It is generally accepted that the earth’s fossil fuels are limited resources and that globally their production will peak in the coming years, as it did for oil production in the US in the 1960s and the North Sea in the 1990s, and prices will continue to rise. Coupled to the environmental impact of burning fossil fuels and the security of energy supply it is evident that renewable energies will have to contribute more to the world’s ever rising demand for energy.

Wind power systems have developed to be prominent suppliers of renewable electricity. Since the 1980s installed power has increased dramatically as prices have fallen contrasted to the rise in oil and gas. Today, production is barely able to keep up with demand and manufacturing has reached the state of a high-tech industry.

To date, most R&D dollars have gone into industrial or utility sized wind turbines. This investment has allowed large scale wind farms to compete with conventional power producers to energize the grid. In 2007 wind turbines generated more than 1% of global electricity. Statistics released by the European Wind Energy Association (EWEA) show that in 2008, 43% of all new electricity generating capacity built in the European Union was wind.

Wind energy installed in 2008, source: World Wind Energy Report 2008, Renewable Energy World Jan/Feb 2009

Country	Capacity installed (MW)	Added capacity 2008	% total electricity generated
USA	25,170	8,351	1%
Germany	23,902	1,655	7%
Spain	16,740	1,595	11%
China	12,210	6,298	1%
India	9,587	1,737	2%
Italy	3,736	1,010	2%
France	3,404	949	2%
United Kingdom	3,288	899	2%
Denmark	3,160	35	20%
Portugal	2,862	732	11%
Canada	2,369	523	1%

 

The same is not true for small commercial and residential wind turbines. Although, small electricity generating wind turbines have been in use since the 1920s or 1930s, they have not proliferated as their larger industrial counterparts have done. In fact many smaller turbines are based on older inefficient designs that do not take into account aesthetics or ease of installation. Combined with the advent of modern power electronics, today’s turbines can now be connected to the grid with the aid of a frequency converter, whereas in the past, a battery was generally used for storage. Combined with smart, efficient, inexpensive designs; small wind turbines are poised to become a substantial source of energy. As can be seen in the figure below the growth in the U.S. over the last few years has been impressive. The UK market has also experienced an exponential growth over the last several years, driven by higher energy prices than in North America and a progressively aware consumer base. In 2008 an estimated £33M worth of small wind turbines will be installed and an additional £9M exported. The UK has experienced an annual growth rate of over 80% based on units installed and over 100% based on revenues between 2005 to 2008, with similar growth rates expected over the next decade.

Growth of US small wind market

The basic principles that govern an industrial or utility sized wind turbine still apply to commercial and residential wind turbines, although the design and manufacturing process can be significantly different. A wind turbine converts a portion of the wind’s kinetic energy into mechanical energy by rotating the turbine’s blades. This mechanical energy is then converted into electrical energy by a generator attached either directly or through a set of gears to the turbine shaft. In most systems this energy is then passed through an inverter and used to power your home/business or else it is sent to the grid or stored by batteries.

Configuration of different types of wind turbines

From this equation it is important to notice that the amount of power your turbine produces is proportional to the speed of the wind cubed. In other words if you double the wind speed, your power output increases by a factor of 8! Therefore, turbine siting is extremely important and a turbine’s rated power is meaningless unless it is situated in a location with adequate wind speeds.

Manufacturer’s generally give their turbine a rating e.g. 1kW. This is its rated power, usually at an unrealistically high wind speed of approximately 12.5m/s or 28mph. This is quite a windy day, generally, a commercial/residential wind turbine will only experience wind speeds this high less than 10% of the time. A more realistic wind speed is 5.5m/s or 12mph (check out the wind atlases and determine the average wind speed in your area). An even better measure is how much energy the wind turbine produces in a month measured in kWh. This number can then be easily compared to your consumption from your utility bill. Once again make sure that the calculation uses a realistic average wind speed.

Good question! Most countries provide a wind atlas or series of wind maps giving the average wind speed at various heights above ground level. Click here to access a compilation of wind atlases from around the world. This is a useful starting point. However, it is important to observe that wind speed increases with height, so make sure you are referencing the appropriate height. It is common practice to use an empirical relationship between height and wind speed

Mean wind speed across Canada at 30 meters in height (source: www.windatlas.ca/en/map

Trees, other buildings, terrain, season and a host of other factors also need to be taking into consideration as they will affect local wind speeds and can cause undesirable turbulence. However, buildings can also be used to funnel and accelerate the wind. Ideally a wind potentiometer should be located in your desired turbine location for sufficient period to record your particular wind speeds. Combined with a windsock, a Wind Rosetta can be drawn of your exact wind resource.