Balancing seasonal variability in low-carbon electricity systems: A review of technologies and strategies

Global transitions to net-zero electricity systems are accelerating the replacement of fossil-fuel generation with variable renewable energy, especially wind and solar, whose output varies systematically across regions and seasons. Unlike dispatchable sources, these renewables introduce variability across multiple timescales, most prominently a persistent mismatch between seasonal patterns of electricity supply and demand. Managing this mismatch is critical for maintaining adequacy, reliability, and affordability in deeply decarbonized electricity systems. In this review, we assess the principal strategies available to address seasonal imbalances, including long-duration energy storage, cross-sectoral flexibility, renewables overcapacity, hybrid storage configurations, and expanded interregional transmission. We define seasonal storage as bulk systems capable of storing energy for durations exceeding one month, and evaluate candidate technologies based on capital cost, round-trip efficiency, self-discharge, lifetime, technology readiness, and cross sector integration potential. Our synthesis highlights that no single strategy is adequate across all geographies, demand profiles, or resource conditions. Instead, leveraging synergies and managing trade-offs among diverse flexibility options, e.g., storage duration, energy-specific cost, self-discharge, and siting constraints, is essential for building resilient, net-zero electricity systems capable of managing seasonal dynamics worldwide. The review also identifies key research gaps in integrated multi-timescale storage modelling, valuation of seasonal services under climate and interannual variability, design and assessment of hybrid storage architectures, techno-economic and environmental evaluation across siting contexts, and the system, environmental, and institutional factors as well as policy enablers shaping cross-sectoral integration.