انرژی باد شهری: برخی از دیدگاه های بالقوه و چالش ها Urban wind energy: Some views on potential and challenges

1. Introduction Wind has been used as an energy source since ages. The power of wind was used to sail ships, to mill grain and to pump water. Wind power is currently considered as one of the most viable alternatives to fossil fuels because it is renewable, widely distributed and clean with no greenhouse gas emissions produced during operation. In most cases, the energy of the wind is harnessed through large wind-power plants to supply economical clean power. However, in urban and suburban areas, the land is limited and this is considered a major restriction for the installation of large plants. An alternative option is to resort to buildingintegrated wind energy systems. Much less attention has been given to wind energy installations near buildings (Campbell and Stankovic, 2001; Beller, 2009; Sharpe and Proven, 2010). The concept of on-site micro wind energy generation is interesting because the energy is then produced close to the location where it is required. Campbell and Stankovic (2001) distinguish between three categories of possibilities for integration of wind energy generation systems into urban environments: (1) siting stand-alone wind turbines in urban locations; (2) retrofitting wind turbines onto existing buildings; and (3) full integration of wind turbines together with architectural form. Category 2 and 3 are often referred to as “building-integrated wind turbines”. Most of the early actual installations of wind turbines in urban contexts have been established in category 1 (Sharpe and Proven, 2010). They were generally conventional Horizontal Axis Wind Turbines (HAWT), intended to be mounted on the top of masts in fairly open areas. The performance of these systems has been reported to be very site-specific (Peacock et al., 2008) and in many cases the proximity to buildings has decreased the performance (e.g. Mithraratne, 2009). Campbell and Stankovic (2001), Mertens (2006), Lu and Ip (2009) and Balduzzi et al. (2012a), among others, investigated the potential to take advantage of augmented airflow around buildings, addressing both category 2 and category 3 applications. Category 2 includes traditional or newly developed wind turbines that can be fitted onto either existing buildings or new buildings, without the need for specially modifying the building form. Examples are the roof-mounted ducted wind turbine by Grant et al. (2008), the modern adaptation to the Sistan wind energy mill by Müller et al. (2009), the Crossflex design by Sharpe and Proven (2010), which is a new development of a Darrieus turbine form, and the 3-in-1 wind–solar and rain water harvester with power-augmentation-guide-vane (PAGV) for a Vertical Axis Wind Turbine (VAWT) by Chong et al. (2011). Finally, category 3 consists of modified building forms for full integration of wind turbines. Well-known examples of buildings designed for integration of large-scale wind turbines are the Bahrain World Trade Center (2011), the Strata Tower in London (2011) and the Pearl River Tower in Guangzhou, China (2011). Fig. 1 shows the Bahrain World Trade Center Towers, where three wind turbines facing the prevailing wind direction are suspended on bridges between the two towers of the center.