San Francisco Department of the Environment

Buying a Small Wind Turbine, A Consumer Guide and FAQ

There are currently (5) small wind turbine installations in San Francisco. One can consider purchasing a small wind turbine if the proposed site has wind speeds of at least 10 mph or 4.4 m/s (meters per second), and the average electricity bill is over a $150 per month. It is important to make any energy conservation and efficiency changes at the site before looking into a small wind turbine.

The American Wind Energy Association (AWEA) recommends obtaining and reviewing product literature from several manufacturers, and researching those you want to pursue to ensure they are recognized businesses. It is important to find out how long the warranty lasts and what it includes, and ask for references of customers with installations similar to the one you may be considering. Ask system owners about performance, reliability, maintenance and repair requirements, and whether the system is meeting their expectations.

Frequently Asked Questions (FAQ)

1) How do wind turbines work?
The blades of a wind turbine spin when wind passes through them; this motion causes a shaft to rotate inside of a generator, which then produces electricity.

2) What is a small wind turbine?
Small wind turbines, also known as “small wind generators,” are used for residential or commercial buildings. The City and County of San Francisco defines small wind turbines as having a rated capacity of 50 kilowatts (kW) or less.

3) What is “urban wind”?
“Urban wind” refers to wind energy technologies that are appropriate for urban environments.

4) What is the difference between a “Horizontal-Axis” and “Vertical-Axis” wind turbine?
The vast majority of wind turbines are three-bladed, “propeller-shaped” devices that spin around an axis that is parallel – or horizontal – to the ground. These are called “horizontal-axis wind turbines,” or “HAWTs.” A “vertical-axis wind turbine,” or “VAWT,” has a rotor that revolves around an axis that is perpendicular – or vertical – to the ground, similar to a barbershop pole or corkscrew. Many variations of HAWTs and VAWTs exist or are under development. HAWTs utilize a horizontally mounted rotor shaft on top of a tower and have blades resembling propellers. VAWTs have rotor shafts that are oriented vertically and are often produced in Darrieus (egg-beater) or Savonius (wind scoop) configurations.

5) What turbine size do I need for my building?
The size of your turbine depends on how much electricity you use. A single-family home in SF uses approximately 5,232 kilowatt-hours (kWh) of electricity per year (about 436 kWh per month). A commercial building’s electricity use can be significantly higher depending on the building, and would therefore require bigger wind turbines. Depending upon the average wind speed in the area, a wind turbine rated in the range of 1-5 kW would be required to make a significant contribution to meet this demand.

6) How much does a wind system cost?
Small wind energy systems can cost anywhere from $5,000 to $40,000 depending on the kW size. Well-sited small wind turbines can usually pay for themselves within 15 years, about half their serviceable lifetimes, if the right incentives are applied. VAWTs are relatively new to the market which means that prices for the systems are not readily available, but prices can range from around $5,000 to $15,000, not including installation costs.

7) How do I determine the wind resource at my site?
Wind experts recommend the installation of anemometer, a device that measures wind direction and speed, for at least 12 months. The anemometer is usually installed on a pole or tower where a small wind turbine can be placed. Anemometers are typically installed for a year because wind has seasonal changes; for example, when winds tend to be stronger in the spring. The SF Environment is currently developing a SF Wind Map to help San Franciscans get a better understanding of their wind resource in their neighborhood.

8) How are small wind turbines mounted?
Because wind speeds increase with height, the wind turbine should be mounted on a pole or tower. In general, the higher the pole or tower, the more power the wind system can produce. The pole or tower can also raise the turbine above the air turbulence that can exist close to the surface because of obstructions such as buildings, trees, and hills.

9) Can I connect my system to the utility grid?
Small wind energy systems can be connected to the electricity distribution system - these are called grid-connected systems. If the turbine cannot deliver the amount of energy you need, the utility makes up the difference. However, you should contact your utility before connecting to their distribution lines to address any power quality and safety concerns. Your utility can provide you with a list of requirements for connecting your system to the grid.

10) How reliable are wind turbines? Will I have to perform much maintenance?
Most small turbines have only 2-3 moving parts and are designed for a long life (20 - 30 years). However, as with any other hard-working machine, it must be operated safely and in compliance with the manufacturers specifications and parts must be maintained and occasionally repaired.

11) Are there any federal or state incentives for small wind turbines?
Owners of small wind systems can receive an uncapped federal investment tax credit for 30% of total installed costs. At the state level, the California Energy Commission’s (CEC) Self-Generation Incentive Program offers rebates for wind systems at $1.19 per watt, up to 3 MW. 

12) How do I apply for a small wind turbine permit in San Francisco?
The SF Department of Building Inspections (DBI) is currently accepting applications for small wind turbine permits. Permits for small wind turbines have been prioritized by DBI as written in the revision of the AB-004. Residents can apply for rooftop and ground level installation permits. DBI is also required to inspect the proposed site before a permit can issued. See the Panning Department's standards for the review of applications here. Wind permitting fees are reported in the range of $1,000 to $5,000, depending on whether public notification is required, by vendors who have completed projects in San Francisco.

13) Is there anything I should watch out for when buying a small wind turbine?
Most of the popular models of small HAWTs operate at about the same efficiency. The energy production you should expect will be closely related to the swept area of the rotor blades, which is based on the diameter of the rotor. If you are offered a HAWT that promises to power your whole house with a turbine that is much smaller than conventional products, ask for more details. Because VAWTs are just starting to enter the marketplace, their efficiencies are much harder to predict. Always get several bids from different companies and ask for references from prior customers.

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