There is little experience of the operation of small wind turbines mounted on domestic buildings in urban environments and little data on their performance in terms of power generation, service life and maintenance. This BRE Trust-finded study shows that, in addition to the initial embodied carbon and efficiency of the turbine, the payback period is highly sensitive to local wind conditions, transport costs, maintenance requirements and the life of the turbine. It reveals large variations in output of micro-wind turbines in a city such as Manchester and a windy location such as Wick in Scotland, and between the outskirts and town centres in windy locations. In windy locations, micro-wind turbines can generate enough energy to pay back their carbon emissions within a few months or years but in large urban areas, micro-wind turbines may never pay back their carbon emissions. Life cycle costing suggests that, even in favourable urban locations, financial payback is unlikely for all but the most durable, efficient and low maintenance turbines. This work confirms the need for a more rigorous method for estimating the electricity generated from building-mounted micro-wind turbines and for research and innovation in technology, planning and urban design to maximise the effectiveness of the turbine installations. 47 pages. Benefits: * Provides a rigorous analysis of all the factors that influence the power that small wind turbines can generate in urban areas * Studies the whole life costs and carbon emission costs of micro-wind turbines *Case studies for three locations - Manchester, Wick and Portsmouth