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Has Affordable, Efficient Rooftop Wind Power Arrived?
Of the 10,500 small wind turbines installed last year, 99 percent were attached to giant constructed towers in rural areas. Rooftop wind turbines—constituting 1 percent of the market—have a huge potential in urban and suburban areas. But the products, which are heavy, noisy and require permanently attaching wind-catching blades to homes, have not yet caught on. One inventor thinks his unique turbine is just what the market is looking for. Are rooftop turbines set to take off?

By Tyghe Trimble
Published on: June 17, 2009


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KEYWORDS
wind power
alternative energy
electricity

Small-scale wind turbines are a $156 million industry with impressive growth numbers; the 10,500 sold last year constituted a nearly 70 percent increase for the industry. The benefits of such home home wind systems are numerous: instant independence from the grid, payback periods that can be as little as five years (with an existing subsidy), and demonstrating that 20 percent wind power—the government's stated goal for the country's energy mix for 2030—can be achieved by any individual in less than a year. On the other hand, if you live in an urban or suburban area, wind turbines are likely to be more trouble than they are worth.

Up above the rooftops—and, often, treetops—wind flows are relatively unimpeded, according to the American Wind Energy Association's small-wind advocate, Ron Stimmel. But "wind behaves very differently near built structures," Stimmel says, because houses and other buildings cause a lot of turbulence at roof level. If you live in or near a metropolitan area, however, installing a tower is likely not an option. Either you won't have the square footage or local regulations prohibit erecting tall structures. "This is why there's a lot of interest in selling roof turbines," Stimmel says. But vibrations, sound, price and the complexity of installation has left this market mostly untapped: Nearly 99 percent of small wind turbines installed today are attached to a tower, with just 1 percent constituting rooftop rigs. "It's an appealing option," Stimmel says, "but unless it's done very carefully, there are a lot of obstacles."

Imad Mahawili, a chemical engineer and long-time wind energy consultant, has designed a unique wind turbine that he says solves the biggest problems associated with rooftop systems. His rig is a wind turbine turned inside-out—the gear system typically sitting in the center of the blades has been removed and the whole thing is enclosed in a wheel lined with magnets. The result is a 95-pound system with 20 replaceable blades that can generate power with even 2-mph winds.

In a typical turbine, "It takes 7 to 8 mph to overcome the resistance of gears," Mahawili says, "and the loss from gears on average at any speed costs about 20 to 25 percent in aerodynamic efficiency." So Mahawili removed the gear system, replacing it with a simple hub and bearings. Then, "We looked at the wheel system, near the hub," Mahawili says, and found that "for 1 rpm [revolution per minute], the velocity at the rim of the wheel is nine times faster." In response, he placed the magnets that he uses to create electricity (in place of a gearbox) near the rim. Finally, Mahawili designed the turbine to have a high, 120-degree directional acceptance of wind—especially efficient for turbulent gusts—and made the blades so that they could be individually replaced if debris or storm winds break them. All of these design specifications "drive cost down, simplify the product and improve productivity," he says.

Still, even a device this streamlined could find catching wind in a suburban neighborhood an arduous task. "If you have a solar panel and you put it under a maple tree, the sunlight will still come through, but [the tree is] blocking a lot of the resource," Stimmel says. The same goes for wind whipping through obstacles in a neighborhood like tall houses and walls or barriers to nearby highways. "Computational fluid dynamics studies for individual rooftops might be necessary for each of these systems," he says. And in a dense city, "the best rooftop system you can get is an array of solar panels. It's simply a matter of physics."




PRICE BREAKDOWN:
Honeywell Wind Turbine
Homeowners installing small-scale wind-energy systems—with a capacity under 100 kilowatts—get 30 percent of cost discounted by the government. This credit is extended until Dec. 31, 2016. State incentives can further compound the savings.

Price Per Unit /// About $4500 prior to the 30 percent federal tax credit. Afterward, the price drops to about $3150.

Price Per Watt /// $2.25 per watt without installations (where costs vary). Expect that price to roughly double with installation. With the 30 percent federal tax credit, the price works out to about $1.58 per watt without installation. This price reflects only one year of use. Given five years without repair costs, the price drops to 22.5 cents per watt, just roughly double the current national average.


Kilowatt-hours per year /// In average class-four winds, according to Imad Mahawili's calculations (see his chart, below), the Honeywell Wind Turbine can put out as much as 2042 kilowatt-hours per year.

Payback period: The Energy Information Administration lists average U.S. residential electricity prices at 11.23 cents per kwh, as of February 2009. A turbine that puts out 2000 kwh a year saves $224.60 annually at that price, making the payback period just under 20 years on a $4500 panel. (The government rebate would lower the payback period to about 14 years.)

Drawbacks: Installation will require an electrician and a major overhaul of the roof—Honeywell plans to provide the experts for those who buy the turbine, at a price. Turbulence, reliability of wind speed and county restrictions could all be problems.

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Reader Comments (35)
Latest 100 comments displayed. Retrieving comments...Show all comments
35. RE: Has Affordable, Efficient Rooftop Wind Power Arrived?
It is good that minds are working on stuff, but device would be more expensive to maintain and purchase then its final payback. I work in the energy field and like to see new ideas, but I have to agree with a previous poster your money would be better spent on improving your homes multiple existing energy losses and inefficient building systems. Don't fall for this modern hype and end of world doomsday Cap N trade also.....Cap N Trade will destroy this country.......When you hear doomsday talk be very afraid that someone is spinning a large tale.........many people who preach this have lots of money invested waiting to reap the benefits of cap n trade.......

34. RE: Has Affordable, Efficient Rooftop Wind Power Arrived?
Most places have wind in a prevailing direction, and a second direction, that occurs from time to time. Airports align runways to accommodate this. Vertical axis machines catch wind from any direction, even updrafts, and are not required to "point" at the wind. What say you? Also what are the decble levels, and KW in 10 - 20 mph wind? Thanks

33. RE: Has Affordable, Efficient Rooftop Wind Power Arrived?
YES. It is an incredible system with an unlimited future potential & growth

32. RE: Has Affordable, Efficient Rooftop Wind Power Arrived?
Website: msn
I live in a rural area and have enough land to set it on the ground, say a cement pad. Would it work as well at ground level? I could place it at least 50 - 100 feet away from buildings. I feel then i would just have to cable it to the house? installation?

31. RE: Has Affordable, Efficient Rooftop Wind Power Arrived?
Calculating payback in dollars is only part of the equation. We have to also consider, as a society, the long term value of moving away from petroleum-based energy sources. As an individual, what is the ROI of not burning the generating capacity of one windmill in oil for the next twenty years? It's not easy to know this, but it's ultimately the more important question.

30. RE: Has Affordable, Efficient Rooftop Wind Power Arrived?
what is energy production @ an average windspeed of 11 meters per second and what is the maximum produced power @ that windspeed

29. RE: Has Affordable, Efficient Rooftop Wind Power Arrived?
As an electrical engineer all I have to say is this thing is a joke, nothing more than a toy. It might make some Greenies feel good but they would actually be doing the world more harm. The problem is this device does not provide net energy if you start with the $5.500 dollars worth of conventional carbon energy it took to make the device. Not to mention the carbon energy that will be required to install this device. And do you really believe it will last 20 years? The output is so low that it has no practical use other than perhaps some small lighting. A far better solution in a home or business, which would have a great impact, would be to conserve the less expensive energy that we all ready have by implementing conservation methods most people know about but refuse to observe. These methods would include updating appliances and fixture in the home to highest efficiency now available. Using more intelligent thermo and lighting controls that would reduce energy usage when not need. By doing these things we would have a true net impact on the use of carbon energy not to mention our wallet.

28. RE: Has Affordable, Efficient Rooftop Wind Power Arrived?
A good step in the right direction. but the cost is still to high for any major upgrad you need the pay back to be under 8 years inrealty it should be under 7 and if you want this to work it should pay for it self in 5 years without govemerent helpand that includes instilation and maintenance so unless you can get the price down to under $2,000 istalled including taxes you can for get your dreeams of seeing your windmiles on most rof tops. would love to see it work and would love to invest in the technology I am a Technology Educator and have been pushing for somthing like this for years but you need to get the cost down down down. remember it is not always the best technology that wins but the one that gets the job done and cost less will always win. what is better selling 1,000 and making $100 each or selling a !,000,000,000 and making $1.00 each good luck

27. RE: Has Affordable, Efficient Rooftop Wind Power Arrived?
The tax incentives are vital to help move us in the right direction, but the bottom line is that companies wishing nervous Americans to invest in these systems, which I am 110% behind, MUST put their money where their mouth is - they must stand behind the product in 100% warranty. At least in the inital 5-10 years of forcing this thinking into our heads. I think the ultimate solution is 100% off-the-grid, while still attached to grid..and that this be a combined wid/solar system. Thus, nationally we are not thrown into the dark ages when worst case scenarios occur, and that when not in worst cases net-metering allows clean power to flow backwards into the grid. And all the other benefits. I applaud Honeywell and even comapnies like GE and BP for seeing the future behind fossils, even if they really didn't wish to, but I say to them this is not a no-brainer for the avg Joes...pull up to pump and go out of sight out of mind...you are going to have to go the extra mile to make us 100% comfortable with the change over. You will invest on the front end and profit on the back end of your work in the next decade. You, we, need to do this - quickly.

26. RE: Has Affordable, Efficient Rooftop Wind Power Arrived?
One thing alot of people don't think about is what is energy going to cost in 5 or 10 years. I know my electric bill has increased in the last 10 years.

25. RE: Has Affordable, Efficient Rooftop Wind Power Arrived?
The tax incentives are vital to help move us in the right direction, but the bottom line is that companies wishing nervous Americans to invest in these systems, which I am 110% behind, MUST put their money where their mouth is - they must stand behind the product in 100% warranty. At least in the inital 5-10 years of forcing this thinking into our heads. I think the ultimate solution is 100% off-the-grid, while still attached to grid..and that this be a combined wid/solar system. Thus, nationally we are not thrown into the dark ages when worst case scenarios occur, and that when not in worst cases net-metering allows clean power to flow backwards into the grid. And all the other benefits. I applaud Honeywell and even comapnies like GE and BP for seeing the future behind fossils, even if they really didn't wish to, but I say to them this is not a no-brainer for the avg Joes...pull up to pump and go out of sight out of mind...you are going to have to go the extra mile to make us 100% comfortable with the change over. You will invest on the front end and profit on the back end of your work in the next decade. You, we, need to do this - quickly.

24. RE: Has Affordable, Efficient Rooftop Wind Power Arrived?
Can they miniaturize this to replace roof vents where it would work of hot air exiting your attic as well as from wind?

23. RE: Has Affordable, Efficient Rooftop Wind Power Arrived?
How well will it hold up in a high wind area, and how much will it produce at one time?

22. RE: Has Affordable, Efficient Rooftop Wind Power Arrived?
We have a 40K 3 phase wind generator and to date it has cost us way more than it has made us and we're looking at a "never gonna payback" senario due to down time and maintenance. This whole green energy harvesting stuff is a bunch of crap. There is potential in the wind farms, but let's be honest. This little thing ,with the average winds most people have, won't even power 1 (one) light bulb. I must restate the obvious. "There aint no such thing as a free lunch."

21. RE: Has Affordable, Efficient Rooftop Wind Power Arrived?
Its great, I am a fan of alternative energy. i beleive this is a great enhancement in the existing design. Deffinitely this product will have a great market. It is very well known that natural resources are depleting very fast. we must shift to alternative energy sources. And more over this is a free source. only that equipment is little costly. Hope the prices come down and payout perioud is reduced to 1 to 2 years.

20. RE: Has Affordable, Efficient Rooftop Wind Power Arrived?
The very fact that such a radically different design has already been created makes it necessary to rethink the huge, industrial wind towers, with their 200 and 300 ft. long blades, going up all over the country at huge cost to taxpayers as developers rush to grab their share of tax subsidies. Fertile farm land is disappearing, health issues to those living nearby are beginning to surface, as is the recognized decimation of bird and bat populations. We'll be paying for the mistakes these 400+ foot tall behemoths will cause for generations.

19. RE: Has Affordable, Efficient Rooftop Wind Power Arrived?
Website: www.turbotricity.com
You have to be very careful with stresses on a roof. Concrete does not have any tensile strength, and unless a building has been specifically designed to take a turbine, you are in danger of damaging the entire structure. For city dwellers in most regions, I would wait for Nanosolar et al to get the price of their panels down to $1 a watt. Its a proven, durable and maintenance free technology. We produce a 2.5kw turbine for domestic houses, but pretty much refuse to put them in sites with mean wind speeds below 5m/sec. This industry has to be honest about payback times. Twenty years payback is a 5% ROI, better than most investments, provided that the system is designed to last a lifetime.

18. Has Affordable, Efficient Rooftop Wind Power Arrived?
How much wind is produced by a heat pump condensor fan? If that wind would suffice enough force all year, would that pay off?

17. RE: Has Affordable, Efficient Rooftop Wind Power Arrived?
this info blows me away, its about time that someone came up with this. Keep up the good work

16. RE: Has Affordable, Efficient Rooftop Wind Power Arrived?
Generating energy with a bicycle, is a two-fer worth considering. It works quite well, and one gets a bit of exercise.

15. RE: Has Affordable, Efficient Rooftop Wind Power Arrived?
I'm doing a bit of web research on this device. I live 25 miles outside of chicago, average wind speed of 10.4 mph. My house uses a lot of electricity per year due to the fact we rent our basement and we gave them space heaters to control temperature and since they don't pay for utilities they get run alot. During this last winter we had an electric bill of $300 and a gas bill of $200 in the same month. The limited research I've looked at shows an IL grant program that will pay 60% of the costs (if you apply and are approved) for residential wind turbine, combine that with the 30% federal and you get 90% of your installation costs covered. That makes for an immediate payback. I know this is taking advantage of tax money taken from others, but I might as well grab a share if it's there for the taking.

14. RE: Has Affordable, Efficient Rooftop Wind Power Arrived?
Website: http://rooftopwind.biz
I like honeywells design but please consider my design. If anyone out there is interested please contact me.

13. RE: Has Affordable, Efficient Rooftop Wind Power Arrived?
Vertical wind turbines work in 360 degrees (not just 120) and have been using the technic of putting the mags at the outer edge for many years. This so called break thru is a gimmick. There is less then a half a watt of power in a 2 mph wind. Many cities are setting up ordnaces to protect thier people from wind manufactures who have no shame!

12. RE: Has Affordable, Efficient Rooftop Wind Power Arrived?
Website: terry@wordworks.me
oops. This turbine isn't eligible for tax incentives in California, the only state with a HAWTs and VAWTs list right now.

11. RE: Has Affordable, Efficient Rooftop Wind Power Arrived?
They mentioned in the video to install compact florescent lights to increase your savings. Why not install super efficient, but slightly expensive LED lights all thru your house with motion sensors, install cutoffs for all your standby energy hog appliances, etc. and you could probably get to 30% savings with almost no investment.

10. RE: Has Affordable, Efficient Rooftop Wind Power Arrived?
Have you people never heard of the time value of money? I know I had to take an engineering economics class where we covered all those deadly details. The payback period of this device is a lot longer than your 14 years, especially since you did not add in the cost of installation. Thinks 40 or 45 years. And isn't there a controversy in the UK right now about these same devices where the manufacturers finally had to admit that they actually cost more than they save. And lastly do you think one of these things would even survive to make it thru the payback period?

9. RE: Has Affordable, Efficient Rooftop Wind Power Arrived?
Note that the cost of installation and maintenance is mentioned but not included in this article. Reinforcing a roof is not an inexpensive process. Permits and inspections must occur as well. Payback calculations must take into account installation and maintenance as those costs will effect payback times - sometimes significantly. Warranty considerations should be considered especially on a new design. After all, none of these units have been running for 20 years so longevity is unknown. The issues with rooftop wind/solar power are significant. Though I'm a huge fan of alternative power (especially point of use), such alternatives have a long way to go to be anywhere near cost-effective.

8. RE: Has Affordable, Efficient Rooftop Wind Power Arrived?
County restrictions a problem? Become a ham and put your turbine on top of your reinforced, FCC exempted antenna. Voila! Problem solved.

7. RE: Has Affordable, Efficient Rooftop Wind Power Arrived?
Have you people never heard of the time value of money? I know I had to take an engineering economics class where we covered all those deadly details. The payback period of this device is a lot longer than your 14 years, especially since you did not add in the cost of installation. Thinks 40 or 45 years. And isn't there a controversy in the UK right now about these same devices where the manufacturers finally had to admit that they actually cost more than they save. And lastly do you think one of these things would even survive to make it thru the payback period?

6. RE: Has Affordable, Efficient Rooftop Wind Power Arrived?
But there are places where 25 mph winds are common on the daily or seasonal cycle - so rooftop wind harvesting is not D-O-A, despite the commenter's pessimism.

5. not touching my roof
How likely is such a contraction to increase the danger of getting my roof ripped off during a storm? That would be my #1 concern.

4. RE: Has Affordable, Efficient Rooftop Wind Power Arrived?
Unfortunately, one would have to maintain access to the grid for the days when the wind didn't blow, and pay the minimum fee to keep the connection-at least here in rural Iowa.

3. RE: Has Affordable, Efficient Rooftop Wind Power Arrived?
Wonderful piece of work here by this engineer, I commend him. There are places where this will work very well. 1. areas without trees, think deserts, 2. areas where trees are sparce and the lower level of trees has been trimmed, think farmhouses on the plains.

2. RE: Has Affordable, Efficient Rooftop Wind Power Arrived?
Nope! Pesky problem is that wind energy decreases by 8 for a halving in wind speed. Lets say the turbine is rated to produce 1kW for a 24mph wind which is rare for most rooftops and likely very turbulent. An occasional 12mph wind gets you 125W. But typical 6-3mph wind range will get you a paltry 16W-2W range. I doubt rooftop turbines can ever payback plus they suffer to much turbulence.

1. RE: Has Affordable, Efficient Rooftop Wind Power Arrived?
Mmhh. There are so many poles (telephone, electricity) already installed all over the places, not to mention the high voltage line pilons, that could easily host one if not couple of such wind turbines. Now, either elec companies start energy harvesting, or they could lease the poles to other companies to do the job. Oh, but I am an energy-harvesting fan :-)



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