Abstract—This work presents a comparison between the Annual Energy Output (AEO) of two commercial vertical-axis wind turbines (VAWTs) for a low-wind urban site: both a drag-driven and a lift- driven concepts are examined in order to be installed on top of the new Via dei Giustinelli building, Trieste (Italy). The power-curves, taken from the product specification sheets, have been matched to the wind characteristics of the selected installation site. The influence of rotor swept area and rated power on the performance of the two proposed wind turbines have been examined in detail, achieving a correlation between rotor swept area, electrical generator size and wind distribution, to be used as a guideline for the calculation of the AEO. Keywords—Annual Energy Output, micro-generation technology, urban environment, Vertical-Axis Wind Turbine I. INTRODUCTION AND BACKGROUND HE urgent need to reduce dependence on fossil fuels is being met, at least in part, by the development of wind turbines: the awareness of the limited resources of fossil fuels and the rising concern for the effects of the increased amount of greenhouse gases in the atmosphere have given the wind turbine industry a push forward. In late 1997, the Commission of the European Union published its White Paper [1] calling for 12% of gross energy demand of the European Union to be contributed from renewables by 2010. As pointed out by Campbell et al. [2], while rapid development of huge on- and off-shore wind farms proceeds at high rate, examples of integration in the urban environment – closer to prime consumers of energy such as buildings, remain scarce. Nevertheless, small scale wind turbines installed within the built environment may soon become a commercial reality in Italy, as a result of both advancements in technology and new financial incentives provided by the government. Small scale wind energy conversion systems installed within the built environment is classified as micro-generation technology: as observed by Bahaj et al. [3], such turbines have the potential to reduce built environment related CO 2 emissions coupled with reductions in consumers’ electricity costs. Moreover, the produced energy can be fed directly into the grid of the building, determining a reduction of its external energy demand. Some of the specific technology and design Marco Raciti Castelli is Research Associate at the Department of Mechanical Engineering of the University of Padua, Via Venezia 1, 35131 Padova, Italy (e-mail: marco.raciticastelli@unipd.it). Ernesto Benini is Associate Professor at the Department of Mechanical Engineering of the University of Padua, Via Venezia 1, 35131 Padova, Italy (e-mail: ernesto.benini@unipd.it). issues in the use of wind energy in buildings have been described by several authors: • Mertens [4] focused on the design of buildings that maximize wind harvest and examined a set of turbines that provide power for buildings; • Stankovic et al. [5] focused on the potential for exploiting wind power in urban areas, identifying three main categories of project, that is small wind and retrofitting, large-scale stand-alone turbines and building-integrated turbines; • Van Bussel and Mertens [6] provided a literary review of the technical potential of small wind turbines on buildings, considering small VAWT, whose typical dimensions are around 10 to 20% of the characteristic building height, as a good solution. The Savonius rotor was not considered well suited for urban installations, due to a fairly low power coefficient. Also standard Darrieus wind turbine was rejected, due to its too high noise level, while the modification of the Darrieus concept - obtained by reducing the design angular velocity and by applying blade sweep in order to minimize noise production - was considered the best solution for application on existing buildings; • Heat et al. [7] by considering the urban landscape to be an array of cubes, described a method for calculating the surface roughness length and displacement height of the urban boundary layer wind profile. The wind flow around a simple pitched-roof building was also simulated using Computational Fluid Dynamics (CFD), adopting a semi- logarithmic inflow profile. An array of similar pitched- roof houses was then modeled using CFD, in order to determine the flow characteristics within an urban area. Mean wind speeds at potential turbine mounting points were studied, and optimum mounting points were identified for different prevailing wind directions. A methodology was finally proposed for estimating the energy yield of a building-mounted turbine from simple information, such as wind atlas wind speed and building density; • Raciti Castelli et al. [8] presented the results of two- dimensional CFD simulations of the flow field around a vertical-axis wind turbine rotor, with emphasis on noise generation and propagation, for application in the built environment. The effect of the central shaft on overall rotor noise emission was analyzed using the Ffowcs- Marco Raciti Castelli and Ernesto Benini Comparison between Lift and Drag-Driven VAWT Concepts on Low-Wind Site AEO T World Academy of Science, Engineering and Technology International Journal of Environmental and Ecological Engineering Vol:5, No:11, 2011 669 International Scholarly and Scientific Research & Innovation 5(11) 2011 scholar.waset.org/1307-6892/14505 International Science Index, Environmental and Ecological Engineering Vol:5, No:11, 2011 waset.org/Publication/14505