Review of energy storage integration in off-grid and grid-connected hybrid renewable energy systems: Structures, optimizations, challenges and opportunities

Hybrid renewable energy systems (HRES), which integrate multiple renewable energy sources, have emerged as a promising pathway toward sustainable energy solutions. However, renewable energy sources face challenges such as intermittency and variability, which can limit their reliability and effectiveness. As a result, energy storage systems (ESSs) play a critical role in enhancing the stability and dependability of renewable energy systems. Nevertheless, ESS integration in HRES presents several concerns, such as appropriate configuration, optimal sizing, cost-effectiveness, that require further investigation and development. Thus, this paper comprehensively examines ESS-integrated HRESs designed for off-grid and grid-connected applications. It explores different types of ESSs, highlighting their integration into various HRES structures, their contributions, existing research gaps, and aspects such as techno-economic evaluation and environmental impact. Furthermore, the paper provides an in-depth analysis of optimization techniques, focusing on critical factors such as objective functions, constraints, and the application of single and hybrid metaheuristic methods. In addition, the review delves into key issues and challenges, including technical, financial, socio-economic, cultural, and regulatory barriers. The paper also identifies potential opportunities for the future development of ESS-integrated HRES, emphasizing advanced technologies, supportive policy frameworks, public awareness, and research collaborations. The comprehensive discussions and key findings presented in this review aim to serve as a valuable resource for researchers, policymakers, and industry professionals, contributing to the advancement of sustainable and resilient energy solutions.