WIND TURBINES ON APARTMENT BUILDINGS A PROMISING OPTION
18 November 2006 - Delft University of Technology

In addition to the large wind turbines that are primarily found in rural areas or in the sea, smaller wind turbines are also now starting to appear in built environments, for example, on top of apartment buildings. PhD candidate Sander Mertens researched the possibilities for utilising such wind turbines.

Mertens' PhD thesis mainly focused on situations in which the building served to concentrate the wind energy for the wind turbine. According to Mertens, this 'concentrator-effect' is required for the wind turbine's cost-effectiveness in built environments. Concentrators are able to compensate for the built environment's lower average wind speeds (compared to open rural areas). Mertens' research found that, for example, the pressure differences between the front and back of an apartment building could be used to very good effect. These pressure differences occur because the wind compresses the air against the facade on one side of the building, and pulls it away on the other, downward wind side of the building. Wind turbines can benefit from the high wind speeds that are generated in a large, round gap in an apartment building.

Saving on the energybill
Mertens identified three types of concentrators and concluded that the 'on the roof or on the side of the building' option, and the 'in gaps in buildings' option, were the most promising. The first option theoretically results in a half-bowl shaped building having the highest concentration: a wind factor of three to four (if the wind comes from all sides).

Nevertheless, Mertens also concluded that the energy production is restricted for all options, because wind turbines can only benefit from the higher wind speeds if they are relatively small in comparison to the building. Yet, these turbines still offer many advantages; for example, they deliver the energy there where it is used, in the built environment, and they can be placed 'behind the electricity meter'. The energy they produce is therefore directly and totally (100%) converted into savings in the electricity bills of the users. For the large wind turbines located in rural areas, the production company's return rate of savings is only around 30%, Mertens says.

Mertens therefore concludes that wind turbines placed in the built environment and using the concentrator-effects are very promising future energy sources. However, noting that this technology is still in an early stage of development, he believes this technology will first be used for utility buildings. These small turbines are not yet sufficiently developed for private residences.

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