The extensive deployment of renewable energy sources (RES) across modern energy infrastructure has introduced significant operational complexity, necessitating the development of advanced data-driven control strategies to ensure reliable and efficient system operation. Among these approaches, reinforcement learning (RL) has emerged as a promising paradigm for managing renewable generation and coordinating interconnected energy subsystems under uncertainty and dynamic operating conditions. The current paper presents a comprehensive review of RL-based control applications across RES-integrated energy domains, including power grids, microgrids, and building energy systems. The paper begins by outlining the fundamental characteristics of these smart grid energy environments along with the mathematical foundations of RL and its principal algorithmic families. A structured analysis of recent peer-reviewed studies is then conducted, with the literature systematically categorized according to the corresponding energy domain. A high number of impactful selected studies are further examined across multiple key dimensions, including RL methodologies, agent architectures, reward design, baseline control strategies, RES-integrated technologies, and control objectives. Based on this multi-dimensional evaluation, the review identifies emerging trends and highlights dominant design patterns across power grid, microgrid, and building-level applications. Finally, the observations are critically discussed and future research directions are outlined towards the development of scalable, practical, and reliable RL-based energy management solutions for next-generation smart grid systems.