Major Sources of Energy

There are several sources of energy humans use today, some more frequently than others, mainly because of issues of cost and accessibility. Most renewable and non-polluting energy sources are not widely used as they are difficult to harness and process in the required quantities needed to meet the world's energy demands.

Oil

• Oil is by far the most popular form of energy and is used to fuel almost the entire transportation sector. It is found in most parts of the world, with the major producers being Russia and Saudi Arabia. It contributes considerably to air pollution and can cause devastating oil spills in offshore drilling accidents.

Coal

• Coal, which is mined underground, is the main energy source used for electricity in the U.S. It is also used to produce iron and steel. Although one of the most popular energy sources, it contributes significantly to air pollution. Coal reserves are estimated to be able to last for another 250 years at current rates of consumption.

Natural Gas

• Natural gas can be quite difficult to source but still accounts for around 24 percent of the world's energy. Natural gas is nonrenewable and expected to run out in about 50 years, although methane recovered from landfills is considered renewable.

Biomass

• Biomass includes material such as wood and recently decayed plant and animal waste; thus, it is renewable. Biomass was once a major energy source, as wood was burnt for heat and cooking. Biomass can be used to produce electricity when waste is burnt. Burning waste is less polluting than oil or coal, although the smell is unpleasant. Biomass can even produce products originally generated from nonrenewable energy, such as methane and gasoline. Biofuel crops can be fermented to produce ethanol.

Solar Energy

• The Sun is by far the most important energy source for the planet. It is directly involved in all energy sources currently utilized, and it will not be depleted for another 4 billion years. Despite this, direct solar energy is not used as much as other energy types, as the Sun's rays are difficult to capture. Solar panels have been developed to capture solar rays and transform them into energy, such as heat and electricity; however, this method is not widely popular as the Sun does not shine uniformly on all parts of the world because of clouds and the angle of the Earth's tilt.

Wind

• Wind is mainly used to generate electricity. Wind energy can be captured by turbines. Most wind turbines are found on land, but some are located offshore. Wind does not as yet contribute much to electricity supplies as wind blows inconsistently.