Due to their intermittency and variability, Renewable Energy Sources (RES) pose significant challenges as their integration into the electric power grids progresses, such as power quality and grid instability. For this reason, among others, Energy Storage Systems (ESSs) have emerged as a tool for facilitating integration. This paper provides a comprehensive review of different types of ESSs, including Battery Energy Storage Systems (BESS). It details their applications and techniques employed in optimally siting and sizing them, with the goal of offering a swift reference for scholars, researchers, and designers working in the power and energy sectors. The review established that no single storage technology can address all the power system applications because different storage technologies have different power ranges (from kW to GW) and also charge/discharge times. Furthermore, Pumped Hydro Storage (PHS) constitutes 96% of the global energy storage capacity currently in operation, with molten salt and lithium-ion batteries taking the largest share of the remaining 4% of capacity. It is also established that most storage systems are utilized to offer operating reserves and ancillary services, followed by arbitrage, renewable energy curtailment reduction, and load leveling; the least application area is in transmission and distribution upgrade deferrals. Finally, various strategies are found in the literature for obtaining the optimal size of BESS, including decompositioncoordination algorithm, Genetic Algorithm (GA), and Unified Particle Swarm Optimization (PSO).