Coal is one of the largest sources of physical energy in the world. More than one billion tons of coal is converted into energy per year within the United States, and more than two billion tons per year in China. Coal, a fossil-fuel, is turned into electric energy when it is burned at very high temperatures to boil water for steam. The steam spins a turbine which in turn operates a spinning generator. The generator distributes electricity into the power grid.
Hydroelectric power, also known as hydropower, is the use of water for the creation of electric energy. This source is considered a cleaner form of physical energy than fossil fuels because the power plants that produce hydroelectric power do not contribute greenhouse gases. Hydroelectric power is also inexpensive to produce as opposed to energy sources that come from non-renewable elements like coal. Typically, the water used to generate hydroelectric power is stored in reservoirs at a high elevation, with flow controlled by a man-made dam. The water flows quickly through a turbine which spins a generator that produces the electric energy.
Wind converted into electric energy is a clean alternative to other energy sources such as nuclear power and fossil fuels. This source is environmentally friendly, as wind does not deplete supplies of any natural resources of the earth. A wind turbine is erected high to catch as much wind as possible. Wind turns a turbine, which is connected to magnetic generators to produce electricity. The electricity is then sent to the power grid.
Pros and Cons
Each of these physical energy sources have pros and cons. Coal is an efficient but not a particularly environmentally friendly source of energy. Hydroelectric energy is efficient and basically clean, yet it alters the natural systems of rivers and adversely affects animals and plant life. Wind power is clean, yet it is not the most efficient source of energy because the amount of wind cannot be controlled nor predicted. Choosing a source or a combination of sources of energy is often dependent on the environment of a given area.