January 13th, 2009

Wind Power for Every Rooftop?

Posted by Jason Pelletier, Low Impact Living

Stumble it!digg it add to del.icio.ustechnorati

These days, there are more and more options for those of you who want a small wind turbine out in the yard or on your roof. Residential wind power systems range from the standard to the somewhat bizarre, and come in sizes that can power several major appliances all the way up to your whole house and beyond. In the right conditions, residential wind power can be much more economical than other renewable energy options such as solar or geothermal.

Traditional propeller-type wind turbines remain the best options for residential settings outside of urban areas. They are efficient and time-tested, and the leading manufacturers of these turbines have been at it for a long time. Two of the leaders are Bergey Windpower and Southwest Windpower. Bergey makes several versions of its Excel turbine suitable for home wind power use. The Excel can be connected to the electrical grid and is big enough to power an entire home.

Southwest Windpower makes the Skystream 3.7 turbine (shown above), an innovative machine that has a number of advances specifically targeted to residential users. It is meant to be tied to the electricity grid, and in reasonably windy conditions could power an average home.

In the past few years, a number of new manufacturers have come out with radical turbine designs intended to make wind turbines easier to install and better for tightly packed suburban and urban environments. Most of these turbines are vertical axis wind turbines, or VAWTs. Instead of spinning on a horizontal axis like their propeller-based cousins, VAWTs rotate around a vertical axis. The key advantages are that they can be quieter, are more amenable to the swirling wind conditions found in urban environments, and can have a smaller overall footprint (both tower width and height). The downsides? The companies that make them don’t have long track records, and the turbines are less efficient because a portion of each turbine is always spinning into the wind.

One example is Mariah Power, who makes the Windspire wind turbine (shown in the upper right image above). Each Windspire turbine is 30 feet tall and two feet wide, and it resembles a sculpture as much as it does a renewable energy device. The cylindrical structure makes it very quiet and compact, meaning you could install multiple turbines alongside one another for more power. Each unit should provide from 10-50% of the electricity for a typical home depending on where you live in the country.

Another example is Helix Wind. The company make several vertical axis turbines that, in my opinion, most closely resemble a ram’s horn. The complex (and weird or beautiful, depending on your sensibilities) design efficiently transforms variable winds into clean electricity. Their largest model, the S594, can provide 50-100% of a typical home’s electricity use under the right conditions.

So, now that you’re intrigued, should you run out and buy a new wind turbine for your rooftop or back yard?

Not so fast - there are some major caveats with residential wind power. The first is pretty self-explanatory - you need quite a bit of wind. Ideally it should be windier more often than not, and the harder the better. The energy that wind turbines generate is proportional to the cube of wind speed, which means that a wind turbine in 20 mph of wind will generate EIGHT times as much energy as the same turbine in 10 mph of wind (all other factors being equal). Ideal spots for wind power are coastal areas with steady sea breezes, or open expanses such as the Great Plains where winds really howl.

Second, the turbine should be as high as possible and well away from any obstructions. We’ve seen many Photoshop images or illustrations of wind turbines on rooftops in urban areas, but the truth is that there’s just more wind the higher you get off the ground or rooftop. As an example, the wind speed at 50 feet above ground will be about 25% faster than the wind speed at 60 feet. That’s great if you’re on the 90th floor of a skyscraper, but not if you own a one-story home in a typical neighborhood. The buildings, structures and trees in urban areas play havoc with wind speeds and directions. That wind turbine happily spinning five feet above your garage might look good, but it will perform much better (2x better or more) if it’s 50 feet higher. And payback period is all about performance. Typical guidelines for horizontal turbines are that the bottom of your turbine should be 3x above the nearest upwind barrier, or 25 feet above any upwind obstacles within 300-500 feet (whichever is higher).

Third, getting the required permits and approvals to install a home wind turbine can be thorny. There are a number of issues with wind turbines that you don’t have to face with solar panels. There’s a perceived noise issue, although testing of modern turbines doesn’t support this negative. There can be an impact on views, especially if you’ve elevated your turbine into the proper wind zones.  Some people and jurisdictions are worried about safety should a turbine fall, but the American Wind Energy Assocation states that there haven’t been any injuries from falling turbines in 25 years. And, there’s a concern about the impact of turbines on birds and wildlife. This is a major issue for utility-scale turbines, but the National Audubon Society in California found that small wind turbines pose little or no additional risk to our feathered friends. The net result of all of this is that depending on where you live, you’ll have to go through a somewhat complicated permitting process. A good installer can help navigate the process, so choose wisely! (we have a number of good wind energy installers in our service providers directory.)

We hope that the technology, zoning laws and financial incentives all improve to the point that small wind turbines are a common sight on our skylines. Until then, we applaud those urban wind pioneers among you who are willing to overcome the challenges of small wind. Should you choose that path, here are some additional resources that talk about the challenges and how to manage them:

• An overview of the permitting issues, and another permitting, siting and safety discussion based on California’s experiences with small wind turbines from the American Wind Energy Association;
• Guidelines on installation from Skystream / Southwest Windpower;
• A review of the latest “production” small turbines from Home Power Magazine.

(UPDATE: Please read this more recent post on some of the pitfalls of installing wind turbines on or near buildings. The conclusions emphasize the importance of using the tools and resources above to guide your siting decisions.)

Popularity: 15% [?]