Friday, April 17, 2009

Residential Wind Turbines


Got big breezes?

Small-scale wind turbines have become a viable, if not yet mainstream, means of powering homes with clean, renewable energy. You've probably seen clusters of huge wind turbines in rural areas. Those wind farms produce power for the utility grid. A residential wind turbine is much smaller, and rather than multiple turbines, a home typically has just one.
Residential Wind Turbines

Unlike a windmill that pumps water or turns a grinding wheel, a wind turbine generates electricity from the wind's kinetic energy-that's the energy of motion. When wind moves the turbine's blades, it turns a shaft connected to an electrical generator. The generator feeds electricity to your home.

Most residential wind power installations are grid-connected, so when the wind isn't blowing, you still get power from the utility grid. Off-the-grid installations in rural areas rely on banks of batteries to store electricity for use when the wind dies down. Although a wind turbine costs a lot upfront, it will reduce your electricity costs now and serve as a hedge against rising energy costs in the future.

Top Tips

At home

  • Conserve first. Before thinking about wind power, work on getting your home's energy use as low as possible.

  • Know your wind speed. For a wind turbine to be cost effective, it needs ample, consistent wind. Most systems require speeds of at least 7 to 10 miles per hour before they start producing power, and 12 to 20 mph provides the best performance. As wind speed increases, power output increases dramatically. Wind resource maps, published by the U.S. Department of Energy, can help you assess the aeolian potential in your area.

  • Know your codes. Check your local zoning and building codes and homeowner's association covenants to see if you are going to bump up against height or other permitting restrictions. It may be possible to obtain a variance, but that could be a costly or time-consuming process.

  • Consider your space. Wind turbines don't require a lot of space. But to avoid conflicts with neighbors, wind industry advocates say that for turbines up to 3 kilowatts (kW), you should have half an acre or more. For systems from 3 to 10 kW, you should have at least an acre.

  • Talk to your neighbors. Before moving ahead with a wind turbine purchase, discuss your plans with your neighbors and invite their questions. Think of it as an opportunity to educate the community about the benefits of clean, renewable energy. Some people consider wind turbines unsightly, while others delight in the sight of them spinning. Others are concerned about noise, but experts say that a typical residential wind turbine makes less noise than a washing machine or an air conditioner. That means you'd be unlikely to hear it inside your house, and your neighbors wouldn't hear it at all. And in case you're wondering, a wind turbine won't interfere with TV or radio reception.

When shopping, look for

  • The right size. If your system is connected to the utility grid, it's usually sized to ensure that your annual electricity production is no greater than your annual electricity use. That's because the electric company will not pay you for excess production. Small residential wind turbines are usually 10 kW or less. It's rare to see more than one turbine installed on a residential property, because it's cheaper to install one large turbine than multiple smaller ones. A typical 10-kW turbine will have a 20- to 25-foot blade diameter, although smaller systems with smaller blades are available.

  • The right height. Wind turbines are mounted on tall towers. Although some 40-foot turbines are available, the optimal height is 80 to 100 feet. To avoid turbulence, which diminishes performance, the bottom of the turbine's blades should be at least 10 feet above the tops of trees, buildings, or other structures that are within 300 feet of the turbine. Higher is usually better. According to the American Wind Energy Association, if the height of a 10-kW turbine is increased from 60 to 100 feet, the system cost will increase by 10% but the power output will increase by 29%.

  • Durability. The towers are usually made from steel and are either self-supporting or guyed. Guyed towers have guy wires anchored at a distance from the tower's base, so they require more space. Self-supporting towers are heftier and costlier.

Other Considerations

  • Wind power is most cost competitive in areas where electricity costs are at least 10 cents a kilowatt-hour, and in rural areas where it would be very expensive to extend the utility lines to the house. The average cost of a residential wind turbine system is $5 to $7 per watt, which is comparable to that of a photovoltaic (or "solar") system. A 3-kW turbine on a 60- to 80-foot tower would cost about $15,000 to $21,000, including all components and installation.

  • Wind turbines require little maintenance and should last 20 to 30 years. The system will pay for itself within 6 to 30 years, according to the American Wind Energy Association, depending on average wind speed, the tower's height, and your electricity cost. In areas with high electricity costs, wind turbines pay for themselves more quickly.

  • In remote regions, an "off-the-grid" or independent wind turbine system may be more cost effective than running wires to connect with the utility grid. With these off-the-grid systems, the home is powered entirely by wind, with a bank of batteries storing excess electricity for use when the wind isn't blowing.

  • In states with "net metering" laws, most residential wind installations are connected to the local utility's electricity grid or "on-the-grid." (More than 30 states have net metering laws; check the DSIRE database to find out about your state.) This allows you to feed any excess electricity your system may generate into the grid. And when the wind is quiet, your home draws the electricity it needs back out of the grid. Your electricity meter tracks the outputs and inputs. Over a 12-month period, you pay only for the electricity you used above what your system produced. Unfortunately, these net metering laws also stipulate that the utility company need not pay you for surplus electricity you may have generated over the same period. For this reason, most people size their system so that it won't produce more than their expected annual electricity use.

  • Off-the-grid installations need batteries to provide power at night and during cloudy periods. Most grid-tied systems don't include them because they drive up the system's price. But if there's a local power outage, utility companies require an automatic shutdown of your power and everyone else's--for the safety of utility line workers out repairing power lines. If you want the security of having back-up power during grid outages, you'll need to add batteries to your system.

Benefits... you
A residential wind turbine reduces the environmental impacts of your electricity consumption and provides you with more predictable energy costs. your wallet
If your electric bills run $60 to $100 per month, a 3kW turbine could reduce them by 30% to 60%. In remote locations, installing a wind turbine may be less expensive than extending power lines to your home. the Earth
Wind turbines produce renewable energy with no air or water pollution and no greenhouse gas emissions. According to the American Wind Energy Association (AWEA), a small residential wind turbine can offset 1.2 tons of air pollution and 200 tons of greenhouse gases over its life--that's the equivalent of taking 33 cars off the road for one year. Wind turbines do kill birds in some locations, but according to the AWEA, a house cat, car, or sliding glass door is a greater threat to birds than a small-scale wind turbine.

Common Mistakes

Believing exaggerated claims. If it sounds too good to be true, it probably is. Beware of dealers claiming their products offer extraordinary efficiencies. The American Wind Energy Association says that most small turbines operate at comparable efficiencies. And beware of products touted as working well at low wind speeds. There's very little energy available at wind speeds below 12 mph.

Getting Started

  • Most wind turbines are professionally installed, although confident DIYers with strong technical skills could purchase the components and do it themselves. Ask any contractor the following questions:

    • How many years has the contractor has been in the wind energy business and how many residential installations has he or she done? Interest in renewable energy is on the upswing and many contractors are new to the business.

    • What specific services will the wind energy contractor provide? Many offer a "turnkey" service: they'll analyze your site and energy needs, design an appropriate system, procure the equipment and materials, handle the utility company and rebate paperwork, obtain any necessary permits, and install the system.

    • Are the bids you received based on comparable information? When evaluating bids, make sure they are for the same type and size system. The bids should include all costs associated with buying and installing the system, including hardware, installation, permits, and grid connection. The bids should also state the expected energy output in kilowatt-hours.

    • Unlike PV systems whose capacity can be expanded by adding modules if your electricity demand grows, a wind turbine's capacity is fixed. Work closely with the contractor to carefully assess your current and anticipated future energy needs to make sure you get the right-size wind turbine for your needs.

    • For general advice on what questions to ask contractors and other tradespeople, see our "What to Ask Your Contractor" article.

  • Many people finance their wind turbine with a home equity loan or by folding the cost into a new construction loan. Check out the Database of State Incentives for Renewables and Efficiency, DSIRE, for information about government incentives to reduce costs.

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