Energy Output Estimation for a Small Wind Turbine Positioned on a Rooftop in the Urban Environment with and without a Duct

Nowadays, wind turbines in general, but also urban wind turbines attained acceptance to a certain extend. Conceptual designs and some examples in reality exist, where small-scale wind turbines have been implemented close to buildings or even integrated in the building structure. This work is aiming to estimate how much energy a wind turbine could produce in the built environment, depending on its integration and configuration.

On the basis of measurements taken on the rooftop of H.C. Ørsted Institut in Copenhagen, which is located in an urban area, a comparison of fictive free standing turbines with ducted turbines of the same type was carried out. First, a prevailing wind energy direction was detected with rough mean velocity and frequency calculations.

Next, a duct was aligned with the direction, where the highest energy potential was found. Further calculations were conducted with more detailed wind velocity distributions, depending on the wind direction sectors. The duct’s wind velocity amplification capability was set to 14%, while a total opening angle of 30⁰ was assumed to be accessible from both sides.

With the simplifying assumptions and the uncertainties at the location of measurement, the free standing turbines had an energy potential of 300kWh/m2/a for the horizontal axis wind turbine (HAWT) and for the vertical axis wind turbine (VAWT) 180kWh/m2/a. For the ducted turbines an energy output of 180kWh/m2/a was found for the HAWT configuration, while the VAWT configuration reached an output of 110kWh/m2/a.

The available wind had an energy potential of 730kWh/m2/a. Evaluating these results it seems as a free standing turbine is preferable, when only considering the power output, whereas the ducted version comprises properties, which are important considering the requirements needed in the inhabited area such as safety and noise issues.