Sept. 15, 2002

(Bergey Windpower BWC-1500, 1500watt turbine)

Wind Power can be an ideal source of energy in locations where the average wind velocity is high enough. It is also a good option when combined with solar and other alternative energy sources. When it's bad weather and cold in winter your solar installation may not produce that much power, this is where a wind turbine can supplement to meet your energy needs.

Here's a brief low-down on wind power :

(taken from www.energyalternatives.ca)

Wind Energy

Wind energy has been used for centuries, for grinding grain, pumping water and generating electricity. Small wind turbines were an important source of electricity for rural families in North America in the 1920’s and 1930’s. Wind energy faded into the background with the rural electrification efforts of the 1940’s and the development of reliable small engine generators.

Modern small wind turbines are technically advanced and reliable; incorporating permanent magnet alternators, sophisticated electronics, and innovative blade materials.

Wind and Solar
In many Canadian locations a wind turbine is an excellent supplement to a solar electric system. Small wind systems are often combined with photovoltaics because seasonal variations in wind and solar resources are complementary. Most places in Canada do not have adequate wind to use as a primary power source. Locations such as the prairies that have constant prevailing winds are most suited to wind power. Contrary to popular beliefs, coastal areas are not always the best sources of power as the winds are not constant and predictable such as the prairies.

Battery Size
Wind is a variable resource. The winds may be calm for a week or more, but when it does become windy it often blows very hard - most notably in the winter. For this reason wind energy systems usually require a larger battery to take advantage of the energy when it is available and store it for extended calm periods. In wind only systems the battery storage should be designed for 10 days of autonomy or more.

Site Selection
Wind flowing over the surface of the earth is slowed by the friction of the ground. Objects such as trees and houses create turbulence. This reduces the energy a turbine can extract from the wind and stresses on the turbine components. The higher a turbine is placed the more power is generated. A wind turbine should be at least 33 feet (10 meters) above any object within a 330 foot (100 meter) radius. Local geography also needs to be considered.

Wind Speed
The power of the wind is easy to feel and the sight of a wind turbine rotating in the wind provokes a lot of interest. Proper location is critical to the success of a wind turbine installation. The determining factor of a good location is the amount of wind that is available. If there is an average wind speed of 8 mph (13 km/h) or higher, wind power may be a viable source of electricity. The power available in the wind increases with the cube of the wind speed — if the wind speed doubles the power available increases by eight!

Maintenance
Unlike photovoltaic modules, wind turbines have moving parts. Periodic maintenance of bearings, brushes and shafts is required. It is important when installing a wind generator to consider how easy it will be to access the generator and remove it.

Towers are a critical component of wind power systems. Proper location and height of tower are necessary to get maximum energy from a wind turbine. Improper tower design or installation may result in personal injury, property damage or a damaged generator and will very likely result in less than satisfactory performance from your wind turbine.

Installation
You should be completely familair with the installation procedures before you begin. Safety equipment should be used at all times. Local building departments may have bylaw or zoning restrictions for towers.

Tower Height
Wind generator operation is dependent on the quantity and quality of the wind hitting the blades. Turbulent wind will reduce the power output as the turbine swings back and forth hunting for the wind. The unequal stresses caused by turbulence, and the variation in wind speed between the upper and lower blades of a wind turbine installed too close to the ground will reduce power output and wind turbine life.

Wind speed increases rapidly with tower height. Doubling tower height increases the available wind power by about 40%. It is often more economical to install a higher tower rather than purchasing a larger generator. A wind generator should be installed a minimum of 33 feet (10 meters) above any obstruction within 330 feet (100 meters).

Tower Construction
Guyed towers are economical and are able to withstand very high winds if properly installed. They require a fairly large area of cleared land around the tower to facilitate the installation of the guy lines. To supply the desired amountof support and keep the stresses on the tower to a minimum, the guy lines should extend as far as possible around the tower to a maximum radius of 80% of the tower height. Guyed towers may be either lattice towers or tubular towers. The tubular towers are frequently designed for tilt up installation. They have the advantages of easy installation and turbine maintenance.

Self-supporting towers are the least visibly intrusive wind turbine towers. They can be installed in rough terrain with a minimum of cleared area. Very small wind turbines may be installed on a short self-supporting tubular tower, but larger turbines require a lattice tower.

Building Your Own
Smaller residential wind turbines may be economically mounted on a home built tower. Steel water pipe may be used to construct a tilt-up tubular tower. We also sell tower kits that include everything you need except the pipe and the anchors, which can generally be purchased locally more conveniently.

Grounding
Tower grounding rods and wire provide lightning protection and assure a low resistance path to ground. The grounding wire should be straight, without sharp angles. A free-standing tower poses a special problem because its base acts as an insulator.

Although wind generators may cost less per watt than a comparable PV array, finding the right location is critical. The determining factor is the amount of wind available at the chosen site.

Measuring the Wind
There are three primary ways of determining how much wind is available.
1. Installing an anemometer.
2. Using existing data.
3. Visual observations.

Anemometer
An anemometer is the most accurate way to determine wind speed. For a large installation it usually takes several years of readings, an anemometer, a data logger and a computer to compile accurate data. Unless you plan on spending $15 000 or more on a wind energy system, this is usually not a necessary step.

There are inexpensive anemometers that can be read manually on a daily or weekly basis. For a small residential wind generator a minimum of three months of data should be recorded and correlated with another source of wind data. Some people install a small wind generator and use it as an anemometer if they are planning for a much larger installation.

Existing Data
Existing data can often be obtained from the local airport or meteorological stations. Other places to contact would be universities, colleges and radio stations. The Canadian government compiles wind data in catalogue form, and information is available on the internet. Wind speeds can vary a great deal within a small area, so this information should be correlated with another method like the Griggs-Putnam Index.

Griggs-Putnam Index
The Griggs-Putnam Index is the simplest and quickest method of determining average wind speed. Flagging of foliage (deformation of branches away from the prevailing wind) is correlated with average annual wind speed. If you have a flag at your site and the flag is stiff in the wind for a few hours a day then the site is a good candidate for wind power.

How much wind is enough?
As a general rule, an average annual wind speed of at least 10 mph (16 km/h) is necessary for a cost effective wind power installation. If wind power is being used as seasonal back up for a solar electric system, or if less power is required during calm periods of the year this rule can be modified. Use the average wind speed for the season in which you need the power.

How much power do I get?
Average annual wind speed is used to predict annual energy output. There is some variation in annual energy output because some locations have gusty, intermittent winds and other locations have steady trade winds. Different locations may have the same average wind speed yet produce very different amounts of energy.

To determine how much power is available on a daily basis. The Annual Energy Output must be divided by 365 days to give the Daily Energy Output. For the purposes of battery based system design this Daily Energy Output must be divided by the System Voltage to give the Daily Amp-Hours.

Example In a 12 volt system, where the average annual wind speed is 10 mph, the AIR 303 will produce 140 kWh.

Therefore, if you have an energy budget of 32 amp-hours per day the Air 303 will supply the power you require at an average annual wind speed of 10 mph.

The Danish Wind Turbine Manufacturers Association http://www.windpower.dk/tour

Copyright 2001-2003  Peter Ferlow