1.5.11Motion, Forces and Energy
Geothermal Energy — Cambridge IGCSE Co-ordinated Sciences 0654 - Physics Revision Notes & Topical Questions
5 min read 8 parts Lesson 34 of 36
Section 1 of 8Heat from inside the Earth
1
The interior of the Earth is very hot.
2
Some heat is left over from the formation of the planet and much is released by radioactive decay of elements such as uranium and thorium.
3
Hot rock lies close to the surface in volcanic regions such as Iceland, New Zealand and parts of Kenya.
4
Geothermal energy does not depend on the Sun.
5
It is considered renewable because the heat supply is vast and continually replaced.
Section 2 of 8How a geothermal power station works
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Water is pumped down a deep borehole into hot rocks.
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The rocks heat the water, which may turn to steam.
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The hot water or steam rises up a second pipe to the surface and turns a turbine connected to a generator.
4
The steam is cooled and condensed and the water is returned underground to be reheated.
Energy chain
- Energy chain thermal energy of the hot rocks, thermal energy of the steam, kinetic energy of the turbine, electrical energy.
Some sites have natural hot springs or steam that can be used directly.
Section 3 of 8Direct heating
Direct heating
Hot water from boreholes can be piped to homes, greenhouses and swimming pools, as in Iceland.
This is very efficient because the heat does not have to be converted to another form.
Section 4 of 8Advantages
Very reliable
- Very reliable heat is available day and night in all weather.
Little carbon dioxide is produced in operation and no fuel is burned.
Small land area compared with the output.
Low running costs once the plant is built.
Useful for both electricity and direct heating.
Section 5 of 8Disadvantages
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Only suitable where hot rocks are near enough to the surface, so sites are limited.
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Drilling deep boreholes is very expensive.
3
Gases such as hydrogen sulfide or carbon dioxide can be released, with a smell and some pollution.
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Local hot spots can cool if heat is taken faster than it flows back.
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Drilling and pumping water into rocks may cause small earthquakes.
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Conversion to electricity is only about 10% to 20% efficient at low-temperature sites.
Section 6 of 8More from the specification
More from the specification
Nuclear power stations
- Nuclear power stations fission reactions in nuclear reactors generate steam to drive electrical turbines without consuming fossil fuels.
Tidal and solar energy
- Tidal and solar energy tidal barrages harness predictable water flow, while solar panels convert light directly into electricity.
Thermal energy store
- Thermal energy store geothermal power taps into subterranean thermal energy stores heated by radioactive decay in the Earth.
Geothermal Power Generation
- Geothermal power stations tap thermal energy stored within hot subterranean rocks, heating water to produce steam that drives turbines and electrical generators.
Non-Solar Energy Resources
- While fossil fuels, wind,
- and hydroelectric energy originate from solar radiation, geothermal energy, nuclear fission,
- and tidal energy do not derive from the Sun.
Solar Cells vs Solar Thermal Panels
- Photovoltaic solar panels directly convert sunlight into electrical power,
- whereas solar thermal panels absorb radiant energy to heat domestic water stores.
Nuclear Fusion in the Sun
- Nuclear fusion reactions in the Sun fuse hydrogen nuclei into helium, acting as the primary energy source that drives Earth's weather, winds,
- and fossil fuel reserves.
Energy stored
- W = ½QV = ½CV²What the symbols mean: W or E = energy stored (J) · Q = charge (C) · V = p.d. (V) · C = capacitance (F)
Energy transferred
- W = V Q, in joules.What the symbols mean: E or W = energy transferred (J) · Q = charge (C) · V = potential difference (V) · I = current (A) · t = time (s)
Biofuel
- Fuel made from recently living plant or animal material.
Fossil fuel
- Fuel formed over millions of years from dead plants and animals.
Solar panel
- A device that uses sunlight to heat water.
Solar cell
- Device that converts light energy directly into electrical energy.
Global warming
- Rise in the average temperature of the Earth.
Hydroelectric power
- Electricity generated from water flowing down from a reservoir.
Renewable resource
- A resource that is replenished at the same rate as it is used.
Energy store
- Where energy is held, such as kinetic or chemical.
Fusion
- Joining of light nuclei into a heavier one.
Hydroelectric
- Electricity from water flowing down from a high reservoir.
Section 7 of 8Key terms
| Term | Meaning |
|---|---|
| Geothermal energy | Thermal energy from hot rocks inside the Earth. |
| Radioactive decay | Natural process in which unstable nuclei release energy. |
| Borehole | A deep narrow hole drilled into the ground. |
| Turbine | Machine turned by steam to drive a generator. |
| Direct heating | Using hot water from underground to warm buildings. |
Section 8 of 8Exam technique
1
Saying geothermal energy comes from the Sun — it comes from the Earth's interior.
2
Thinking geothermal can be used anywhere — the hot rocks must be near enough to reach.
3
Saying it releases no gases at all — some sites release hydrogen sulfide or carbon dioxide.
4
Forgetting that the water is pumped down and returned for reuse.
5
Confusing geothermal with solar heating of water.
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