Balancing Ukraine’s energy system: challenges under high renewable energy penetration and the COVID-19 pandemicTetiana Kurbatova, Iryna Sotnyk, Olha Prokopenko, Roman Sidortsov and Yu-xia TuE3S Web Conf., 280 (2021) 05007DOI: https://doi.org/10.1051/e3sconf/202128005007