Electrical energy storage systems and renewable sources: the state of the art

This paper outlines the state of the art in the field of electrical energy storage systems in the perspective of a widespread use of renewable energy sources; this is a subject of primary importance in view of the decision of the European Union to reduce CO2 emissions in the next future while increasing the incidence of renewables. Among the various electrical energy storage systems, the following systems are treated: conventional and innovative bat-teries, supercapacitors, flywheels, fuel cell / hydrolizer systems, superconducting magnetic energy storage (SMES) systems, thermal energy storage (TES) systems. The paper also analyzes the strategies for the integration of storage systems with facilities for power generation from renewable sources on one hand and with the distribution network on the other, emphasizing the fundamental role played by distributed generation (DG). The work shows that the technological improvement of electrical en-ergy storage systems can help meeting the growing electricity demand in a sustainable and eco-compatible way, favoring the diffusion of renewable sources. Despite various obstacles, research and development in the electrical energy storage field in Italy are active and able to bring innovative and useful contributions.