Nordic cities are often perceived as frontrunners of urban sustainability and their planners increasingly embrace and combine environmentalist ideas with communicative planning approaches. We argue that how corporatist networks promote green growth strategies that can undermine sustainability targets is often overlooked. In this article, we examine how the City of Copenhagen is failing in its efforts to become the world’s first carbon-neutral capital by 2025 partly because of corporatist capture of the decarbonisation agenda. Taking a phronetic social science approach we shed light on the production of knowledge and counter-knowledge in planning conflicts over energy infrastructure, in particular the iconic €530 million Copenhill waste-to-energy plant in Denmark. On one side of the conflict was a green coalition that initially blocked the proposed energy megaplant to defend the city’s ambitious climate targets. On the other side was a corporatist coalition who subsequently succeeded in strong-arming the city council to accept the plant, even though that meant carbon emissions would increase significantly, instead of decreasing. We focus on this U-turn in the planning process as a case of dark planning and a knowledge co-creation fiasco. Our findings reveal how the sustainability concept can be utilised as an empty vessel to promote private sector export agendas. We suggest that environmentalist ideals may stand stronger in planning conflicts if they link up with a broader alternative socio-economic agenda capable of attracting coalition partners. The lesson to be learned for green coalitions is that it is crucial to combine expert, local, and political knowledge to be able to “read” the power configuration and develop strategic and tactical capacity to challenge dominant discourses.