Advances in hybrid renewable energy systems coupled with mechanical energy storage: Progress and challenges

• The integration of mechanical energy storage into renewable energy systems was investigated, emphasizing recent advancements and experimental findings. • Various configurations, technologies, and control strategies were examined for enhancing system performance. • Techno-economic-environmental challenges were highlighted, such as efficiency limitations, ecological impacts, and scalability issues. • Case studies were presented, such as the PHES integration with wind and PV, highlighting practical feasibility and scalability. Hybrid renewable energy systems (HRES) have gained attention as an effective approach to address the variability and intermittency issues of standalone renewable energy technologies. Coupling these systems with mechanical energy storage systems (MESS) enhances energy reliability and long-term sustainability. This review provides an assessment of recent advances in HRES-MESS integration, examining key system configurations, major storage technologies, and essential control strategies. Special focus is given to the primary technical, economic, and environmental challenges associated with MESS, including high capital costs, conversion inefficiencies, ecological impacts, and site-specific limitations. Recent case studies and advancements are highlighted to demonstrate practical feasibility and scalability of these systems. While several MESS technologies are already deployed in real-world applications, many innovations and performance improvements remain at the laboratory or demonstration scale. Focused efforts are thus required to accelerate the transition of these developments toward full-scale implementation, enabling MESS to compete effectively with more mature energy storage solutions in commercial hybrid energy systems.