1- Introduction: Energy Sources
Energy can be considered in two categories - primary and secondary.
Primary energy is energy in the form of natural resources, such as wood, coal, oil, natural gas, natural uranium, wind, hydro power, and sunlight.
Secondary energy is the more useable forms to which primary energy may be converted, such as electricity and petrol.
Primary energy can be renewable or non-renewable:
Renewable energy sources include solar, wind and wave energy, biomass (wood or crops such as sugar), geothermal energy and hydro power.
Non-renewable energy sources include the fossil fuels - coal, oil and natural gas, which together provide over 80% of our energy today, plus uranium.
In this century, the only energy resources available for economic large-scale electricity generation are likely to be gas, coal and nuclear.
Oil has generally become too expensive to use for electricity and it has the great advantage of being a portable fuel suitable for transport. Wherever possible it is conserved for special uses, such as transport and in the petrochemical industry.
Gas can be seen in the same way as oil, as being too valuable to be used for uses such as large-scale electricity generation. But after the oil price shocks of the 1970s, increased exploration efforts revealed huge deposits of natural gas in many parts of the world and today these are extensively used for power stations. The main virtue of gas however is that it can be reticulated safely and cheaply to domestic and industrial users and burned there to provide heat very efficiently. It is also a valuable chemical feedstock.
Coal is abundant and world production is about 3.5 billion tonnes per year, most of this being used for electricity. It dominates the scene, and produces 38% of all electricity worldwide, while uranium produces 16%.
Uranium is also abundant, and technologies exist which can extend its use 60-fold if demand requires it. World mine production is about 35,000 tonnes per year, but a lot of the market is being supplied from secondary sources such as stockpiles, including material from dismantled nuclear weapons. Practically all of it is used for electricity.
Table (13): Energy Conversion Typical Heat Values of Various Fuels