the edX FAQ page.
I can use the Energy Resources Page.
I can search the web and beleive anything I read.
I can search the web and carefully check what I find.
I can read books on energy and the environment written in the last five years.
I can read books on energy and the environment written fifty years ago.
Background Questions
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Background Questions
These questions help you decide if you have appropriate background knowledge for this
course. They cover the kinds of introductory physics and chemistry we assume
students are comfortable with, as well as some small calculations. Please answer
quickly with your best guess, and try to finish in less than 15 minutes.
Annotate
Unit Conversion
Many of the problems on this page require you to convert from one unit to another - for
instance, from miles to kilometers, or from gigajoules to kilowatt-hours. There are many
different resources available online to help you with these conversions, and we
encourage you to become familiar with one of them and use it throughout the course.
Some options include:
Using a search engine, like Google or Bing, and typing in "20 miles in kilometers"
Using a site designed for unit conversions, like UnitJuggler.
Using a tool like Wolfram Alpha, which does unit conversions and also has curated data
on energy costs and energy content.
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Annotate
Power or Energy?
0.5/1 point (graded)
Some of these options are examples of energy, and some are examples of power. Put a
check in the box for all the examples of power.
Which of these are examples of power?
This sandwich has 600 Calories
That exercise burns 500 Calories/hour correct
Our household used only 100 kWh of electricity last month
My computer uses 60 watts of electricity correct
partially correct
Explanation
Calories and kilowatt-hours are both measurements of energy. Watts and calories per
time are both measurements of power.
Submit
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Review
Sandwich-Powered
0/1 point (graded)
How many watts do I consume if I eat a 600-Calorie sandwich in 600 seconds?
watts incorrect
4180
4180
Explanation
Each calorie is 4.18 joules of energy. 600 food calories becomes 600,000 regular
calories, which is 2,508,000 joules of energy. If we consume this over 600 seconds, the
rate of consumption is 4,180 watts.
Partial credit is awarded for an answer that missed the conversion between food
calories and regular calories.
Submit
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These options follow the Submit button.
Hint Show Answer
Coal Mine Growth
4180
Schlumberger-Private
0/1 point (graded)
A local coal mine grows by 12 acres per year. How many square meters per day is this?
square meters per day incorrect
133.047452055
133.047452055
Explanation
We convert this unit as follows:
12 acres1 year⋅1 year365 days⋅4046.86 m21 acre=133.0 m2/day
Submit
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Power per Person
0/1 point (graded)
Humanity used 160,000 Terawatt-hours of energy in 2015. If there are 7.4 billion people
on earth and 8766 hours per year, how many Watts did each person use on average?
Watts/person incorrect
2467
2467
Explanation
We can do this problem by converting TWh to Watt-hours, then dividing by the number
of hours in a year and the number of people on earth, as follows:
160000 TW⋅hours⋅1012 Watts1 TW⋅17.4×109 people⋅8766 hours=2500Watts/
person
Submit
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Atom Facts
1/2 points (graded)
This is a two-part question. Answer both parts before hitting the "Check" button.
Which particles have about the same mass? Check two boxes, or check the box
marked "none" if they all have very different masses.
Proton correct
133.047452055
2467
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Neutron correct
Electron
None
correct
Which particles appear in equal numbers in all uncharged atoms? Check two boxes, or
check the box marked "none" if uncharged atoms tend to have different numbers of all
of these things.
Proton correct
Neutron
Electron correct
None
incorrect
Explanation
Protons and neutrons are very similar in mass; electrons are about 2000 times lighter
than either of them. Uncharged atoms have equal numbers of protons and electrons.
Heavier atoms generally have a greater number of neutrons than protons.
Submit
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Review
Chemical Equations
0.5/1 point (graded)
Some of the chemical equations below might represent real-world reactions. Others are
nonsense. Mark all of the equations that are valid, and leave the invalid ones unmarked.
NaCl2+H2O→HCl+12NaOH
2Na+Cl2→2NaCl correct
6H2O+6CO2→C6H12O6+6O2 correct
Pb+H2S→Au
Course Content Questions
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These questions cover content from within this course, including facts and calculations.
Don't worry if you struggle with them - these are exactly the things that we're teaching!
If you find them all easy you probably don't need to take the course.
These questions serve several purposes:
1. They give you a taste of what you'll be able to do when you complete the course,
2. They serve as a benchmark of progress, for you and for us, and,
3. They help you see areas where you're strongest and weakest going into the course.
Please answer quickly with your best guess, and try to finish in less than 40 minutes.
Please spend no more than 10 minutes on each of the calculation problems near the
end.
There are detailed answers to each question that you can read after attempting it. We
encourage you to read these, but not to spend too long figuring them out if you don't
understand them right away. That's what the rest of the course is for.
Annotate
Electric Grid Efficiency
0.2/1 point (graded)
What is the average efficiency of electric grids in developed countries? That is, what
percentage of the electrical power generated at power plants actually makes it to end
users in countries like Australia, the UK, and the US?
% incorrect
94
1
Hint: Much too low.
Explanation
The World Bank keeps detailed data on electricity generation and losses in different
countries. More than 90% of generated electricity is delivered to consumers in all
developed countries, with an amazingly high average efficiency of 94%. The world
average is 92%, but some countries are much lower, like India at 85%.
Submit
94
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show answer. These options follow the Submit button.
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Review
Coal Power Efficiency
0.2/1 point (graded)
What is the efficiency of a typical coal-fired power plant? That is, what percentage of the
thermal energy from burning the coal is successfully turned into electricity?
% incorrect
35
1
Hint: Much too low.
Explanation
Coal plants vary, but are typically around 35% efficient. Some older plants are much
lower, and some advanced plants are much higher (near 50%), but most in the world
are in the mid 30's.
Submit
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Review
First Climate Change Treaty
0/1 point (graded)
In what year did the first global treaty regarding climate change enter into force? Please answer
with a number, e.g. '2016' incorrect
1994
1
Explanation
35
1994
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The first international treaty regarding climate change was the UN Framework
Convention on Climate Change, which was signed in 1992 and entered into force in
1994 (though it set no binding limits on greenhouse gas emissions).
Submit
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SPENDING ON CLIMATE CHANGE
In your opinion, about how much of total global GDP should be spent on managing
climate change? This is an opinion question with no right or wrong answer
RESULTS
3%
35%
10%
35%
1%
14%
30%
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13%
0.1%
4%
Results gathered from 159 respondents.
FEEDBACK
There is no right answer here, but keep in mind how serious high responses (over 10%)
are. The US' notoriously high military expenditure is only 3.5% of its GDP today. Even at
the peak of World War II, when many common goods were rationed, people were
conscripted into the military, and many civilian factories were converted to make
equipment for war, the US only spent 1/3 of its GDP on the military.
ECONOMIC IMPACT OF CLIMATE CHANGE
What is your best estimate of the future economic impact of climate change by 2050 as
a % of global GDP lost due to climate change damages? Assume a 'business-as-usual'
scenario (greenhouse gas emissions continue to rise with little concerted effort to
control them).
This number is highly uncertain, but some answers are more plausible than others.
RESULTS
6-10%
32%
11-20%
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32%
1-5%
19%
21-50%
12%
Over 50%
5%
Less than 1%
1%
Results gathered from 161 respondents.
FEEDBACK
Most academic estimates place the damage around 1-5% by 2050. There is
tremendous uncertainty, but it's hard to make a case for how damage would be more
than 20%.
Mortality Rates
3/3 points (graded)
This problem has three parts. Answer all three before clicking the "Check" button.
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How many premature deaths are caused by energy-related water pollution each year?
Almost zero
Thousands correct
Millions
Hundreds of millions
How many premature deaths are caused by energy-related air pollution each year?
Almost zero
Thousands
Millions correct
Hundreds of millions
How many premature deaths are currently caused by climate change each year?
Almost zero
Thousands correct
Millions
Hundreds of millions
Submit
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Correct (3/3 points)
Review
Sulfur and Carbon
0/2 points (graded)
This problem has two parts. Answer both before clicking the "Check" button.
Every year humanity emits millions of tons of sulfur and billions of tons of CO2. Sulfur
forms particulate air pollution that kills around 1 million people per year, and CO2 raises
global average temperatures, 0.8°C above pre-industrial temperatures so far.
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Suppose humanity continued to emit air pollutants and CO2 following “business-asusual”, and then suddenly in 2050 cut emissions of both to 0.
Approximately how long would it take for sulfate-driven mortality from particulate matter
to fall by 50%?
a week correct
a year
hundreds of yearsincorrect
thousands of years
Approximately how long would it take for global temperatures to drop halfway from their
peak to pre-industrial average?
a week
a year
hundreds of yearsincorrect
thousands of years correct
Explanation
It will only take a few days for most of the air pollution to fall out of the atmosphere and
stop affecting peoples' lungs and cardiovascular systems. There is some residual
mortality that would last longer. However, carbon dioxide lingers in the atmosphere for
much longer, and the resulting temperature change will be with us for thousands of
years.
Submit
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Relative Cost of Energy
1/4 points (graded)
Please compare the prices of each of the below to crude oil on an energy basis. Select
the closest answer. For example, if coal cost 8 times as much as crude oil for the same
amount of energy, you would answer "Much more." If electricity cost 10% less than oil,
you would select "Less." There is some regional variation in these prices, so try to
imagine world average prices if you can.
This is a multi-part question. Make sure you answer all the parts before clicking
"Check".
Natural Gas costs _________ than crude oil for the same amount of energy
Much less (less than 1/3 the cost of oil)
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incorrect
Much less (less than 1/3 the cost of oil)
Coal costs _________ than crude oil
incorrect
Much less (less than 1/3 the cost of oil)
Electricity for a large industrial consumer costs _________ than oil
incorrect
More
Electricity for a home consumer costs _________ than oil
correct
Much more (more than 2x the cost of oil)
Explanation
In July 2018 oil prices are around $72/barrel, and since there are ~6.1 GJ of energy in 1
barrel of oil, it costs $11.8/GJ. Natural gas costs $2.85/MMBTU, which translates to
$2.85/GJ, about a quarter the price of oil. Coal costs only $2/GJ in the US, 1/5 the price
of oil, though it has the largest regional variations. Electricity for large industrial
customers is around $.07/kWh on average, which translates to $20/GJ, higher than oil,
and it's much higher yet in some areas with high electricity prices. Electricity for home
consumers is usually significantly higher than for industrial customers, around $.13/kWh
on average, which is $36/GJ, dramatically more expensive than oil (but more useful -
electricity for a lightbulb is much more convenient than burning oil for light).
These relationships were qualitatively the same when oil and gas prices were much
higher before the 2014 crash (~$100/barrel and ~$5/MMBTU), with the main exception
being that electricity for industrial customers was comparable to the price of oil rather
than being much higher.
Submit
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Much less (less than 1/3 the cost of oil)
More
Much more (more than 2x the cost of oil)
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Answers are displayed within the problem
Review
Fraction of Energy From Fossil Fuels
0/1 point (graded)
What fraction of humanity's energy supply is in the form of fossil fuels?
% incorrect
80
1
Explanation
About four fifths (80%) of total energy appropriated by humans is from fossil fuels. The
next highest source is nuclear energy at 7%. Fossil's portion of human energy supply
has fallen slightly in recent decades (down from 90% in the 1970's) thanks to the growth
of renewables. But it is still dramatically higher than all of human history before 1850,
when close to 100% human energy was from biomass.
Submit
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The History of Fossil Fuels
0/1 point (graded)
England was the first country to industrialize. In what year did it first get more than half of its
energy from fossil fuels? incorrect
1905
\(\)
Explanation
Fossil fuels first overtook biomass (mostly trees and crops) as England's primary energy
source around the year 1900, which you may find surprisingly recent.
Submit
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80
1905
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Review
Fraction of Energy From Fossil Fuels - In The Future
1/1 point (graded)
What do you think the fraction of human energy from fossil fuels will be in 2050? This is an
opinion question with no right answer. correct
50
\(\)
Explanation
The answer is marked as 50, but it accepts a range from 0 to 100. We just had to put in
a number; we don't consider 50 to be the "correct" percentage.
Submit
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Composition of Global Energy Supply
1/8 points (graded)
Estimate the fraction of global primary energy supplied by the following sources. Use
rough numbers and don’t worry about ensuring that they sum to exactly 100%.
This is a multi-part question. Make sure you answer all the parts before clicking
"Check".
Biomass % incorrect
7.5
\(\)
Coal % incorrect
25
\(\)
50
7.5
25
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Hydropower % correct
1.8
\(\)
Natural Gas % incorrect
20
\(\)
Nuclear Power % incorrect
3.5
\(\)
Oil % incorrect
34
\(\)
Solar % incorrect
.05
\(\)
Wind % incorrect
.05
\(\)
Explanation
These values are taken from the IEA's Sankey Diagram. Wind and solar together make
up less than .05% of the world's primary energy supply. These values are very different
for individual countries - the IEA Sankey tool allows you to look at different countries
and see, for example, how much higher the fraction of coal is in China and how much
higher the fraction of solar and wind is in Germany.
Submit
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1.8
20
3.5
34
.05
0.05
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Fraction of Energy as Electricity
0/1 point (graded)
What percentage of global energy used by consumers is in the form of electricity?
% incorrect
20
\(\)
Explanation
About one fifth (20%) of energy used by consumers globally is in the form of electricity.
Despite the complexity of generating and distributing it, this number has increased
steadily since the late 1800's because electricity is so incredibly convenient and useful.
The International Energy Agency has good data for issues like these. Some of it can be
accessed graphically at http://www.iea.org/sankey/ which shows energy supplies
(primary energy) on the left and how energy flows to end uses on the right. We'll cover
how to interpret these kinds of "sankey diagrams" in this course.
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Energy for Computing
0/1 point (graded)
What percentage of worldwide electricity consumption is used for computing devices?
% incorrect
8
\(\)
Explanation
This is difficult to estimate, but is likely in the range of 5-10% as we'll discuss further in
the "Energy Demand and Efficiency" Section of the course.
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20
8
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Calculating The Cost of Mitigating CO2 Emissions
0/1 point (graded)
Suppose gasoline has an emissions factor of 91g of CO2/MJ and costs $1.52/liter, and
biodiesel has an emissions factor of 54g of CO2/MJ and costs $1.92/liter. You may
assume gasoline and biodiesel both have energy densities of 38 MJ/liter.
What is the cost of mitigating CO2 by switching from gasoline to biodiesel, in dollars per
kilogram of CO2 emissions prevented? We'll cover how to do calculations like this in the
course, so don't worry if you struggle. Give it your best effort but please don't spend
more than 10 minutes on it.
dollars per kg CO2 incorrect
0.284495021337
\(\)
Explanation
The cost of mitigation is equal to the additional cost for biodiesel divided by the carbon
savings that it provides. Since the masses above are given in grams, we will need to
convert to kilograms.
\[ \frac{$1.92/L - $1.52/L}{\left(91 \ g/MJ - 54 \ g/MJ \right)} \cdot \frac{1 \ L}{38 \ MJ}
\cdot \frac{1000 g}{1 kg} = $0.284\]
Submit
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Calculating Levelized Cost of Electricity from Coal
0/1 point (graded)
A proposed coal power plant has a capital cost of $3450 per kW of generating capacity.
It is expected to run for 94% of the year. Its overall thermal efficiency is 39%. Fixed
operations and maintenance (FOM) costs have been estimated at $48/kW-year, and
variable O&M costs have been estimated at $0.0063/kWh. Coal costs $1.2/GJ. The
capital charge factor (or capital charge rate) is 13%.
0.284495021337
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What is the levelized cost of electricity for this plant? We'll cover how to do calculations
like this in the course, so don't worry if you struggle. Give it your best effort but please
don't spend more than 10 minutes on it.
dollars per kWh incorrect
0.077355224805
\(\)
Explanation
We need the final answer in dollars per kilowatt-hour, so we will convert all power units
to kilowatts and all times to hours in this answer.
Fixed Costs: Our fixed costs are the financing on the plant and the fixed O&M costs.
The capital cost of $3450, at a charge factor of 13% becomes a yearly cost of $448.50
per kilowatt. If we are using the plant for 8230 hours per year, our fixed costs come out
to:
\[ \frac{$448.50}{8230 \ kWh} + \left( \frac{$48}{1 \ year} \cdot \frac{1 \ year}{365 \cdot 24
\ hours} \right) = $0.0600 \ per \ kWh \]
Variable Costs: We have two variable costs: fuel, and the O&M costs. One gigajoule is
278 kilowatt-hours, so our cost for coal is:
\[ \frac{$1.20}{1 \ GJ} \cdot \frac{1 \ GJ}{278 \ kWh} = $0.00432 \ per \ kWh. \]
With our plant's 39% efficiency, the effective cost for our fuel is higher:
\[ \frac{$0.00432 \ per \ kWh}{0.39} = $0.0111 \ per \ kWh \]
Adding in variable O&M costs, we get a total of:
\[ $0.0111 + $0.0063 \ per \ kWh = $0.0174\]
Total Cost:
\[ $0.0600 + $0.0174 = $0.0774 \ per \ kWh \]
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Outside References
1/1 point (graded)
Did you use any outside references (like Wikipedia) when finding answers to these
questions? It's ok if you did - this question is for our research purposes.
No, I did this all on my own.
I consulted outside resources for mathematical calculation only.
0.077355224805
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I consulted outside resources to look up scientific facts.
I consulted outside resources for both calculations and scientific facts. correct
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Simple Sankey
1/1 point (graded)
Consider the Sankey diagram below, which represents the monthly flow of money for a
couple, from income to shared bank account to expenses.
Diagram created using SankeyMATIC
Which of the following statements is definitely true?
We cannot tell whose income was used to pay for what expenses
The couple is going into debt
The husband pays all of the bills
20% of the couple's combined income goes to taxes correct
Answer
Correct:
Correct!
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Sankey Diagram Assignment
Here's a Sankey diagram for the US, produced by Lawrence Livermore National
Laboratory. We used this to make the simplified US Sankey diagram you saw in the
video lecture. It's in units of Quadrillion BTU ("Quads"). 1 Quad is slightly more than 1
EJ. Click on the image for a larger version.
Figure 1. This Sankey diagram of the US energy system in 2015 shows the flow of energy from intitial
resources like petroleum and coal, through conversions like electricity generation, and to end users,
which are divided into four major sectors. As mentioned in the video lecture, take the numbers for
"rejected energy" with a grain of salt. Source: LLNL.
We can use this to do some interesting calculations. For example, David mentioned that
almost all coal in the US is used to generate electricity, but here we can see that a small
amount is used for other purposes. What percentage is used for electricity? We can see
that 14.3 Quads were used for electricity generation, out of 15.7 Quads used in total, or
90%. Another thing we can notice is the differences in electricity consumption between
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sectors – the Residential sector consumed 4.78 Quads, or 38% of the total 12.6 Quads
of electricity generation, while the Transportation sector consumed only .03 Quads, .2%
of the total generation.
Annotate
Petroleum for Transportation
0/5 points (graded)
What percentage of Transportation is powered by petroleum?
% incorrect
92
\(\)
Explanation
Total transportation use was 27.7 Quads; petroleum provided 25.4 Quads of that, which
is about 92%.
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Electricity from Coal
0/5 points (graded)
What percentage of primary energy flowing into electricity generation came from coal?
% incorrect
38
\(\)
Explanation
Total electricity generation use was 38 Quads; coal provided 14.3 Quads of that, which
is about 38%.
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Low Carbon Sources
0/5 points (graded)
92
38
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What percentage of all US primary energy came from "low carbon" sources (biomass,
geothermal, wind, hydro, nuclear, solar)?
% incorrect
18
\(\)
Explanation
Total US primary energy was 97.5 Quads. Biomass provided 4.72, geothermal
provided .224, wind provided 1.82, hydropower provided 2.39, nuclear provided 8.34,
and solar provided .532. The total is about 18 Quads, which is also about 18% of the
total.
Remember that this chart uses the "accounting trick" David mentioned, where the
primary energy from direct-to-electricity sources like hydro, wind, and solar is multiplied
by 3 to represent the amount energy required from fossil fuels or nuclear power to
generate the same amount of electricity.
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Natural Gas Consumption
1/1 point (graded)
Which sector of the economy had the most direct natural gas consumption?
Residential
Commercial
Industrial correct
Transportation
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Rooftop vs Utility Solar
0/1 point (graded)
Some solar energy is shown flowing into the Residential sector, representing rooftop PV,
and some into electricity generation, representing utility-scale solar installations.
18
Schlumberger-Private
How do these flows compare in magnitude?
They are about the same. correct
There is notably more utility-scale solar power.incorrect
There is notably more rooftop solar power.
Explanation
Rooftop solar power provided about as much electricity as was generated by electricity
companies in 2015.
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Sankey Diagram Assessment Part 2
Here's a Sankey diagram for the world in 2013, from an interactive tool freely available
from the International Energy Agency. This is a great source for looking up the energy
supplies and uses in different countries and regions since the 1970's. It has some
important differences from the LLNL Sankey; for example, it shows imports and exports,
shows the transformation of oil in refineries, and lumps residential and commercial
energy use together as "Other." It uses units of "Million tons of oil equivalent" ("Mtoe")
and petajoules. At the bottom you can see options to scroll through different years and
look look at different graph types, like line graphs of some of the individual flows to
easily visualize them over time. These diagrams do not use the "factor of 3" accounting
that we discussed in the video and that is used in the LLNL diagram above, so the
amount of energy flowing into electricity generation from renewables like wind and solar
is equal to the actual amount of electricity they generate.
Again, you can click on the image to view a larger version, or on the link above to get an
interactive version.
Figure 2. This Sankey diagram of the world's energy system in 2013 shows the flow of energy from initial
resources like petroleum and coal, through conversions like electricity generation, and to end users,
which are divided into three major sectors. Source: IEA.
Please visit the interactive version and explore it a bit for interesting trends. Then
answer these questions.
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Annotate
Coal for Electricity Around the World
0/1 point (graded)
You can click on the "Power Station" box to see the composition of inputs to electricity
generation.
Did coal's fraction of energy supplied for world electricity generation increase or
decrease from 1990 until 2013?
Stayed about the same
Decrease incorrect
Increase correct
Explanation
The change was from 41% to 49%, which is about a one-fifth increase.
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World Electricity Growth
0/1 point (graded)
Look at the actual generation coming out of the power plants on the diagram.
How much did world electricity generation grow from 1990 to 2013?
About doubled correct
About 50% increase incorrect
Stayed about the same
About 50% decrease
Dropped to near zero.
Explanation
The change was from 1017 Mtoe to 2006 Mtoe, so the amount roughly doubled.
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Angola Fossil Exports
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0/5 points (graded)
Some countries that produce fossil fuels use very little of them, and export heavily. Let's
examine Angola. Set the country in the IEA tool to "Angola" to see the Sankey diagram
for that country. What fraction of Angola's total Production and Imports (all energy types)
were exported in 2013?
% incorrect
83
\(\)
Explanation
Angola exported 85.26 Mtoe, out of the 102.82 Mtoe they produced in total. This is
about 83%.
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Japanese Coal Production
0/5 points (graded)
Japan's coal mining industry has waned in recent decades after being unable to
compete with cheap coal imports, to the point that the IEA's tool shows no local
production in 2013 (though there is in fact a small amount). Scroll through the years
1973-2013 for Japan using the slider on the bottom of the page. You will see a steady
decline in local coal production. What percentage of Japan's total coal supply came
from local production in 1973?
% incorrect
30
\(\)
Explanation
In 1973, Japan produced about 17.9 Mtoe, and imported 41.3 Mtoe. This made its
production about 30% of its total supply.
\[ \frac{17.9 \ Mtoe}{17.9 \ Mtoe + 41.3 \ Mtoe} \]
Coal Use in the USA
1/1 point (graded)
How is coal used in the United States?
83
30
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Mostly for industrial applications
Almost entirely for electricity generation correct
About equally split between electricity and transportation
Mostly converted into liquid or gas fuels
Coal Use in the China
1/1 point (graded)
How is coal used in China?
Split between electricity and industry correct
Almost entirely for electricity generation
Mostly for industrial applications
Mostly converted into liquid or gas fuels
Energy Growth
1/1 point (graded)
Which region of the world is currently growing most quickly in terms of energy use?
South America
China correct
Europe
The United States
Africa
India
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US Oil Usage
1/1 point (graded)
Where does most of the United States' oil energy get used?
For electricity generation
For lighting
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For trade with other countries
For transportation correct
What's a commodity?
0/1 point (graded)
When we say that a particular good is a commodity, what does that mean in this context?
Commodity goods have preference- or taste-based attributes that change how specific people
buy them.incorrect
All versions of a commodity are treated as identical as long as they pass some basic quality
standards correct
A commodity good can be created anywhere in the world.
Price Assignment
Knowing where to find energy prices and being able to reference them quickly is a key
skill for energy experts.
In the video lecture you heard David mention that US electricity prices used to be
heavily influenced by oil prices, but aren’t anymore since the US stopped generating
significant amounts of electricity from oil. Let’s practice looking up historical energy
prices by investigating this claim. Check out the Energy Resources page for suggested
data sources for these questions. In general the US EIA has great historical data on
energy use and prices in the US.
Annotate
Oil and Electricity
1.6666666666666667/10 points (graded)
First let’s see if the spike in oil prices corresponded with a spike in electricity prices in
the US from 1973 to 1974.
This is a multi-part problem. Fill in all boxes before submitting your answer. Some
questions ask for "change" in prices - if you find an increase use a positive number, and
for a decrease, enter a negative number.
What were the oil import prices in 1974 as a percentage of the 1973 prices?
% incorrect 1
Schlumberger-Private
280
\(\)
How much did US retail electricity prices change from 1973 to 1974?
% incorrect
11
\(\)
Oil made up what percentage of energy supply for electricity generation in the US in
1973? You can get this data from multiple sources; the IEA Sankey diagram might be
the quickest.
% incorrect
19
\(\)
How much did US oil import prices change from 2009 to 2011?
% incorrect
65
\(\)
How much did US average residential electricity prices change from 2009 to 2011?
% incorrect
-3
\(\)
Oil made up what percentage of energy supply for electricity generation in the US in
2009? % correct
1
\(\)
Explanation
Oil prices increased from $22/bbl to $61/bbl from 1973 to 1974. 1974's prices are 280%
of 1973's prices.
1
1
1
1
1
Schlumberger-Private
Electricity prices increased from $0.135 / kWh to $0.15 / kWh from 1973 to 1974, an
11% increase.
The IEA sankey diagram says that oil accounts for 19% of electricity generation in the
US in 1973. The EIA says closer to 17%. This problem accepts both answers. Both
agree that the percentage in 2009 was about 1%.
Oil prices in the US went up from $66/bbl in 2009 to $109/bbl in 2011.
Average residential electricity prices were $0.128 / kWh in 2009, and went down to
$0.124 / kWh in 2011, so the answer there would be -3%.
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Oil and Electricity - Are they connected?
0/1 point (graded)
What claim is supported by this data?
The US has NOT significantly reduced its electricity generation from oil, and oil
prices thus have MORE influence on US electricity prices.
The US has NOT significantly reduced its electricity generation from oil, but oil
prices have LESS influence on US electricity prices anyway.
The US has significantly reduced its electricity generation from oil, and oil prices
thus have MORE influence on US electricity prices.incorrect
The US has significantly reduced its electricity generation from oil, and oil prices
thus have LESS influence on US electricity prices. correct
None of these claims are supported.
Answer
Incorrect:
A 3% decrease is not only less impact than an 11% increase, it's even in the wrong
direction.
Explanation
Though we cannot always take just two data points to examine a trend, these particular
times have been selected as good representatives of the overall way things are
happening. As we make less of our electricity from any one particular source,
fluctuations in that source's cost will have less impact on the cost of electricity.
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Coal in Japan and Europe
0/5 points (graded)
How much more did Japan pay for coal in 2014 than typical prices in Europe, on a
percentage basis? If Japan paid $10 while Europe paid $5, you would answer 100%.
% incorrect
12
\(\)
Explanation
Japan paid about $84/ton, while Europe paid an average of $75/ton. Japan paid 12%
more.
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Gas Prices in the USA and Germany
0/10 points (graded)
David mentioned that increased gas production in the US, coupled with the difficulty
exporting it, have driven gas prices down in the US. Let’s see if BP’s data on gas prices
supports this claim.
This is a multi-part problem. Fill in all boxes before submitting your answer.
What was the percentage difference between US gas prices and German gas prices in
1997? Answer with a negative sign if the US prices were lower. If the US price was $20
and the German price was $22, you would answer -9% (since 20/22 - 1 = -9%)
% incorrect
-4
\(\)
How did US gas prices in 2014 compare with German prices? Answer with a negative
sign if the US prices are lower. If the US price was $20 and the German price was $22,
you would answer -9% (since 20/22 - 1 = -9%)
% incorrect
1
1
1
Schlumberger-Private
-52
\(\)
Explanation
All values are looked up from the BP link above. In 1997 the prices were $2.53/mmbtu
for the US, and $2.64 for Germany. In 2014 the prices were $4.35/mmbtu in the US, and
$9.11 in Germany.
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Gas Price Trend
1/1 point (graded)
Is the trend found above consistent when comparing the US against other countries in
the report? That is, did the US gas price fall relative to all other countries from the late
1990's through 2011?
Yes, the US price has fallen against all other countries in the report. correct
No, the US price rises against some countries and falls against others.
No, the US price has risen against all other countries in the report.
The report does not contain this information.
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Review
Energy in Developed Economies
0/20 points (graded)
David mentions a few times during the course that the energy inputs into developed
economies is about 5% of GDP. Let’s try estimating this now, using data from the US.
Fortunately, the EIA has detailed data on the total revenue from sales of electricity to
consumers, which does a lot of the job for us. Looking at the LLNL sankey diagram, we
can see that if we have data for the total cost of electricity, the main remaining inputs
into the four sectors of the economy are natural gas and oil. (There’s also a small
amount of coal and biomass and tiny amounts of geothermal and solar, which we’ll
ignore.) We can find data for the price of oil and gas delivered to different sectors, and
use that to get the total cost of those two resources. Combined with the total cost of
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electricity, we’ll have a pretty good estimate of the total cost of energy inputs into the US
economy. You’ll also get lots of practice using sankey diagrams, looking up energy
prices, and converting units.
This is a multi-part problem. Fill in all boxes before submitting your answer.
According to the EIA, how much did all the customers in the US pay for electricity in
2015, in billions of USD?
billions of $ incorrect
388
\(\)
According to the LLNL 2015 Sankey Diagram, how much natural gas was used by the
Residential Sector in 2015, in EJ?
EJ incorrect
5.01
\(\)
According to the EIA, how much did the Residential Sector pay on average for natural
gas in 2015, in dollars per gigajoule? Use the real (inflation-adjusted price).
$/GJ incorrect
9.2
\(\)
Given the amount of natural gas used by the Residential Sector and the average price
paid, what was the total amount that the Residential Sector paid (in billions of dolalrs)
for natural gas in the US in 2015?
billions of $ incorrect
46
\(\)
Explanation
Part 1: See Table 2 of the EIA for the first question.
Part 2: Refer to LLNL and convert from Quads to EJ.
1
1
1
1
Schlumberger-Private
Part 3: If you look at this table from the EIA (provided on the Energy Resources page)
you’ll see an average price for the Residential Sector of $10.38/thousand cubic feet. To
convert we can use the Conversion Sheet Page’s value of .04 GJ/m3
to convert this to
$9.2/GJ.
Part 4: Multiply your answer from part 2 (in gigajoules) by your answer from part 3.
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Commercial Sector Gas
0/5 points (graded)
Please repeat the same process above for the cost of natural gas to the Commercial
Sector. How much did the US Commercial Sector pay for gas in 2015? Use the LLNL
Sankey Diagram for gas consumption, and the EIA for commercial gas prices.
billions of $ incorrect
24.5
\(\)
Explanation
There were 3.5 EJ consumed, at a price of $7.89 per thousand cubic feet or $7/GJ.
\( 3.5 \ EJ \cdot $7/GJ = $24.5 \ billion \)
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Industrial Sector Gas
0/5 points (graded)
Please repeat the same process above for the cost of natural gas to the Industrial
Sector. (Notice how much lower the cost of gas is for industrial customers!) How much
did the US Industrial Sector pay for gas in 2015? Use the LLNL Sankey Diagram for gas
consumption, and the EIA for industrial gas prices.
billions of $ incorrect
33.6
\(\)
Explanation
1
1
Schlumberger-Private
There were 9.88 EJ consumed, at a price of $3.84 per thousand cubic feet or $3.4/GJ.
\( 9.88 \ EJ \cdot $3.4/GJ = $33.6 \ billion \)
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Petroleum in Transportation and Industry
0/15 points (graded)
Let's look at the amount the Transportation and Industrial Sectors paid for petroleum in
2015. (The other sectors consume relatively small amounts, so we'll ignore them here.
This is a multi-part problem. Fill in all boxes before submitting your answer.
Assume that the Transportation Sector pays the same price for all of its petroleum
consumption, and that it's equal to the average price of gasoline. How much is this in
$/GJ? Use the EIA's "Regular Gasoline Retail Price."
$/GJ incorrect
19
\(\)
Given that price and the total consumption of petroleum by the Transportation Sector
(from the LLNL Sankey Diagram), how much did the transportation sector pay for
petroleum in total in 2015?
billions of $ incorrect
509
\(\)
Finally, how much did the Industrial Sector pay for petroleum in 2015? For simplicity,
you can assume that this sector pays the average price of oil in the US. For the price of
oil, you can use the EIA’s "average price of imported oil." For petroleum consumption,
use the LLNL Sankey Diagram.
billions of $ incorrect
66
1
1
1
Schlumberger-Private
\(\)
Explanation
Part 1: According to the EIA, gasoline was $2.52/gallon in 2015. Using the energy
density of gasoline (~35 GJ per cubic meter, as indicated on the Conversion Sheet), and
converting from gallons to cubic meters, this is $19/GJ.
Part 2: Since the transportation sector used 26.8 EJ of petroleum in 2015, the total cost
was 26.8 EJ * $19/GJ = $509 billion
Part 3: The industrial sector uses 8.65 EJ of oil. With a cost of $46.7/barrel and an
energy density of 6.1 GJ/barrel, the total cost was $66 billion.
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Total Energy Cost
0/10 points (graded)
This is a two-part problem. Fill in both boxes before submitting your answer.
Adding up all of your answers above, how much in total did US consumers pay for
energy in 2015? billions of $ incorrect
1068
\(\)
What percentage of 2015 US GDP is this?
% incorrect
5.95
1
1
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Levelized Cost Definition
0/1 point (graded)
Which of the following is the best definition of levelized cost?
The average cost of something over time. correct
A perfect, all-inclusive metric for how good an energy technology is.incorrect
The price of electricity.
Explanation
Levelized cost is a broadly useful measurement that can apply not only to energy, but
also to other commodities and goods. However, it only gives us an idea of what
something will cost over time - it doesn't tell us anything about (for example) how much
pollution is involved.
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Fixed Costs
1/1 point (graded)
Imagine you’re computing the levelized cost of a furnace, in $/month. Which of the
following are relevant fixed costs? Choose all that apply.
The price of the furnace
The cost of fuel
The cost of air filters
The cost of a yearly maintenance contract
The cost of maintenance done after every 1000 hours of operation
Chest Freezer
0/10 points (graded)
Schlumberger-Private
Your teaching fellow, Daniel, was recently deciding whether to buy a chest freezer. This
would allow him to buy more food in bulk, which would save him about $29/month, but
he also would have to pay for the freezer and its electricity. What is the levelized cost of
freezing Daniel's food in dollars per month given the following assumptions?
The freezer costs $198 to buy.
It uses 21 kWh/month.
Electricity costs 18 cents per kWh.
Because he’ll probably be moving to another city in a few years, assume he keeps it for 2 years.
dollars per month incorrect
12.03
Calculating CCF
0/5 points (graded)
What is the capital charge factor for a loan with an interst rate of 8% for 30 years? Make
sure to answer to at least three significant figures.
incorrect
0.0888274333873
\(\)
Explanation
The formula is as follows:
\[ CCF = \frac{rate}{ \left( 1 - ( 1 + rate )^{-years} \right) } \]
In our case, this comes out to:
\[ CCF = \frac{0.08}{ \left( 1 - ( 1 + 0.08 )^{-30} \right) } = 8.883 \% \]
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1
1
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Loan Duration Difference
0/10 points (graded)
Many power plants can last much longer than the 20-30 years assumed in most LCOE
calculations, often 50 years or more. This affects the LCOE estimates for solar farms,
where almost the entire LCOE is from capital costs that are multiplied by the CCF.
How much lower is the CCF for an 8% loan over a 50 year period compared to the
same loan over a 20 year period?
For example, if the 50 year period has a CCF of .06 and the 20 year period has a CCF
of .1, you’d answer 40%.
% incorrect
19.7436569063
\(\)
Explanation
The formula is as follows:
\[ CCF = \frac{rate}{ \left( 1 - ( 1 + rate )^{-years} \right) } \]
In our case, for the longer time this comes out to:
\[ CCF = \frac{0.08}{ \left( 1 - ( 1 + 0.08 )^{-50} \right) } = 8.174 \% \]
And for the shorter case, we get:
\[ CCF = \frac{0.08}{ \left( 1 - ( 1 + 0.08 )^{-$shortyears} \right) } = 10.185 \% \]
The fractional change is:
\[ \frac{10.185 - 8.174}{10.185} = 19.744 \% \]
So the longer loan is 19.744% better when it comes to CCF, though it will cost more
overall in the long run.
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Levelized Cost for a Cheap Car
0/20 points (graded)
In the video on levelized cost of driving, Daniel mentioned that given how little most
people drive in a year, they generally can save money by buying a cheaper car than a
Prius even if it has higher fuel consumption. Let’s investigate that claim now, assuming
1
Schlumberger-Private
a car similar to a Ford Fiesta. The capital cost to buy it is substantially lower, as are the
yearly taxes and insurance, but the fuel consumption is about 50% higher.
The car costs $14000 to buy.
The capital charge factor is 0.23, the same as the Prius.
The taxes, fees, and insurance each year total to $1000.
You drive the car 20000 km/year, the same as the Prius.
Variable operation and maintenance (VOM) costs add up to $0.019 per kilometer.
Fuel costs $1.90 per liter.
The car can travel 100 km on 7.2 L of fuel.
Part 1: What is the total fixed cost in dollars per kilometer?
dollars per km incorrect
0.2075
\(\)
Part 2: What is the variable cost in dollars per kilometer?
dollars per km incorrect
0.1558
\(\)
Part 3: Is the total levelized cost higher or lower than the Prius (in the video above)
given these assumptions? Enter the word "higher" or "lower". If the numbers are within
10% of each other, enter the word "same".
incorrect
lower
Coal Plant LCOE
0/30 points (graded)
1
1
1
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Consider a coal plant with the following characteristics:
Capital cost of $2800 per kW
CCF of 0.13
FOM costs of $96 per kW-year
Fuel costs of $0.95 per GJ
Utilization of 78% (about 6837 hours per year)
VOM costs of $0.0054 per kWh
Efficiency of 31%
Part 1: What are the fixed costs in dollars per kilowatt-hour?
$/kWh incorrect
0.0672762479744
\(\)
Part 2: What are the variable costs in dollars per kilowatt-hour?
$/kWh incorrect
0.0164322580645
\(\)
Part 3: What is the total LCOE in dollars per kilowatt-hour?
$/kWh incorrect
0.0837085060389
\(\)
Part 4: Is the LCOE more sensitive to the capital cost or to the fuel cost? For example,
does doubling the capital cost affect the LCOE more or less than doubling the fuel cost?
Enter the word "capital" or "fuel". If the numbers are within 10% of each other, enter the
word "same".
1
1
1
Schlumberger-Private
incorrect
capital
Part 5: Let’s look at the effect of a carbon tax. The simplest way to do this is to add a
price for carbon emissions to the cost of the fuel (coal). We’ll assume a commonlydiscussed carbon tax of $20/tCO2. Looking at our Conversion Sheet, we can see that
coal emits 90 kg of CO2/GJ; multiplying these emissions by $20/tCO2 gives us an
additional $1.8 per GJ to add to the cost of the coal, almost tripling it! What’s the new
LCOE with this carbon tax?
$/kWh incorrect
0.104611731845
\(\)
Part 6: Would the same carbon tax have more or less of an effect on a natural gas
plant? Enter the word "more" or "less". If the numbers are within 10% of each other,
enter the word "same".
incorrect
less
Cost of Mitigation
1/1 point (graded)
Which of the below is the right general expression for cost of mitigation?
Cost of Clean Option+Cost of Dirty OptionPollution of Dirty Option+Pollution
of Clean Option
Cost of Clean Option−Cost of Dirty OptionPollution of Dirty Option−Pollution
of Clean Option
correct
Cost of Dirty Option−Cost of Clean OptionPollution of Dirty Option−Pollution
of Clean Option
1
1
1
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Solar Sidewalk
0/20 points (graded)
In 2014 the Netherlands installed the world’s first solar bike path. Let’s compute the cost
of mitigation relative to electricity from coal. Of course, the sidewalk probably wasn’t
intended to be a cost-effective electricity option. It's designed for qualitative rather than
quantitative value, to raise awareness. However, there are real proposals to scale up
this kind of technology to large numbers of sidewalks and roadways, so cost analysis is
relevant.
The project cost $3.75 million for ~30kW of installed capacity (based on typical
150W/m2 solar panels). Assume a CCF of 9%, and a utilization of 8% (probably
generous for solar panels flat on the ground in the Netherlands). You may ignore all
other costs.
Part 1. What is the levelized cost of electricity from the solar sidewalk?
$/kWh incorrect
16.0420944559
\(\)
Part 2. What is the cost of mitigation (in $/tCO2) relative to coal electricity at $0.09/kWh
and 0.9 kg CO2/kWh. You may assume the solar sidewalk causes 0 kg
CO2 emissions/kWh.
$/tCO2 incorrect
17724.5493954
Pizza Mitigation
0/10 points (graded)
A pepperoni pizza costs $10 and causes 0.8 tons of CO2 emissions. A super deluxe
veggie pizza costs $13 and causes 0.4 tons of CO2 emissions. What’s the cost of
mitigation for choosing the veggie pizza?
$/tCO2 incorrect
7.5
1
1
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Pizza Mitigation Comparison
1/1 point (graded)
Looking at the McKinsey Mitigation Cost Curve below, how cost-effective a mitigation
strategy is the pizza approach?
Fantastic
Pretty good correct
Awful
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Mitigation Cost for Biodiesel
0/10 points (graded)
Part 1. Imagine you have a diesel-powered car, and you can buy either diesel or
biodiesel fuel (which is possible in some parts of the US). The cost of biodiesel is
$34/GJ, and the biodiesel causes 21 kg CO2 emissions per GJ over its lifetime. The
diesel costs $26/GJ and causes 84 kg CO2emissions per GJ over its lifetime (4 times
more!!). What is the cost of mitigation of choosing biodiesel?
$/tCO2 incorrect
126.984126984
\(\)
Part 2. What carbon tax would be required to make the biodiesel cost the same as the
diesel?
$/tCO2 incorrect
126.984126984
1
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Nitrogen Oxides
0/1 point (graded)
Please read the third page of this report on NOx from the US EPA:
https://web.archive.org/web/20150209034608/http://nchh.org/Portals/0/Contents/EPA_N
itrogen_Oxides.pdf (PDF download, 700k)
Which of the below are true of NOx? Select all that apply.
Contributes to nitrogen pollution of water bodies, leading to eutrophication and lack
of oxygen correct
Reduces IQ of exposed individuals
Forms irritants that can excacerbate respiratory and heart diseases correct
Contributes to formation of ozone correct
In the US, mostly emitted by factories and other industrial sources
7.47
Lifespan Decrease from PM2.5 Exposure Where You Live
0/5 points (graded)
In the first box below, enter the PM2.5 level where you live again (in μg/m3
). This should
be the same value you entered above. Then, in the bottom box, enter the reduction of
lifespan (in years) that would result from a lifetime at that pollution level relative to a
pollution-free lifetime. Use the dose-response relationship mentioned in the video
lecture (around 1:55).
Be sure to fill both boxes before hitting "Check".
PM2.5 micrograms per cubic meter incorrect
Life Expectancy Decrease years incorrect
Explanation
As mentioned in the video lecture, an increase of PM2.5 exposure of 10 μg/m3
is
associated with a decrease in lifespan of 3/4 of a year, which is .075 years per ug/m^3
(.75/10). To answer this question multiply your PM2.5 level by .075.
7.47
0.56025
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Comparing Deaths from Air Pollution and Climate Change
0/1 point (graded)
The present-day premature deaths from air pollution are how many times larger than
the estimated premature deaths from climate change in 2050?
.5x (climate change deaths higher)
1x (they're the same) incorrect
10x (air pollution deaths significantly higher) correct
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Air Pollution Impact
0/1 point (graded)
The air pollutant that has the most impact on human health globally is...
NOx
Lead
Carbon Monoxide incorrect
Particulate matter correct
Natural vs. Human Emissions
1/1 point (graded)
David just asked: how big is the human-caused movement of carbon from deep
underground to the atmosphere relative to similar natural processes, like emissions
from volcanic vents?
What do you think? This a "guessing" problem. You will have unlimited attempts, and
we'll reveal the answer in the next video.
One percent as much - nature moves more carbon from geosphere to atmosphere
every year
Half as much
About as much
Schlumberger-Private
Twice as much
One hundred times as much - human activity moves far more CO2 than
nature correct
Using the References
0/10 points (graded)
It's good for you to be able to look up historical and current CO2 emissions and
concentrations. This problem gives you some practice. Please refer to the Energy
Resources Page for recommended references to answer these questions:
How many times higher was the concentration of CO2 in the atmosphere at the
beginning of 2015 than it was upon the release of the first IPCC Assessment Report on
climate change in 1990? A rough answer is fine.
If the answer was four times as high, you would enter "4".
incorrect
1.12
Explanation
In January 2015 the level was about 397, and in 1990 it was about 355. 397/355 =
1.12%. Answers from 1.02 to 1.22 are accepted.
In 2012, China emitted how many times as much CO2 as the next highest emitting
country?
If the answer was four times as high, you would enter "4".
incorrect
2
Explanation
In 2012 China emitted ~10,000 MtCO2, and the next-highest emitter (the US) emitted
~5000 MtCO2. Answers from 1.7 to 2.3 are accepted.
Most countries' CO2 emissions have increased steadily over time, but they can decrease
for multiple reasons, including reduced energy use. Russia is one such example. How
much higher were Russia's CO2 emissions in 1990 than in 2012?
If the answer was four times as high, you would enter "4".
1
1
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incorrect
1.5
CO2 from Land Use Change
0/5 points (graded)
Let’s look at Figure 6.1 (pg 471 in the second reading) for a more quantitative
understanding of where our emitted CO2 goes.
First, note that this figure uses petagrams of carbon, not CO2. This is convenient when
examining the full carbon cycle, because of all the different forms carbon atoms go
through in such a cycle. It's predominantly in the form of CO2 in the atmosphere (and
thus we mostly talk about CO2emissions and concentrations), but when it’s absorbed
into the ocean or by plants the carbon atoms from CO2 end up in carbonic acid or in
plant sugars. This figure only tracks the mass of the carbon atoms involved, to avoid
these complexities.
So then, the anthropogenic flux of 7.8 PgC from fossil fuels in the figure means that
humanity released 7.8 petagrams of carbon atoms per year as a result of fossil fuel use.
(Almost all of that carbon is in the form of CO2.) To figure out the total mass of the
CO2 we released from fossil fuel use (not just the mass of carbon), we can use the
molecular weights of CO2 (44 grams/mol) and carbon (12 grams/mol). In this case:
\[ 7.8 \ PgC \cdot \frac{44 \ g/mol}{12 \ g/mol} = 28.6 \ Pg \ of \ CO_2. \]
Using the same approach and the information on the figure, what mass of CO2 did we
release did due to land use change?
Pg incorrect
4.03
Updated Values
0/1 point (graded)
Figure 6.1 uses average data for the period 2000 thru 2009, so it’s a bit dated. How
does the mass of CO2 in the figure compare to humanity’s 2012 CO2 emissions? The
values in the figure are...
...about 40% lower than the 2012 values.
...about 15% lower than the 2012 values. correct
1
1
Schlumberger-Private
...about 5% lower than the 2012 values.
...about the same.
...about 5% higher than the 2012 values.
...about 15% higher than the 2012 values.
...about 40% higher than the 2012 values. incorrect
Explanation
In 2012, humanity emitted about 15% more carbon dioxide than the yearly average from
2000 thru 2009.
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Anthropogenic Carbon Flux
0/5 points (graded)
What is the total anthropogenic flux to the atmosphere, including both fossil fuels and
land use, in PgC? We're looking for the flux to the atmosphere, not the net flux (don't
subtract out red fluxes from atmosphere to land or ocean). incorrect
8.9
\(\)
Explanation
According to the figure, fossil fuels provide about 7.8 Pg, and land use provides about
1.1 Pg, so the total is about 8.9 Pg.
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Carbon from Atmosphere to Ocean
0/5 points (graded)
How much net carbon is going directly from the atmosphere into the ocean each year?
Answer in PgC incorrect
1.6
\(\)
Explanation
1
1
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According to the figure, 2.3 Pg goes into the ocean from the atmosphere, while 0.7 Pg
comes out. This gives us a total of 1.6 Pg of Carbon.
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Carbon from Atmosphere to Land
0/5 points (graded)
How much net carbon is going directly from the atmosphere into the land on net each
year? Answer in PgC incorrect
4.3
\(\)
Explanation
According to the figure, the land flux is 1.7 Pg (the historical value) plus 2.6 Pg (the
anthropogenic values) for a total of 4.3 Pg of Carbon.
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Carbon Absorption
0/5 points (graded)
Clearly, the ocean and land are absorbing a significant chunk of our carbon emissions
and helping to slow climate change as a result.
What percentage of our emissions are they absorbing? % incorrect
66
\(\)
Explanation
To find this percentage, we make a fraction, with the ocean and land sinks on top and
the carbon emissions on the bottom:
\[ \frac{1.6 \ Pg + 4.3 \ Pg}{8.9 \ Pg} = 0.66 \]
This is 66%.
The Fate of Carbon
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Looking at the carbon cycle figure, it can be tempting to speculate how long it would
take for the atmosphere to return to pre-industrial levels of carbon if we stopped our
emissions. Unfortunately, the carbon cycle is a dynamic system, and we can’t make a
simple estimate just by looking at that figure.
Instead we can turn to careful research on the fate of emitted carbon detailed in Box 6.1
(in the second article). This box looks at the fate of a pulse of CO2, but because
CO2 stays in the atmosphere for so long, all of our emissions over the last few centuries
behave almost exactly the same as a pulse (see this paper on the lifetime of CO2 for
more details, PDF download, 258 KB). Thus, we can think of this box as describing
what would happen to our emitted CO2 after we stopped emitting. Said differently, if we
stopped adding carbon to the atmosphere, how long would it take for all that we have
added since the industrial revolution to come back out?
Annotate
CO2 Removal Mechanism Speed
0/1 point (graded)
Which are the two fastest mechanisms by which CO2 is removed from the atmosphere?
Select both answers.
Ocean invasion correct
Reaction with calcium carbonate
Silicate weathering
Land uptake correct
incorrect
Explanation
Land uptake happens in 1-100 years. Ocean invasion happens in 10-1000 years.
Calcium Carbonate reactions and silicate weathering are much slower, taking 1-
10 thousand years for Calcium Carbonate, and up to one million years for weathering.
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CO2 Remaining
0/10 points (graded)
Let’s look carefully at Figure 1 within Box 6.1. These figures show the amount of
CO2 remaining after a pulse, over different timescales (100 years, 1000 years, and
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10000 years). The first two (a and b) only show the results from a 100 PgC pulse, equal
to roughly 25 years worth of carbon accumulation at today’s rate. The last chart shows
the results over 10000 years for pulses of different sizes, where it’s obvious that pulse
size can affect the amount of CO2 remaining.
Use this figure to answer the following questions:
If a pulse of CO2 were released 50 years ago, what percentage of it would remain in our
atmosphere right now?
% incorrect
50
\(\)
How what if the pulse were 100 years ago?
% incorrect
40
\(\)
1000 years?
% incorrect
25
\(\)
Explanation
The values can be read off the graph on page 473.
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Long-Term CO2 Remaining
0/10 points (graded)
If humanity follows a "business as usual" trajectory, with no significant attempts to slow
emissions, and then suddenly stops emissions in 2100, we will have emitted about 2100
Pg of carbon since the beginning of the industrial revolution.
1
1
1
Schlumberger-Private
Over long times, we can consider this as a single "pulse." How much of a 2100 PgC
pulse would remain after 2000 years? Make your best guess.
% incorrect
28
\(\)
How much will remain 10000 years later? Again, make your best guess.
% incorrect
18
Projected Temperature Increase (RCP8.5)
0/1 point (graded)
Take a look at SPM2.6 (page 11).
What is the central projection of temperature increase in 2100 under RCP8.5 (the dark
red line)?
1° C incorrect
2° C
3° C
4° C correct
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Projected Sea Level Rise (RCP8.5)
1/1 point (graded)
What is the central projection of mean sea level rise in 2100 under RCP8.5?
No substantial rise
0.25 meters
0.5 meters
0.75 meters correct
1
1
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1 meter or more
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Projected Sea Level and Temperature Rise (RCP2.6)
0/5 points (graded)
Which of the following accurately describes the temperature and mean sea level rise
projections for RCP2.6?
Temperature and sea level both increase steadily over the whole century
Sea level rise stabilizes sooner than temperature doesincorrect
Temperature stabilizes mid-century, but sea level rise still has not stabilized by
2100 correct
Surface Temperature Change by Location
5/5 points (graded)
Take a look at SPM.7 (page 12).
Which of the following accurately describes the geographical distribution of increase in
surface temperatures?
It's spread evenly across the whole globe
It's more extreme near the poles correct
It's more extreme near the equator
Climate Prospectus
Now let's turn to the American Climate Prospectus 2014 (PDF download, 14.7 MB), a
report produced by an interdisciplinary team of climate scientists, economists, and risk
analysts to provide policy-relevant information about some economic impacts of climate
change in the US. They do not attempt a comprehensive estimate of all impacts, instead
focusing in detail on four major climate changes (temperature, precipitation & humidity,
sea level, and extreme weather) and six major impacts (coastal damages, temperaturerelated mortality, labor productivity, agricultural productivity, crime, and energy demand).
Like the IPCC, they use four RCP's as the basis for their projections.
If you cannot access that version of the Prospectus, please try this locally hosted
copy instead.
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Please read "Using this Assessment" and "A Framework to Build On" (pages 7-10) to
get an introduction to the report, its intent, and its limitations.
Excluded Impacts
2.5/5 points (graded)
Look carefully at Figure 1.2 on page 9 of the Climate Prospectus.
Which of the following impacts are excluded from the report? Select all that apply.
Changes in hurricane activity
Impacts on grains, soy, and cotton
Impacts on all crops other than grains, soy, and cotton correct
Extreme-weather-related health effects] correct
partially correct
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More Sea Rise Projections
0/5 points (graded)
In Chapters 6 thru 11 the report goes through each of its 6 major impacts in detail. For
brevity, we’ll just look closely at one, damage to coastal communities, and then look at
the summary of all 6 impacts at the end of the report.
First, look at Figures 4.11 and 4.12 (page 32) for projected mean sea level rise. Figure
4.11 is very similar to Figure SPM.6 from the IPCC report. Which of the following
accurately describe Figure 4.12? Select all that apply.
Local sea level rise projections differ substantially around the coast of the
US correct
Sea level rise is generally higher on the western coast than the eastern coast
Sea level rise is generally less at higher latitudes, and greater towards the
equator correct
incorrect
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Predicting Property Damage
0/5 points (graded)
Next, please read all of pages 87, 88, and 89, and look at Figures 11.12-11.4 on page
92 and Figure 11.15 on page 93; these sections cover projected damages due only to
sea level rise. Then read “Changes in Hurricane Frequency and Intensity” on pages 95
and 96 for additional projected damages due to an increase in hurricanes.
How did the researchers translate projected local sea level rise and hurricane activity
into dollar values of property damage? Check all that apply.
They assumed all property below sea level would be destroyed in future coastal
storms.
They used a detailed model used by insurance companies and government officials
to estimate coastal storm damage. correct
They extrapolated from historical data on the costs of past hurricanes to predict
future coastal storm damage.
incorrect
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Property Loss
0/5 points (graded)
Consider Figure 11.15. What is the median estimate of increased annual property
losses due to SLR late this century under RCP8.5?
billions of $ incorrect
21.5
\(\)
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Heaviest Losses
1/1 point (graded)
These losses clearly won’t be evenly distributed across the whole country. Look back at
Figure 11.14. What fraction of that median estimate is expected to be incurred by the
most severely affected state?
Actually, the figure indicates that losses will be evenly distributed.
About ten percent.
About twenty percent.
About half. correct
About eighty percent.
Almost all of the losses will be in the most severely affected state.
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Hurricane Activity and Loss
0/1 point (graded)
Look at Figures 11.17 and 11.18. How much do projected increases in hurricane activity
raise the average annual losses?
No change in loss from increased hurricane activity.
50% increase in loss from increased hurricane activity.
3x increase in loss from increased hurricane activity. correct
10x increase in loss from increased hurricane activity. incorrect
Mid-to-late-century Impacts
We encourage you to skim the other five chapters on impacts (5 thru 10) to see how the
researchers estimated other impacts, like combining experimental studies on crops with
historical data on crop productivity and weather to project productivity changes due to
climate change, or combining laboratory and field studies of worker performance under
different temperatures to project changes in labor productivity.
Schlumberger-Private
For now, we'll go straight to the concluding chapters. Please read "Summing Up" on
pages 115 and 116, and look carefully at Figures 13.22 and 13.23 to see a summary of
the six impacts' projected effects on the US economy in the middle of this century and
late this century, under RCP8.5. Make sure to compare the relative severity of impacts
as estimated here to your guesses at the beginning of this section. Also look at Figure
13.24 to see how all 6 impacts affect each US state.
Note that the researchers used two methods to translate human lives lost (mortality) into
dollar values. The first method is the "income method," which involves estimating the
(discounted) income the deceased person would have earned over their lifetime (a
pretty limited estimate of what human lives are worth!). The second method is to
multiply all mortalities by the "value of a statistical life (VSL)," or around $7 million. This
is the standard approach for most US governmental cost benefit analysis, and the
precise dollar value is the result of "willingness to pay" studies where researchers either
directly or indirectly solicit from people how much they would be willing to pay to reduce
the risk of mortality. This is a deeply contentious topic (for example see Cass Sunstein's
spirited discussion). The researchers argue that the income method is probably the
minimum that anyone would say a life is worth, and the VSL method is probably near
the maximum (especially since it counts the life of a teenager as equally valuable as a
95-year-old), so they use both to show a plausible range of impacts without suggesting
either as the best method.
Annotate
Seeing the Bright Side?
1/1 point (graded)
Examine Figure 13.24. Are there some states that might benefit on net from these 6
impacts, even under RCP8.5 late this century?
No, every state will be harmed by the impacts of global warming.
Yes, some states might benefit from the impacts of global warning. correct
It is impossible to say, at this level of detail, what the impacts will be.
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Seeing the Dark Side?
Schlumberger-Private
1/1 point (graded)
Look back at Figure 13.24 again. Is there a region projected to incur only costs, and no
benefits?
No, every state will benefit to some extent from the impacts of global warming.
It is impossible to say, at this level of detail, what the impacts will be.
Yes, some states will only suffer from the impacts of global warning. correct
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Unequal Harm
2/5 points (graded)
Which two of the following impacts are MOST unequally distributed between US states?
Labor
Agriculture correct
Energy
Coastal Damage correct
Mortality based on measures other than VSL
partially correct
Explanation
Agriculture and Coastal Damage have the most uneven impacts across the country,
ranging from no impact in many states (due to a lack of agriculture or coastline), to
several percent of that state’s economic output in others.
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Comparing Mortality Estimates
0/1 point (graded)
Examine Figure 13.23. Which of the following statements about mortality estimates is
most accurate?
Schlumberger-Private
The income method makes mortality one of the smallest impacts, while the VSL
method makes it by far the largest, roughly ten times as much as all the other impacts
combined. incorrect
The income method makes mortality one of the smallest impacts, while the VSL
method makes it by far the largest, roughly as much as all the other impacts
combined. correct
The income and VSL methods produce nearly identical results.
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Report Summary
1/1 point (graded)
Lastly, look at Figure 14.1 on page 123. This summarizes most of the results of the
report (and uses its more conservative estimates, excluding changes in hurricane
activity and using the income method for mortality). The "Direct" estimates are similar to
what we’ve seen throughout the rest of the report; the "RHG-MUSE" estimates include
macroeconomic effects, for example the way that decreases in agricultural productivity
in one region affect food prices across the country.
What is the "likely range" estimate of the economic impacts of these climate impacts
late this century, under RCP8.5?
close to 0%
1-3% correct
5-10%
Over 15%
Two Percent
1/1 point (graded)
Dr. Keith mentioned that producing 30 TW of power using solar energy would take up
2% of the Earths' land surface area. Approximately how large an area is this?
The size of Russia
The size of Canada partially correct
The size of India correct
The size of Peru
Schlumberger-Private
The size of Italy
The size of Cuba
Land Use Assignment
In the previous lecture you heard David make some quick estimates of land use
requirements. Now try doing some for yourself.
Annotate
Ethanol for Transport Part 1
0/5 points (graded)
This set of problems asks you to answer a complex question: How much land would be
required to power all of US transportation with corn ethanol?We'll break this down into
parts.
First, let's start with the raw energy requirement. How much energy did US
transportation consume in 2017 (in EJ)?
EJ incorrect
29.64
\(\)
Explanation
LLNL flowcharts are a quick way to look up US data. In this case, it shows 28.1 quad
BTU or 29.64 EJ for transportation consumption. IEA sankey diagrams are also good,
though usually not as up-to-date.
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Ethanol for Transport Part 2
0/5 points (graded)
Ethanol has an energy density of .021 GJ/L. How many liters of ethanol are required to
supply US transportation demand?
Liters incorrect
1
1
Schlumberger-Private
1.4*10^12
\(\)
Explanation
Using the energy density for ethanol and the EJ/GJ converstion factor, we get:
\[ \frac{29.64 \ EJ}{0.021 \ GJ/L} \cdot \frac{1000000000 \ GJ}{1 \ EJ} = 1.4 \times
10^{12} \ Liters \]
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Ethanol for Transport Part 3
0/5 points (graded)
Optimistic estimates of corn ethanol productivity in the US are around \( 3.5 \times
10^5 \ liters/km^2 \) per year. How much land would be required to supply enough
ethanol for all of US transportation demand?
sq km incorrect
4*10^6
\(\)
Explanation
\[ \frac{1.4 \times 10^{12} \ Liters}{3.5 \times 10^5 \ Liters/km^2} = 4 \times 10^6 \
km^2 \]
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Ethanol for Transport Part 4
0/5 points (graded)
How does this compare to the total US land area used for agriculture? Choose the
closest answer. Make sure to use "total agricultural land" from whatever source you
choose, including many things like permanent cropland, pasture land, etc.
95% less
50% less
Almost the same correct
1
Schlumberger-Private
50% more incorrect
100% more
Explanation
Estimates of US agricultural land are around 50% of the total land area of the country.
That's half of \(9 \times 10^6 km^2 \), so agricultural land is around \(4.5 \times 10^6
km^2\). The land needed to provide corn ethanol for all transportation demand is thus
about the same as the total land the US currently uses for agriculture, and half the land
area of the entire country!
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Solar Energy Supply Part 1
0/5 points (graded)
Let's look at a closely related question: that of supplying the United States' energy
needs with electricity generated by Solar PV. We'll look at just the existing electrical
needs first.
As before, we'll start with the demand question. How much electricity did the US
generate on average in 2017, in TW?
TW incorrect
0.42
\(\)
Explanation
Roughly 0.42 TW, using data from the LLNL sankey diagram. The US generated 12.5
Quad BTU of electricity, and 12.5 Quad BTU / year = .42 TW. There are other good
sources with slightly different numbers, like the EIA. This problem accepts answers
within 15% of the listed value.
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Solar Energy Supply Part 2
0/5 points (graded)
1
Schlumberger-Private
How much land would be required to meet this demand with solar installations in sunny
locations in the southwest US that produce \( 15 \ W/m^2 \) on average?
sq km incorrect
28000
\(\)
Explanation
Including the conversion factor from watts to terawatts, we get:
\[ \frac{0.42 \ TW}{15 \ W/m^2} \cdot \frac{10^{12} \ W}{1 \ TW} = \ 28000 \ km^2 \]
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Solar Energy Supply Part 3
0/5 points (graded)
How much land would be required if the solar installations were in the much-less-sunny
northeast US, producing \( 7.5 W/m^2 \) on average?
sq km incorrect
56000
\(\)
Explanation
With half as much incident energy, we need twice as much land:
\[ \frac{0.42 \ TW}{7.5 \ W/m^2} \cdot \frac{10^{12} \ W}{1 \ TW} = \ 56000 \ km^2 \]
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Solar Energy Supply Part 4
0/5 points (graded)
Now let's look at the land needed for solar to supply all the energy needs of the USA.
Since the electricity can be used with nearly 100% efficiency at point-of-use, we can just
look at the land needed to meet the amount of energy for "Energy Services" in the LLNL
sankey diagram.
How much energy was consumed as "energy services" in the US in 2017, in EJ?
1
1
Schlumberger-Private
EJ incorrect
32.8
\(\)
Explanation
31.1 Quad BTU = 32.8 EJ.
We don’t need to supply as much energy as the current primary energy supply, since
much of that is fossil energy with large efficiency penalties in electricity generation or in
engines.
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Solar Energy Supply Part 5
0/5 points (graded)
If we scattered modern solar installations across the US, with higher concentrations in
sunnier areas, we might be able to get \( 10 \ W/m^2 \) average performance for all of
them. How much land area would this require to supply all US energy services?
sq km incorrect
104000
\(\)
Explanation
Conceptually, all we need to do is divide the yearly energy requirement by the energy
density of our solar cells in order to get the answer. However, we will also need to
convert EJ to Joules, years into seconds, and square meters into square kilometers in
order to get the result in units that we like.
\[ \frac{32.8 \ EJ/year}{10 \ W/m^2} \cdot \frac{10^{18} \ J}{1 \ EJ} \cdot \frac{1 \ year}
{365 \cdot 24 \cdot 3600 \ seconds} \cdot \frac{1 \ km^2}{1000000 \ m^2} = 1.04 \times
10^5 \ km^2 \]
We don’t need to supply as much energy as the current primary energy supply, since
much of that is fossil energy with large efficiency penalties in electricity generation or in
engines.
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1
1
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Solar Energy Supply Part 6
0/5 points (graded)
Choose the closest answer.
How does this compare to the total US land area used for agriculture?
95% less correct
50% less
Almost the same
50% more incorrect
100% more
Lifespans of Air Pollutants and CO2
0 point possible (ungraded)
As mentioned in the video, the different lifespans of air pollutants and greenhouse
gases have important implications for policy. Please answer two questions about these
lifespans below. Make sure to answer both before hitting the "Check" button.
Which of the following is closest to the half-life of air pollutants like SO2 and ozone in the
troposphere?
A week correct
100 years incorrect
1000 years
1 million years
Which of the following is closest to the half-life of CO2 in the troposphere?
A week
100 years
1000 years correct
1 million years
Peer grade, self grade
Schlumberger-Private
Data Lookup Practice: Germany and Natural Gas
0.0/10.0 points (graded)
Let’s practice looking up data from BP’s Statistical Review of World Energy, 2018 (PDF
download, 6.5 MB). This is a free, yearly report with lots of great data about energy, and
it’s especially good for data on fossil energy trade and prices. You can answer these
questions just by looking at the PDF version of the report, but more detailed data is also
available in Excel format.
This is a multi-part problem. Fill in all boxes before submitting your answer.
Let’s estimate how much Germany paid for imported natural gas in 2017.
How much gas did Germany import on net in 2017? Subtract exports from imports, and
answer in billions of cubic meters.
bcm incorrect
87.7
1
What was Germany’s average import price? Answer in dollars per million BTU.
$/MMBTU incorrect
5.62
1
How much did Germany pay for its gas imports in 2017?
$ incorrect
18.6*10^9
1
Explanation
The first two values are looked up using the link above. The amount imported can be
found on page 35, and the average price on page 33.
For part 3, the amount that Germany paid is:
Volume times energy density times cost per energy, with a conversion factor, or...
87.7×109m3⋅0.04 GJ1 m3⋅5.62 $/MMBTU⋅0.947 MMBTU1 GJ=$18.6 billion
1
1
1
Schlumberger-Private
Note: as a rule of thumb remember that 1 GJ = 1 Millon BTU - it's correct to within 5%.
So the cost per MMBTU is nearly the same as cost per GJ.
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Cost of Carbon Mitigation for Biofuels
0/15 points (graded)
Biobutanol has long been proposed as an alternative to gasoline that could be better
than ethanol. Estimate the cost of mitigation of switching from gasoline to biobutanol.
At the moment gasoline costs $0.64/liter in the US, and optimistic estimates of
biobutanol costs are around $1.14/liter. For greenhouse gas emissions, we’ll need to
use lifecycle estimates that account for emissions at all stages of production and use,
since biofuels lead to emissions from cars but involve negative emissions when plants
used to make fuels absorb CO2. Lifecycle estimates of gasoline are 3.5 kg CO2e/liter;
lifecycle estimates of biobutanol have substantial uncertainty, but 1.7 kg CO2e/liter is a
good central estimate. As with most alcoholic biofuels, biobutanol is less energy-dense
than gasoline, 30 MJ/liter as opposed to gasoline’s 35 MJ/liter.
Give the cost of mitigation in $/tCO2e.
dollars per ton CO2 incorrect
454.945054945
\(\)
Explanation
The cost of mitigation is the cost of reducing emissions over the amount of emissions
reduced. To get to that, we'll need a common basis on which to compare these values.
Let's use a single megajoule of fuel as our base.
One MJ of biobutanol costs:
\[ \frac{$1.14 / Liter}{30 \ MJ / Liter} = $0.0380 /MJ \]
One MJ of gasoline costs:
\[ \frac{$0.64 / Liter}{35 \ MJ / Liter} = $0.0183 /MJ \]
One MJ of biobutanol produces:
\[ \frac{1.7 \ kg/Liter}{30 \ MJ / Liter} = 0.0567 \ kg/MJ \]
One MJ of gasoline produces:
\[ \frac{3.5 \ kg/Liter}{35 \ MJ / Liter} = 0.1000 \ kg/MJ \]
1
Schlumberger-Private
Now we can make a fraction where all the MJ units will cancel out, and we'll just have
the cost per mass. The cost of mitigation for one kilogram is thus:
\[ \frac{$0.0380 - $0.0183 }{0.1000 \ kg - 0.0567 \ kg } = $0.4549/kg \]
Multiplying by 1000 to get the cost per ton, we have $455 per ton of CO2 via this
method.
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CO2 from your Light Bulb
0/10 points (graded)
A 60 W light bulb is used for 15 hours a day. The electricity for this bulb comes from a
natural gas fired power plant that operates with 53% efficiency. How much CO2 is
emitted per day to power this light bulb? Make a simple estimate of the CO2 emissions
from the power plant, ignoring transmission losses.
kg CO2/day incorrect
0.305660377358
\(\)
We mentioned earlier in the course that energy technologies in developing countries
often have much lower efficacies than those in developed countries. Let’s look at one
example, lighting via kerosene lamps, which are common in developing countries but
about 150x less effective than incandescent lightbulbs at turning energy into useful light.
If a family wanted just one tenth of the light provided by the 60 W lightbulb, they’d need
to consume 15x as much power, or 900 W. If a family ran 900 W worth of kerosene
lamps for just 2 hours each day, how much CO2 would this emit? You may assume that
kerosene produces the same emissions as gasoline.
kg CO2/day incorrect
0.44064
\(\)
Explanation
1
1
Schlumberger-Private
Let's do the lightbulb first. Burning natural gas that contains one GJ of energy produces
about 50 kg of CO2. Since our plant is 53% efficient, we need to adjust to get the true
value:
\[ \frac{50 \ kg \ per \ GJ}{0.53%} = 94.34 \ kg \ per \ GJ \]
The total number of GJ we are using is:
\[ 60 \ W \cdot 15 \ hours \cdot \frac{3600 \ sec}{1 \ hour} \cdot \frac{1 \ GJ}
{1,000,000,000 J} = 0.00324 \ GJ \]
Our emissions are therefore:
\[ 94.34 \ kg/GJ \cdot 0.00324 \ GJ = 0.306 \ kg\]
Now let's turn to the kerosene question. We'll go through a similar process, but we don't
need to adjust for the efficiency of a power plant. The total number of GJ of kerosene
we are using is:
\[ 900 \ W \cdot 2 \ hours \cdot \frac{3600 \ sec}{1 \ hour} \cdot \frac{1 \ GJ}
{1,000,000,000 J} = 0.00648 \ GJ \]
The kerosene emissions are therefore:
\[ 68 \ kg/GJ \cdot 0.00648 \ GJ = 0.441 \ kg\]
And that's for just 2 hours, at one tenth of the light produced.
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Levelized Cost Goes Bananas
0/20 points (graded)
In the Costs section, Daniel mentioned that the fixed cost dominates the levelized cost
of driving for most personal vehicles. However, this can change for different vehicles,
like large trucks. Let’s try computing the levelized cost of driving in $/km for an 18
wheeler with the characteristics below. Then, we'll use this information to estimate how
much shipping contributes to the cost of bananas.
The truck costs $150000 to buy.
It can haul 16000 kg of bananas.
The capital charge factor is 0.21.
The taxes, fees, and insurance each year total to $12000.
The truck is driven 210000 km/year.
Variable operation and maintenance (VOM) costs add up to $0.018 per kilometer.
Schlumberger-Private
Fuel costs $1.05 per liter.
The truck can travel 100 km on 49 L of fuel.
Part 1: What are the fixed costs in dollars per kilometer?
dollars per km incorrect
0.207142857143
\(\)
Part 2: What are the variable costs in dollars per kilometer?
dollars per km incorrect
0.5325
\(\)
Part 3: It’s also interesting to look at how much shipping contributes to the final price of
goods. It often ends up being surprisingly low. Using the levelized cost of driving above,
how much does driving contribute to the final price of bananas that are shipped by 18-
wheeler from Los Angeles to Denver (1600 km)? Answer in $/kg of bananas. For
reference, bananas sell for around $1.25/kg in the US.
dollars per kg incorrect
0.0739642857143
\(\)
Part 4: Finally, let’s look at the incredibly low fuel use of container shipping over the
ocean. It usually takes 6-7x less fuel to ship a given payload a given distance than it
would to drive it. If the bananas were shipped 6000 km over the ocean from Ecuador to
Los Angeles, was more fuel used for ocean shipping or truck shipping from LA to
Denver? Enter the word "ocean" or "truck". If the numbers are within 10% of each other,
enter the word "same".
incorrect
truck
Explanation
Fixed Costs: Our fixed cost will be the financing for the truck plus the yearly taxes,
fees, and insurance, divided by the total number of kilometers driven.
1
1
1
1
Schlumberger-Private
\[ \left( $150000 \cdot 0.21 + 12000 \right) \cdot \frac{1}{210000} = $0.207 \ per \ km \]
Variable Costs: The variable costs here are the fuel and the VOM costs.
\[ \left( \frac{$1.05}{1 \ L} \cdot \frac{49 \ L}{100 \ km} \right) + $0.018 \ per \ km = $0.533
\ per \ km \]
Now for the bananas. We'll divide the total cost of shipping by the mass of bananas that
we can ship.
\[ 1600 \ km \cdot ( $0.207/km + $0.533/km ) \div 16000 \ kg = $0.074/kg \]
This is about ten percent of the price of bananas. It excludes the salary of the truck
driver, but since the trip is only ~20 hours, their salary and benefits would probably be
around $500, or just $.03/kg. The cost of fuel really dominates the cost of shipping.
For Part 4, the comparison is easy: it costs more for truck shipping. Ocean shipping
uses less fuel per distance by a factor of six to seven to one. The distance is higher in
this case, but only 6000/1600 = 3.75x higher. Ocean shipping beats land shipping for
this distance.
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Fossil Fuels in Daily Life
3.3333333333333335/20 points (graded)
Let’s estimate the mass of fossil fuels required to power the daily life of an American.
We can use the fossil fuel primary energy from the 2015 LLNL Sankey diagram and
divide by a US population of about 322 million. Using primary energy like this will help
us capture indirect energy use, like the energy required to make the devices people
use, though it will, of course, still be just an estimate.
Part 1: What amount of natural gas is used per person each day in the US? Divide total natural
gas primary energy by population and days in a year, and answer in units of MJ.
MJ incorrect
254
\(\)
Part 2: What mass of natural gas is this?
kg incorrect
4.9
\(\)
1
1
Schlumberger-Private
Part 3: Do a similar calculation to estimate the mass of coal per person each day.
kg incorrect
5.22
\(\)
Part 4: Do a similar calculation to estimate the mass of petroleum per person each day.
kg incorrect
6.76
\(\)
Part 5: How does the total amount of fossil fuels we use compare to the mass of food
consumed by a typical person each day? Most people eat between 1.5 and 2 kg of food per day.
About 10 times more correct
About 2 times more
About the same
About half as much
About one tenth as much
Part 6: Using the emissions factors on the conversion sheet, how much CO2 is released per
person each day from the fossil fuel consumption you estimated above?
kg CO2 incorrect
46
The Impact of Exercise
5/10 points (graded)
If you haven’t already, take a moment to read the blog post Daniel and David wrote
leading up to the course exploring the climate and land impacts of bike riding. Then let’s
try estimating the impacts of hearty-healthy exercise.
Part 1: What’s the impact of a previously-sedentary individual following American Heart
Association guidelines for exercising? Assume that the person starts to jog 4 times per
week, for 31 minutes each, at 9 km/hr, burning an additional 65 kcal/km. Assume their
diet leads to 2.6 g CO2e/kcal, typical for an American. How much CO2 is released?
1
1
1
Schlumberger-Private
kg CO2/year incorrect
163.4568
\(\)
Part 2: What percentage of recent US per capita emissions is this? Since the estimate
of dietary greenhouse gas intensity involves big contributions from gases other than
CO2, make sure to use a per capita yearly emissions statistic that also includes other
gases, like those from the CAIT data explorer. This problem has wide error tolerance
since you could get different numbers from different sources.
% correct
0.990647272727
\(\)
Explanation
Part 1:
\[ \frac{4 \ times}{1 \ week} \cdot \frac{52 \ weeks}{1 \ year} \cdot \frac{ 31 \ minutes}
{ 60 \ min/hour} \cdot \frac{9 \ km}{ 1 \ hour} \cdot \frac{65 \ kcal}{1 \ km} \cdot \frac{2.6 \
gCO_2e}{1 \ kcal} = 163457 \ gCO_2e/year. \]
163457 grams is 163 kilograms.
Part 2: The USA emits something like 16.5 tons of CO2e per person per year, which is
16500 kilograms. 163 kilograms / 16500 kilograms = 0.99%. The question accepts a
wide range of answers, since there are many different estimates of US per-capita
emissions.
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Lightbulb vs Driving Emissions
0/15 points (graded)
Imagine that you drove your car to work, only to realize that you accidentally left a
lightbulb on. In terms of CO2 emissions, is it worth making a trip home from work to turn
off the lightbulb?
Make the following assumptions:
1
1
Schlumberger-Private
The lightbulb uses 100W, and would be on for an extra 8 hours if you don’t drive home to
turn it off.
Electricity has an emissions intensity of .6 kg CO2e/kWh (close to the US average).
The drive would be very short, just 5 km round trip (the US average is closer to 45 km),
in a Prius taking only 5 L/100km.
You can use a lifecycle emissions factor of 3.2 kg CO2e/liter of gasoline (a bit higher than
what you find in the Conversion Sheet).
How much CO2 will the electricity for the light bulb release?
kg CO2e incorrect
0.48
\(\)
How much CO2 will the car release?
kg CO2e incorrect
0.8
\(\)
What if Daniel walked home to do this? His round trip would be a 6.5 km walk, burning
about 200 kcal in total. He estimates that his diet has an emissions intensity of 2 g
CO2e/kcal, a bit below the American average. How much CO2 would Daniel release in
this walk?
kg CO2e incorrect
0.4
\(\)
Explanation
When driving, it's not worth it, even for this short trip in an efficient car.
The lightbulb’s impact is: 0.1 kW * 8 hours * 0.6 kg CO2e per kWh = 0.48 kg CO2e
The car’s impact is: 0.05 L/1km * 5 km * 3.2 kg CO2e/liter = 0.8 kg CO2e
When walking, it’s worth the trip in terms of CO2, though probably not in terms of time
spent.
Walking impact: 200 kcal * 0.002 kg CO2e/kcal = 0.4 kg CO2e
1
1
1
Schlumberger-Private
As a practical consideration, Daniel would need to walk quickly: he needs to get home
before the electricity for the bulb is responsible for 0.08 kg of CO2! Otherwise, he might
as well stay at work and be more cautious next time. There's also the question of
whether Daniel can make up the time he lost at work! Making your decisions
based only on CO2 is not necessarily a good idea in certain situations.
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Energy in Food Waste
0/5 points (graded)
You can find lots of examples of articles (like this one) proclaiming how wasteful
developed countries are with food, and how we could address our environmental
problems by capturing food waste to make natural gas or transportation fuels. How
much energy could we really save if we captured all food waste?
The USDA estimates that 1100 kcal/day go to waste each day per person in the US.
How much is this as a percentage of 2015 US daily per capita energy consumption?
% incorrect
0.53
\(\)
Explanation
The US yearly energy consumption in 2015 was 97.5 Quads/year, or about \( 1.03
\times 10^{11} \ GJ \). Per person, per day, that means we use:
\[ \frac{ 1.03 \times 10^{11} \ GJ/year }{ 365 \ days/yr \cdot 322 \times 10^6 people} =
0.875 \ GJ/day \ per \ capita \]
For countries with the highest energy-per-capita, about 1 GJ per day is a typical rating
and a good rule of thumb, so we are pretty close to that.
The food waste has a total energy of 1100 kcal, which is 4.6 MJ, or 0.0046 GJ.
Our food waste is thus about (0.0046 / 0.875 = ) 0.53% of daily per capita consumption.
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Mitigation Cost of Solar Cell Phone Charger
0/10 points (graded)
In an upcoming section of the course we’ll look carefully at rooftop and industrial solar
PV. For now, let’s look at the mitigation cost of using a small, portable solar charger,
something commonly reviewed on tech websites. In general, energy system
technologies become more cost-effective with scale, so we can guess these might be
expensive mitigation options, but they do have some advantages over larger systems,
like not requiring installation costs or staff to clean and maintain them.
The cheapest chargers Daniel could find were $10 at the time of this writing. They
would take around 5 hours to charge a typical 11 Watt-hour smartphone battery under
bright sunlight.
Part 1: What is the levelized cost of electricity from this system, if it’s used to charge an
11 Wh battery every day of the year? Use a modest individual capital charge factor of
0.15; you may neglect all costs other than the $10 purchase price.
$/kWh incorrect
0.37
\(\)
Part 2: What is the mitigation cost for Daniel to use this sytem instead of using grid
electricity? Assume grid electricity costs $0.20/kWh, with 0.5 kg CO2e emitted per kWh.
Answer in dollars per ton of CO2.
$/tCO2 incorrect
340
\(\)
Explanation
Part 1: Levelized Cost
\[ $10 \cdot \frac{0.15}{.011 \ kWh \cdot 365 \ days/year} = $0.37/kWh \]
Part 2: Cost of Mitigation
\[ \frac{$0.37 - $0.2}{0.5 \ kg \ CO_2e/kWh - 0 \ kg \ CO_2e/kWh} \cdot \frac{1000 \ kg}{1
\ ton}= $340/tCO_2 \]
This is pretty high, but not bad for such a small device! If it were capable of charging
two phones per day it would even start to save money in regions with expensive
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electricity. However, it probably couldn’t do that consistently over a full year, given the
limited availability of sunlight and how long it takes to charge.
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How Green is an Electric Car?
0/15 points (graded)
One possible worry about electric cars is that they're currently powered by dirty
electricity. But proponents, as quoted in this story on the issue, claim that they're still
cleaner than traditional cars even if their electricity comes from fossil fuels because of
how efficient large-scale electricity production is and how efficient electric motors are.
Let's investigate for ourselves.
Let's look at the worst-case scenario, an electric car powered entirely by electricity from
coal. Assume the car is a Nissan Leaf. How many kWh does it take to go 1 km, under
"average" driving conditions? Try looking online to find the information that you need for
this answer. We'll accept a range of answers for this.
kWh incorrect
0.18
\(\)
How many kg of CO2e emissions would this lead to? Use the median estimate from the
figures at the US National Renewable Energy Laboratoryfor the emissions intensity of
coal electricity.
kg/km incorrect
0.18
\(\)
What are the per-km emissions from a standard American car? Assume a fuel economy
of 9.5L/100km, with gasoline that has a lifecycle impact of 3.2 kg CO2e/liter.
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kg/km incorrect
.304
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Strengths of the Grid
0.6/1 point (graded)
Thinking back on the ten facts that David presented, consider the strengths and
weaknesses of our current system. Mark all of the boxes below that indicate a strength
of our electric grid.
The reliability of the grid correct
The efficiency of transmission through the grid correct
The age of the transmission poles and other equipment
The flexibility of electricity as an energy source correct
The ease with which the grid can be controlled
Demand for Solar and Oil
1/1 point (graded)
Why do renewable generators almost always get to feed their power into the grid, while
oil-burning plants often only operate a small percentage of the time that they could
operate?
There are fewer oil-burning plants than solar plants, so solar plants are run more
often.
It costs nothing to operate a solar plant for an extra hour, while oil plants are
expensive to run. correct
Oil-burning plants are highly polluting, and solar plants create no pollution while
operating.
This actually isn't true: oil-burning plants are more often in operation than solar
plants.
Dominant Source of Electricity
5/5 points (graded)
What is the dominant surce of electricity under the default conditions? That is, what has
the most generation and most capacity built?
Gas
Coal correct
Solar
Battery
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Solar Capacity
0/5 points (graded)
What is the amount of solar capacity built? GW incorrect
0.3933
\(\)
Explanation
You can read this in the "Capacity" column.
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Earliest Solar Power
5/5 points (graded)
What is the earliest hour with solar generation?
6 AM
7 AM correct
8 AM
9 AM
Answer
Correct:
8 AM is also accepted, since it is difficult to see the power delivered at 7 AM.
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Coal at Noon
0/5 points (graded)
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How much coal power is being generated at noon? GW incorrect
1.6
\(\)
Explanation
You can read this value from the column for hour 12 on the graph.
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Utilization
0/5 points (graded)
Which generator has the highest utilization under the default conditions?
Gas incorrect
Coal correct
Solar
Battery
Explanation
You can read this in the "Utilization" column.
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Summer Load
0/5 points (graded)
Now switch the input scenario and load curve to "Summer".
How is the summer load curve different from the default?
It has a lower evening minimum incorrect
It has a stronger afternoon peak correct
There is no overnight minimum
Explanation
The afternoon peak is higher for the summer, as air conditioning demands increase.
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Increased Charge Factor
0/5 points (graded)
Still using the summer settings, set the CCF to 0.2. What will happen? Take a guess
and then run the simulation.
What happened when the charge factor increased?
High capital cost generators are penalized correct
Solar and batteries become the dominant options
The cost of electricity goes down
No change incorrect
Explanation
You should see that gas became the dominant energy provider. Gas has the lowest
capital cost out of the three generator types.)
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Why?
0/5 points (graded)
Why did increasing the CCF have the effect that it did?
Lower CCF’s reduce the levelized costs of electricity incorrect
CCF’s are more relevant for fossil generators than renewables
A high CCF increases the weight of capital costs in the levelized cost of electricity,
so capital-intensive options like coal and renewables are penalized correct
Explanation
The higher the CCF, the more money one needs to pay for electricity when the cost of
the plant is taken into account. Plants with higher capital costs are hit harder by this
effect, and become less cost-effective.
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Untaxed Coal
0/10 points (graded)
Using the default settings, try pressing the “Cost vs Intensity Curve” button.
In the case of a $0/tCO2 carbon tax, how much coal capacity is built?
GW incorrect
1.56
\(\)
Explanation
You can read this value from the column for "Capacity" on the table.
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Pricing fossil fuels out of the system
0/5 points (graded)
Mouse over each point to take a look at the carbon price and capacities built. How much
higher does the carbon tax need to be to eliminate natural gas than to eliminate coal?
$10/tCO2 higher
Twice as high incorrect
Ten times as high correct
Explanation
Natural gas emits substantially less carbon than coal. Carbon taxes will not quickly force
natural gas out of the market.
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Decarbonizing the Grid
0/5 points (graded)
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Let’s play with the 2010 and 2015 US scenarios. In 2015 US solar and battery prices
were lower than in 2010, but natural gas prices were lower as well. How did these
factors influence the carbon price needed to remove natural gas from the grid?
Was the minimum carbon price to remove all natural gas lower in 2010 or 2015?
In 2010 incorrect
In 2015 correct
Same value for both years
Explanation
You can use the Cost vs. Intensity curve to find this answer. Look at the top-left-most
point, where the carbon intensity has dropped to zero. In 2015, setting the carbon price
to $370 removed natural gas from the grid. In 2010, the price needed to be $850 per ton
of CO2! So the drop in solar prices has had more of an effect in this regard, with gas
now being less costly to drive out of the system.
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Cost of Mitigation
0/10 points (graded)
We can see that the response of the system is very sensitive to carbon price, with a
substantial amount of coal generation being built with a carbon tax of $20/tCO2 and
none being built at $30/tCO2.
What is the cost of mitigation of a $20/tCO2 tax (relative to the default of $0/tCO2)?
Keep in mind that the increased electricity cost with a carbon tax is partially due to the
construction of more expensive generators, and partially due to tax payments on any
emissions from the remaining fossil generators. From society’s perspective, those tax
payments will be used somewhere else in the economy and shouldn’t count towards the
cost of mitigation. You will need to calculate the cost of electricity for the $20/tCO2 and
$30/tCO2 cases with the cost of the carbon taxes taken out.
$/tCO2 incorrect
3.88
\(\)
What is the cost of mitigation of a $30/tCO2 tax (relative to the default of $0/tCO2)?
Don't forget the reminder from above.
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$/tCO2 incorrect
23.4
\(\)
Explanation:
For the $20/ton tax:
The new electricity cost is $.088/kWh. To find the cost with direct contribution from
carbon tax subtracted out, we can subtract the carbon price times the carbon intensity
of the electricity (which is equal to the total carbon tax payments).
\[ $.088/kWh - .73 \ kg \ CO_2/kWh \times $.02/kgCO_2 = $.0734/kWh \]
The cost of mitigation is then:
\[ \frac{$.0734/kWh - $.073/kWh}{.833 \ kgCO_2/kWh - .73 \ kgCO_2/kWh} \cdot
\frac{1000 \ kg}{1 \ ton} = $3.88/tCO_2 \]
For the $30/ton tax:
The new cost of electricity is $0.094/kWh. Without the direct contribution of the carbon
tax, that comes to:
\[ $.094/kWh - .228 \ kg \ CO_2/kWh \times $.03/kgCO_2 = $.0872/kWh \]
The cost of mitigation is then:
\[ \frac{$.0872/kWh - $.073/kWh}{.833 \ kgCO_2/kWh - .228 \ kgCO_2/kWh} \cdot
\frac{1000 \ kg}{1 \ ton} = $23.4/tCO_2 \]
Note: this exercise is for pedagogical purposes only. The simulation isn’t nearly precise
enough to estimate the actual cost of mitigation of these carbon prices in the real world,
so don’t let this convince you that $30/tCO2 is much better than $20/tCO2, just that the
results of a carbon price can be surprisingly sensitive to changes in the price
Explanation for old version of problem:
Cost of mitigation of a $20/tCO2 tax:
\[ \frac{$.088 - $.073}{0.833 - 0.73} = $145 \ per \ ton \ CO_2 \]
Cost of mitigation of a $30/tCO2 tax:
\[ \frac{$.094 - $.073}{0.833 - 0.228} = $34.7 \ per \ ton \ CO_2 \]
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Peak Load Shifting
2.5/5 points (graded)
Check out the "Peak Load Shifting" load curve, which makes the demand curve flatter
by shifting some peak demand to the evening. Which of the following are true when you
"Plan System" with the "Peak Load Shifting" load curve?
CO2 emissions per kWh go down relative to the default load curve
Electricity cost goes down, due partly to higher utilization rates that can be achieved
with flatter demand correct
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Capital-cost-intensive options generally benefit correct
More solar capacity is built when the minimum carbon price to eliminate coal is
implemented
partially correct
Explanation
In general, peak load shifting favors generators that are capital-intensive and need high
utilization rates to keep their costs low. In this case, shifting peak loads to the evening to
flatten the demand curve ends up favoring coal in particular which can run all day, and
hurts solar a bit since more load is shifted to times when the sun isn’t out. When a
carbon tax is used to drive coal out of the system, this peak load shifting still slightly
penalizes solar relative to the default arrangement.
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Peak Load Shifting Continued
2.5/5 points (graded)
Which of the following might help encourage a lower-carbon grid under the default
settings with peak load shifting? Note: The goal is to make the grid carbon-free; a switch
from coal to gas is not enough.
Raising the CCF
Shifting more load to peak solar generation hours rather than night correct
Including wind power (try looking up hourly generation of wind farms) correct
Raising the price of coal by 15%
partially correct
Explanation
Raising the price of coal could help, but with our parameters a 15% increase doesn’t
affect solar capacity at all. Raising the capital charge factor is unlikely to help since
solar is the most dominated by capital costs of any option. Load shifting to peak solar
generation times instead of the night could definitely help, though we don’t implement it
here; in the upcoming section on solar power David will mention some ways this could
happen, for example using excess solar electricity midday to cool a reservoir that could
be used to cool buildings in the evening when the sun is down.
Including wind power could help encourage lower-carbon generation because it tends to
generate most in the morning and evening, which would compliment solar’s midday
peak. For a detailed analysis of combining all-low-carbon generators to manage
variability and meet demand, check out Delucchi and Jacobson's 2011 Energy Policy
paper.
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How low do solar and batteries need to go?
5/5 points (graded)
As we'll discuss in the upcoming section on solar power, the costs of solar electricity
and batteries are declining quickly. Let's use this interactive to estimate how low they'll
need to go for an all-solar-and-batteries system to be the cheapest.
Try using the default settings but simultaneously decrease the capital cost of solar and
batteries by integer factors (e.g. decrease both by a factor of 2, then factor of 3, etc).
How far do they need to decrease to have an all-solar-and-batteries system? Keep in
mind that the default settings represent an approximate average of North America and
Europe in recent years; more detailed results for particular regions will vary.
Factor of 2
Factor of 3 correct
Factor of 4
Factor of 5
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How low do solar and batteries need to go if gas is cheap?
0/5 points (graded)
Low natural gas prices make it much harder for renewables to be the cheapest option.
Repeat the previous problem but use the "US 2015 Average" scenario, which has a
much lower natural gas price.
Simultaneously decrease the capital cost of solar and batteries by integer factors (e.g.
decrease both by a factor of 2, then factor of 3, etc). How far do they need to decrease
to have an all-solar-and-batteries system?
Factor of 2
Factor of 3
Factor of 4 incorrect
Factor of 5 correct
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Solar Resource Assignment
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The Cost of Solar Tracking
0/15 points (graded)
Is the extra capital cost of tracking and fixed-tilt systems worth it? Let’s investigate. For
each question, Use a capacity factor derived from NREL. You can find this most quickly
from the map, as is done on the Solar Resource page. You may ignore non-capital
costs.
This is a multi-part question. Make sure to enter all your values before hitting "Check".
What is the LCOE of a horizontal plate installation in Arizona? Assume $1750/kW
capital cost, and a CCF of 0.1.
$/kWh incorrect
0.087
\(\)
What’s the LCOE of a fixed-tilt installation in Arizona, pointed south at latitude? Assume
$1800/kW capital cost (only a slight increase), and a CCF of 0.1.
$/kWh incorrect
0.076
\(\)
What’s the LCOE of a N-S axis tracking installation in Arizona, pointed south at latitude?
Assume $1950/kW capital cost, and a CCF of 0.1.
$/kWh incorrect
0.059
\(\)
Explanation
LCOE in this case counts only capital costs, making it a quick calculation:
\[ LCOE = \frac{CapCost \cdot CCF}{8766 \ hours/year \cdot Capacity} \]
This comes out to $.087/kWh for the horizontal plates, $.076/kWh for the plates pointed
south at latitude, and $.059/kWh for the tracking installation pointed south.
Comparing the tracking installation to the horizontal plates, it will take about 7,140 hours
of operation to make up the difference. This may sound like a lot, but it's only two years
worth of daylight operation in Arizona.
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Outsourcing European PV
0/15 points (graded)
Instead of building PV systems in Europe, European countries could partner with north
African countries to build PV there and import the electricity along HVDC lines. Use
SolarGIS maps to estimate the levelized cost of electricity of solar installations in
southern Germany and Libya. Assume $1800/kW capital cost and a CCF of .1. You may
neglect all other costs.
This is a multi-part question. Make sure to enter all your values before hitting "Check".
What's the capacity factor for a flat panel, horizontal to the ground in south Germany?
The conversion is similar to the one for Boston on the Solar Resource page, but slightly
different because SolarGIS uses kWh/m2
-yr rather than kWh/m2
-day.
% incorrect
13.1
\(\)
Assume that the installation in Germany is a fixed-tilt system, which has a 20% higher
capacity factor than you estimated above. What's the LCOE, using the above
assumptions?
$/kWh incorrect
0.131
\(\)
Assume that the installation in Libya is also a fixed-tilt system, with a 20% higher
capacity factor than the GHI from SolarGIS's map (and use the irradiance value from
roughly the center of the country). What's the LCOE, using the above assumptions?
$/kWh incorrect
0.067
\(\)
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Explanation
Part 1:
\[ Capacity = \frac{1150 kWh/(m^2 yr)}{8766 \ hours/year \cdot 1 kW} = 13.1\% \]
Part 2:
LCOE in this case counts only capital costs, making it a quick calculation:
\[ LCOE = \frac{CapCost \cdot CCF}{8766 \ hours/year \cdot Capacity} \]
This comes out to $.131/kWh for Germany, $.067/kWh for Libya. Note: we did this the
standard way for this course, using the capacity factor, but you could have just plugged
the kWh/m2
-yr number directly into the LCOE formula.
Cost of Solar Electricity
0/5 points (graded)
Estimate the cost of electricity in a highly favorable site like the US southwest.
Assume capital costs have continued to fall and are now at $1000/kW. This would be a
big government project with a very low CCF of 0.06. Fixed operations and maintenace
cost (FOM) is $5/kW-yr, and the installation will be a tracking system with capacity factor
of 0.37.
$/kWh incorrect
0.02
\(\)
Explanation
You may wish to review the Costs section if you are having difficulty calculating LCOE.
The LCOE for this plant is:
\[ \frac{$1000 \cdot 0.06 + $5}{ 0.37 \cdot 8766 \ hours/year } = $0.02/kWh \]
This is an unbelievably low cost for electricity! But the source is intermittent - it
generates only when the sun is shining.
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Cost of Hydrogen
10/10 points (graded)
Now let’s estimate the cost of hydrogen produced with this electricity.
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This 2014 report by the US DOE estimates that hydrogen produced at large scales via
electrolysis would cost $4.3/kg, with $3.5/kg of that cost coming from electricity.
However, that electricity is produced at a rate of $.065/kWh, not at our cheaper rate.
How much would the electricity part of the cost be with our cheaper solar power? Give
your answer in $/kg of H2.
$/kg H2 correct
1.08
\(\)
Explanation
Multiply the original electricity cost by a fraction made out of the electricity costs:
\[ $3.50/kg \cdot \frac{$0.02}{$0.065} = $1.08 \ per \ kg \ H_2 \]
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FOM Cost Increase
0/5 points (graded)
Unfortunately, the intermittent nature of solar power will mean that the hydrogen plant's
hardware will be left idle more often. This means that fixed costs will contribute more to
the cost of hydrogen. The original estimate had fixed costs at $0.8/kg when the plant
had 90% utilization. Now that it only has 37% utilization, what are the fixed costs in
$/kg?
$/kg H2 incorrect
1.95
\(\)
Explanation
Multiply the old fixed costs by a fraction composed of the utilization factors:
\[ $0.80/kg \cdot \frac{90\%}{37\%} = $1.95/kg \]
This is a big increase! We could run the plant on grid electricity when the sun isn’t
available to improve utilization, but in this case it has little effect on the cost of H2, so
we’ll neglect that option.
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Energy Cost of Hydrogen
0/5 points (graded)
Using the new fixed and variable costs that you determined above, what is the total cost
of hydrogen produced by solar power? Answer in dollars per gigajoule.
$/GJ incorrect
21.6
\(\)
Explanation
Adding the previous values together, we get $3.03 per kilogram. Hydrogen's energy
density is 0.14 GJ/kg, and we can divide to get our total cost of $21.6 per gigaloule.
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Pump Price
3.75/5 points (graded)
Which nations had gasoline pump prices substantially (more than 15%) higher than this
in 2014? Select all that apply.
Norway correct
USA
India correct
Germany correct
partially correct
Explanation
As an example: Germany had a cost of $1.8 USD per liter at the pump for gasoline.
Gasoline's energy density is 35 GJ/m3
, which is 0.035 GJ/liter. Dividing, we find a total
cost of $51.40 per GJ.
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Is this as good as it looks?
3.75/5 points (graded)
Why doesn’t this actually represent a huge cost savings opportunity for some of those
nations above? You may want to read this article on gasoline prices before answering.
Choose all of the answers that apply (and there may be more reasons we don't list
below).
We only calculated cost to produce hydrogen, not to store or transport it. correct
Infrastructure hurdles raise the price of a hydrogen economy correct
Hydrogen vehicles have lower fuel economy
Many nations' gasoline prices are only higher than the US's because of
taxes. correct
Community Electricity Demand
0.0/5.0 points (graded)
First let’s estimate the village's electric demand. Assume the system needs to power the
following devices for a village of 50 households:
Mini fridges: one per household, .15 kWh/day each
Lights: 25 W of LED’s per household averaging 4 hrs/day
Phones: 4 cell phones per household with 5 Wh batteries charged every other day
Computers, TV’s, etc: .1 kWh/day per household
Air Conditioning: one for small schoolhouse, 1.5 kW used for 4 hrs/day
What’s the total demand per day? kWh incorrect
24
1
Explanation
Per-person expenses: 0.15+(0.025×4)+(4×0.005÷2)+0.1=0.36 kWh
Community-wide costs: Just the school's AC. 1.5 kW×4 hours=6 kWh
Total for 50 people: 0.36×50+6=24 kWh
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Capital Cost
0.0/5.0 points (graded)
Next let's estimate the capital cost of the solar system in dollars per kilowatt. Use Figure
7 from the US National Renewable Energy Laboratory’s 2015 US Photovoltaic Prices
and Costs Breakdown report.
Since this will be a small system, use values for residential systems. For simplicity,
include only the hardware costs and installation labor (sometimes called "direct labor")
costs, and assume that the installation labor only costs half as much as in the US. You
may ignore all other costs (permitting, profit, supply chain costs, etc).
$/kW incorrect
1475
1
Explanation
The costs are: $0.70 for the module, $0.29 for the inverter, $0.12 for the rack, and $0.20
for the balance-of-system materials. Installation labor, at half the US rate, would be
$0.165. The total for all of that is $1.475 per watt, which is $1475 per kW.
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Critical Factors
0.0/5.0 points (graded)
What other figures are critical for estimating the levelized cost of electricity for this system?
Operations and maintenance
Capital charge factor correct
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Capacity factor correct
incorrect
Note: Make sure you select all of the correct options—there may be more than one!
Explanation
Operations and maintenance costs are significant but small. Given the low cost of labor
in the region we can neglect this cost. For capital-cost-dominated renewables, the two
other critical figures are the capital charge factor and capacity factor.
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Capacity Factor
0.0/10.0 points (graded)
What's the capacity factor? SolarGIS has nice maps for Global Horizontal Irradiation.
Adjust the GHI for northwestern Mali upward by 20% (multiply by 1.2) to very roughly
account for the gain from tilting the panels at latitude.
% incorrect
29.4
1
Explanation
The map shows about 2150 kWh per square meter per year. To find the percentage of
the maximum power, we set up a fraction, and adjust upward by 20%:
2150 kWh/m2/yr1 kW/m2⋅8766 hrs/yr⋅120%=29.4%
Because of the different values in the map, this problem accepts answers between 27%
and 32%.
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LCOE
0.0/10.0 points (graded)
What is the LCOE for this system? Assume a capital charge factor of 0.1
$/kWh incorrect
0.057
1
Explanation
The total cost takes into account both the CCF and the capacity factor:
$1475/kW⋅10%/yr29.4%⋅8766 hrs/yr=$0.057/kWh
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LCOB
0.0/10.0 points (graded)
Assume that the village would like a modest 2 kWh battery backup system, costing
$500/kWh. Unfortunately, the batteries have a much shorter lifespan than the solar
panels, only around 8 years at the village's usage rate, leading to a higher CCF of .15.
What’s the additional LCOE that the batteries will add to the system? Ignore any costs
of operating the battery, or electric losses.
$/kWh incorrect
0.017
1
Explanation
The batteries will cost $1000 in total. Using our standard LCOE approach, we find:
$1000⋅15%/yr24 kWh/day⋅365 days/yr=$0.017/kWh
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1
1
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Energy density
1/1 point (graded)
As David mentioned, nuclear power is basically one hell of a way to boil water, and the
steam it generates turns a turbine and generates electricity much like in a natural gas or
coal plant. But as he described, the method of extracting thermal energy from the fuel is
very different – rather than combusting the fuel, we rely on nuclear chain reactions. The
total amount of energy extracted from a given unit of fuel is called the “burnup,” and is
usually around 50 GW-days of thermal energy per ton of uranium in modern plants (this
“burnup” is analogous to the heat of combustion for fossil fuels).
In terms of mass, how much more energy dense is nuclear fuel at a burnup of 50 GWdays/ton than gasoline (use gasoline's higher heating value)? Note that this question is
about real nuclear power plants and is different from the comparison David made in the
first video involving the energy released from an individual fission or fusion (so you'll
actually need to do a calculation).
100 times more energy dense
100,000 times more energy dense correct
10,000,000 times more energy dense
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Cost of fuel
1/1 point (graded)
What’s the cost of fuel, in $/GJ, for a nuclear plant that extracts 50 GW-days/ton of fuel,
with fuel costing $2500/kg?
$.6/GJ (much less than any fossil fuel) correct
$2/GJ (about the same as inexpensive coal)
$8.5/GJ (a typical natural gas price in Euorpe in recent years)
Nuclear LCOE
0/15 points (graded)
Compute the cost of electricity (in units of $/kWh) from a nuclear power plant under the
following assumptions.
Schlumberger-Private
Fixed O&M is 75 $/kW-year.
Variable O&M is $.0075/kWh
Capital cost is $5500/kW
capital charge factor is 10%
Utilization is 85%
Plant thermal efficiency is 35%
Each ton of uranium oxide fuel provides 50 GW-days of thermal energy
Fuel cost is $2,500,000 per ton
$/kWh incorrect
0.097
\(\)
What percentage of the total LCOE is due to fuel costs? % incorrect
5.87
\(\)
Explanation
50 GW-days comes out to \( 1.2 \times 10^9 \ kWh \) of thermal energy.
Fuel costs \( $2.5 \times 10^6 \div 1.2 \times 10^9 \ kWh_{th} = $.00208/kWh_{th} \)
where the "th" subscript denotes thermal energy. We still need to factor in efficiency to
get the fuel’s cost per kilowatt-hour. The terms in the equation below are the fixed costs,
the variable O&M, and the fuel cost.
\[ LCOE = \frac{$5500 \cdot 0.1 + 75}{0.85 \cdot 8766} + $0.0075 + \frac{$0.002}{0.35}
= $0.097/kWh \]
The cost for just the fuel is:
\[ \frac{$0.002}{0.35} = $0.0057/kWh \]
...which comes out to 5.87% of the total LCOE.
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Fuel per Year
1
1
Schlumberger-Private
0/5 points (graded)
How much fuel would a 1 GW plant with an 85% capacity factor and 50 GW-days/ton
burnup consume in a year, in metric tons?
tons incorrect
17.75
\(\)
Explanation
1 GWe plant at 85% capacity produces
\[ 1 \ GW \cdot 0.85 \cdot 8766 = 7.45 \times 10^9 \ kWhe \]
in one year. This requires
\[ \frac{7.5 \times 10^9}{0.35} = 2.13 \times 10^{10} \ kWh \]
of thermal energy per year. To find the mass, we use the per-ton energy density: 50
GW-days comes out to \( 1.2 \times 10^9 \ kWh \) of thermal energy.
\[ \frac{2.13 \times 10^{10} \ kWh}{1.2 \times 10^9 \ kWh/ton} = 17.75 \ tons \]
Each plant requires about 18 tons of uranium oxide per year.
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The Equivalent Coal Plant
0/5 points (graded)
What mass of coal would an equivalent coal plant consume in a year, in metric tons?
Assume the same 1 GW power, 85% capacity factor, and 35% thermal efficiency.
tons incorrect
2.85*10^6
\(\)
Explanation
As before, we need to supply \( 2.13 \times 10^{10} \ kWh \) of thermal energy.
To find the mass, we use the energy density of coal:
\[ \frac{2.13 \times 10^{10} \ kWh}{0.027 \ GJ/kg} = 2.85 \times 10^6 \ tons \]
2.87 million tons of coal, compared to 17.75 tons of uranium oxide.
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1
1
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US Nuclear Waste 2014
0/5 points (graded)
Without reprocessing, all of this nuclear fuel will become "spent fuel" waste. When
stored in a container, the waste usually has a density around .25 tons/m3
. The EIA
estimates that in 2014 the US generated about \( 8 \times 10^{11} \) kWh from nuclear
power. Given this information, estimate the volume of waste from nuclear power in the
US in 2014.
cubic meters incorrect
7600
\(\)
Explanation
For 1 GW plants we established 17.75 tons of spent fuel per \( 7.45 \times 10^9 kWh \).
This comes out to \( 2.38 \times 10^{-9} \ tons/kWh \). According to the IEA, the USA
produced \( 7.97 \times 10^{11} \) kWh of electricity via nuclear power in 2014. The total
amount of waste in 2014 was therefore...
\[ 7.97 \times 10^{11} \ kWh \cdot 2.38 \times 10^{-9} \ tons/kWh = 1900 \ tons \]
If the density is 0.25 tons/m3
, the volume will be:
\[ \frac{1900 \ tons}{0.25 \ tons/m^3} = 7600 m^3 \]
For reference, consider that an Olympic swimming pool is about 2500 m3
.
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Doubling US Nuclear Capacity
5/20 points (graded)
1
Schlumberger-Private
Now imagine that the US, in response to climate change, decides to double its yearly
output of nuclear electricity. What volume of spent fuel would be generated in 50 years
at this level of production with current technology?
cubic meters incorrect
760000
\(\)
How does that compare to the \( \approx 3 \times 10^5 m^3 \) of commercial spent fuel
waste in the US currently?
10 times all our spent waste so far.
2 or 3 times all our spent waste so far. correct
About the same as all our spent waste so far.
About 1/3 of all our spent waste so far.
A tenth of all our spent waste so far.
What mass of waste would be generated? tons incorrect
190000
\(\)
How does this compare to the mass of waste that could be stored in the US's Yucca
Mountain facility, which stores approximately 70,000 metric tons? Select the closest
answer.
10 times what Yucca Mountain can handle.
2 or 3 times what Yucca Mountain can handle. correct
About what Yucca Mountain can handle. incorrect
About 1/3 of what Yucca Mountain can handle.
A tenth or less of what Yucca Mountain can handle.
Explanation
Parts 1 and 2:
1
1
Schlumberger-Private
\( 7600 \ m^3/yr \cdot 2 \cdot 50 \ years = 7.6 \times 10^5 \ m^3 \), about 2.5x current
levels of nuclear waste.
Parts 3 and 4:
\( 1900 \ tons \cdot 2 \cdot 50 years = 2 \times 10^5 \ tons \), about 2.7x what could be
stored in Yucca mountain
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Yucca Mountain Costs
0/5 points (graded)
Finally, let's make a crude estimate of the cost of storing waste in Yucca Mountain. If
Yucca Mountain cost $100 billion total over its lifetime (to build, transport and store the
waste, etc) and stored 70,000 metric tons of waste, how much does it add to the cost of
electricity for the plants that store their waste there? Assume the plants extract 50 GWdays of thermal energy for each ton of waste, and have 35% efficiency.
$/kWh incorrect
0.00333
he importance of capital cost
0/1 point (graded)
As David mentioned, capital costs are very important for nuclear power but are highly
uncertain in many regions. Let's compare the LCOE of nuclear electricity to wholesale
electricity using two different capital costs for nuclear, $4000 and $8000/kW. How much
higher is the LCOE of nuclear electricity using the following assumptions than wholesale
electricity at $.065/kWh? If the LCOE for nuclear was $.195/kWh, you would answer
"200% higher." For now you may ignore the contribution of nuclear waste storage (a
later problem will include it).
Nuclear plant capital costs of $4000/kW and $8000/kW, CCF of .11
Fixed operations and maintenance $100/kW-yr, utilization 85%
VOM $.002/kWh, Fuel $.6/GJ, efficiency 35%
1
Schlumberger-Private
25% higher than wholesale for $4000/kW and 100% higher for $8000/kW correct
10% lower than wholesale for $4000/kW and 50% higher for $8000/kW
100% higher than wholesale for $4000/kW and 200% higher for $8000/kW incorrect
50% lower than wholesale for $4000/kW and equal for $8000/kW
Estimating the effects of exposure
0.5/1 point (graded)
David described how cancer risks from radiation exposure are commonly calculated,
with a 1 person-Sievert (person-Sv) dose corresponding to an additional 5% cancer
mortality risk. The risk is conservatively assumed to be linear in dose, so a 2 person-Sv
dose corresponds to an additional 10% cancer mortality risk, and a .01 person-Sv dose
corresponds to an additional 0.05% cancer mortality risk.
The 1979 Three Mile Island accident in the US lead to an average exposure for civilians
around the plant of 14 microSv. What is such a person's additional cancer mortality risk?
.00007% correct
1%
.05% incorrect
The accident exposed 2 million people to such a dose. What is the expected number of
cancer mortalities due to this exposure?
none
1.4 correct
2.9
16
Nuclear power's cost of mitigation
1/2 points (graded)
Before you move on to some readings offering different views on nuclear power, let's try
a cost-of-mitigation-style question. Instead of making some assumptions and working
out the cost of mitigation, let's work backwards to see what capital cost would be
necessary for nuclear power to have a low cost of mitigation of $25/tCO2.
If we want a cost of mitigation of $25/tCO2, and wholesale electricity currently costs
$.065/kWh and causes .5 kg CO2/kWh of emissions, what LCOE will the nuclear power
need to have?
This is a two-part problem. Answer both parts before hitting "Check."
Schlumberger-Private
$.067/kWh
$.091/kWh incorrect
$.078/kWh correct
What capital cost would be required for a nuclear plant with the following assumptions
to have that LCOE? You're welcome to use a tool like wolfram alpha to solve for the
capital cost, or to do it by hand. Once you calculate it, take some time to compare this
capital cost to recent capital costs in different countries as discussed in The Economist's
View. This will be a useful thing to know when evaluating the divergent arguments about
the costs of nuclear power, and should be helpful when you write your essay in the next
section.
Assumptions: CCF of .11, with 90% utilization; FOM of $100/kW-yr; VOM of $.002/kWhr, Fuel cost of $.6/GJ, and thermal efficiency of 36%; waste storage cost of $.005/kWh
$3150/kW
$3750/kW correct
$5300/kW
$8000/kW
Peer grade, self grade
Schlumberger-Private
Cost of Mitigation for a Gas Furnace
0/1 point (graded)
What's the cost of mitigation of installing an efficient natural gas furnace, using the
following assumptions? (These are based on Daniel's actual home heating usage and
furnace purchasing options).
A low-efficiency furnace costs $1000, and is 79% efficient.
A high-efficiency furnace costs $1800, and is 93% efficient.
Either furnace will be used to supply 100 GJ of heat per year (not including losses due to
inefficiency).
Gas costs $9.90/GJ and has lifecycle emissions of 65 kg CO2e/GJ. (Note that this is
higher than the combustion-only emissions on the Conversion Sheet.)
Installation cost $2050, the same for both furnaces.
Use a CCF of 0.16.
Calculate levelized cost of heating for each using only purchase price, installation, and
yearly heat supply (including fuel cost and efficiency). Then calculate the emissions of
each, and use the levelized cost and emissions to calculate the cost of mitigation.
$/tCO2 incorrect
Energy Cost of Crude Oil
0/5 points (graded)
What’s the cost of crude oil, in $/GJ? Use a major spot price (Brent, WTI, etc) and use
an average for 2017. Keep in mind that spot prices have occasionally been twice as
high as the 2017 average since that year.
$/GJ? incorrect
8.8
Energy Cost of Gasoline
0/5 points (graded)
1
1
Schlumberger-Private
What’s the cost of gasoline in the US, in $/GJ? Use World Bank or EIA data for US retail
or pump price for the year 2017. Keep in mind that prices can easily be 2x as high in
other countries.
$/GJ? incorrect
19
\(\)
Explanation
Gasoline costs about $2.528/gallon, and provides 35 GJ/m3
. The resulting price is
$19/GJ
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Energy Cost of Vegetable Oil
0/5 points (graded)
What’s the cost of store-bought vegetable oil, in $/GJ? An average retail price for the
US for this isn’t easy to find, so you can use the lowest price Daniel could find, $1.6/liter.
You can find lots of resources online for the energy density of vegetable oil (notice how
similar it is to gasoline).
$/GJ? incorrect
46
\(\)
Explanation
Many online sources are around 8.4 kcal/mL, or .035GJ/liter, the same as gasoline.
$1.6/liter / .035 GJ/liter = $46/GJ
Note that vegetable oil can be much cheaper on the bulk market. If you're willing to
purchase it by the ton, with a minimum order of 100 tons, you can get it for around $200
per ton, which is about $0.184 per liter. We're not sure where you'd want to store
108,600 liters of sunflower oil.
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Energy Cost of Bananas
1
1
Schlumberger-Private
0/5 points (graded)
What’s the cost of bananas in $/GJ? Use a US average retail price of bananas (you can
find this from many sources, including the Bureau of Labor and Statistics, and the UN
FAO, or if you’ve shopped in the US you could probably take a good guess since this
problem has wide tolerance). You can find lots of resources for the energy density of
bananas; use an estimate for medium-sized bananas that includes the skin of the
banana (which is part of the purchase price; medium-sized with skin is around 160-200
grams).
$/GJ? incorrect
520
\(\)
Explanation
Most sites seem to indicate ~2400 kJ/kg for medium sized bananas with skin. The US
BLS’s “Average Retail Food and Energy Prices” and FAO’s “Banana Market Review”
give prices around $1.25/kg.
$1.25/kg / 2400 kJ/kg = $520/GJ after conversion.
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Energy Cost of Electricity
0/5 points (graded)
What’s the cost of residential electricity in the US, in $/GJ? Use the US-average
residential price for 2017 from the EIA.
$/GJ? incorrect
35.8
\(\)
Explanation
The US average cost is $0.129/kWh, which is $35.8/GJ after conversion.
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Energy Cost of Batteries
1
1
Schlumberger-Private
0/5 points (graded)
How many times higher is the cost of AA batteries than residential electricity?
Use a price of $.25/battery (reflecting a bulk order online; retail prices in stores are
usually much higher). They have a voltage of 1.5V and around 1200 mAh when used in
low discharge applications, for around 1.8Wh of energy total.
about the same
10x higher
100x higher incorrect
1000x higher correct
stimating Carbon Reduction
These problems will help you estimate the carbon savings (in CO2e) of different
measures you might take to reduce your impact. Notice how the results compare to
many popular "ways to shrink your carbon footprint" lists, which often include things like
unplugging electronics and printing double-sided, and detailed breakdowns of current
carbon footprints, which usually emphasize the dominance of transportation, diet, and
home heating and cooling for most people. The answers are all multiple-choice-style for
expediency and to help you compare orders of magnitude, but please avoid guessing.
We recommend that you carry out all of the calculations fully to get a numerical value
before choosing an answer.
We purposefully avoid some important things you could do because estimating them
accurately is beyond the scope of this class. Examples include changes to building
envelope or insulation, or setting an automatic thermostat. We included a mix of things,
from simple behavioral changes to moderate technology upgrades to showerheads or
furnaces to major changes like moving into or building a smaller house. We also give
fairly specific scenarios for the problems below. These are usually close to US
averages, but please feel free to try this exercise on your own with data from your life.
That will help you see what major opportunities you have for impact reduction.
Commuting
0/5 points (graded)
How much CO2 can be saved every year by reducing a car commute by half (roughly
equivalent to carpooling with one other person)? Assume the average US commute is
30 km round trip, with 250 commutes per year, in 8 L/100km vehicles, with 3.2 kg
CO2e/L of fuel (lifecycle intensity of fuel).
~1-3 kg CO2e/yr
Schlumberger-Private
~10-30 kg CO2e/yr
~100-300 kg CO2e/yr incorrect
~1000-3000 kg CO2e/yr correct
Explanation
This problem is primarily one of unit conversion:
\[(30-15) \ km/day \cdot 250 \ days/year \cdot 8L/100km \cdot 3.2 \ kgCO_2e/L = 960 \
kgCO_2yr \]
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Shower energy use
1.6666666666666667/5 points (graded)
This is a multi-part problem. You have only two submissions. Enter all responses
before hitting "Check".
How much CO2 can be saved every year by installing a low-flow showerhead? Assume
the shower is used for 8 minutes of warm showering per day with an 11 L/min
showerhead, using 2.8 kWh of electricity (mostly for water heating), and the new
showerhead will use only 5.5 L/min for 1.4 kWh of electricity use per day.
~1-3 kg CO2e/yrincorrect
~10-30 kg CO2e/yr
~100-300 kg CO2e/yr correct
~1000-3000 kg CO2e/yr
How much CO2 can be saved every year by reducing shower length from 8 minutes to 5
minutes? Assume the shower has an 11 L/min showerhead, using 2.8 kWh of electricity
for 8 minute showers.
~1-3 kg CO2e/yrincorrect
~10-30 kg CO2e/yr
~100-300 kg CO2e/yr correct
~1000-3000 kg CO2e/yr
Schlumberger-Private
Note that these two measures (shorter showers and low flow showerheads) interact - if
you do one, doing the other will have less of an impact than it would have on its own. If
you already installed the low flow showerhead, how would the savings from reducing
shower length be reduced from the number you calculated for the problem above?
The shower-length-reduction savings would be 1/4 as much if the low flow
showerhead had already been installed
The shower-length-reduction savings would be 1/2 as much if the low flow
showerhead had already been installed correct
The shower-length-reduction savings would be the same
Explanation
For the low-flow showerhead:
\[ 1.4 \ kWh \cdot 365 \ days/yr \cdot 0.5 \ kgCO_2e/kWh = 256 \ kgCO_2e/yr \]
For shorter showers:
\[ \frac{3}{8} \cdot 2.8 \ kWh/day \cdot 365 \ days/yr \cdot 0.5 \ kgCO_2e/kWh = 208 \
kgCO_2e/kWh \]
Combining the two means that the shower-length-reduction savings would be 1/2 as
much.
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Diet
0/5 points (graded)
This is a multi-part problem. You have only two submissions. Enter all responses
before hitting "Check".
How much CO2 can be saved every year by reducing an individual's meat consumption?
Assume the average diet yields 10 kg CO2e/day, a vegetarian diet yields 7 kg
CO2e/day, and a vegan diet yields 5 kg CO2e/day. (Estimates of the carbon footprint of
diets are quite uncertain; see Appendix A of the "Biking vs Driving" blog post Daniel and
David wrote for a discussion of some references and methodological difficulties).
What's the yearly CO2 savings for an individual switching from an average diet to a
vegetarian diet?
~1-3 kg CO2e/yr
~10-30 kg CO2e/yr incorrect
~100-300 kg CO2e/yr
Schlumberger-Private
~1000-3000 kg CO2e/yr correct
What's the yearly CO2 savings for an individual switching from an average diet to a
vegan diet?
~1-3 kg CO2e/yr incorrect
~10-30 kg CO2e/yr
~100-300 kg CO2e/yr
~1000-3000 kg CO2e/yr correct
Explanation
Switching from omnivore to vegetarian is a 3-kg improvement per day:
\[ 3 kgCO_2e/day \cdot 365 \ days/year = 1100 \ kgCO_2e/yr \]
Switching from omnivore to vegan is a 5-kg improvement per day:
\[ 5 kgCO_2e/day \cdot 365 \ days/year = 1800 \ kgCO_2e/yr \]
By far biggest meat impact is from beef. One can get a good chunk of the average
omnivore-to-vegetarian benefit simply by avoiding beef and lamb.
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Lighting
0/5 points (graded)
How much CO2 can an average household save, per person each year, by upgrading all
of their lighting to LEDs? Assume that the average household has 3 people and
currently uses 1700 kWh for lighting per year, with 2/3 of their bulbs being
incandescents (15 lumens/W) and 1/3 of their bulbs being some mix of CFL's and LED's
(140 lumens/W). Assume that they consume the same amount of light (in lumens)
before and after the uprade.
~1-3 kg CO2e/yr incorrect
~10-30 kg CO2e/yr
~100-300 kg CO2e/yr correct
~1000-3000 kg CO2e/yr
Explanation
The starting average value in lumens per watt is \( \frac{2}{3} 15 + \frac{1}{3} 140 = 57 \
lm/W\). The average after replacement will be 140 lumens/watt. This will result in a
savings of:
Schlumberger-Private
\[ \frac{83}{140} \cdot 1700 \ kWh/yr \cdot 0.5 \ kgCO_2e/kWh \div 3 \ people = 168
kgCO_2/yr \]
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Printing
0/5 points (graded)
How much can an individual save by printing double sided? Assume that their paper
weighs 4.5 grams per page, takes 10 kWh/kg to make and deliver to them with a carbon
intensity of ~.4 kg CO2e/kWh (to account for the mix of electricity and fossil fuels used),
and that they would otherwise print 3000 single sided pages. Assume that the only
benefit of double sided printing is a reduction in paper use.
~1-3 kg CO2e/yr incorrect
~10-30 kg CO2e/yr correct
~100-300 kg CO2e/yr
~1000-3000 kg CO2e/yr
Explanation
This problem is primarily one of unit conversion:
\[ 4.5 \ g/page \cdot 1500 \ pages/yr \cdot 10 \ kWh/kg \cdot 0.4 \ kg CO_2e/kg = 27 \ kg
CO_2e/yr \]
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Cell Phone Charger
5/5 points (graded)
How much CO2 can an individual save each year by unplugging their cellphone charger
when it's not in use? Assume that it consumes at most 1W when plugged in but not in
use, and that it's only used for 4 hours each day.
~1-3 kg CO2e/yr correct
~10-30 kg CO2e/yr
~100-300 kg CO2e/yr
Schlumberger-Private
~1000-3000 kg CO2e/yr
Explanation
This problem is primarily one of unit conversion. Typical wall electricity causes about 0.5
kg of CO2 emissions per kWh.
\[ 1 W \cdot 20 \ hrs/day \cdot 365 \ days/yr \cdot 0.5 \ kg CO_2e/kWh = 3.6 \ kg
CO_2e/yr \]
You can read more about the low impact of idle chargers in David MacKay's
excellent Sustainable Energy here, and about the more considerable impact of other
idle electronics in a different part of his book here.
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Air travel
0/5 points (graded)
How much CO2 can an individual save each year by flying 10000 km less? (This is
roughly the round trip distance of a flight across the US, or from the eastern US to
western Europe.) Assume the flight takes 4.5L/100-passenger-kilometers and that jet
fuel provides 35 MJ/liter and causes 90 kg CO2e of emissions per GJ.
~1-3 kg CO2e/yr incorrect
~10-30 kg CO2e/yr
~100-300 kg CO2e/yr
~1000-3000 kg CO2e/yr correct
Explanation
This problem is primarily one of unit conversion:
\[ 1 \ flight \cdot 4.5 L/100 km \cdot 0.035 \ GJ/liter \cdot 90 \ kgCO_2e/GJ = 1400 \ kg
CO_2e/yr \]
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Furnace
0/5 points (graded)
How much CO2 can a household save, per person each year, by upgrading from an 80%
efficient gas furnace to a 95% efficient gas furnace? Assume that the household has 3
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people and consumes 70 GJ of heating each year (not including the losses due to
inefficiency).
~1-3 kg CO2e/yr incorrect
~10-30 kg CO2e/yr
~100-300 kg CO2e/yr correct
~1000-3000 kg CO2e/yr
Explanation
We need to look at the difference between the enegry consumed in each furnace, and
find the emissions saved from that difference:
\[ \left( \frac{70 \ GJ}{0.8} - \frac{70 \ GJ}{0.95} \right) \cdot 65 \ kg CO_2e/GJ \div 3 \
people = 300 \ kg CO_2e/yr \]
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Home size
0/5 points (graded)
How much CO2 can a household of 3 save, per person each year, by reducing the size
of their home by 50% (roughly the difference between US homes in the 1950's and
today)? Assume that they currently use 50 GJ of electricity and 50 GJ of natural gas per
year, and that energy use is linear in home size with a slope of approximately 1/2 (so a
20% reduction in home size leads to 10% reduction in energy use, etc; for more on this
relationship see US Green Building Council). Only count the savings from electricity and
natural gas (though note that the embodied energy in homes can be substantial, making
the savings larger than you'll calculate here for construction of new homes of different
sizes).
~1-3 kg CO2e/yr incorrect
~10-30 kg CO2e/yr
~100-300 kg CO2e/yr
~1000-3000 kg CO2e/yr correct
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Peer grade, self grade
lectric Grid Efficiency
1/1 point (graded)
What is the average efficiency of electric grids in developed countries? That is, what
percentage of the electrical power generated at power plants actually makes it to end
users in countries like Australia, the UK, and the US?
% correct
90
Exact answer: 94%
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Coal Power Efficiency
1/1 point (graded)
What is the efficiency of a typical coal-fired power plant? That is, what percentage of the
thermal energy from burning the coal is successfully turned into electricity?
% correct
50
Around 35%
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90
50
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SPENDING ON CLIMATE CHANGE
In your opinion, about how much of total global GDP should be spent on managing
climate change? This is an opinion question with no right or wrong answer
RESULTS
1%
100%
0.1%
0%
3%
0%
10%
0%
30%
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0%
Results gathered from 2 respondents.
FEEDBACK
There is no right answer here, but keep in mind how serious high responses (over 10%)
are. The US' notoriously high military expenditure is only 3.5% of its GDP today. Even at
the peak of World War II, when many common goods were rationed, people were
conscripted into the military, and many civilian factories were converted to make
equipment for war, the US only spent 1/3 of its GDP on the military.
Mortality Rates
3/3 points (graded)
This problem has three parts. Answer all three before clicking the "Check" button.
How many premature deaths are caused by energy-related water pollution each year?
Almost zero correct
Thousands
Millions
Hundreds of millions
How many premature deaths are caused by energy-related air pollution each year?
Almost zero
Thousands
Millions correct
Hundreds of millions
How many premature deaths are currently caused by climate change each year?
Almost zero correct
Thousands
Millions
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Hundreds of millions
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Composition of Global Energy Supply
8/8 points (graded)
Estimate the fraction of global primary energy supplied by the following sources. Use
rough numbers and don’t worry about ensuring that they sum to exactly 100%.
This is a multi-part question. Make sure you answer all the parts before clicking
"Check".
Biomass % correct
10
Coal % correct
20
Hydropower % correct
2
Natural Gas % correct
20
Nuclear Power % correct
4
Oil % correct
10
20
2
20
4
40
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40
Solar % correct
0.05
Wind % correct
0.05
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Energy Prices
4/4 points (graded)
Please compare the prices of each of the below to crude oil on an energy basis. Select
the closest answer. For example, if coal cost 8 times as much as crude oil for the same
amount of energy, you would answer "Much more." If electricity cost 10% less than oil,
you would select "Less." There is some regional variation in these prices, so try to
imagine world average prices if you can.
This is a multi-part question. Make sure you answer all the parts before clicking
"Check".
Natural Gas costs _________ than crude oil for the same amount of energy
correct
Coal costs _________ than crude oil
correct
0.05
0.05
Much less (less than 1/3 the cost of oil)
Much less (less than 1/3 the cost of oil)
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Electricity for a large industrial consumer costs _________ than oil
correct
Electricity for a home consumer costs _________ than oil
correct
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Sulfur and Carbon
2/2 points (graded)
This problem has two parts. Answer both before clicking the "Check" button.
Suppose humanity continued to emit air pollutants and CO2 following “business-asusual”, and then suddenly in 2050 cut emissions of both to 0.
Approximately how long would it take for sulfate-driven mortality from particulate matter to fall by
50%?
a week correct
a year
hundreds of years
thousands of years
Approximately how long would it take for global temperatures to drop halfway from their peak to
pre-industrial average?
a week
More
Much more (more than 2x the cost of oil)
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a year
hundreds of years
thousands of years correct
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Fossil Fuel Remaining
1/1 point (graded)
Compare humanity's current annual primary energy supply to estimates of the total
remaining fossil fuel resource (the "ultimately recoverable resource"). How much larger
is the total fossil fuel resource?
Around 10 times larger than annual primary energy supply
Around 500 times larger than annual primary energy supply
Around 1,000 times larger than the annual primary energy supply correct
Around 1,000,000 times larger than the annual primary energy supply
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