Monday, June 14, 2010


Windmills are a familiar image associated with farms and Holland and are a special class of a wind turbine. The blades or propellers on a wind turbine are built to capture the wind and move, generating electricity. The constant wind blows the angled blades of the familiar windmill pushing them in a circle. If the mechanical energy thus captured is used directly to pump water, or grind grain, the machine is called a windmill. If the mechanical energy is instead converted to electricity the machine is called a wind turbine. The basic concept of a wind turbine is the wind turns the blades, which spin a shaft, which connects to a generator and makes electricity. This is the opposite of a fan, where the electricity is used to create a breeze. There are two main types of wind turbines, horizontal-axis and vertical axis. Horizontal-axis wind turbines (HAWT) have the rotor shaft and electrical generator on top of the tower, and must be pointed into the wind. The horizontal axis is the most familiar type of wind turbine. Turbines used in wind farms for commercial production of electric power are usually three-bladed and pointed into the wind by computer-controlled motors. Vertical axis wind turbines have the rotor shaft arranged vertically and the wind blades lined up horizontally. This type of turbine does not need to be pointed into the wind to be effective and may be suited to smaller installations. Vertical-axis turbines may be able to solve the main generation problems for home users including aesthetic concerns, space requirements and sound levels. This website lists all the micro wind turbines currently available, though I warn you the list is mind boggling.

The wind turbine is an attractive idea for renewable power generation and might fit into my goal of reducing my purchased power by an additional 50%. However, before you jump to buy one, you need to determine if your site is suited for a micro turbine. Ed Begley Jr. who is involved in marketing a new wind turbine design was dismayed to find his own home was not suitable for a turbine. In order for a wind turbine to work, the wind must blow at a sustained and consistent level. The economics of a wind system are very sensitive to the average wind speed in the area. As a general rule of thumb even for a micro turbine 8-10 mph average wind speed is necessary to produce any meaningful amount of electricity. The US Department of energy has a map so that you can get a general idea of the wind, but wind is a totally local phenomenon. Winds are created by uneven heating of the atmosphere by the sun, irregularities of the Earth's surface, and the rotation of the Earth. As a result, winds are strongly influenced and modified by local terrain, bodies of water, weather patterns, vegetative cover, and other factors. Though I live in an area rated as having poor wind potential by the DOE, I think I may have a prevailing breeze (wind?) to the river. The only true way to know if your site is a candidate for a wind turbine is to actually monitor the wind for an extended period of time.

Installing monitoring equipment can be an expensive exercise, but actual measurement of the wind speed could determine if any of the micro turbine designs coming onto the market might be suited for my site. Before choosing which type of turbine is best for a particular site, some sort of wind speed measurement should be taken for a few consecutive months (or ideally, a full year). With long term wind measurements an accurate average wind speed can be calculated, as well as determining likely maximum wind speeds. Armed with this information, a turbine can be chosen that will maximize performance at the average wind speed, as well as one that will withstand the likely maximum wind forces to avoid catastrophic failures.

In addition to adequate wind (or too strong wind), there are other issues involved with wind turbines appearance; danger to birds and sound. Wind energy is seen as a ‘green energy solution’ that is renewable and generally good for the environment. These turbines, however, also emit infrasounds. According to Rosemary Stephen PMed, EOH, IPM, Elements: Environmental Health Intelligence, “In general, humans can perceive audio frequency ranges between 16 to 20 Hz (cycles per second) at the lower limit of hearing ... Infrasounds are in the lower range, at or below, the 20Hz frequency range…A small percentage of the population have a very acute sense of hearing A 1998 study done in the Netherlands “indicated that 15% of the population is possibly involved (affected), 3% definitely” experiencing “sensations that may be attributed to low frequency or even infrasound.” For the segment of the population who can perceive infrasound, the frequency resembles a loud, continuous, highly irritating noise.” This small portion of the environment is impacted by proximity to wind turbines. As for appearance we all have to deal with neighbors and family and because wind turbines generally need to clear the tree line, they are not subtle. My solar panels can not be seen by my neighbors under normal circumstances, but a wind turbine could be viewed by anyone on the road.

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