Doctoral Thesis / Dissertation from the year 2020 in the subject Engineering - Power Engineering, Cairo University, language: English, abstract: This thesis presents a complete reliability, availability, and maintainability (RAM) analysis of the variable renewable energy (VRE) systems. Three operating concepts of the wind energy conversion systems (WECS) are considered based on the acceptable speed range of generators, while seven practical layouts of large-scale grid-connected systems are considered for the solar-PV systems. Elaborated RAM analysis of each system associated with each operating concept for the WECS and each layout of the solar-PV systems is presented starting from the subassemblies level to the subsystem level then the overall system. This thesis is purposed to describe the method of reliability, availability, and maintainability analysis of repairable and non-repairable systems using the exponential PDFs. It is also aimed to explore the method for improving the availability of these systems by managing the effort using availability importance measures of each subassembly. This analysis will also be utilized to studying the criticality of the subassemblies or subsystems of the system in order to continuous improvement. After doing this, this thesis also extends to look into the overall system availability. This analysis is a good tool for helping to identify the critical subsystems or subassemblies of the system that need more attention for improvement.