Evaluation of the Influences of Different Roof Shapes on the Flow Properties and Performance of Small Wind Turbines

Abstract

Small wind turbines offer a complement to photovoltaic systems and are becoming an interesting solution in the wake of rising energy prices. The measurement results indicate that some locations on and around the building are not suited for installing wind turbines, while others show increased wind potential. Due to limited space, rooftop mounting is an interesting alternative to free mounting on a mast from a technical point of view. For this reason, the influence of roof shapes on the flow on and behind the building was measured and the performance of two different types of small wind turbines was investigated. The turbines assessed in the project are VertikonM with a vertical axis and helix-shaped rotor blades, and Superwind 1250 wind turbine with a horizontal axis and centrifugal force pitch control. The results showed that there is an average increase in wind speed of 0.2 m/s on gable roofs at hub height (7 m). In comparison, there is an increase of 0.4 m/s on flat roofs at hub height (7 m). In relation to the performance of the turbines, high turbulence on the roof seems to cancel out this effect. The performance of the horizontal axis small wind turbine has not increased in comparison with gable roof and free-standing mast. For the vertical-axis turbine, a power increase by a factor of 2.23 was achieved between free-standing mast and gable roof. Vertical wind flow above the gable roof was identified as the main cause for power increase. The experiment was conducted on the Lichtenegg energy research park (Lower Austria) and its results make it possible to better identify all effects that affect the turbine output power.