The activists Tuesday scaled a 328-foot cooling tower and tried to hang a banner reading "PGE coal kills" at the Turow power plant in Bogatynia, part of the state-owned energy corporation PGE, the third-largest in Poland. Winds were too strong to allow them to hang the flag effectively, the Greenpeace website and Polskie Radio/Polish Press Agency reported.
They agreed to come down after spending 12 hours on the tower, Polskie Radio reported.
"Twenty-one people were charged with trespassing and one of them has heard the additional charge of stealing walkie-talkies that belonged to a security guard," said police spokesman Antoni Owsiak.
Twelve activists from Poland, Slovakia, the Czech Republic, Finland and Hungary climbed the tower, the radio station said.
The Greenpeace website said the group wants PGE to "reduce emissions from the combustion of coal, and a larger proportion of renewable energy in the balance ... so as to minimize the impact of energy production on people's health and lives."