Energy Sources: Overview

What is Energy?• Definition

– “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• Questions

– How is it produced?– Why is electricity so useful?

• Usefulness of electricity– Many electrical appliances– Readily converted to other forms of energy with high efficiency

• Mechanical (electric motors), heat, light, etc

• Methods of Production– Fossil fuel combustion– Nuclear power– Hydroelectric power– Other

• Geothermal power, solar power, wind turbines, fuel cells & batteries

• Storage– Main problem (cannot be easily stored)– What are the main methods of electricity storage?

• 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)• Four-stroke cycle engines

– Also called Otto cycle engines

– ICEs: pistons moved by expansion due to fuel combustion

1. Intake stroke

2. Compression stroke

3. Power stroke

4. 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.”

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T T

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Maximum efficiencyof a heat engine is