Review of energy storage technologies for sustainable power networks

A significant percentage of the global energy demand is expected to be met through widespread supply of renewable electricity in the near future. However, renewable energy outputs are variable due to a stochastic characteristic of their sources. Electrical power system operators around the world are faced with difficulties of integrating these variable power sources into the existing power grids. Energy storage systems are one of the possible solutions for mitigating the effects of intermittent renewable resources on networks, allowing increased renewable energy utilization, and providing flexibility and ancillary services for managing future electricity supply/demand challenges. This paper presents a comprehensive review of energy storage technologies that are currently engaged for power applications, including pumped hydro, compressed-air, battery, flywheel, capacitor, supercapacitor, superconducting magnetic and thermal systems. The study compares the characteristics of these systems, and presents their technological development status and capital costs. Some directions for future work are also highlighted. Furthermore, particular attention is paid to some new storage technologies such as: adiabatic, underwater, isothermal and small-scale compressed-air; sub-surface, seawater and variable-speed pumped hydro, and pumped heat systems, which hold opportunity for future smart electrical grid applications, but there is need for more research to actualize their promising potentials.