L5 - Energy for Electricity 1

objectives

Energy for Electricity

• Industrial societies spend huge amounts of energy.
• Much of it is supplied by electricity which comes from generators in power stations.

Thermal Power Stations

• In most power stations, the generators are turned by turbines, blown round by high pressure steam.
• To produce the steam, water is heated in a boiler.
• The thermal energy comes from burning fuel (coal, oil, or natural gas) or from a nuclear reactor.
• Nuclear fuel does not burn.
• Its energy is released by nuclear reactions which split uranium atoms.
• The process is called nuclear fission.

Energy Spreading - Sankey Diagrams

• Thermal power stations waste more energy than they deliver.
• Most is lost as thermal energy in the cooling water and waste gases.
• For example, the efficiency of a typical coal-burning power station is only about 35% - in other words, only about 35% of the energy in its fuel is transformed into electrical energy.
• The diagram below shows what happens to the rest:

• Typical energy-flow chart for a thermal power station. A chart like this is called a Sankey diagram
• The thickness of each arrow represents the amount of energy.

• Engineers try to make power stations as efficient as possible.
• But once energy is in thermal form, it cannot all be used to drive the generators.
• Thermal energy is ; the energy of randomly moving particles (such as atoms and molecules).
• It has a natural tendency to spread out.
• As it spreads, it becomes less and less useful.
• For example, the concentrated energy in a hot flame could be used to make steam for a turbine. But if the same amount of thermal energy were spread through a huge tankful of water; it would only warm the water by a few degrees. This warm water could not be used as an energy source for a turbine.