The Folly of Building-Integrated Wind

This summary is a shortened, condensed version of the Full Article.

Executive Summary

Rooftops are elevated above ground, where it’s windier, creating the potential for electricity to be generated from wind, and then used right where it’s needed. Wind energy can make a strong visual statement about environmental priorities. But is building-integrated wind a good idea?

Wind speed typically increases with height. Putting wind turbines on top of buildings should allow them to take advantage of height without an expensive, full-size tower. Building geometry can enhance wind turbine performance, by accelerating wind as it curls over the parapet or by funneling air flow toward turbines. Most of our electricity is used in buildings, and generating the electricity on site reduces the need for transmission, with its losses and infrastructure costs. In addition to this practical benefit, wind turbines spinning on a building provide a visible testament to a building owner’s commitment to the environment.

Unfortunately, building-integrated wind often doesn’t live up to its promise. On top of even very tall buildings, wind flow is highly turbulent, while turbines need a strong laminar flow to work well. The increased wind velocity at building parapets can only be successfully harvested in a fairly narrow band, which limits the potential size and output of wind turbines. Because the turbines are small, the economics are not as attractive as with larger wind turbines. Noise and vibration from wind turbines are stubborn problems that are among the greatest obstacles to integrating them into buildings. It is not unheard of for large, free-standing wind turbines to occasionally shed a blade. Even if the building owner is willing to accept that risk, an insurance company may not be.

Perhaps the greatest impediment to building-integrated wind energy is the economics. While large free-standing wind turbines provide the least expensive renewable electricity today, small wind turbines are far less cost effective, and when small turbines are put on buildings, the costs go up while the production drops. Putting wind turbines on a building to advertise the greenness of a company or organization is a compelling idea—as long as those turbines spin most of the time. Unfortunately, many turbines mounted on buildings frequently lack strong enough wind to operate. Commuters who glance up at stationary turbines may conclude that wind energy doesn’t work very well.

There’s a wonderful synergy in the idea of combining form and function by generating electricity with turbines that reach into the sky on the buildings they will help to power. But in most cases, at least with today’s technology, it just doesn’t make sense.

DISCUSSIONS

Reader-contributed comments related to The Folly of Building-Integrated Wind - EBN: 18:5. Comments are listed with newest at the top.

AeroVironment Products Discontinued Posted by Nadav Malin on Feb 8, 2012, 04:43 AM
Further evidence of the folly of this pursuit? As of summer 2011 AeroVironment has dropped its wind turbine line entirely. And they were probably the most sophisticated company in the business.

Wind Cube Posted by Laura Millberg on Jul 10, 2009, 05:04 PM
Does anyone know anything about the installed efficiency of the Wind Cube by Green Energy Technologies of Akron, Ohio, compared with the rooftop wind installations reviewed in the EBN article? A wind cube was just installed on the Crown Battery Manufacturing Corporation in the Lake Erie Business Park of Port Clinton, Ohio. For details, see http://www.wkyc.com/news/state/ohio/news_article.aspx?storyid=117224&catid=23

Re: Check the math Posted by Mark Piepkorn on May 22, 2009, 08:12 PM
We asked Jerry about Rick's comment. Jerry said, "He's right about the math. 3000 feet."

More reality checking... Posted by John Gant on May 21, 2009, 01:10 PM
David Mackay, Cambridge University, published a new book based on current technology and objective engineering on many energy generation strategies. He clearly describes the capabilities and limits of wind power (in England), and also reveals dissatisfacotry performance of micro-turbines.

Learn more here: http://www.inference.phy.cam.ac.uk/withouthotair/cB/page_268.shtml

Check the math Posted by Rick Vance on May 21, 2009, 06:57 AM
I think Yudelson is trying to say that you would have to increase the height from 10 feet to 3,000 feet to achieve the 40% increase in average wind speed (10 feet to the power of 3.5)? Not 30,000 ft.

Doesnt seem right that the average wind speed at the top of a building that is over 5.5 miles tall is only 40% greater than at the top of a basketball rim.

But I do agree that building integrated wind is generally a bad idea. Good article.

"The Folly of Building Integrated Wind" is right on the mark. Posted by Jerry Yudelson on May 1, 2009, 08:47 PM
This is a great feature article on a subject that architects and owners absolutely don't understand when they advocate for putting wind turbines on buildings.

Since I was trained as an engineer, I always tell them it's a stupid idea, for some very fundamental reasons. For example, I think you should have mentioned two key flaws in the case for wind on buildings, based on the simple physics of wind power: wind power is directly proportional to the swept area of the turbine and to the CUBE of the wind velocity.

There is little swept area to work with on buildings AND most buildings (and cities) are not built in very windy places, for a good reason: a place with 10 to 12 miles per hour average annual wind speed (minimum conditions for an economically successful wind farm) is a very uncomfortable place to live.

Cities are in river valleys, not on ridgetops for a good reason (beyond access to water); they're more protected from wind. So, wind power on buildings loses out for two fundamental reasons: no swept area and no sustained wind speed of any consequence. That's why the capacity factors are so low.

As for wind speed increasing with height, the increase only goes as the 1/7-power of the height, so to get an increase of 40% in average wind speed from say 10 feet above the ground (i.e., an increase equal to the square root of two), you'd have to increase the height by a power of 3.5 (or 30,000 feet), particularly in dense urban areas. Not going to happen.

As Paul Gipe (an old friend) says, a thoroughly bad idea, for all kinds of reasons.

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Wind Turbines on the Parapet

EBN: Product Review - August 2006

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