Energy can be compared using several different metrics
Energy can be produced from a variety of different sources, both natural and man made. These sources can be compared scientifically, but also in terms of how they are used and the effects of this use.
Function
Some energy sources are more suited to some functions than others. For example, coal, when used as a feed in a coal-fired power plant, is a effective means of generating electricity. Crude oil, by contrast, is seldom used in power plants, but, when refined into gasoline, is an excellent fuel for internal combustion engines.
Effects
The use of different energy sources produces a number of different side effects, such as different types of pollution. The combustion of gasoline and coal, for example, produce a number of carcinogens and greenhouse gases. Energy derived from wind power, by contrast, produces almost no pollution. Some, however, consider wind turbines unsightly--another effect of the source.
Efficiency
Energy can also be compared on the basis of economic efficiency, with some sources capable of generating more energy for less money than other sources. For example, energy generated from the burning of coal remains significantly cheaper than energy derived from solar panels.
