Energy Sources: Overview

What is Energy? Definition Units The Value of Energy “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 Transportation Agriculture 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 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 Hydroelectric power Ultimate sources: the sun (the hydrologic cycle) Renewable 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 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