[en] The United Kingdom is engaged in an initiative to invest in the growth of city centres and to establish higher housing densities for new developments. An increase in energy and resources will be needed to supply these built environments. The Climate Change Act in the United Kingdom stipulates that along with this growth, an 80 per cent reduction in carbon dioxide (CO₂) emissions from 1990 levels should be met by 2050. While part of the expected reductions in buildings will come from energy efficiency, the rest will come from low and zero carbon (LZC) energy generation. LZC technologies must be developed using zero carbon on-site or near-site sources. This paper considered the feasibility of meeting the energy demand of urban buildings and the ability to meet zero carbon via on-site sources and the physical and technical limitations associated with this. It defined what sources of energy should be considered as on-site incident resources. The on-site incident energy yield was then assessed and compared against the annual energy demand for a range of urban densities. A mixed-use development site, typical of southeast England was used to assess the availability of on-site incident energy against which the urban densities energy demands are compared. The on-site energy sources considered in this study were meaningfully quantified and qualified in order to determine to what extent they can supply energy to an urban site, not just reduce CO₂ emissions. Energy demand models were used along with solar radiation estimates for urban areas. The study showed that given the projected energy demand, meeting on-site annual energy requirements sustainably is achievable even at high urban densities, but the demand may be greater than the yield in a given month. The study also showed that sharing infrastructure allows for energy to be better balanced to serve the urban form, particularly in heating systems. 16 refs., 3 tabs., 7 figs