Topic 8: Energy, power Topic 8: Energy, power and climate change and climate change

Topic 8 OverviewTopic 8 Overview

8.1 Energy degradation and power generation 8.1 Energy degradation and power generation

8.2 World energy sources 8.2 World energy sources

8.3 Fossil fuel power production 8.3 Fossil fuel power production

8.4 Non-fossil fuel power production 8.4 Non-fossil fuel power production

8.5 Greenhouse effect 8.5 Greenhouse effect

8.6 Global warming8.6 Global warming

Using thermal energyUsing thermal energy

Second law of ThermodynamicsSecond law of Thermodynamics

It is impossible to take heat from a hot It is impossible to take heat from a hot object and use it all to do work without object and use it all to do work without losing some to the surroundingslosing some to the surroundings

Degraded energyDegraded energy

Any process that involves energy Any process that involves energy transformations results is some energy being transformations results is some energy being transferred to the surroundings.transferred to the surroundings.

This is in the form of thermal energy and heats This is in the form of thermal energy and heats up the surroundings.up the surroundings.

This thermal energy can not be used to do This thermal energy can not be used to do useful work.useful work.

This process is called This process is called ‘degradation’ of energy.‘degradation’ of energy.

Sankey DiagramsSankey Diagrams

These are diagrams of energy flow for These are diagrams of energy flow for systems.systems.

They show the energy transformations in a They show the energy transformations in a system.system.

It is possible to identify where the energy It is possible to identify where the energy has been degraded from the diagram.has been degraded from the diagram.

Consider a simple electrical circuit:Consider a simple electrical circuit:

The energy could be The energy could be as shown belowas shown below

There are also energy transfers that are not There are also energy transfers that are not useful to us. useful to us.

In the example above, the lamp also transfers In the example above, the lamp also transfers energy to the surroundings by heating. If we energy to the surroundings by heating. If we include this energy transfer, the diagram looks include this energy transfer, the diagram looks like this: like this:

Useful energy

Degraded energy

Sankey diagrams summarise all the energy transfers Sankey diagrams summarise all the energy transfers taking place in a process. taking place in a process. The thicker the line or arrow, the greater the amount of The thicker the line or arrow, the greater the amount of energy involved. energy involved. The Sankey diagram for the lamp (below) shows that it The Sankey diagram for the lamp (below) shows that it transfers most of the energy by heating, rather than by transfers most of the energy by heating, rather than by light. light.

Notice that the total amount of Notice that the total amount of energy transferred to the energy transferred to the surroundings is the same as surroundings is the same as the amount of electrical the amount of electrical energy. energy. Energy has been conserved. Energy has been conserved. Energy is always conserved, Energy is always conserved, it is never "lost", although it is never "lost", although some energy transfers are some energy transfers are useful and some are not. useful and some are not.

Sankey diagram for solar radiationSankey diagram for solar radiation

Sankey diagram of a dryer sectionSankey diagram of a dryer section

Production of electrical powerProduction of electrical power

The production of electrical power occurs The production of electrical power occurs in a series of stages.in a series of stages.

Producing steamProducing steam

In a fossil fuel power In a fossil fuel power stationstationA fossil fuel is burnt in a A fossil fuel is burnt in a furnace, producing hot furnace, producing hot gases.gases.These hot gases These hot gases convert water into high convert water into high pressure steam in a pressure steam in a boiler.boiler.

In a nuclear power stationIn a nuclear power station

Fission of uranium in a nuclear reactor Fission of uranium in a nuclear reactor heats up carbon dioxide gas.heats up carbon dioxide gas.

This hot gas converts water into high This hot gas converts water into high pressure steam in a heat exchanger.pressure steam in a heat exchanger.

Turbines and GeneratorsTurbines and GeneratorsThe high pressured steam turns a high-The high pressured steam turns a high-pressure turbine.pressure turbine.

The turbine then turns a generator.The turbine then turns a generator.

The generator converts the kinetic energy The generator converts the kinetic energy into electrical energy using the principle of into electrical energy using the principle of electromagnetic induction (rotating coils in electromagnetic induction (rotating coils in a magnetic fieid)a magnetic fieid)