New small turbine technologies - Wind Power Generation and Wind Turbine Design - page 390

Identification of the Purpose of Utilization

Investigation of Technical/Social Conditions

External Conditions
Conceptual Design
Aerodynamic Design
Structural Design

Safety

Wind Turbine
Design

Performance

Tests and Verification
Quality Control

Wind Turbine
Production

Economics

Operation and Maintenance

End of Use

Environment

Figure 1: Lifecycle of a wind turbine.

A general life cycle of a wind turbine is illustrated in Fig. 1. Today SWT
technology has evolved and is required to contribute to energy production and
environment protection much more than before. Therefore, safety, performance,
economics and environment are keen issues.
Discussions will be focused on those issues that are particular with SWTs in
their design procedure in the following sections.

1.1 Defi nition of SWT

SWTs are defi ned as “wind turbines with a rotor swept area smaller than 200 m 2 ,
generating at a voltage below 1000 V a.c. or 1500 V d.c.” in IEC Standard [1]. If
the swept area is less than 2 m 2 , support system need not be included for the SWT.
This is the only one defi nition accepted internationally.
However, basic understandings of SWTs may not be restricted within the
above boundaries. On the rotor size, “Mini” and “Micro” wind turbines with
much smaller rotor diameters or power outputs can be proposed. Also restriction
to electricity-producing systems is not essential. Various styles of application are
possible such as pumping system, some hybrid systems, etc.
The technically important features of SWTs which defer from LWTs are con-
sidered fi rst. With high performance wind turbines of both horizontal- and
vertical-axis types, they are all driven by lift force created on the rotor blades.
Lift is everything and what could affect lift then? They are geometry of aerofoil
section, attack angle and Reynolds number. Only the last one depends on scale
of rotor. Therefore, one reasonable defi nition of SWT may the rotor scales that
are liable to suffer from “ low Reynolds number problem ”.