by Nick Gromicko, CMI®
Wind turbines are structures that capture the wind’s kinetic energy and convert it into electricity.
The basic method by which turbines produce electricity is quite simple, and inspectors may want to familiarize themselves with these increasingly popular constructions. Turbine blades are shaped in such a way that wind causes them to rotate, which then makes a chain of shafts and gears turn. A magnetic rotor in the generator housing spins along a shaft within loops of copper wire bound around an iron core, which generates an electrical current. After this direct current is converted into alternating current, it can then either power a house or be sent into the electrical grid, depending on local net metering laws.
Wind turbines designed for residential use -- sometimes called microturbines -- are typically much smaller in size (both in height and rotor diameter) than their commercial counterparts, as well as their power output. The largest commercial wind turbine is Germany’s REPower 5MW. At 600 feet tall, it is nearly twice the height of the Statue of Liberty and can power 5,000 homes. Microturbines, by contrast, rarely produce more energy than is required by a single home. As of 2009, the United States ranks first in the world in wind power capacity, followed by Germany, China and Spain. Denmark ranks ninth in the world in wind power capacity, but generates about 19% of its electricity from wind. Wind power in China increased twenty-fold from 2005 to 2009.
Types of Wind Turbines
- Horizontal-axis wind turbines have their main rotor shafts and electrical generators located at the top of a tower, pointing into the wind. The blades are placed a considerable distance in front of the tower and are sometimes tilted slightly forward into the wind. This design is efficient because the blades always move perpendicular to the wind, receiving power through their entire rotation. They are typically large and difficult to install, however, and they must be placed some distance apart from one another to minimize fatigue loads due to wake turbulence.
- Vertical-axis wind turbines have their main rotor shafts arranged vertically. The turbine does not need to be pointed into the wind to be effective, which is advantageous in areas where wind direction is highly variable. They also have lower wind startup speeds than horizontal designs, they emit less noise, and they are generally smaller, making them ideal for locations where taller structures are prohibited. They are used infrequently because their efficiency is reduced by the need for their rotors to be close to the ground where wind speeds are typically lower.
Drawbacks to Wind Turbine Usage
- aesthetics. As they are large and typically placed in otherwise natural areas and green space, wind turbines sometimes evoke frustration and opposition. The "not-in-my-backyard" sentiment runs rampant in areas where large wind installations are proposed, such as the offshore Cape Wind Project in Cape Cod, Mass. Microturbines, too, are often the source of friction between neighbors.
- noise and vibration. While commercial wind farms may be noisy, they are generally erected in unpopulated areas. Microturbines are considerably quieter, but their placement in proximity to homes may make their constant “swoosh” sound an annoyance to owners and their neighbors. Roof-mounted microturbines are known to cause excessive vibration, however, and homeowners should consider the inconvenience this may cause.
- birds deaths. Birds are occasionally sacrificed to the rotating blades of wind turbines, but developers usually take avian migratory patterns into consideration before erecting wind farms. Birds are less threatened by residential microturbines.
- upfront costs. Like photovoltaic arrays, wind turbines become profitable only after years of energy savings. Their installation costs can be prohibitive, but federal and state rebates are available to offset upfront costs.
- unpredictable winds. Wind patterns vary by region, and even within particular regions, wind patterns are difficult to predict. Also, homeowners in populated areas have to compete for wind with tall buildings, making wind turbines somewhat impractical. In one of the few studies that analyzed the actual energy production of residential wind turbines, the Massachusetts Renewable Energy Trust was disappointed by the discrepancy between expected and actual performance. In a similar British study, researchers were also dismayed by the lackluster performance of the residential wind turbines tested, finding that one produced so little electricity that it could not even power its own electronics. Microturbines help reduce emissions, and their efficiency may someday increase to the point that they see mainstream popularity, but commercial wind farms are currently far more viable economically.
- local restrictions. Homeowners may be met with resistance from local boards, neighbors and/or homeowners associations.
In summary, wind turbines are available in several designs for residential and commercial use, although they have their drawbacks.