Wind Power and Wind Turbine Technology

Wind turbine technology has developed and matured over the years and this technology now forms an increasingly important part of the world's electricity industry.

Renewable energy is vital in our fight against climate change and technologies such as wind energy can help in building a sustainable electricity generation system for the future.

Wind power can be used to generate electricity, either in parallel with mains supplies, gear or for stand-alone applications with battery back-up.

Positive environmental benefits of Wind energy

It must be stressed that wind energy involves no combustion or nuclear reaction, so it is pollution free. It is renewable and plentiful and free, it is available everywhere, especially in remote areas and often it is windier in mountains and near coastal areas.
There are significant environmental benefits obtained from using a renewable energy device attributed to preventing the release of green house gases associated with fossil fuels.

Wind energy growing rapidly worldwide

Wind Electricity Production target by 2050 Source: International Energy Agency (2010) - Renewable Energy Technology Roadmaps

Wind has the potential to provide 12% of global electricity production in 2050. The growth of renewable energy sources also stimulates employment, the creation of new technologies and new skills.

Small Wind Turbines (SWTs)

Despite the attention given to multi-megawatt wind farms, the markets for autonomous electrical systems and distributed generation using small wind turbines can be attractive if prices of conventional electricity and fossil fuels are sufficiently high, or in many developing countries, where hundreds of millions of people live without access to electricity.

Small wind turbines (SWTs) are used in two main areas:

'Autonomous electrical systems' (also called 'stand-alone', 'grid-isolated' or 'off-grid'), in other words those that are not connected to any larger electrical system and are therefore solely responsible for the control of voltage and frequency.
'Distributed generation', in other words systems with small generators connected to a larger public distribution network, where there is a network operator responsible for overall control (this is also often called 'grid-connected' or 'on-grid' generation).

The market in developed countries is promising for grid-connected and off-grid applications, due to promotion policies (such as capital cost buy-down, feed-in tariffs and net metering), and even more so for developing countries, because of the continuing decrease in specific costs and the increasing need for energy.

Markets and Applications of Small Wind Turbines

The different applications for which SWTs are especially suitable have been summarised in this table for the main two markets identified: off-grid applications and grid-connected applications.

The table shows how isolated systems with SWTs offer solutions for almost any application whenever there is enough wind resource at the site.

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Types of wind turbines

Wind turbines that are fitted directly to a building's structure are currently being developed, and stand-alone turbines on the site of buildings are not uncommon.

There are two basic kinds of turbine: horizontal axis and vertical axis, with variations within these broad classifications.

Vertical Axis Wind Turbine (Darrieus type)

Horizontal axis (HAWTs) turbines are generally more efficient, and most commercial models are of this type. These comprise a central hub supported on a tower with (usually three) evenly spaced blades, and rotate at an almost fixed rate, regardless of wind speed.
Vertical axis (VAWTs) systems can be installed without the need for a tower, and may be easier to integrate with a building's structure.

Turbines characteristics

Wind speeds required

Minimum speeds of 3 m/s are required to allow most turbines to cut-in, and turbines include power regulating devices which operate when wind speeds exceed a safe limit.

Power generated by a wind turbine

The power output of wind turbines depends on two key factors: the swept area of the rotor and the wind speed.

Doubling the diameter would quadruple the swept area and therefore quadruple the output.
Power output increases with wind speed, and the relationship is cubic:
If the wind speed doubles the power output will increase by a factor of around eight.

Siting of Wind Turbines

The placement or "siting" of wind systems is extremely important. In order for a wind turbine system to be effective, a relatively consistent wind-flow is required.

The best locations for wind turbines are away from obstructions which affect air flow, including any features of buildings which may have an effect on airflow. Obstructions such as trees or hills also interfere with the rotors.
Wind speed increases with height, and so turbines often require masts or towers to take advantage of higher wind speeds and to avoid turbulence caused by obstructions.

The amount of Wind Energy available at any location depends on two sets of factors:

Climatic factors: Time of day, season, geographic location, topography, and local weather.
Mechanical factors: Diameter of rotor, and type of turbine.

Need for a Feasibility Study

All these factors must be considered when choosing a site for a wind-powered generator.
Wind characteristics are specific to each location, and initial evaluations of the feasibility of wind power at any particular site will require details of historic meteorological data. A more detailed local assessment will normally be required to establish the affects of local topology, obstructions, etc.

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