'As night fell about us we tended our fallen cohorts by the strobing Gen'rator's glow' - From the Anthem of Thunder Ridge
A Temple produces one unit of Energy, as does each Generator. This Energy pulses from the source, in a fixed-range circle, and feeds any unit built within the circle. Left-clicking on a Temple or Generator will display the limits of its Energy influence.
To place units, you need energy, Each of the Furies produces a unique Energy, and specifically-aligned Battle units need their Fury's particular Energy, or else they can not be placed. For instance, to build a Thunder Cannon, (a Thunder Fury Battle Unit), two units of Thunder Energy and one unit of Sun Energy are required. That is to say, to build the Thunder Cannon it must be constructed in a place where three different Energy sources overlap.
Note: Although unit construction requires Energy, their operation does not. Once placed, Battle Units will fight, Transports will Transport and Generators will generate -until destroyed- regardless of whether there are Energy sources nearby.
Look in Book Seven for a complete listing of the Energy requirements for each Battle Unit.
Sun Energy is another way of saying 'any Energy,' and may be supplied by any Generator. Hence, Sun Units (which require Sun Energy) can feed of any type of Generator.