FUSION-REACTION ENERGY SOURCE' Fusion-reaction energy source is a type of energy production that involves the combination of two or more atomic nuclei to form a single, heavier nucleus. This process releases a large amount of energy, which can be used to generate electricity. The most common fusion-reaction energy source is nuclear fusion, which is the same process that powers the sun and other stars. SOL is an acronym for 'self-sustaining nuclear reaction, ' which is the goal of many fusion-reaction energy sources.