The coal blocked one of the entrances of the Eskom Megawatt Park office.
The activists said in a statement that the dump was in protest at Eskom’s construction of the coal-fired Kusile power plant.
“Eskom should end its addiction to coal and shift massive investments to large-scale renewable energy projects,” Greenpeace spokesperson Mbong Akiy said in a statement.
The 15 activists held up banners urging the state-owned group “to clean up its act and stop coal”.
Police officials did turn up at the offices but no arrests were made. Eskom has also not yet made any mention of whether or not it will lay charges.
An Eskom spokesperson took the activists’ list of demands but said that that the government was responsible for decision on how to generate power and not the electricity supplier.
But Greenpeace’s Melita Steele said both Eskom and government were to blame for the coal power choice versus the “cleaner” option of renewable energies such as wind and solar power.
“Instead of locking South Africa into a dirty energy future by investing in Kusile , Eskom should be investing in people and green jobs,” said Steele.
“To date, Eskom’s investments in renewable energy are limited to tiny projects of 100MW of wind and 100MW of solar. This illustrates Eskom’s lack of commitment to a sustainable future for South Africa.”