WARSAW, Poland (AP) — Energy experts were working Tuesday to restore full operations at Poland’s biggest power plant after a network failure switched off 10 of the brown coal-fueled plant’s 11 units. Poland needed emergency energy imports from Germany, Sweden, the Czech Republic and Slovakia to fill in for the suddenly missing power supply. It was a second major outage since 2015 at the lignite-fired Belchatow plant, which provides up to 20% of the energy in Poland. The outage was felt across Europe’s continent-wide network of power grids. Officials said the outage occurred due to the failure of a power station where 10 of Belchatow’s units are connected. Poland’s chief energy distributor said Tuesday that restarting them is a big challenge.