 The Energy Hierarchy. The Energy Hierarchy is a classification of energy options, prioritized to assist progress towards the more sustainable energy system. It is a similar approach to the waste hierarchy for minimizing resource depletion, and adopts a parallel sequence. The highest priorities cover the prevention of unnecessary energy usage both through eliminating waste and improving energy efficiency. The sustainable production of energy resources is the next priority. Depletive and waste producing energy generation options are the lowest priority. For an energy system to be sustainable, the resources applied to producing the energy must be capable of lasting indefinitely. The energy conversion should produce no harmful byproducts, including net emissions, nor waste which cannot be fully recycled. And it must be capable of meeting reasonable energy demands.