Heading Towards 100% of Renewable Energy Sources Fraction: a critical overview on Smart Energy Systems planning and flexibility measuresLorenzo Mario Pastore, Gianluigi Lo Basso, Matteo Sforzini and Livio de SantoliE3S Web Conf., 197 (2020) 01003DOI: https://doi.org/10.1051/e3sconf/202019701003