An active area of energy research is in the realms of nuclear fusion. Fusion is the combination of two small atoms to form a new bigger atom along with the release of a large amount of energy. The most common reaction is between isotopes of hydrogen (deuterium and tritium) to form helium. At the present, fusion is only a theoretical source of energy, but one that if properly developed be a significant provider of electricity in the future.
The advantages of fusion include nearly unlimited fuel and a extremely high energy output with no radioactive heavy metal by-products, as are seen in the common nuclear fission reactors. Fusion is a very clean and very reliable. However, the high energy reactions involved in fusion are difficult to control and the prodution of energy by fusion would be much more expensive than other means such as nuclear fission and coal using current technologies.