Transcript Energy Sources Overview

Energy Sources: Overview
What is Energy?
• Definition
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“The capacity to do work.” What is work?
“Movement that occurs against a restraining force.”
Work = force x distance
Many types/forms of energy
• Heat, light, sound, electrical, kinetic, etc
– Heat energy
• Due to random movement of atoms/molecules
• Heat flow between two bodies in thermal contact is determined by their
relative temperature. Temperature is measure of “average” heat content.
• Units
– SI unit: joule, J.
– Older unit: calorie, cal. 1 cal = 4.187 J.
• Food calories are really kilocalories
• The Value of Energy
– We do not value energy, just the services it provides (heat,
transportation, light, movement, etc)
Uses of Energy
• Energy Sectors
– Utilities
• Power plants (generation of electricity)
• Electricity is distributed and used in homes and businesses
– Heat, light, power to appliances, etc
– Transportation
• Travel powered by combustion engines
– Agriculture
• Tractors and other labor-saving devices
– Industrial
• Manufacture of materials
• Energy to provide other goods and services required by society
– Domestic
• Home heating
• Backup generators
Comparison of Energy Sources
• What Criteria to Use?
– Cost
• Internal vs external costs
– Resources
• Nonrenewable
• Renewable
• Exhaustible
– Impact on environment/health
– Versatility
• Variety of potential uses
– Energy content
• How measured?
– Per unit mass
– Per unit volume
Environmental Impact
• In what ways does our energy system impact our
environment? List as many as you can.
– Recovery & Refinement
• Mining
• Dam construction
• Waste generation
– Transport & Storage
• Spills, leaks
– Energy Production
• Air pollution
• Thermal pollution
• Waste generation
– Waste Disposal
• Spent fuel (esp nuclear)
Energy Sources
• What are our main sources of energy?
– Fossil fuels
• Oil, natural gas, coal
• Nonrenewable
• Environmental impacts?
– Nuclear fission
• Sources: uranium, plutonium
• Nonrenewable
• Environmental impacts?
– Hydroelectric power
• Ultimate sources: the sun (the hydrologic cycle)
• Renewable
• Environmental impacts?
– Other sources
• Solar heating, solar power, photovoltaics, geothermal, tidal,
biomass energy, wind energy
Energy Production by Source (2003)
Global
OECD Countries
OECD = Organization for Economic Cooperation and Development
• 30 member countries committed to democracy and a market economy
• all members are “first world” countries, including the US, the EC, Australia, and
Canada.
Energy Production by Region (2003)
Global
OECD Countries
US Energy Sources: Historical Trends
Transitions: wood  coal  petroleum
Current main sources in US:
•Petroleum
•Natural Gas
•Coal
•Nuclear fission
•Hydroelectric
US Energy Flow (2000)
Electricity Production
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Questions
– How is it produced?
– Why is electricity so useful?
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Usefulness of electricity
– Many electrical appliances
– Readily converted to other forms of energy with high efficiency
• Mechanical (electric motors), heat, light, etc
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Methods of Production
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Fossil fuel combustion
Nuclear power
Hydroelectric power
Other
• Geothermal power, solar power, wind turbines, fuel cells & batteries
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Storage
– Main problem (cannot be easily stored)
– What are the main methods of electricity storage?
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Chemical (storage batteries; hydrogen generation)
Capacitors
Mechanical batteries
Hydroelectric storage
Importance of Electric Motors
• Replaced steam-mechanical
engines (figure on the left)
–Inefficient
• Lots of energy lost to friction
• Less than 10% efficiency
• Entire assembly must be running
–Prone to failure
• Failure anywhere in transmission line
shut down the entire apparatus
–Inflexible
• Could not control power at individual
stations
–Dangerous
• Lots of moving parts
–Cumbersome
–Noisy
Electricity Production
Thermoelectric Power
• Types of Thermoelectric Power Plants
– How is the heat generated?
– Combustion of chemical energy sources
• Based on energy produced by a combustion reaction
• King Coal
– Nuclear power plants
• Based on nuclear fission
Thermoelectric Power Plants
Heat Engines
• Question
– What is a heat engine?
– A heat engine is any device designed to convert thermal energy
into mechanical energy
• The thermal energy can originate from a variety of other energy
sources (chemical energy, nuclear energy, etc)
• Conversion is usually due to the thermal expansion of a gas
– Examples
• Thermoelectric power plant
• Internal combustion engines in motor vehicles
• [Reverse heat engines: refrigerators (heat pumps).]
Internal Combustion Engines (ICEs)
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Four-stroke cycle engines
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Also called Otto cycle engines
ICEs: pistons moved by expansion
due to fuel combustion
Intake stroke
Compression stroke
Power stroke
Exhaust stroke
Efficiency of Heat Engines
• Source of the Energy
– Where does the energy come from in chemical/nuclear reactions?
• Energy Transformations
– What are the energy transformations that occur in a power plant?
• Efficiency of Transformations
– Can they be 100% efficient? Why or why not? If not, what limits the
ultimate efficiency?
• Thermodynamics
– First Law of Thermodynamics
• Energy can be neither created nor destroyed.
• “There is no such thing as a free lunch.”
– Second Law of Thermodynamics
• The total entropy (“randomness”) of the universe can never decrease.
• “You can’t break even.”
Maximum efficiency
of a heat engine is
Th  Tc
Th