1. Topic 8: Energy, power and climate change

2. Topic 8 Overview 8.1 Energy degradation and power generation 8.2 World energy sources 8.3 Fossil fuel power production 8.4 Non-fossil fuel power production 8.5 Greenhouse effect 8.6 Global warming

3. Using thermal energy Second law of Thermodynamics It is impossible to take heat from a hot object and use it all to do work without losing some to the surroundings

4. Degraded energy Any process that involves energy transformations results is some energy being transferred to the surroundings. This is in the form of thermal energy and heats up the surroundings. This thermal energy can not be used to do useful work. This process is called ‘degradation’ of energy.

5. Sankey Diagrams These are diagrams of energy flow for systems. They show the energy transformations in a system. It is possible to identify where the energy has been degraded from the diagram.

6. Consider a simple electrical circuit: The energy could be as shown below

7. There are also energy transfers that are not useful to us. In the example above, the lamp also transfers energy to the surroundings by heating. If we include this energy transfer, the diagram looks like this:

8. Useful energy Degraded energy Sankey diagrams summarise all the energy transfers taking place in a process. The thicker the line or arrow, the greater the amount of energy involved. The Sankey diagram for the lamp (below) shows that it transfers most of the energy by heating, rather than by light. Notice that the total amount of energy transferred to the surroundings is the same as the amount of electrical energy. Energy has been conserved. Energy is always conserved, it is never "lost", although some energy transfers are useful and some are not.

9. Sankey diagram for solar radiation

10. Sankey diagram of a dryer section

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

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

13. In a nuclear power station Fission of uranium in a nuclear reactor heats up carbon dioxide gas. This hot gas converts water into high pressure steam in a heat exchanger.

14. Turbines and Generators The high pressured steam turns a high- pressure turbine. The turbine then turns a generator.

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