27-Energy Overview#
Learning Outcomes:
Review Energy Units and “Horse Sense”
Understand the different energy types
Understand quantities and fractions of energy used in US
Understand the growing energy demaands by 1/2 the worlds population in BRICS countries
Understand some of the challenges and opportunities in the energy sector
Show code cell source
# import needed packages
import numpy as np
import matplotlib.pyplot as plt
Units Review#
BTUs: British Thermal Units
Energy required to raise 1 pound of water by 1 degree Fahrenheit
Calories
Energy required to raise 1 gram of water by 1 degree Celsius
Joules
1 calorie = 4.184 Joules
Watts
Power or rate of energy use in Joules per second
A human can generate about 300 Watts of power on an exercise bike for a sustained time period
Kilowatt-hours
Energy used by a 1 kW device in 1 hour
Quad: 1 quadrillion BTUs
This is the amount of energy in 170 million barrels of oil
Example Unit Problems#
How many BTU’s to heat 1 L of water from 60°F to 212°F?
Show code cell content
Cp = 4186 # J/kgK, specific heat of water
#specific heat of water in BTU/lbmF
Cp_BTU = 1.0 # BTU/lbmR, specific heat of water
rho = 1000 # kg/m^3, density of water
vol = 1/1000 # m^3, volume of water (1 L)
mass = rho*vol*2.20462 # lbm, mass of water (1 L)
E = Cp_BTU*mass*(212-60)
print(f'Energy required to heat 1 L of water from 60F to 212F: {E:0.0f} BTU')
Energy required to heat 1 L of water from 60F to 212F: 335 BTU
How many BTUS’s to vaporize that same 1L of water at 212°F?
Show code cell content
#water heat of vaporization
Hvap = 970.3 # BTU/lbm, 2260 kJ/kg
E = Hvap*mass
print(f'Energy required to vaporize 1 L of water: {E:0.0f} BTU')
Energy required to vaporize 1 L of water: 2139 BTU
Energy Types#
Fossil
Coal
Oil
Natural Gas
Tar Sands
Nuclear
Solar
Photovoltaic
Concentrated Solar Power
Renewable
Wind
Hydro
Geothermal
Biomass
Ocean
US Energy by Source with Losses#
Source: https://flowcharts.llnl.gov/sites/flowcharts/files/2022-04/Energy_2021_United-States_0.png
Source: https://flowcharts.llnl.gov/sites/flowcharts/files/2023-10/US Energy 2022.png
How many cubic miles of oil are used in the US in a year?
About 1 cubic mile
There are significant losses in use of the energy. For example, a coal plant is only about 33% efficient in converting the energy in coal to electricity. A gasoline engine is only about 20% efficient in converting the energy in gasoline to motion. The rest is lost as heat.
Energy loss example#
The energy density of gasoline is about 45 MJ/kg. If a car gets 30 miles per gallon (at 60 miles per hour), how many MJ of energy are used to go 30 miles? What is the efficiency of the car?
How will you set this up?
Assumptions:
Force from drag is \(F_d = 1/2 \rho v^2 C_d A\), where \(\rho\) is air density, \(v\) is velocity, \(C_d\) is drag coefficient, and \(A\) is frontal area. The drag coefficient for a car is about 0.3, the frontal area is about 2 m^2, and the air density is about 1.2 kg/m^3.
The resistance from rolling friction, \(F_r = C_r m g\), where \(C_r\) is the coefficient of rolling friction, \(m\) is mass, and \(g\) is acceleration due to gravity. The coefficient of rolling friction is about 0.01 for cars and the mass of the car is about 1500 kg.
The energy of a moving car is \(E = 1/2 m v^2\).
The energy of a force acting over a distance is \(\int F dx\).
Show code cell content
vel = 60*5280/3600/3.281 # m/s, velocity of car
masscar = 1500 # kg, mass of car
Cr = 0.01 # rolling resistance coefficient
Cd = 0.3 # drag coefficient
gravity = 9.81 # m/s^2, gravity
Fr = masscar*gravity*Cr # N, rolling resistance force
rho_air = 1.2 # kg/m^3, density of air
Area = 2 # m^2, frontal area of car
Fd = 0.5*Cd*Area*rho_air*vel**2 #N, drag force
dis = 30*5280/3.281 # m, distance to travel
Work = (Fr + Fd)*dis + 1/2*masscar*vel**2# J, work done
print(f'Work done to move car 30 miles at 60 mph: {Work/1e6:0.0f} MJ')
# efficiency of car
rhogas = 700 # kg/m3, density of gasoline
volgas = 1/264.172 # m3, volume of gasoline
Egas = 45e6*rhogas*volgas # J, energy in gasoline
print(f'Energy in 1 gallon of gasoline: {Egas/1e6:0.0f} MJ')
print(f'Efficiency of car: {Work/Egas*100:0.1f}%')
Work done to move car 30 miles at 60 mph: 20 MJ
Energy in 1 gallon of gasoline: 119 MJ
Efficiency of car: 16.9%
BRICS#
The BRICS countries (Brazil, Russia, India, China, South Africa) are expected to use more energy as development continues.
Increasing Energy Use#
source: EIA.org, International Energy Outlook 2021
Energy per Person#
Energy Future#
Some Comments:
Coal is declining due to its challenges:
Mercury, SOx, NOx, CO2, and particulates
Natural Gas is increasing due to its lower emissions, abundance, and economics
Petroleum will face a slow decline but there is not yet a feasible replacement as a transportation fuel and as a raw material for chemical production
Transition to renewables will not/cannot happen on order of 10 years (maybe even 30) without societal upheaval
Nuclear is a viable option but has its own challenges
Energy storage is likely to grow in importance
Ultimately, we’ll need to use many forms of energy
Energy Growth Consequences#
Increasing energy use has consequences:
Increasing CO2 emissions
Air pollution
Water use
Land use
Resource use
Waste generation
etc.
D&C 104: 17 Says: “For the earth is full, and there is enough and to spare; yea, I prepared all things, and have given unto the children of men to be agents unto themselves.”
And the next verse says: “Therefore, if any man shall take of the abundance which I have made, and impart not his portion, according to the law of my gospel, unto the poor and needy, he shall, with the wicked, lift up his eyes in hell, being in torment.”
Energy Ethics#
Per the AICHE Code of Ethics (https://www.aiche.org/about/code-ethics), and the National Society of Professional Engineers (https://www.nspe.org/resources/ethics/code-ethics) engineers should “hold paramount the safety, health, and welfare of the public.”
How does that ethics code apply to helping developing nations get access to energy?