Energy Sources

Section: Motion, Forces & Energy | Syllabus: Cambridge IGCSE Physics (0625)

Where Our Energy Resources Come From

nearly all of our energy resources ultimately come from radiation released by the Sun, either directly (e.g. solar cells, solar panels) or indirectly (e.g. fossil fuels, biofuels, wind, waves)
three energy resources do not come from the Sun:
- geothermal energy - from the radioactive decay of materials inside the Earth
- nuclear fuel - energy stored in the nucleus of atoms
- tidal energy - from the gravitational pull of the Moon and Sun on the oceans

Extended Only

the Sun releases its energy by nuclear fusion, in which small nuclei (mainly hydrogen) join together to form larger nuclei, releasing huge amounts of energy
research is currently being carried out into whether nuclear fusion could be used to generate large-scale electrical power on Earth

fossil fuels (coal, oil and natural gas) store chemical energy formed from the remains of dead plants and animals over millions of years
biofuels (e.g. ethanol, biodiesel, wood) store chemical energy from recently living plants or animals
both release their stored chemical energy by combustion (burning)
in a power station: burning the fuel in a boiler heats water to produce steam; the steam turns a turbine; the turbine drives a generator, producing electricity

Chemical energy in a fuel is transferred to electrical energy via a boiler, turbine and generator

advantages:
- can generate large amounts of energy on demand, and are easy to store and transport
- biofuel crops can be regrown, so biofuels are renewable
disadvantages:
- fossil fuels are non-renewable - they are used up far faster than they can form
- burning fuels releases carbon dioxide (CO₂), which contributes to global warming
- growing biofuel crops uses land that could otherwise be used to grow food

hydroelectric power: water stored at height behind a dam flows down through pipes, transferring its gravitational potential energy to kinetic energy, which turns a turbine connected to a generator
tidal power: a barrage built across a river estuary uses the rise and fall of tides, caused by the gravitational pull of the Moon and Sun, to drive turbines
wave power: the up-and-down motion of ocean surface waves drives turbines to generate electricity

Water stored behind a dam transfers gravitational potential energy to electrical energy

advantage: renewable, and produces no greenhouse gases once built
disadvantages:
- hydroelectric dams need a suitable river valley and a large area of land, which can flood habitats and displace communities
- tidal and wave power stations are limited to particular coastal locations and can disrupt marine ecosystems

geothermal energy comes from heat produced by the radioactive decay of materials deep inside the Earth
cold water is pumped down into hot underground rocks, usually in volcanically active regions; the steam produced rises back up and drives a turbine connected to a generator
geothermal energy does not depend on the Sun - it comes from radioactive decay inside the Earth

Geothermal power stations use heat from radioactive decay deep inside the Earth

advantage: available at any time, day or night, and does not depend on the weather
disadvantages: only economical in regions with volcanic or tectonic activity, and initial set-up costs are high

nuclear fuels, such as uranium-235, store energy in the nucleus of their atoms
in a nuclear power station, nuclear fission - the splitting of large nuclei into smaller ones - releases large amounts of heat energy
this heat boils water to produce steam, which turns a turbine connected to a generator, producing electricity

Nuclear fission in the reactor core produces the heat used to generate electricity

advantage: produces very large amounts of energy from a small amount of fuel, without releasing CO₂
disadvantages: produces radioactive waste that is hazardous and difficult to dispose of safely, and accidents can cause serious environmental contamination

solar cells use light from the Sun to generate electrical power directly
solar panels absorb infrared and other electromagnetic waves from the Sun to heat water directly, without generating electricity first

Solar cells generate electricity directly; solar panels use the Sun's radiation to heat water

advantage: renewable, produces no greenhouse gases while operating, and needs no fuel
disadvantage: intermittent - only generates useful amounts of energy during daylight, and output depends on the weather and location

wind is caused by the Sun heating the Earth's surface unevenly, creating differences in air pressure that make air move
wind turbines use the kinetic energy of moving air to turn blades connected directly to a generator, producing electricity without needing a boiler

Wind turbines transfer the kinetic energy of moving air directly into electrical energy

advantage: renewable, and produces no greenhouse gases while operating
disadvantages: unreliable, since it only generates electricity when the wind blows, and wind farms take up large areas of land or sea

each energy resource can be compared in terms of its renewability, availability, reliability, scale and environmental impact:

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