Tower Design and Manufacture - Small Wind Turbines: Analysis, Design, and Application - page 199

Chapter 10
Tower Design and Manufacture
10.1 Introduction
As with other basic design decisions, such as the number of blades and whether the
rotor is upwind or downwind, there is a larger variety of tower types for small
turbines than for larger ones. This chapter concentrates on the main types: stand-
alone monopoles, guyed poles or lattices, and non-guyed lattice towers of two
main forms. Table 10.1 lists the main tower types with their advantages and
disadvantages. Traditionally, lattice and guyed-towers have been the most com-
mon but the widespread deployment of grid-connected small turbines has lead to
monopoles taking over, largely because they do not need guy-wires. Lattice towers
come in two basic types: those made from steel angle or other sections which are
assembled on site, and tubular lattice towers that are pre-fabricated in sections.
Site issues, foundations, and tower loads during raising and lowering are covered
in Chap. 12 . This chapter concentrates on design and fabrication. The key design
requirements are to ensure that the maximum design stress is below the allowable
material stress, no tower member in compression will buckle, and the tower's
lowest natural frequency is not likely to be significantly excited by blade passing
frequencies. Note that the IEC Simple Load Model (SLM) described in Chap. 9
mandates only the first requirement. Some manufacturing issues such as corrosion
resistance by galvanising will be described briefly.
Not all small wind turbines have towers, and some have shortened, or specially
built ones: examples include building-mounted turbines and micro-turbines used
for yachts. This feature of micro turbines is recognized in IEC 61400-2 which
allows turbines of swept area less that 2 m 2 to be certified independently of the
tower. Large wind turbine tower design is more complex than the simple use of
safety factors described in this chapter, see, for example, Lavassas et al. [ 1 ] and
Sect. 3 of Baniotopoulos [ 2 ].
The following IEC load cases are considered: Load Case A for fatigue during
normal operation, B for loads during yaw, and Load Case H: Parked wind loading
where it will be assumed that the rotor is stationary.