Energy Basics

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Energy Basics
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The situation

• A lot of the energy in the world comes from oil
  but oil is nonrenewable, eventually there will be
  a crisis

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First law of thermodynamics

• Energy can be neither created nor destroyed, it
  changes form
• Pushing car uphill chemical to potential
• Car rolling downhill potential to kinetic

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Pendulum

• At sides high potential/no kinetic
• At bottomhigh kinetic/no potential
• Requires recharging so..

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Second Law of Thermodynamics

• When you use energy, you lower its quality
• When you restart the car the burning of gas
  creates waste heat (low quality)

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Energy Efficiency

• First law efficiency
• Ratio of amount of energy delivered to the
  amountof energy supplied to meet that need

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Furnace example

• Keeps home at 18C if outside
• is 0
• Burning nat.gas or oil and delivers 1 unit heat
  per 1.5 units extracted by burning
• Is 67

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Second Law Efficiency

• Ratio of minimum available work needed to actual
  work used
• Takes into account the quality of energy

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Why second law efficiency is lower

• Oil or nat gas burn at a thousand degrees even
  though you only need 18

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Heat Engines

• First and second law efficiency nearly equal
• From table 15.1, the amount of waste heat is 2
  times the amount of energy delivered

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Energy Sources

• US has 5 of population but uses 25 of energy
• 90 of us energy is from fossil fuels

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Alternative to fossil fuels

• Geothermal
• Nuclear
• Hydropower
• Solar

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Energy Consumption by sector

• Residential and commercial 36
• Transportation 28
• Industrial 36

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Changes in Energy consumption

• Conservation - change in use patterns
• Efficiency improvements - design changes
• Cogeneration - use of waste heat

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Changes part 2

• 60 of us energy from
• Heating and cooling of homes and offices
• Water heating, steam production
• automobiles

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Building design

• Designing buildings to have lower energy needs
• Window overhangs, for example
• Mods such as double paned windows and weather
  stripping

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Industrial Energy

• See fig 15.4 - note leveling of energy use in
  1970s
• Industry has already made great improvements,
  including cogeneration

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Automobile Design

• Although the book claims a move towards smaller
  vehicles this has not been a recent trend
• A recent trend in efficiency is hybrid vehicles
  which burn gas but also run on a battery
  sometimes, resulting in high mileage

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Energy Policy

• Hard Path
• Status Quo, continued dependence on current,
  centralized energy supply depending on
  improvements in technology and discovery of new
  reserves

• Soft Path
• Renewable resources
• Diverse sources tailored to end use
• Flexible, lowtech, understandable to many
• Matched in geography and end use
• High Second law efficiency

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Integrated Energy Management

• Integrated means, integrated with the ecosystem
  - It generally implies low environmental impact,
  diverse sources, and decentralization.

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Integrated Energy Management (2)

• Reliable sources of Energy
• Low impact to local, regional, and global
  environments
• Help ensure long term enviro quality and fair
  distribution of resources

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Energy Units

• Joule energy 1 newton-meter
• Standard metric prefixes can be used, the US uses
  on the order of exajoules (1018) per year
• Another energy unit is BTU (british thermal unit)
  or quad

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Energy units (2)

• Power Energy/time - the rate of energy used.
• Watt is a unit of Power 1J/s
• Standard prefixes yield kW (kiloWatt, MegaWatt,
  GigaWatt)

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Energy Units (3)

• One commonly used hybird unit is kWh
• Since 1 W J/s, in multiply Wxh, the time unit
  cancels out and power (a rate) again becomes
  energy (an amount)
• Huh????see next slide

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Huh?

• Power (Watts) is a rate - like mi/h so its like
  asking, how fast are you driving? Not how far did
  you drive?
• Wh is like multiplying mi/h time h, which would
  give you just mi - how far did you go?

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