Site Assessment and Installation - Small Wind Turbines: Analysis, Design, and Application - page 255

• Some mixture of the above methods. The outcomes of the UK ''Warwick trials'',
Encraft [ 2 ], are a good example. This study analysed the performance of a large
number of mainly building-mounted turbines and deduced correction factors for
use with interpolated wind atlas data.
• Wind speed measurement. It is possible to buy cheap weather stations with cup
anemometers and simple data loggers. For reasons that should be apparent by
now, the anemometers should be placed as close as possible to the intended hub
height, but this is not always easy or cheap. Monitoring for a year at least is
recommended, both to document seasonal variations and to allow comparison to
nearby long-term averaged data to judge whether the monitoring period is close
enough to typical.

Site assessment can include noise and visual impact. There is little to add to the
discussion of turbine noise in Sect. 1.3 and the spreadsheet described there and
available from the online materials can be used to assess noise at the location(s) of
''relevant receiver(s)'' to see if the total noise level, i.e. that of the turbine plus
''background'' significantly exceeds the background level.
Visual impact is a personal issue but can be significant. For example, the
turbine in Fig. 10.2 has a cable run of 400 m to the controller in order for the
turbine not to interfere with the panoramic views from the farmhouse it powers.
For multiple installations of small turbines, the cost of full site assessment may
well be justified. The general procedure is to first identify likely regions of high
average wind speeds from wind atlas data or other sources, or monitoring using
standard cup anemometers and wind vanes as shown in Fig. 12.2 . This mast has an
anemometer and wind vane at heights of 9 m and 15 m and is a smaller version of
the large masts, often 50 m high, used for large wind turbines. Wind monitoring is
usually followed by computer modeling to identify the best locations. A calculated
flow over a building is shown graphically in Fig. 12.3 .

12.3 Optimum Tower Height

Because many manufacturers offer a range of tower heights, a major part of site
assessment is deciding what tower height to use. It is impossible to give detailed
recommendations but the following simple analysis shows some aspects that
should be considered. Table 12.2 lists the retail prices of the Skystream 2.4 kW
turbine and its four tilt-monopole towers as of March 2010.
A fit to this data gives the total turbine price, P total ,as

P total ¼ a þ bh ð 12 : 1 Þ

a = $US6,389 and b = $US486.8/m. It is reasonable to expect that transport,
foundation, and installation costs, which are not included in ( 12.1 ), would scale
partly on total cost but also have a component specific to each site. These costs are
ignored, along with details of project finance which would require estimates of