Data centres are involved play two different and complementary roles in Smart Cities' energy policies with two roles: as ICT infrastructures supporting Smart City resource optimization systems - and more in general, delivering for ICT services to the citizens - and as large energy consumers. Therefore there are huge expectations on data centres being able to run at the highest levels of renewable energy sources: this is the great challenge of DC4Cities project.DC4Cities addresses these requirements optimizing data centre operations as well as software running in the data centre for minimal energy consumption and adaptivity to external energy constrains, targeting the 80% usage of renewable energy sources.The goal of DC4Cities is to let make existing and new data centres become energy adaptive, without requiring any logistics modification to the logistics, and without impacting the quality of the services provided to their users. Finally new energy metrics, benchmarks, and measurement processes will be developed and proposed for the definition of new related standards.DC4Cities will promote the data centres role as an "eco-friendly" key player in the Smart Cities energy policies, and will foster the integration of a network of local renewable energy providers (also interconnected with local Smart Grids and microgrids) to support the pursued increase of renewable energy share.