In this paper, an improved energy policy making and assessment framework based on human, nature, and system dimensions is described first in conjunction with a systematic assessment procedure including analytical hierarchy process (AHP) to manage and analyze huge and diverse sets of information belonging to a wide time span. A new sustainability index is introduced and incorporated into the assessment procedure to present the sustainability status of any energy system by a single criterion. Using the framework and procedure, Iran power generation system is then assessed as a case study from a sustainability point of view by defining and manipulating many indicators over half a century. The results reveal that the dimensions of the system are located in a sustainable bandwidth. However, the temporal trends of the dimensions show an unbalanced development of the system. The assessment provides an essential first step for improving the current electricity policies of the country.