Energy Technology research improves the efficiency of energy production and distribution systems, a key requirement for many advanced technologies and spacecraft. Each new level of Energy Technology unlocks the ability for other technologies to be researched, and allows the development of more sophisticated ships and defenses.
Researching higher levels of Energy Technology also increases the efficiency of Fusion Reactors. While not used by new players, Fusion Reactors eventually surpass Solar Plants in efficiency for the number of fields used. A single increase in Energy Technology increases the power output of all a player’s fusion reactors, on every planet.