Tower Design and Manufacture - Small Wind Turbines: Analysis, Design, and Application - page 206

Now consider an example design, the octagonal, tapered 18 m galvanized steel
tower shown in Fig. 10.2 for an Aerogenesis 5 kW wind turbine. The photo shows
the turbine and tower before and after it was raised for the first time with the gin
pole still attached. Chapter 12 has a further discussion of raising and lowering. The
main tower and turbine parameters are listed in Table 10.2 . The base diameter, d h ,
and the section thicknesses were chosen iteratively to keep the capacity factors to
0.6 or less. It is important to note that there is no obvious procedure for doing this,
so an optimisation method would be valuable, especially if it included a measure
of cost in the objective function. The other parameter to note is the turbine thrust,
T max , which was determined from the SLM as described in Chap. 9 . No load or
material safety factor has been applied to this value. The actual tower has extra
bracing in the bottom section so that its CF for buckling is considerably lower than
shown in the Matlab output.
The main parameters for the tower are given in Table 10.2 . C d for an
octagonal section is 1.4 from AS 1170.2 [ 12 ]. This value is used because it is
larger than that in Table 9.5 taken from IEC 61400-2. It is common for different
standards to have conflicting requirements and the fact that towers must satisfy
IEC 61400-2 as well as relevant local codes means, in practice, that the design
will usually be the most conservative possible. This argument should also apply
to T max but this would not allow comparison to the FEA values which were
based on the data in Table 10.2 .

Table 10.1 The main types of towers for small wind turbines

Type Main advantages Main disadvantages

Monopole Aesthetically pleasing Usually requires more steel

More expensive to make
and transport

Guyed Cheap, minimal material

Tower natural frequency can be adjusted
through guy wire tension
Good grounding for lightning

Cannot be used in urban
settings
Not vandal proof

Sectional
lattice

Cheap to transport
Assembled on site

Relatively short lifetime as
corrosion can start in joints

Tubular
lattice

Easy to make, are light and stiff
Relatively long lived without galvanising

Less protection for electrical
cables

Table 10.2 Parameters for octagonal tapered tower example

Parameter Value Parameter Value Parameter Value

h 18 m N s 3 U 50 m/s

m tt 170 kg T max 2200 N E 200 GPa

d o 0.17 m d h 0.41 m C d 1.4

7800 kg/m 3

F y 350 MPa q tower m t 531 kg

t 1 , t 2 3.75 mm t 3 4.3 mm
Note that the tower mass does not include the slip-fit overlaps, the turbine mounting flange or the
baseplate