The UC problem and ELD problem are the most important optimization concerns in the EPS. An unfavourable solution for the ELD can greatly affect the generation schedule, negatively. The objective of the ELD is to allocate the power demand among committed generators in the most economical way while, at the same time, satisfy all the physical constraints. For as long as the cost curve is linear or convex, the ELD problem can be solved using deterministic methods. But in reality, some generators have constraints that cause the cost curve non-convex. Moreover, restrictions like ramp rates and prohibitions of operation zones all introduce discontinuities thus adds more to the ELD complexity. The introduction of RES and its intermittent nature makes the ELD problem even more complex that deterministic methods do not apply. Some metaheuristics are employed.