Transforming electrified railway into mechanical energy storage for electricity system decarbonization

Decarbonizing electricity requires vast energy storage capacity worldwide, but constructing dedicated storage assets creates substantial capital, material and embodied carbon burdens. Electrified railways already exchange energy with electricity systems through traction and regenerative braking, but their inherent potential as mechanical energy storage remains unexploited. Here we show that modulation of train operations can transform electrified railways into Electrified Rail-Based Energy Storage. By analyzing 326,034 inter-stop train operations, we estimate its global potential at 190 gigawatts in 2025 and 315–579 gigawatts by 2050. Capacity expansion models for China, Europe and India indicate that it can reduce investment in conventional storage by 11.9–20.0%, corresponding to an extrapolated global value of US$14.9–35.1 billion annually. Without increasing total system cost, electricity systems with this flexible resource could further reduce operational CO 2 emissions by 94.3–258.9 million tonnes per year. Electrified railways can therefore complement conventional storage technologies for electricity system decarbonization.