Supplementary Material for Chapter 25
Go with the Flow: Analyzing Energy Use and
Efficiency in the U.S.
This chapter is published as:
Wagner JD. 2016. Go with the flow: Analyzing energy use and efficiency in the
U.S. In: Byrne L (ed) Learner-Centered Teaching Activities for Environmental and
Sustainability Studies. Springer, New York. DOI 10.1007/978-3-319-28543-6_25
James D. Wagner
Biology Program, Transylvania University, Lexington, Kentucky, USA
[email protected]
This file contains the following supplementary material:
 A: Instructor’s Guide
… beginning on p. 1
B: Student Worksheet (Blank and Answer Key) … beginning on p. 4
 C: 2013 Energy Flow Diagram
… beginning on p. 8
(https://flowcharts.llnl.gov/archive.html)
Page 0
Supplementary Material A: Instructor’s Guide
Background Information and Explanation of Calculations
Introduction to the charts
Lawrence Livermore National Laboratory (LLNL) has been analyzing energy use at the national level and
creating their distinctive flow charts since the 1950s (Austin, A.L., Winter 1973). Each major source of
energy is represented by a distinctive color (or pattern fill for the pre-1995 early black and white versions)
that initiates on the left side of the flowchart and splits and flows to the right side of the chart into pale
pink/yellow boxes that represent major sectors of the economy – electricity generation, residential1,
commercial, industrial, and transportation. The residential sector is private and institutional residences.
The commercial sector incorporates a wide array of institutions including service industries, malls, shops,
businesses not engaged in transportation or manufacturing, religious and non-profit institutions, health,
social and educational institutions and government buildings. In addition any electricity used to light
streets and highways are included in the commercial sector. The industrial sector is what you would
expect but it also includes mining, construction, agriculture, and the extraction of aquatic and timber
resources. Transportation sector includes both private and public vehicles that are used to transport
people and commodities. Interestingly, transportation also includes the movement of natural gas via
pipelines of which 97% of the natural gas used in transportation is consumed by compressors transporting
natural gas in pipelines.
Non-US alternatives to the data
The International Energy Agency has a database that utilizes the Sankey chart format to represent energy
use for all countries in the world. http://www.iea.org/sankey/. It is not as complete as the LLNL flowchart
but it may be adopted for this exercise.
The United Kingdom maintains a similar flow chart at this website
https://www.gov.uk/government/collections/energy-flow-charts
Australia produces a version of the energy flow flowchart which they archive at the bottom of this
website http://www.australianminesatlas.gov.au/mapping/downloads.html
The World Bank maintains broad statistics on energy use by country.
http://data.worldbank.org/indicator/EG.USE.COMM.FO.ZS
Sankey is the name of the chart type that is utilized by LLNL. An internet search for Sankey Energy Flow
<country> sometimes locates a version of the chart for non-US countries.
Conducting the calculations
This biggest challenge for the students in doing the calculations and filling out the worksheet is
determining the denominator in the calculation. At the top of the chart is the estimated total US energy
use given in quads or exojoules. Regardless of the units, this value (for the 2013 flowchart it is reported as
~97.4 Quads) becomes the denominator for Table 1 & 2 which explore the US reliance on fossil fuels and
green energy sources and the relative energy demands by sector. For example, using the 2013 flowchart
one determines the US reliance on Fossil Fuel energies by summing Petroleum (35.1), Coal (18) and
Natural Gas (26.6) to determine that that 81.8%2 of US energy used derived from fossil fuels. Table 3
1
Prior to 2003, the flow charts merged residential and commercial sectors into a single sector which may create a
minor challenge when comparing trends from the 1990s onward.
2
79.7 quads/97.4 quads
Page 1
focuses within a sector so the denominator in that table is based upon the number listed within the box for
the sector label (e.g., in the 2013 flowchart Residential is 11.4 quads).
Table 2: Relative Energy Demands by Sector
Filling out this table will allow the students to see what relative energy demands are required for electrical
generation, residential, commercial, and industrial demands and the amount of energy used in
transportation. These data will help the students recognize that 2/3 of the energy utilized by the US
economy is dedicated to making electricity and transporting people and commodities. This information
will be used by the students to assess the data calculated for Table 3 when discussing where efforts should
be made to increase efficiencies in energy use. Electrical generation is done at relatively smaller number
of power plants (6,997 in 2012) compared to the 254 million vehicles registered in the US in 2012
(Transportation 2013).
The other goal of this calculation is to show students that nearly all types of energy sources are utilized to
generate electricity. In addition, the conversion of the various forms of energy into electricity is a major
component of the US energy budget representing 39.2% of the total energy used (38.2 quads/97.4 quads).
Even though a wide array of energy sources are used to create the electrical energy, 65% of the electrical
generation came from the combustion of fossil fuels with the majority of that coming from the burning of
coal (16.5 quads/38.2 quads = 43.1%).
Rejected Energy
Rejected energy represents the energy lost through inefficiencies in the system. Based on the first and
second laws of thermodynamics, not all the energy used will be converted to work as some of it is also
converted (“lost”) to the production of heat. To determine how much energy is lost as rejected energy for
each sector, LLNL used conversion estimates based upon known efficiencies for each sector (Kaiper
2003). Electrical generation involves the production of steam to turn turbines and those systems are
known to be about 33% efficient in converting energy consumed into electrical energy. In the U.S. about
6% of the electricity produced is lost in transmission and distribution
(http://www.eia.gov/tools/faqs/faq.cfm?id=105&t=3).
Residential and commercial sectors were assumed to be around 75% efficient which is a function of space
heating/cooling being 60% efficient and other electrical uses 90% efficient. LLNL assumes for the
industrial sector an 80% efficiency rating3. LLNL assigned transportation efficiencies to 20% which
corresponds to an average efficiency of all vehicles based upon the efficiency of the internal combustion
engine. Obviously hybrid cars and diesel vehicles have higher efficiencies than 20% but their abundance
is not great enough to shift the average efficiency of the total 254 million vehicles registered in the US.
Table 3: Energy Inefficiencies across Sectors.
This table will allow the students to calculate values of energy inefficiency for each sector. To calculate
these values, take the value listed within the pale gray stream and divide that by the value reported within
the specific sector box. When students realize overall energy inefficiencies in residential sector is 34.9%
(2013) and transportation wastes 79% of the energy it uses, it facilitates an energetic discussion about
how we can improve each sector and the limitation to our improvements. It is obvious that transportation
needs major improvements in energy efficiency but one of the challenges is that our new cars now have
operational lifespans of 11.4 years (Transportation 2013) which means any changes to new technology in
vehicles would take years to cascade through the transportation sector.
3
This seems overly optimistic since the US Department of Energy has determined for manufacturing and mining
have efficiencies of only 68% (US Department of Energy 2004). The overall higher energy efficiency LLNL assigns
to manufacturing may be from construction and agricultural activities that are also within the industrial sector.
Page 2
Some alternative discussion prompts include:
 The process of fracking to extract liquid petroleum also results in large amounts of natural
gas to be burned at the extraction site instead of collecting it for use in a phenomenon known
as flaring. The light created from the amount of flaring that is currently occurring at major
fracking sites in the US is visible from space (Krulwich 2013). This exercise indicates that
natural gas is a very flexible energy source which could be used in a variety of sectors so
should we allow fracking companies to just burn it off instead of collecting and utilizing it as
an energy source?
 In arguments against our reliance on petroleum from fracking and oil sand extraction (e.g.,
Keystone pipeline controversy) it is often said we should invest more in solar and wind
technologies. Is that a logical argument given how fossil fuels and renewable energy sources
are used in the US economy?
i. How much does the U.S. economy rely on fossil fuels to operate?
ii. How do we define renewable and conventional energy sources and carbon and
carbon-less energy sources (EPA 2015)?
iii. Why is most of the renewable energy used in the generation of electricity (NREL
2015)?
Additional Reading
MacKay, David, JC. (2008) Sustainable Energy – without the hot air. UIT Cambridge, ISBN 978-09544529-3-3. Available free online from www.withouthotair.com. This is an excellent free book
for a primer on traditional and sustainable energy and its use in western industrialized societies. It
has a British orientation but it is easy to read and based on quantitative reasoning.
The National Academies (2015) http://needtoknow.nas.edu/energy/energy-use/ Data are based upon the
same chart used in this exercise but it goes into detail about specifically what is happening within
each of the sectors.
Ratner, M and Glover, C (2014). U.S. Energy: Overview and Key Statistics. A comprehensive report with
great flowcharts that show energy use by type, sector and gives trends for the past 60 years.
Published by the Congressional Research Service but is archived by the Federation of American
Scientists. http://fas.org/sgp/crs/misc/R40187.pdf
References
Austin, A.L., Winter SD (1973) U.S. Energy flow charts for 1950, 1960, 1970, 1980, 1985, and 1990.
Lawrence Livermore Laboratory, University of California
EPA (2015) Green Power Market. In: EPA website. http://www.epa.gov/greenpower/gpmarket/. Accessed
24 Feb 2015
Kaiper G V (2003) U . S . Energy Flow Trends — 2001.
Krulwich R (2013) A Mysterious Patch Of Light Shows Up In The North Dakota Dark. In: Krulwich
Wonders. http://www.npr.org/blogs/krulwich/2013/01/16/169511949/a-mysterious-patch-of-lightshows-up-in-the-north-dakota-dark.
NREL (2015) Learning about renewable energy. http://www.nrel.gov/learning/. Accessed 24 Feb 2015
Transportation, USD of (2013) Bureau of Transportation Statistics. In:
http://www.rita.dot.gov/bts/sites/rita.dot.gov.bts/files/publications/national_transportation_statistics/
html/table_01_11.html.
US Department of Energy (2004) Energy Use , Loss and Opportunities Analysis. In: Energy Use, Loss
Opportunies Anal. U.S. Manuf. Min.
http://www1.eere.energy.gov/manufacturing/intensiveprocesses/pdfs/energy_use_loss_opportunities
_analysis.pdf#page=23&zoom=auto,-266,617.
Page 3
Supplementary Material B: Student Worksheet (Blank)
TABLE 1. COMPARISON OF ENERGY SOURCES
Source of Energy
% of US total
Fossil Fuels (petroleum, coal, natural gas)
Carbon free sources (nuclear, solar, wind,
hydroelectric)
Renewable sources (solar, wind, biomass,
geothermal)
Table 2. Relative Energy Demands by Sector
Sector of US
economy
Table 3. Energy Inefficiencies by Sector
% of US total
Sector of US
economy
Electrical Generation
Electrical
Generation
(Electricity Generation
minus amount that becomes
electricity labeled on orange
line)
(Electricity Generation
minus amount that
becomes electricity
labeled on orange line)
Residential
Residential
Commercial
Commercial
Industrial
Industrial
Transportation
Transportation
Page 4
Energy
inefficiencies
(% energy lost)
Supplementary Material B: Student Worksheet (Answer Key)
TABLE 1. COMPARISON OF ENERGY SOURCES
Source of Energy
% of US total
Fossil Fuels (petroleum, coal, natural gas)
(26.6+18.0+35.1)
97.4
79.7
= 97.4 = 0.818 = 82%
Carbon free sources (nuclear, solar, wind,
hydroelectric)
(0.32+8.27+2.56+1.6)
97.4
Renewable sources (solar, wind, biomass,
geothermal)
(0.32+1.6+0.201+4.49)
97.4
12.7
= 97.4 = 0.130
= 13%
6.6
= 97.4 = 0.0678
= 6.8%
Table 2. Relative Energy Demands by Sector
Sector of US
economy
Electrical Generation
(Electricity Generation
minus amount that becomes
electricity labeled on orange
line)
% of US total
38.2−12.4
97.4
Sector of US
economy
Electrical
Generation
= 26%
Energy
inefficiencies
(% energy lost)
25.8
38.2
=67.5%
(Electricity Generation
minus amount that
becomes electricity
labeled on orange line)
Residential
11.4
97.4
= 12%
Residential
3.98
11.4
=34.9%
Commercial
8.59
97.4
= 9%
Commercial
3.01
8.59
=35%
Industrial
24.7
97.4
= 25%
Industrial
4.94
24.7
=20%
Transportation
27.0
97.4
=28%
Transportation
21.3
27.0
=79%
Page 5
This answer key is based upon the 2013 Flowchart ESM-C
(https://flowcharts.llnl.gov/content/energy/energy_archive/energy_flow_2013/2013USEnergy.pn
g).
Table 1. The denominator is the total energy used by the US which is typically listed in the title
at the top of the flowchart. It may be in units of exojoules or Quads but these units do not matter
since they will cancel out in the calculations. Totals will not add up to 100% since solar and wind
appear in both Carbon free and Renewable sources.
Table 2. The percentage of total energy used within each sector is listed in the boxes containing
the label for that sector. However electricity also appears in each of the consuming sectors of the
economy so it must be adjusted to avoid it being counted twice. Total energy used for electricity
generation (38.2 Quads) is reduced by the amount of energy that becomes electricity (12.4
quads) which is consumed by the other sectors. This allows for the totals to equal 100% but it
actually underrepresents the amount of the energy required by electrical generation.
Table 3. This table calculates how much of the energy consumed is lost through inefficiencies
and not used to do work. The lost energy is labeled as Rejected Energy (pale grey) in the
flowchart and is divided by the total energy used by that sector. These totals will not add up to
100% because they are independent of each other and only represent what happens with the
energy consumed within that sector.
Page 6
Some suggested answers to the Activities questions.
Activity 3.
i. How much does the U.S. economy rely on fossil fuels to operate?
1. Over 80% as of 2013
i. How do we define renewable and conventional energy sources and carbon and carbon-less
energy sources (EPA 2015)?
1. Renewable energy sources often are considered sources of energy that are replenished
naturally (solar, wind, tidal) or through resources that can be grown (e.g., corn, sugarcane,
hemp or switch grass).
2. Although technically no major source of energy production is carbon free because
resources are consumed to make the equipment (e.g., solar collecting panels of wind
turbines), bookkeeping of carbon consumption at time of energy production would allow
solar panels, wind turbines, tidal and hydroelectric generation to be carbonless. Nuclear
power requires the production of uranium pellets so it will always have a carbon footprint
during energy production.
ii. Why is most of the renewable energy used in the generation of electricity (NREL 2015)?
1. Electricity is the output in solar and wind energy production
2. Geothermal also makes electricity directly but more frequently it is used to condition
the air or water so to reduce the energy needs to heat or cool the air or water.
Activity 6
i. Which sectors of the US economy use the most and least energy?
1. Transportation (2013 values) was highest, followed by industrial, residential, with the
commercial sector using proportionally the least amount of energy.
2. Electricity production uses 39% of all the energy consumed but it is not its own specific
sector since electricity is then used by each of other four sectors.
Activity 7
1. Why is transportation so inefficient? How can we improve efficiency?
1. Modern gasoline internal combustion engines are at best 25%-30% efficient. Modern
diesels can reach 50% efficiency at best. Internal combustion engines produce waste
through heat and noise.
2. Why is electricity so inefficient in its production?
1. Burning of fossil fuels to boil water for steam to turn turbines is generally only 33%
efficient. Most of the energy is lost in the production of heat.
3. Residential sector wastes about 34% of the energy it requires. What aspects of a home
contribute to this inefficiency ?
1. 42% of the energy consumed in a home is for heating, 6% for cooling. Insulating homes
can reduce the energy demands to condition the air. Water heating uses 18% of the
energy of the home. Switching to on demand heating systems (tankless water heaters) or
insulating water heater can reduce the demands. (http://energy.gov/publicservices/homes)
2. Lighting is 5% and refrigeration is 5%, the remaining 24% is tv, computer, charging
phones, small appliances, etc.
Page 7
Supplementary Material C: Energy flow diagram
Page 8