As the world moves towards a more sustainable development, the energy coming from fossil fuels still produces the greenhouse gases that threaten the world’s climate. The UK government has established targets for the penetration of renewable energy generation and low-carbon alternatives for the electricity production. One of these technologies is microgeneration. In 2006, the UK government launched the Microgeneration Strategy pushing forward micro and small-scale generation as a supplementary source of energy for the country’s growing electricity demand. The proposal is focused on several technologies, including micro-wind and micro-PV, among others. These microgeneration technologies are now a reality and widespread across the distribution networks. Therefore, the analysis of the impact of these systems connected to distribution grids and the benefits of these technologies, alongside with their negative effects on the network is an important research area. Correct modelling of micro and small-scale renewablebased generation technologies implemented in urban areas, however, is not a simple task, as it requires an adequate representation of highly dispersed and uncontrolled generation systems. These systems are small in size, but high in numbers and usually experience large variations in available renewable energy inputs. This thesis presents aggregate models of urban micro and small-scale PV and wind generation systems, which are connected to low-voltage networks. The thesis analyses impact of urban PV and wind generation on the steady-state network performance (power flows and voltage profiles), taking into account variability of energy inputs. The presented analysis is of particular importance for the analysis of the future of power system supplies, which will have significantly higher penetration levels of renewable-based distributed generation technologies, resulting in a much wider range of interactions between microgeneration systems, loads and transmission/distribution networks. In order to perform this analysis, the resource assessment for urban areas has to be carried out to both quantify the potential for each technology and help in their modelling. This has been a challenge since the aggregation of microgeneration systems is far from simple, as the parameters, performance and size varies between different technologies. A solution presented in this thesis is an approach for simple yet accurate aggregation of microgeneration technologies. This approach allows to quantify and analyse their impact and effect on the power supply systems directly in terms of penetration levels and general technology characteristics.