Site Assessment and Installation - Small Wind Turbines: Analysis, Design, and Application - page 254

• The use of wind atlas data now available for many countries, in the form of
average wind speeds at typical heights of 30 or 50 m. 1 Software such as WAsP 2
or 3Tier 3 can interpolate these data to typical turbine hub heights in the presence
of complex terrain, trees, and buildings with some limitations due to the ''lin-
earity'' of the models. WAsP and 3Tier are expensive, so the reader may wish to
explore the free alternative Open Wind. 4 Elmore and Gallagher [ 6 ] describe an
extensive wind resource study for small turbines based on wind atlas data and
document some of its pitfalls. Packages such as Meteodyn 5 and Ansys CFX for
direct computation of the wind flow are probably too expensive for small turbine
siting. A good description of computational studies for micrositing large wind
turbines is given by Strack and Riedel [ 7 ].
• Rules of thumb or guides from experience. A fascinating on-line example of this
is the Danish ''wind shading calculator''. 6 The U.S. Department of Energy
guidelines 7 also give recommendations on minimum distances from the turbine
to buildings, trees, and other obstacles. The next section demonstrates that it is
possible to undertake only a rudimentary optimisation of turbine height, so the
coding of practical experience for choosing height and location will remain a
valuable guide for a long time. Furthermore, there has been significant recent
effort to improve guidelines using wind tunnel modeling, computational studies,
and detailed field measurements, e.g. Brunskill and Lubitz [ 8 ].
• The use of software such as Retscreen, 8 Homer, 9 Hybrid2, 10 and SAM 11 for the
design of renewable energy systems. All include turbine power production
analysis and all are recommended to interested readers. These excellent products
are free—at least in their basic form—and all come with extensive wind and
solar insolation databases. These databases may be augmented by additional
local data from nearby airports, meteorological stations, and pollution moni-
toring sites. Most of the monthly-averaged wind speeds in these resources were
measured at the standard meteorological height of 10 m, so the problem is now
to extrapolate to hub height, rather than interpolating wind atlas data. Extrap-
olation commonly uses the power law (Eq. 1.14 ) or log law (Eq. 1.15 ). It is
error-prone even for moderate hub heights, e.g. Fig. 1 of Lubitz [ 9 ], for the
reasons given above.

1

For example, the Canadian wind atlas is at http://www.windatlas.ca/en/ (accessed 7 Aug 2010).

2

http://www.wasp.dk/ (accessed 7 Aug 2010).

3

http://www.3tier.com/en/ (accessed 7 Aug 2010).

4

http://www.awsopenwind.org/ (accessed 25 June 2011).

5

http://www.meteodyn.com/ (accessed 7 Sep 2010).

6

http://guidedtour.windpower.org/en/tour/wres/shelter/index.htm (accessed 15 Aug 2010).

7

http://www.energysavers.gov/your_home/electricity/ (accessed 30 Aug 2010).

8

http://www.retscreen.net/ (accessed 7 April 2010).

9

https://www.homerenergy.com/ (accessed 19 May 2010).

10

http://www.ceere.org/rerl/rerl_hybridpower.html (accessed 2 Jun 2010).

11

https://www.nrel.gov/analysis/sam/download.html (accessed 7 Oct 2010).