Here's a novel wind tower, Savonius type.

[Lion Kuntz]

http://h2-pv.us/wind/Introduction_01.html
http://h2-pv.us/wind/Big_01.html
http://h2-pv.us/wind/strip_mining/strip_mining.html
http://h2-pv.us/wind/towers_prior_art/towers_prior_art.html

The tower concept has modular levels, each level an independent generator. May be installed in cities without danger of ice-throw, blade-throw hazards on skyscrapers, one or more layers tall.

I had this bashed on another list but would like more critics to go over it.

Only the exterior is shown. The interior and guts are open to many variations, so until the wind force entering into the tower is settled, those variations are not suitable discussion material.

Going back looking over historical prior art in the patent office shows that many have contemplated this kind of concept before.

Where this comes from is I considered big sailing ship type sails of modern superstrong lightweight materials could be raised to funnel more wind into a prop tower swept field. Another influence was somebody's highrise building that had multiple wind gensets around the perimeter of the tower top and I realized how wasteful that would be if all but a few gensets were being blocked by the leading edge of the gensets facing the wind.

This solution is omnidirectional with only one single genset receiving wind from every angle. Easy to fortify against lightning strikes, this bird-safe design is actually named Eagle's Roost. Both solar thermal and solar PV can also be incorporated in the structure for multiple power source harvesting from one structure.

The rooftop alone on a 30' diameter tower is good for 8 kWhs of 13% efficiency PV per sunny hour. Each upper side ledge between stories could also have tracking PV. Nothing stopping these from going on top of existing silos, so that the erections costs are rock bottom.

People don't like living in constant high-wind areas. The best wind is far from the dense population and it costs $1,000,000 mile for transmission lines to carry the juice from Dakota to cities.

Largely protected from the elements by being indoors, these wind generators can be made of lighter more delicate materials and make energy from winds below useful to props and eggbeaters. They can be placed inside cities and towns instead of far outside. San Franciscans LOVE their Golden Gate Park Dutch Windmills and Coit Tower -- they are NOT considered eyesores or visual blight but are picturesque tourist attractions in the middle of public parks. They are also not an appreciable hazard to the pubic safety.

You want WIND in cities? Try walking around the base of Fox Plaza building and see how long before your umbrella turns inside out. Take a walk in the financial district 1 day out of every two on average.



It makes sense to use wind power in North Dakota to make PV instead of electricity. One day's EMC furnace makes 720 kilograms of cast SoG Silicon ingot, good for 600 meters^2 PV after sawdust waste and breakage is accounted for. It takes 50 furnace-days to fill one 18-wheeler semi-trailer with 80,000 pounds of ingots, and the cost of delivery to cities is far less than $1,000,000 a mile for electric lines.

One acre of 13% efficiency polycrystal silicon PV is 3.1 megawatt-hours of electricity per day. One tower can be 5 MW, 10 MW, 15 MW if you make it as tall as you make the prop towers. You can even use the interior space to put the EMC furnaces inside.

Did I mention there are NO DRIVESHAFTS? NONE! In fact, in one alternative there are no windings at all, just flat plate Faraday Disc monopole DC generation.

http://upload.wikimedia.org/wikipedia/en/thumb/a/a8/Homopolar_anu-MJC.jpg/250px-Homopolar_anu-MJC.jpg

http://en.wikipedia.org/wiki/Homopolar_generator
"... Another large homopolar generator was built by Sir Mark Oliphant at the Research School of Physical Sciences and Engineering, Australian National University. It produced 500 megajoules and was used as an extremely high-current source for experimentation from 1962. It was disassembled in 1986. Oliphant's construction was capable of supplying currents of up to 2 megaamperes. ..."

Far less than 30 foot diameter, and just one story tall. Stack these up if you like megawatts upon megawatts of production from small footprints.

If you want high current for aluminum electrolysis or hydrogen electrolysis or carbon arc carbothermic silicon purification furnaces, why produce AC at all? Just produce the DC high-current directly.

[Rob Beckers]

Hi Lion,

In the other thread you mention there hasn't been a single reply to this thread (yet). So here goes.

Probably part of the reason why there's no reply is because we're still short on members. In particular members that are greatly into DIY wind, and are not afraid to talk about novel ideas. Hopefully that'll simply solve itself in time (of course, anyone that knows of a way to get more members should feel free to go ahead!).

Speaking for myself (and maybe others feel the same), the reason I haven't responded is that I really don't have a good idea how this is supposed to work. If there was a working prototype so we have something to look at, and measurements to review, it would be different. As it is now I have a hard time saying something about it, one way or another.

This is in no way meant to discourage you, ideas are what keep humanity moving forward!

-Rob-

[Laurie Forbes]

One thing that caught my eye in the above cited web sites was the claim that conventional HAWTs "see" only a small portion of the wind passing through the swept area (that amount being not much greater than the frontal area of the blades themselves). Even if that were true, I'm not sure just why that would be a particular knock against HAWTs. I don't believe however the claim is true but am not sure exactly why. Perhaps someone can comment further........

[Lion Kuntz]

Hi Lion,
Speaking for myself (and maybe others feel the same), the reason I haven't responded is that I really don't have a good idea how this is supposed to work. If there was a working prototype so we have something to look at, and measurements to review, it would be different. As it is now I have a hard time saying something about it, one way or another.
-Rob-

http://h2-pv.us/wind/Introduction_01.html

The principle involved:

Suppose you have any normal wind generator. You decide that the wind is not strong enough, so you put up a HUGE wall nearby to deflect the wind from that space into the swept area of your generator. Now you have the existing wind plus the deflected wind both converging on your generator.

Obvious problem with that is winds shift directions.

Solution to the direction shift is to conceptualize an omnidirectional funnel to always be turned into the wind no matter which way it blows. That's what this tower is.

36

There are four planes intercepting and funneling the wind, no matter which direction it blows from. This is a TOP VIEW looking down at a side currently facing the wind. On the website link there is a larger version, you get by clicking figure 4.

37

The vertical risers in an assembled tower constitute vanes which deflect wind in a generally clockwise direction. Roughly 60% of the forward moving air has an aperture to enter without blunt obstruction.

The return stroke of the Savonius device is sheltered by the vanes on the left side. No subtraction of motion is encountered by the return stroke of the wind-catchers inside in a circular carousel raceway.

Horizontally the winds are sliced into sections by the protuding wedge shaped ledges. Then, secondly, they are further diced into a series of horizontal and vertical sidewalls which enforce a generally clockwise deflection. The constricted openings then focus the whole force on a much smaller target. In the example shown, the inner openings are about 60% of the size of the outer openings of the four-walled portion.

Including the upper and lower sloped ledges, the focussed wind force is roughly doubled from the ambient wind force, which is a four-fold increase in net power to a smaller catchment area. Thus, lower wind speeds produce useful net power equal to double ambient wind speeds.

It works somewhat in reverse in high winds. As wind force increases the back-pressure increases. Conceptually, some iris device could be used to close down the windows/funnels independently on each layer to take one story off line for maintenance. Natural irising occurs just from high windforce pushing the boundry layer further from the skin of the tower, acting as defacto governor for high-wind conditions that require other generator designs to be feathered and taken offline.

Inside is a concentric raceway around the perimeter of each level of windows.

The lower ledge has a more steep angle than the upper ledge of the wind slicer protusions. This steep upper slope is to minimize rain infiltrations and windblown litter such as leaves and such.

The upper slope is also there to provide a small upwards lift to the windcatchers to reduce gravity friction loading of the generator itself attached to the wind-catcher assemblies.

Any number of possibilities follow from these design parameters. Generators can be small individual units or one large circular ring. They may roll on rails, on wheels, hung from monorail, hydroplane on a water bath, float on electromagnetic levitation, or even several of these combined in one system.

My preference is maglev for a linear generator in a circular curved configuration for AC generation. Alternatively, a homopolar generator of copper sheet over a bed of permanent magnets is ideal for high-current DC generation for megaamperes of electrolysis power.

The wind-catcher assemblies are a circular unit which is one continuous circumference of the raceway carousel. Carbon-fiber composite members generally reminiscent of anemometer cups may be used for imaging something that would work adequately, although I have more aerodynamically sophisticated catchers in mind that address rain infiltration and wind litter issues and some other factors not mentioned.

If going the route of circular-linear induction generators, then small modules placed at frequent intervals are something which can recreate the local electric industries displaced by multinational corporations. Even in Bangladesh they know how to make small motors and generator assemblies. Small units which can be swapped out avoid many issues of downtime and expense of gigantic generators that ultimately will burn out.

By putting the massively weighted parts stationary in the raceway and just minimal weighted windings on the moving carousel, the total net energy per wind-force unit is improved. There are no friction losses due to gears or crankshafts at all. The bulk of rotors is reduced by a massive fraction.

In essence, the wind-catcher plus generator disc is one single integrated part, and in some versions might be the only moving part to the entire generator.

There are NO moving parts outside the building, thus the name "Eagle's Roost" to suggest bird-friendly.

[Lion Kuntz]

One thing that caught my eye in the above cited web sites was the claim that conventional HAWTs "see" only a small portion of the wind passing through the swept area (that amount being not much greater than the frontal area of the blades themselves). Even if that were true, I'm not sure just why that would be a particular knock against HAWTs. I don't believe however the claim is true but am not sure exactly why. Perhaps someone can comment further........

Newton's laws apply: equal and opposite reactions.

The wind in the swept field is averaged, but in very large generators may be double or triple at the high part of the stroke from the lowest part of the stroke. Only molecules directly impacting on blades can impart any force to the blade (on first approximation, on 2nd approximation wind recoil off blades creates some turbulence which is non-linear and is both additive and subtractive requiring complex wind tunnel testing besides sophisticated computer modelling.)

A solid wall impacts all the wind, but stalls it, therefore has no power production. Some optimal medium between maximum and minimum wind interception is designed into prop form and adjustable angles.

The swept area is the total circular volume of space the props pass through, not the blade area that is imparting force. In between props the wind is passing without impact and without power production. There is no Newton's Law of Telekinesis (power at a distance). Sorry.

The ideal wind power generation is computed to be near 60% of the total wind force, often erroneously stated as swept area when it is actually prop area. 60% of props is what you can hope for.

The prop area is 10% of the swept area. 60% of 10% is 6%.

The return stroke in Savonius (eggbeaters) is against the wind, subtracting from total force. Props always have some part acting against the wind while other parts are acting in favor with the wind.

By contrast the towers can hope for 60% of 60% of the swept area, which is 6x or 36% of the actual wind power in the swept area. The return stroke is protected from the wind and does not subtract from the rotational speed.

The towers come on at much lower wind speeds and stay on at higher wind speeds, so not only do they produce 600% compared to equal swept area of prop generators, but they do it over a wider range of wind speeds.

All wind generators have a point of maximum production in a range of winds -- for props this is at their high end of the wind speed range. Outside of this range in both directions power production falls off. The Eagle Roost Towers have a greatly expanded range, and continue above where props are disconnected and feathering for safety reasons.

The Eagle's Roost towers have no blade-throw or ice-throw hazards so they can be in cities on skyscrapers or in towns. Because of their low wind threshold of making useful power they can be closer to the places people live. People don't like living in windy places. The places where big props can be placed are more limited, and more distant from the consumers. More expense is involved negotiating right-of-way and building power high-tension lines. Power losses increase by distance subtracting from the already poor 6% net wind efficiency

The towers were designed to be built of modular duplicate units easily locally constructed virtually in every country in the world. They do not require special equipment or special teams who move state-to-state to do the erection of prop towers. They do not require multinational corporations for anything other than wire and some electronics parts. They are NOT out of reach of local self-help to wind power production. They ought not require Wall Street bond sales to make.

At half the turn-on windspeed of props, the towers are already making some power while the giant props are making nothing. We haven't even looked inside the nacelles to see the differences there: no crankshafts, no gears, practically no friction at all (and in maglev, zero friction). Can you believe that prop generators actually include a FAN inside the nacelle? An electric FAN in a windmill?

The giant props 15 stories tall made of superstrong carbon-fiber composites are exposed to the full ravages of the elements and have to be made strong enough to survive the worst outdoors. Just the inertia of such a prop limits the useful turn-on speed. Indoor windcatchers are partially protected by the building shell from the UV of the sun, burdens of ice, sandblast of dust in the wind, and the most important cause of prop-death, lightning.

The windcatchers inside the tower protection can be lighter, further helping reduce their turn-on efficiency by less mass inertia.

It's not just any single one factor, but the total equation that makes big-for-bigness-sake wind machines a bad direction to keep following.

[Laurie Forbes]

The swept area is the total circular volume of space the props pass through, not the blade area that is imparting force. In between props the wind is passing without impact and without power production. There is no Newton's Law of Telekinesis (power at a distance). Sorry.

The ideal wind power generation is computed to be near 60% of the total wind force, often erroneously stated as swept area when it is actually prop area. 60% of props is what you can hope for.

The prop area is 10% of the swept area. 60% of 10% is 6%.

OK but why then does the calculation of power from a HAWT not include the number of blades or anything related to blade area? As I understand it, a single blade HAWT produces the best power output (but are not used in practice because of other considerations). Two blade units are more pratical and are sometimes used. If what you claim is true, a two blade unit would produce approx. twice as much power as a single blade and a three blade, three times as much. As nothing like this is found in practice, it would suggest that swept area, irrespective of the number of blades, is the determining power output factor.

As well, even if the blades do not "see" all the wind passing through, I still don't view that as a significant downside of a HWAT.

Edit:

I think now I may have answered my own question. The key point here, it seems to me, is that the blades are not two but three dimensional and therefore sweep out a _volume_ of air as well an an area. Also pertinent is the fact that air moving through the swept area moves at finite speed i.e. it moves through the "area" instantaneously but takes a certain amount of time to traverse the swept volume. Therefore, if the blades, with the proper pitch, are moving fast enough through the wind flowing at a certain velocity, those blades will in fact "contact" or "see" all the air passing through the swept volume. Some air will contact near the blades' leading edge, air a bit farther behind will contact near the midpoint, and air a little farther behind still will contact near the training edge. Air following that will in turn contact near the leading edge of the following blade, repeating the cycle. I think this is also evidenced by the fact that the more the blades, the slower the rotor needs to turn for maximum performance at a given wind speed.

[Lion Kuntz]

Edit:

I think now I may have answered my own question. The key point here, it seems to me, is that the blades are not two but three dimensional and therefore sweep out a _volume_ of air as well an an area. Also pertinent is the fact that air moving through the swept area moves at finite speed i.e. it moves through the "area" instantaneously but takes a certain amount of time to traverse the swept volume. Therefore, if the blades, with the proper pitch, are moving fast enough through the wind flowing at a certain velocity, those blades will in fact "contact" or "see" all the air passing through the swept volume. Some air will contact near the blades' leading edge, air a bit farther behind will contact near the midpoint, and air a little farther behind still will contact near the training edge. Air following that will in turn contact near the leading edge of the following blade, repeating the cycle. I think this is also evidenced by the fact that the more the blades, the slower the rotor needs to turn for maximum performance at a given wind speed.

Newton's Laws still apply in every instance, mine, their, your, everybodies. It's been centuries now and nobody has found an exception.

All things are three dimensional. My wind power concept certainly is.

The point is, you have to visualize yourself going down to air molecule size and observing what's going on.

When wind inpacts any surface it will rebound like a pinball or billiard ball, imparting some force as motion to the struck object and some part as change of direction. Turbulence is the reason there is a rule of thumb to keep wind towers apart so that the turbulence does not degrade the downwind ones. I forget what the number is, but it's between 3 and 10 times the swept area.

Why does a kid's pinwheel toy spin in windspeeds far below wind turbine turn-on speeds? Because of blade mass and inertia. The trivial paper or plastic is so light-weight that only a few molecules impacting are required to move it. The pinwheel has a complex shape that harvests a very high percent of the swept area.

38

39

A 2.5MW generator is a heavy mass of metal. The blades have to be able to withstand the highest force they will be exposed. Bigger props means more weight -- it's an engineering compromise to get as much surface impacting wind while cutting down weight.

A mass of 1 ton of copper windings is not going to budge in a mild breeze that spins the plastic toy.

The higher you go, the better the windspeed. Big props don't get lots more power because they are lots bigger, they get it because more of the prop is way up there in the realm of strong winds. The "swept area" is the compromise calculation of the winds up high and down low giving a standardized number that in general tells you something about how high the peak is.

You have a lot of compromises, not just one. Taller structures cost lots more money. Higher winds way up high need stronger towers, again adding to tower costs. You can't justify the costs with a piddly generator, so you have to make it big to payback the costs of the tower. Big generators add more costs to the tower strengthening. Windforces against skyscrapers is major architectural challenges, and they don't generate squat for power. Big generators require big props, which adds to the cost of the tower strengthening. The big generator is now so big that it is making so much heat that you have to have electric fans in the nacelle to cool the generator -- imagine that, FANS inside cooling because the wind is blowing so hard outside? The hollow towers are now so big that they are considered for use as hydrogen storage tanks for low-wind power-smoothing production.

There comes a point where you ditch this 1950s turboprop obsolete mindset and start over from scratch: WHAT does Newton's Laws teach about action-reaction. You might end up with my Eagle's Roost towers or you might end up with Hydrogen balloons holding up suspended power generator gondolas, with the power going down the tether and NO tower at all.

The GE-Misubishi turboprop gee-wizzbang is a thinly disguised 800-year-old dutch windmill, which itself is a thinly disguised 2,000-year-old oxen-driven flour mill. Sailors invented practical windpower 3,000 years before the first electric wind generator. There are other useful wind harvesting concepts which do not involve crankshafts or gears.

This is not "modern technology" and not even efficient technology. After I decided to draw the alternative that is indeed modern, so new in fact it is unique enough that I could patent it, I looked up the prior art patents in the USPTO website.

http://h2-pv.us/wind/towers_prior_art/towers_prior_art.html

Some parts of this had occurred to people before:

http://h2-pv.us/wind/towers_prior_art/TN_us006749399-011.JPG

[Lion Kuntz]

UPDATED: I read this and passed it on without running the numbers. Shame on me. Rob set me straight with links to discussion that got me motivated to run the numbers. Good on Rob. The monthly output is computed to 74 kWhs @ the specified 13 mph average winds, and the power out at 28 mph cannot be even 400 watts. If the price was real cheap, and it worked really good, 100 watts per hour puts it on a par with reputable PV panels. See several msgs below in thread for the math.


http://www.treehugger.com/files/2007/01/magwind_vertica.php

Mag-Wind Vertical Axis Turbine for your Home
by Lloyd Alter, Toronto on 01.22.07
Science & Technology (alternative energy)

40 mw1100.jpg

We get excited about new technologies; sometimes we jump the gun, so it is great to find a product that is new, different and actually available. It's a "Magnetically-Levitated Axial Flux Alternator with Programmable Variable Coil Resistance, Vertical Axis Wind Turbine' , and it has just come on the market. Designed by Thomas Priest-Brown and Jim Rowan in Canada and manufactured in Texas, it"solves 11 different problems that previously limited the development of vertical-axis wind turbines for generation of electricity ." The center hub floats on a magnet, and the coils that generate the power are at the outer ring, with magnets at the tips of the blades flying over them at high speed. It is designed for home installation in urban settings; It is only 4 feet high, so neighbours are unlikely to complain about its appearance. We asked about issues with ice and snow, and were assured that there was no problem. We also asked about noise (often a complaint) and was told that it was inaudible.

41 turbine_test.jpg

Unlike normal turbines, it doesn't mind a little turbulence, works well in developed areas, and gets an extra kick from something called "the roof effect" -evidently "A roof with a 10-foot vertical rise and a 30% angle will provide nearly a 200% increase in the amount of wind energy that is available to be turned into electricity. Compared to the same turbine just sitting on a pole, the roof effect increases the power yielded by operation of the wind turbine dramatically."

Specifications are impressive:

* Productivity: 1100 kWh/month in a 13 mph average wind
* Name Plate: 5 kW rated output in 28 mph wind at sea level with 80% relative humidity.
* Cut-In Speed: Less than 5 mph.
* Top Speed: Greater than 100 Mph.
* Economics: Fully burdened cost over 10 years is 3.5 cents per kW.
* ROI: If current bill is $300 per month or more, then ROI 3 years or less.
* Maintenance & Operation Costs: Minimal
* Deployment: Rooftop Urban or Rural Setting.
* Total Estimated Production Run 2006: 3,500 Units
* Production Units Ready Spring 2006

The first two prototypes have been working all year; Deliveries start in February from ::Magwind Local Canadian distributor is ::Niagara Windpower

[Rob Beckers]

Hi Lion,

Did you follow the discussion on the Yahoo AWEA list a little while ago? This turbine was discussed/analyzed in detail there. The consensus was that the production figures were highly suspect. Because discussion was getting heated it was agreed that the proponent was going to get actual measurements and only publish/discuss this turbine again when those were available.

-Rob-

[Lion Kuntz]

Hi Lion,

Did you follow the discussion on the Yahoo AWEA list a little while ago? This turbine was discussed/analyzed in detail there. The consensus was that the production figures were highly suspect. Because discussion was getting heated it was agreed that the proponent was going to get actual measurements and only publish/discuss this turbine again when those were available.

-Rob-

Nope. Didn't see it. Got links?

[Rob Beckers]

Nope. Didn't see it. Got links?

Yup, go to the AWEA group on Yahoo (http://tech.groups.yahoo.com/group/awea-wind-home/), search for MagWind. That'll give you lots of messages.

-Rob-

[Lion Kuntz]

Yup, go to the AWEA group on Yahoo (http://tech.groups.yahoo.com/group/awea-wind-home/), search for MagWind. That'll give you lots of messages.

-Rob-

OK. Went There. Did that. 66 hits for MagWind. Most of it opinion based on nothing. About 20 only mentioned MagWind in quoted section and added nothing new. About 20 more were arguments about Krystal Planet's marketing methodology or other products in their line. Finally out of about the 26 that survived those culls, we get a lot of opinions based on nothing, or suggestions on how to test the claims, whether wind tunnel or truck testing.

World's First "Magnetic Levitation" Wind Turbines Unveiled in China,
Message #19745 of 20557
Well, I have laid it out really clearly in my recent posts
to the Krystal Planet brass, and on yesterday's conference
call again, that the experts claim there is not physically enough
energy, in the wind cross-section striking the size profile
of the Mag-Wind, to be convertible by any means consistent
with conventional physics, at even 100% efficiency, into the
amount of electric output claimed by the Mag-Wind, or
any amount reasonably close. My impression of these claims
by the experts is that they are saying the Mag-Wind not only
cannot put out its advertised 1100kwh/mo at 13mph wind
speed, but more on the order of 100kwh/mo or less?

My impression of these claims by the experts is not even the writer's own opinion, and the "experts" are not specified.

Nobody on the list was willing to do basic calculation. Regardless of the 3-D shape, the profile of the device is a triangle. In this case can be subdivided in halfs as two right-triangles. The base diameter is not given, but is approximately equal to the height, which is stated as 4 feet. That would give a swept area of 8 square feet.

Here's the MagWind claim:
5 kilowatts (6 horsepower), at 28 mph.

http://www.awea.org/faq/windpower.html
Power in the area swept by the wind turbine rotor:

P = 0.5 x rho x A x V3

where:
P = power in watts (746 watts = 1 hp) (1,000 watts = 1 kilowatt)
rho = air density (about 1.225 kg/m3 at sea level, less higher up)
A = rotor swept area, exposed to the wind (m2)
V = wind speed in meters/sec (20 mph = 9 m/s) (mph/2.24 = m/s)


Formula applied to MagWind:
Swept Area = 8' = 0.7432243 meter square.
0.7432243 x 0.7432243 = 0.55
28 mph = 12.51712 m/s
Air density = 1.23 kg per cubic meter at sea level

formula for power = 0.5 x 1.23 x 0.55 x (12.52^3 = 1962.5) = 663.8 watts

663.8 watts x Betz Law .59% = 391.7 watts net power to the rotator.

This is before friction, reactance and resistance losses.

Now the question I would ask is why the unspecified experts didn't do this? Or how can they be experts at all if they can't do this?

One assumes that the roof slope itself may contribute to the wind force, but an anemometer placed on the roof reading that windspeed would be taking that into account. I should have done it myself before posting, but in my eagerness to get discussion going I skipped it. However, I did attend to due diligence within 24 hours, not carry on for 66 messages.

The fact that "MagWind" doesn't produce it's advertised rating wouldn't change the fact that it does potentially produce something approaching 400 watts (@ 28 mph) in the profile space that a PV panel (8 sq.ft.) would be producing 96 watts.

In other words, people selling something under fraud doesn't negate the use of that thing for object lesson about other things.

Magnetic Levitation with permanent magnets opposed to permanent magnets is not efficient. Unfortunately, magnets require mass, more so if they are permanent than electromagnets, but even electromagnets have mass of windings which must be metal and a core which is heavy metal.

Sheet metal is not as strong or as stiff as carbon-fiber composites (reinforced plastics). It also is heavier.

As I said up in this thread or in another one, I forget at the moment, putting a Savonius rotator inside a protected shell can allow lighter weight materials. The illustrated roof does in fact provide some wind-speed increase, but only in two perpendicular directions, and none in the 90 degree offset direction. Architects ARE concerned about windforces on rooftops, and building codes do take local winds into account in setting building standards. The wind tower I proposed is omnidirectional, does have 4-sided wind guides (funnel). Somebody's objection about MagWind was that at high speed the winds do stand off (boundary effect, and act as a quasi-governor. One complaint about no brake on the MagWind was addressed with irising down the windows. In other words, the MagWind brought out some wisdom which helps establish some proof-of-concept for the towers, even though the MagWind is over-sold or perhaps outright fraud.

Some of the arguments were right on in the AWEA thread, some were not.

After I post this, I'll go back and put a caution note on the posting about MagWind. Since wind force is quadrupled when wind speed is doubled, divide by four to get the approximate 13 mph power. It comes out to ~74 kWh/month. The seat-of-the-pants estimate quoted from AWEA is generous, and I doubt that rooftop 13 mph AVERAGE hourly winds exist many places where people like to live. Most people don't like to live in windy places.

The average power consumption is ~720 kW/mo, so ten of these would be needed IF you had 13 mph average winds.