*Review* **Present and Future of Supercapacitor Technology Applied to Powertrains, Renewable Generation and Grid Connection Applications**

**Gustavo Navarro \*, Jorge Torres, Marcos Blanco, Jorge Nájera, Miguel Santos-Herran and Marcos Lafoz**

CIEMAT, Spanish National Research Centre on Energy, Environment and Technology, 28040 Madrid, Spain; jorgejesus.torres@ciemat.es (J.T.); marcos.blanco@ciemat.es (M.B.); Jorge.Najera@ciemat.es (J.N.); miguel.santos@ciemat.es (M.S.-H.); marcos.lafoz@ciemat.es (M.L.)

**\*** Correspondence: gustavo.navarro@ciemat.es

**Abstract:** Energy storage systems (ESS) are becoming essential as a solution for troublesome industrial systems. This study focuses on the application of a type of ESS, a high-power technology known in the literature as supercapacitors or electric double layer capacitors (EDLC). This technology has had a huge impact during the last decade on research related to the electric traction drives, renewable sources and powergrids. Related to this aspect, this paper summarizes the most relevant scientific publications in the last five years that study the use of supercapacitor technology (SCs) in electric traction applications (drives for rail vehicles and drives for road vehicles), generation systems for renewable energy (wind, solar and wave energy), and connection systems to the electric grid (voltage and frequency regulation and microgrids). The technology based on EDLC and the practical aspects that must be taken into account in the op-eration of these systems in industrial applications are briefly described. For each of the aforementioned applications, it is described how the problems are solved by using the energy storage technology, drawing the solutions proposed by different authors. Special attention is paid to the control strategies when combining SCs with other technologies, such as batteries. As a summary, some conclusions are collected drawn from the publications analyzed, evaluating the aspects in which it is necessary to conduct further research in order to facilitate the integration of EDLC technology.

**Keywords:** supercapacitors; electric traction drives; electrical vehicle; microgrid; renewable energy; energy storage system
