Topic 8: Energy, power and climate change 8.2 World energy sources

Where does the energy of the world comes from?

World energy sources  Sources of energy include  Coal  Oil  Natural gas  Uranium  Solar  Wind  Wave  Tidal  Biofuel  Hydroelectric  Geothermal

Fossil Fuels  Coal, Oil and Natural Gas are fossil fuels.  These are formed from the fossilized remains of plants and tiny organisms buried 600 million years ago.  The Sun is the source of the energy for these fossil fuels.  The burning of fossil fuels releases CO 2 into the atmosphere.

Non-renewable energy sources  Fossil fuels are non-renewable energy sources.  Once the fuel has been used it is exhausted and cannot be replaced.

Renewable energy sources  These are sources of energy that cannot be exhausted.  Examples are:  Solar  Wind  Wave  Tidal  Biofuel  Hydroelectric  Geothermal The Nesjavellir Geothermal Power Plant in Iceland The front of the Pelamis machine bursting through a wave at the Agucadoura Wave Park

 Renewable energy is energy generated from natural resources—such as sunlight, wind, rain, tides and geothermal heat— which are renewable (naturally replenished).

Energy Density of a fuel  The energy density of a fuel is the amount of chemical energy stored per unit mass of a fuel.  Energy density= amount of energy mass of fuel mass of fuel The units for energy density are Jkg -1

The use of energy density  A fuel with a higher energy density will be able to provide more energy per unit mass.  The higher the energy density for a fuel, the more energy that can be transported for the same amount of mass of fuel.

Some approximate energy density values

Choice of fuel  It seems that Uranium-235 would make the best fuel per kilogram because the energy density is very high.  Is high energy density the only concern when choosing a fuel?

Choice of fuel  Nuclear power stations are very expensive to build and the cost for the production of electricity per kilowatt-hr is more expensive than using fossil fuels.  There are also political, social and environmental factors to consider.

 Depending on use and storage of the fuel, the energy density is an important consideration  Chemical composition and heating ability are other factors.  Chemical composition of coal is in terms of its rank, moisture content, volatile content (% of coal lost as vapours), ash and fixed carbon.

 Coal is divided into different ranks depending on the carbon and energy content per unit mass.  Different ranks of coal will produce different amounts of heat. Rank of coal PeatLignite Bituminous coal Anthracite Carbon60%70%80%95% Energy5,500,0006,500,0007,800,0008,600,000

 Because of the high content of volatile matter in peat and lignite, they cannot be transported for long distances because of safety risks. Usually, a power station is located where the mines are.  Coal in some countries have a high sulfur content and this greatly affects the air quality in some areas.  Australian bituminous coal and anthracite is low in sulfur and is a top export fuel in Asia.

Rate of world energy usage in terawatts (TW), terawatts

World use of energy sources

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Advantages and disadvantages of energy sources  When considering which energy sources to use the following factors have to be considered:  Cost of fuel  Availability of fuel  Transportation of fuel  Environmental concerns (waste)  Health concerns