IGCSE Physics / Energy resources and electricity generation
Geothermal energy, solar heating and solar cells revision notes
Edexcel International GCSE Physics (4PH1), chapter 17: Energy resources and electricity generation, specification point 4.18P. Free lesson.
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Geothermal stations use heat from underground rocks to generate electricity. Solar heating panels warm water, while solar cells use light to produce an electric current.
How a geothermal power station works
Hot rocks underground have energy in their thermal store. Cold water is pumped down to the rocks, where it heats up and returns as steam. The steam turns a turbine, transferring energy to the turbine’s kinetic store. The turbine turns a generator, which transfers energy electrically. Drilling deep is very costly, so geothermal stations are practical only where hot rocks are near the surface, mainly in volcanic areas.
How solar heating panels differ from solar cells
Both use energy from the Sun, but they do different jobs. A solar heating panel absorbs infrared radiation. Water runs through pipes behind a black surface, which absorbs the radiation and heats the water. A solar cell absorbs light and transfers energy directly to an electric current. A solar heating panel provides hot water, not electricity. A solar cell provides electricity. Neither method uses a turbine or generator.
How electricity-generation methods fit into groups
Methods of generating electricity can be grouped by how they turn a turbine, or whether they use one at all. Steam turns a turbine: fuel or hot rocks boil water. This group includes coal, oil, gas, nuclear and geothermal. Moving air or water turns a turbine directly: there is no steam. This group includes wind, hydroelectric, tidal and wave. No turbine: solar cells transfer energy from light straight to a current. Solar heating panels are not a way of generating electricity, because they only heat water.
How light levels affect solar cells
Solar cells generate less electricity when less light reaches them. In winter in a cloudy country, the days are shorter and the Sun is lower, so less light reaches the cells. Less energy is transferred from light, which means less electricity is generated.