Sustainability Assessment of Flywheel Energy Storage for Grid Applications

Flywheel Energy Storage (FES) Systems could be exploited to support energy transition maintaining, at the same time, secure conditions in electricity grids. Among the current remunerated services, they can be deployed for Frequency Con- tainment Reserve (FCR) and automatic Frequency Restoration Reserve (aFRR). However, several aspects have to be addressed, such as environmental impacts of these systems, and the costs. Additionally, since the exploitation of scarce raw materials for the assembling, also risk on supply disruption for these materials has to be taking into account. Main indicators exploited to evaluate Flywheels are the Global Warming Potential, the Cumulative Energy Demand, the Levelized Cost of Storage (LCOS) and the Supply Risk Indicator for Raw Materials. Most impact- ing components for Cumulative Energy Demand and Global Warming Potential are represented by the steel-based Vacuum Chamber and the Power Conversion System. Investment costs and charging costs are instead major contributors in LCOS, whereas replacement costs have a small contribution on it. The Supply Risk, assessed first for raw materials and then aggregated for the entire FES, is influenced mostly by Natural Graphite and Aluminium. Results on risk are almost not affected by considering the elements contained within the FES instead of raw materials. Finally, the comparison between greenhouse gases emitted during the manufacturing stage of alternative Storage Technologies shows that FES is the highest emitter, due to a low Energy on Power ratio