In the last years the European Union has actively promoted the renewable energies and the Combined Heat and Power (CHP) also for residential and tertiary buildings. The exploitation of renewable sources and cogeneration seems hampered by the regulatory wall that prohibit for residential, tertiary and commercial buildings the constitution of users clusters. In fact, the unification up to a threshold value of some tens of kVA, at least, can facilitate the installation of renewable energy power plants as solar PV modules or CHP systems (cogeneration) or CCHP systems (tri-generation), overcoming technical and economical barriers and combining several load profiles. The actual distribution system for low voltage LV customers appears inadequate to comply with these goals. At this aim the authors propose the design of a Sustainable Energy Microsystem (SEM) for the integration of different subsystems, currently independent, as final users and high efficiency buildings, dispersed generation from renewable and Combined Heat and Power (CHP) units and subsystems for the urban mobility: metro-transit, trams and recharging of plug- in hybrid and electric vehicles (PHEV) for the surface mobility. The integration is analyzed in the direction of a “smart city” concept, with the optimized and integrated management of many services. These activities are about the general topic of design and construction of nearly zero energy buildings with the use of innovative technologies as home and building automation. The buildings integrated in “energy hub” with dispersed generation and urban mobility systems, constitute the “energy islands” of the future smart grid.