Home wind power is in the news a lot today.
Be forewarned that when it comes to maintenance, challenges, and spectacular failures, wind-electric systems are anything but “upkeep-free” or simple. But if you make good
decisions up front and stay on top of maintenance and repair, your wind-electric system should provide years of energy for your home or business. Read on for some perspective on the three most common mistakes to avoid and the three most important decisions you need to make. Then take a look at the equipment available today, and learn more about making a wise buying decision.
How High?
The most common mistake made with small wind-energy systems is putting a turbine on too short of a tower. As with any renewable electricity system, the collector must have good access to the fuel—it needs good wind, which is somewhat different than other renewable sources. The power available in the wind increases with the cube of the wind speed. This means that there is nearly 100% more power available in 10 mph winds than in 8 mph winds.
While we might perceive some puffs and gusts at ground or rooftop level, there is little usable fuel at these heights. The rule used by experienced wind installers is to place the whole rotor at least 30 feet above any obstacle (usually trees) within 500 feet of the tower or the prevailing tree line, whichever is higher. Keep in mind that you are installing the wind turbine for decades of productivity—trees your turbine may barely clear today may be considerably taller in several years. Get it right at installation time by estimating mature tree growth and sizing the tower accordingly.
In addition to access to winds of sufficient quantity, the 30-foot rule also gets the turbine rotor above much of the turbulence created by any nearby obstructions. While turbulent winds are reduced-quantity winds, they are also reduced-quality winds, putting considerable stress on a wind turbine by their constant buffeting and shifting. Turbulence’s continuous pounding strains all wind turbine components, adding to maintenance requirements and reducing the equipment’s life.
Short towers result in a quadruple whammy: Reduced wind speeds, more wear and tear from turbulence, less electricity, and compromised reliability.
How Wide?
Your wind generator’s “swept area” defines its ability to collect wind, which is, after all, the resource you are trying to tap. Like other renewable technologies, a small collector will collect a small amount of energy; a large collector will collect large amount of energy. If you’re trying to capture enough rainwater to supply your household, water the garden, and wash the cars, you don’t try to collect it in a thimble. And in the same way, you need an adequate “wind collector” to make the amount of energy you need.
Typical small wind turbines that can contribute substantially to a home, farm, school, or business will be 12 to 70 feet in diameter. In our list, we’ve included a few machines that are smaller, but remember that you might not get the energy you need out of these machines. There’s no magic behind the blades of your wind generator that can make dramatically more energy from the same swept area. There’s no substitute for square footage of swept area— the area of the wind that is intercepted by the rotor.
Additional turbines will be added over a four-year period, bringing the planned total for the farm to 341. But with other projects in the works, the farm may not be the world's largest for long.
Seven miles off the coast of Kent, 100 380-foot turbines, spanning 22 square miles and representing two years of construction, have begun to power Britain. Bearing a price tag of 780 million pounds, this is the world’s largest offshore wind farm.
With the opening of this farm, Britain’s capacity to produce wind power will increase by 30 percent. At full capacity, the farm is projected to power 200,000 homes, bringing the nation one step closer to its goal of producing 15 percent of its energy from renewable sources by 2020. Currently it produces 3 percent.
Additional turbines will be added over a four-year period, bringing the planned total for the farm to 341. But with other projects in the works, the farm may not be the world's largest for long.