Positive energy is a resource used by both of the Celestial classes (the Sun Paladins and Anorithil). Many early talents will actually replenish it rather than drain it, shown as negative numbers in costs. It slowly regenerates over time.
Maximum positive energy starts at 50 and is increased by 3 whenever a character gains a level. Positive energy is affected by fatigue.
Positive energy is associated with illumination, light damage, and healing.