Power System Decarbonization: Impacts of Energy Storage Duration and Interannual Renewables Variability

Decarbonization of the electricity sector is one of the major measures in slowing down the pace of climate change. In this paper, we analyze the impacts of energy storage systems (ESS) and interannual uncertainty of variable renewable energy (VRE) on power system decarbonization in 2050. We perform capacity expansion optimization based on technology cost projections and CO2 emission restrictions using 11 years of VRE and load data in Italy's power system, with a particular focus on the role of ESS and its duration. We also explore capacity expansion optimization based on multiple-year vs. single-year data to quantify the impact of VRE interannual variability. Our results indicate high renewables penetration even in the absence of decarbonization policies. In the transition to zero carbon system, CCS plays a minor role due to its carbon capture efficiency. ESS investments contribute to lower system costs by replacing more expensive flexibility resources. However, longer ESS durations have lower marginal value per added kWh ESS. Interannual variability of VRE substantially changes the system's configuration and energy cost. Decision-making based on single-year data substantially increases the systems' operational costs in other years. In contrast, optimizing over multiple years provides a more robust and cost effective generation expansion strategy.