and its impacts are constantly triggering and initiating research and new
solutions for sustainable and climate resilient urban environments. One of
the topics attracting more and more attention are urban wind electricity
generation which has not been addressed much for years due to high
infrastructure required to exploit wind resource (substantial size of the
conventional wind turbines, visual impacts, noise etc.).
and the accompanying conditions are quite complex and can vary not only between
cities but also within one (e.g. highly developed city centre with many buildings
vs city’s riverbank). There are many factors influencing the wind regime upon
which electricity generation is primarily dependent thus making urban wind
turbine design a real challenge. Two most important characteristics of the
urban wind regime are:
lower annual mean wind speeds due to presence of
more turbulent flow resulting from the interaction of
the wind with the buildings and other obstacles.
Higher turbulent flow is especially tricky since it sets the need for turbine’s quick reaction to the changing wind directions, otherwise the output power is significantly reduced. Hence, the answer may lie in either turbine topology handling turbulence well or in finding the least turbulent areas of the urban environment. Considering the latter, promising areas are building-tops (such as one installed on a Chicago apartment building) and open areas on the ground such as parks, sport fields or flood defences.
In addition to
aforementioned demands, an important aspect is structural and visual
integration into the urban settings as well as maintenance and noise which is
particularly relevant in densely populated areas.
When it comes to
turbines’ design, there are two main groups which differentiate based on the orientation
of their axis of rotation, namely:
horizontal axis wind turbine (HAWTs) and
vertical axis wind turbines (VAWTs).
HAWTs are advantageous since they represent more mature technology with higher rotation speeds, lower cost and higher efficiency. However, improvements in the VAWT design increased the viability of wind energy in urban applications. In general, VAWTs perform better with urban turbulence conditions, they are less noisy, low rotational speed and lower power coefficients have been improved.
applications mostly entail VAWT micro wind turbines from 1 kW output to
larger models with outputs exceeding 20 kW. In the EU, urban wind power
units have been installed in Netherlands, UK and France.
Some of these designs are very innovative and well-integrated into the urban surroundings. One example is the so called “Wind Tree”, a product of a French startup which already deployed a few units generating electricity in Paris.
The “Wind Tree” is a wind installation actually imitating a tree with leaves being represented by the small wind turbines. Average height is around 9 meters with diameter of about 8 meters. There are 54 “leaves” per “tree”. Each “tree” represents an installed capacity of 3.5 kW which can generate electricity in wind speeds as low as 4.5 mph. Currently, these installations are marketed for civil engineering and landscaping projects in cities but could be promising with regards to residential use. Some of the current challenges are the requirement of significant installation area, efficiency issues as well the costs.
turbines are not fully developed, mature technologies and many challenges are
still ahead. Feasibility and viability of such projects is yet to be
determined and verified. Additional research will show how promising these
solutions could be in tackling climate change in urban environments.