Germany's plan to scrap coal as a power-generation fuel is off to an inauspicious start with the scheduled opening of a new plant set to spew greenhouse gas pollution for almost two decades.

Protesters are already preparing to disrupt the opening of Uniper SE's Datteln-4 plant in June and could turn the utility into the latest flashpoint in Germany's increasingly fractious debate about the fossil fuel that still generates about a third of the country's electricity.

The mounting tension threatens to disrupt Chancellor Angela Merkel's attempts to build consensus over a 2038 exit date for coal and widen rifts between industry and environmentalists.