CHEME 6660 Fall 2023
Analysis of Sustainable Energy Systems
Problem Set #1 Due: Wednesday, September 27, 2023
Note - List all assumptions and approximations made in arriving to your answers. You can use
the textbook as a source for conversion factors and other needed. You can also use data
available in the library or from other sources on the web to solve these problems but make sure
that you list the primary sources used in your solutions.
________________________________________________________________________
1. What is sustainable? In 25 words or less, describe how you would define sustainable
energy to a 6 grader (10 years old)
2. US Population growth is measurable
(a) The US population is currently about 330 million with an average annual rate of US
population growth for the last 40 years of about 1%. Some demographers predict that the US
population will reach a ½ billion people before the end of the century. Do you agree with their
prediction? If not, what would the average growth rate of the US population have to be to reach
½ billion by 2100. Describe what you think are major factors that currently control the growth of
America’s population.
(b) What if the US decided to limit its population to 400 million people by 2100, develop an
approach to decrease the annual rate of population growth from its current value of 1% to 0% by
2100. Recommend any US laws, policies and/or incentives that would need to be in place to
stabilize the US population at 400 million.

3. Sustainable food shopping - A farming family lives in a rural part of Georgia about 28 miles
from the nearest grocery store. They only go to the store once every week. Last week, when
they were about half way to the store they realize that they forgot to take their canvas reusable
grocery bags with them. They have two choices, 1) drive home and get the canvas bags. Or 2),
drive to the store and use the store’s plastic bags. The family wants to decide what the most
sustainable option is in terms of minimizing overall environmental impacts. There are 4 people
in the family, so about 10 bags are needed to hold all of their weekly groceries. They drive a
small hybrid SUV that gets about 40 miles/gallon of gasoline.
What do you advise them to do? Briefly describe how you arrived at your recommendation
based on measurable sustainability metrics such as energy use, environmental or ecosystem
impacts, and/or other resource requirement tradeoffs involved with both options.
Additional Data:
A polyethylene plastic grocery bag has a mass = 6.8 g
Polyethylene’s polymer composition is represented by [-CH2-]n where n = 10000 to
100000
The heat of combustion of polyethylene is similar to gasoline which is about 44 MJ/kg or
121.59 MJ/gal
A canvas grocery bag has an average mass of 200 g and is made of recycled materials
and has about the same volumetric capacity as a plastic grocery bag
4. US’s transformation to carbon-neutral electric cars:
Eventually in order for the US to become carbon neutral the entire American fleet of cars and
light trucks need to be converted to electric vehicles. You can assume that the average driving
mileage is the same for an electric vehicle as it is for gasoline cars and light trucks. But the
efficiency of an average electric vehicle is 40% better in terms of the electrical energy inputted
(including losses from generating the electricity) versus energy delivered for propulsion versus
conventional gasoline-fueled vehicles. What are the implications of this transformation? In
addition to being able to provide the renewably generated electricity needed, list a few other
major changes that will be necessary.
Data:
According to United States Department of Transportation Federal Highway Administration,
Americans now drive an average of 13,500 miles per year, consuming (on average) 1 gallon of
gasoline per 25 miles driven.
Gasoline = 34.2 MJ/L
1 Gallon = 3.8 Liters
Assume gasoline-fueled vehicle efficiency (fuel to wheels) = 25%(a)
Based on recent testing of state-of-the-art full-size EVs under normal driving conditions, nominal
efficiencies range from about 0.25 to 0.50 kW-hr of electrical energy per mile.
(a) If half of the existing American fleet of 250 million cars and light duty trucks were converted
to fully electric vehicles by 2050, estimate how much electrical energy would need to be
produced annually from US renewable resources to avoid further increases in carbon
(b) Let’s assume that the US has 125 million EVs operating by 2050. Since average daily
driving for most Americans is less than 50 miles, the EVs can be charged at night when electric
power demand is lower. Estimate the MWe capacity that would be needed to charge all 125
million vehicles during an 8 hr period each night when the cars are garaged.
(c) Rapid charging of electric vehicles is another need for a fully transformed electric vehicle
system. Technology exists today for fully charging an electric vehicle in about 20 min or less.
Consider an electric charging station of similar size to a large 5-bay gasoline station that has 20
operating gasoline pumps. As a possible worst case scenario, let’s assume that 20, full-sized
electric vehicles (EVs) each with an maximum operating range of 300 miles show up at the
station at the same time with essentially no charge left on their batteries. Estimate the electric
power capacity that will be needed to fully charge all 20 vehicles in 20 min
(d) Based on your estimate in parts (a), (b), and (c), list any concerns regarding additional
electrical infrastructure needs, costs, environmental impacts, or other issues (life cycle impacts)
that may influence that rate at which rapid charging stations will be deployed? Note that EVs
comprise only about 1% the vehicles currently in use in the US. In 2021, the electric power
generating capacity of the US was about 1 million MW.
5. There is no free lunch when it comes to storing compressed gas
(c) Do irreversible effects exist that would increase the work requirement
above your estimate in part (a) ? What performance metric could be used
to quantify the increase? How would the amount of heat transferred change?