Small-scale distributed renewable energy systems such as building-mounted wind turbines are likely to play an important role in electricity generation. Solar energy is already part of this revolution but requires a large area. Wind turbines are complementary to solar and allow for more efficient electricity generation in windy locations. However, small wind turbines have a bad reputation because of inappropriate placement in areas where there is no wind or on roofs for which they were not designed. In this project, a wind turbine, enclosed in a diffuser, specially designed for the roof of a building, is improved. Currently, this turbine has a good energy extraction efficiency but its application range is narrow as only a few parameters have been studied. In this research project, two tasks will be addressed. In the first task, the contribution of the diffuser is analysed and optimised with respect to different wind directions and inlet valve closure. The geometry of the turbine blade is a key parameter of any wind turbine. In the second task, an optimisation approach will be developed to evaluate different blade geometries and identify the blade characteristics that will lead to higher energy extraction.