E x a m i n i n g P h y s i c a l a n d M e t a p h y s i c a l P e r f o r m a n c e
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need for better integration of the wind turbines into urban landscape through
experimentation of various design alternatives. There is also need to educate people
about the positive effects a wind turbine could have on their energy bills and carbon foot
print.
Reliability of Urban Wind Energy
Fluctuations in the wind speeds and amount of energy produced in comparison with
conventional methods are the two major factors that affect the use of wind turbines.
Fluctuations in the wind speeds can be dealt by increase in the reliability of the devices
that can predict the amount of energy in the wind on a particular site and through
sophistication of the wind turbine technology itself. Wind turbine would not be available
to generate electricity if the wind speed is either less than the cut in speed or more than
the cut off speed. Payback periods and reliability of the wind turbine depends on the
amount of time the wind is available within the range of the wind turbines cut in and cut
off speeds. As the technology itself has started growing in the recent past, most of the
manufacturers in the field are less experienced. Lack of data on long term analysis of
installed small wind systems is one of the reasons that are holding back the number of
people that are willing to explore this early development stage. Wind turbines have
moving parts exposed to all weather condition which can limit its life, though most
manufacturers quote 25 years of life span. Wind turbines can be economical if right
amount of wind energy is available, 5.5m/s or more of average wind speeds annually are
believed to be economically viable conditions. Advancements in the technology are
reducing the cut in speed for the wind turbines. Wind turbines are available in the
markets which have a cut in speed of 3.5m/s VAWTs have the advantage of low cut in
speeds.
VAWTs vs. HAWTs
Vertical axis wind turbines are gaining market rapidly. Due its recent entry into the
market there is lack of data on the onsite performance details of these systems.
Manufacturers have more experience in dealing with already established HAWTs while
VAWTs are new and hardly proven beyond their theoretical advantages. VAWTs have a
wider variety of designs which are believed to be more aesthetically pleasing, silent and
capable of adapting to varying wind directions more easily than reputed HAWTs. The
amount of material per m
2
swept area used in VAWTs is comparatively more than that of
HAWTs (Refocus 2003) (Fig.19). Yet there is significant scope in the expansion of its
market rapidly, mainly because of its advantages over HAWTs especially in small wind
systems. The main disadvantage of VAWTs is that it has to be placed closer to the
ground which makes it less feasible for megawatt wind turbine installation. At an urban
scale there would be no issue of height as the turbine is small, thus the load on the mast
is lower. VAWTs have a cut in speeds as low as 2.5m/s to 3m/s.
