The group says it had a deal two years ago with billboard company Pattison Outdoor to display an ad in Edmonton, but it was cancelled without explanation.
The ad said: "When there is a huge solar energy spill, it's just called a nice day. Green jobs, not more oil spills.''
Pattison wouldn't say at the time why it backed away, but Greenpeace suggested the company didn't want to offend oil industry advertisers.
Mike Hudema with Greenpeace says the group recently spotted a Pattison billboard in Calgary with an ad from Friends of Science.
The billboard reads: "The sun is the main driver of climate change. Not you. Not CO2."
Pattison did not return calls seeking comment.
Calgary-based Friends of Science argues human-induced climate change is a hypothesis that needs debate. Its website calls climate fluctuations a natural phenomena.
Greenpeace's solar energy ad eventually did find a home. It was given space by another company on its solar-powered electronic billboard.