Coal, a fossil fuel, is the energy source for approximately half of all electricity produced in the United States. When coal is burned, chemical potential energy is transformed into thermal energy, light energy, and sound energy. Only the thermal energy is used for electricity production. Light and sound energy dissipate into the environment, immediately reducing efficiency. In addition, much of the thermal energy also dissipates into the environment. Some is conducted away by the metal that surrounds it or is lost through the smokestack, but most thermal energy loss occurs when hot water is cooled in cooling towers or dumped into a nearby lake or river. While energy is never created or destroyed, its transformation and transfer do not result in 100% usable energy. At a power plant, any energy that does not leave the plant as usable electricity is “waste energy.”
Efficiency is also reduced by using some of the generated electricity to operate the power plant. The power plant uses electricity for lighting, appliances, elevators, and office area air conditioning, just like any other factory or business. Electricity also powers conveyor belts, the coal crusher, pulverizer and blowers. It is also used to purify and pump water for the boiler. In each of these instances, electricity is used in the making of electricity. This further reduces the percentage of energy that reaches consumers.
Because of coal's relationship to carbon dioxide emissions and global warming, improving energy efficiency at coal burning power plants is a research focus in the United States. In short, as fuel efficiency increases, the quantity of coal burned to produce an equal unit of electricity decreases. When less coal is burned, less carbon dioxide is produced, which is a necessary step toward lowering carbon dioxide emissions.
Fuel efficiency is only one component of the energy debate. Other factors related to the use of coal include mining hazards and costs, pollution from byproducts of both mining and burning coal, the nonrenewable nature of coal as an energy source, and the economic impacts on both producers and consumers of coal-powered electricity when changes occur.