Will TMA Wind Blow Away the Competition? (vertical wind generator technology)

PESN.com ^ | 1 Feb 07 | Sterling D. Allan

[saganite]

CHEYENNE, WYOMING, USA -- On January 20, I was able to meet the TMA Wind company executives, Ron Taylor and Duane Rasmussen, and view their test site just outside Cheyenne, Wyoming. Though it was a seven-hour drive each way, in the middle of a cold and sometimes snowy passage from the Salt Lake City area, I thought it was a trip well worth taking.

From my perspective, I am inclined to agree with TMA's assessment that they have the next big thing in wind technology. Their design will overturn the past scientific dogma that says that vertical turbines can't produce as well as the typical propeller-like, horizontal blades.

TMA has done extensive research and development over the past eleven years, including wind tunnel and on-site testing to come up with an optimal, patented vertical axis wind turbine design that operates at around a 40% wind conversion efficiency, doesn't kill birds, can be installed more densely per given real estate, runs much more quietly, has nearly no vibration, doesn't need to be installed as high, and can be blended in better with landscape -- all at a price that is competitive with the best horizontal wind turbine designs presently in use.

At lower average wind speeds, from between 10 and 35 mph, the TMA turbine design has a comparable generation cost to the most cost-effective horizontal wind turbines -- in the range of between 3.5 and 4.0 cents per kilowatt-hour. But at higher wind speeds, where the horizontal turbines have to be shut off, the present TMA turbine designs can keep generating all the way up to 65 mph, where the return on investment comes even faster.

The higher-speed limitations are not in the structure, but in the generator, which should not be over sped, lest it burn out. A generator could be selected for high-wind-speed areas. The mechanical structure itself is engineered to withstand into the category 5 hurricane classification, which begins at 156 mph.

When they first started the company, they were hoping to find a niche in the high-wind scenarios (class 6 and 7 winds), where horizontal turbines can't go. They have been pleased to confirm through wind tunnel testing that their design is also competitive even at the lower wind speeds. Eventually, the design could also be applied downward into river and tide harnessing applications, but the company is postponing those applications in order stay focused in their launch of the wind applications.

Their most recent prototype outside Cheyenne has been grid-connected for nearly three months, complete with all the certifications required for that to happen. TMA expects that within a month they will have sufficient power curve data from installed capacity that will enable them to definitively prove the superiority of the design. They have just been awarded their third U.S. patent, so now all they are waiting for is the newest power curve data to give them the green light to launch full steam ahead. The company is presently in various stages of negotiation with a number of international clients to license construction of the turbines commercially.

Many components in the TMA design are off-the-shelf items, including the generator, the bearings, the gear box, the braking mechanism, and the electronics. The turbine and the support structure are the only specialized component in the design, and those are things that "can be easily produced by any quality fabrication shop."

Before installing a turbine, TMA will analyze the wind data available for the target site to see what the average wind speeds are as well as the most frequent direction. (Such data is already available for many locations worldwide.) The design is then tailored for those parameters. While the design is omni-directional, it is engineered to optimize the wind from one direction, where its efficiency is between 40 and 45%, while wind coming from the back side might be 30%, which is still better than what horizontal turbines do.

In addition to a turbine, the TMA design has a wind-capture mechanism via protruding funnel-like air foil structures that direct the wind into the rotating turbine. The advantages of this are comparable to the concentrated solar designs that focus the sun's energy onto photovoltaic cells, for example, reducing the number of expensive components in the system. The TMA design thus incorporates a "concentrated wind" aspect. That particular design feature constitutes an important part of the patented intellectual property of the company.

During their research and development phase, TMA tried around 300 iterations in wind tunnels, and built nine turbines for on-site testing. "The newest turbine we are testing out-performed what we saw in the wind tunnel," said Ron Taylor, Chairman of TMA.

The TMA design is scalable from 1 kW up to 1 MW, though the company does not plan to build anything larger than 500 kW. "If a one megawatt turbine goes down with a mechanical problem, that's a lot of generating capability that goes off line at once." And it is more time-consuming to fix larger devices than smaller ones. The longest a 500 kW unit might be down would be one day (assuming availability of personnel and spare parts). The lower thrust bearing of the turbine is a split-bearing design for easy replacement, if and when necessary.

Vertical v. Horizontal

The advantages of TMA's vertical axis design over the traditional horizontal wind turbine design are many. The "concentrated wind" aspect mentioned above is one.

The air-foil design of the TMA turbine is such that not only does the wind push the one foil forward, but it pulls the foil coming back toward the direction of the wind (Bernoulli's Principle).

Because the generator is near the ground where it is easily accessible, the maintenance costs on a TMA design are considerably less of what they are for a horizontal design where the equipment is high up in the exposed air.

The TMA design is much more stable due to the tripod arrangement of the air foils that direct and accelerate the wind into the rotor. Therefore the footings only need to be about 48 inches deep on a 250 - 500 kilowatt TMA turbine, compared to 10 to 20 feet on a comparable horizontal axis turbine footing. (Ref.) Also, whereas the moving blades on the horizontal design are fixed to one point at the hub, there are two points of connection (top and bottom) on the TMA design. This also causes vibration to be nearly non-existent in the TMA design, whereas the vibrations from horizontal turbines have been documented to rattle dishes two or three miles away. The TMA design does not produce communications interference, which has been a problem with horizontal wind farms.

Wind shear does not effect the vertical axis design, which can handle changes in wind direction with no problem, being nominally omni-directional, while such changes create tremendous stresses on the blades of horizontal-design turbines.

Because TMA's turbine spins 1.1 times the speed of wind, it doesn't pose the hazard to birds or bats that the horizontal turbines do, with their fast-turning blades, which approach near supersonic speeds at the tips of some of the larger turbines. The birds and bats don't perceive them coming and get whacked.

The efficient aerodynamics of the turbine are such that it has a low wake signature (the air turbulence that tumbles out the back side), which allows more of the turbines to be installed per square foot of real estate, per kilowatt produced, than what horizontal turbines allow because of their larger wakes. Taylor says that they can fit two to three times as much power density on property as horizontal wind turbines.

There are visual advantages as well. The TMA design sits lower to the ground, and the stationary air foils can be colored or camouflaged to blend into the surrounding scenery. Alternatively, the air foils could also be lined with solar panels for secondary power generation -- a feature not available in the horizontal turbine pillar design.

NREL v INEL

Traditionally, the U.S. National Renewable Energy Lab (NREL) has questioned the feasibility of vertical-axis wind turbines, and has favored the horizontal prop design.

However, representatives from the Idaho National Energy Lab (INEL) have visited TMA's Cheyenne test site, and have become believers in the plausibility of the vertical axis design.

[ridesthemiles]

There is one of these turbines near the intersection of the I-5 and I-405 in northern San Fernando Valley in California. Been there for years. Most people don't have a clue what it is. I do not know the level of efficiency of it, but if I were to put up wind turbines, this is the type I would look into.

[ridesthemiles]

I pulled up their website. If the photos there indicate the structure, they are much larger than the one I posted about earlier. The one I have seen in SF Valley is about 8 times the size of a telephone pole, and has vertical slits for the air to get in and turn the shaft. I don't know who owns it or what it cost, but it is very unobtrusive.

[Richard-SIA]

How about just down-stream of existing power dams?

Secondary power generation, easily connected to the existing distribution network.

[saganite]

You might have seen a test model. There are several companies working on various types of vertical axis wind generators to include small ones you can install for home energy production.

[Ramcat]

The one I have seen in SF Valley is about 8 times the size of a telephone pole, and has vertical slits for the air to get in and turn the shaft. I don't know who owns it or what it cost, but it is very unobtrusive.

Seems like it would make a great privacy fence?

[Dixie Yooper]

You would have to get them very close to the surface to get John Kerry, he's a windsurfer.

[Uncledave]

Actually, I'm intrigued by VAWT designs -- hope they can find a place in the industry.

[visualops]

That's a good idea.
Speaking of farmers- I glanced over an article about "boutique farming" where farmers are growing more specifically what people request and selling direct to consumer with no middleman. I think they mentioned Massachusetts of all places had a high proportion of direct-to-market farming.

[visualops]

Apparently.

[listenhillary]

Bump

[Robert A Cook PE]

Interesting. Very interesting.

I like the points brought up, and the rather straight-forward presentation of the improvements.

less "hype" in the writeup (after words) generally means more thought in the design (beforehand) = more success in the field (bottom line).

[Robert A Cook PE]

True: The "horizontal" shaft turbines have the shaft (as implied) halfway up the propeller diameter - so the generator is off the ground (on top of the support tower) in a very large housing.

For large power -> large propeller -> very large tower -> very large foundations. Lots of weight up high = large moment arm for vibration, lots of movement, lots of of trouble lifting the replacement parts (hundreds or thousands of pounds of machinery or replacement bearings, bushings, brushes, magnets, etc. up for maintenance. Propeller "wing" maintenance is difficult (these things are the size of a 737 wing, and just about as complex. (Though flaps are much simpler.)

A vertical shaft machine puts the weight of the generator at the bottom. N moment arm, and the generator room is "wlk-in" and low cost. Generator mass is low down, helping to stabilize the weight of the "pole" as well, so the "pole" to the upper bearing is much less complex = much cheaper.

Simple bearing components at the top of the tower (no elctrical generator!) means much easier, and much less, and much cheaper maintenance for does has to go on top.

As you pint out, the wind turbine is closer to the ground, so apparent efficiency is less. BUT - what you can do is use a (relatively cheap) tripod or post to "raise" the bottom of the pole up. You're NOT raising the generator (just using a longer vertical shaft) and your able to use a wide tripod or 4-post support at the bottom to reduce foundation costs. but you've still raised the average height of the vertical turbine 25 - 35 feet. If need be,, these guys seem to think they don't need that extra height. (I disagree, but I don't have their equations for low speed economies. My opinion, as soon as they start needing to sell in low wind (12-15 mph average) environments, they'll start raising the base a bit. It's still much less than a horizontal prop perched with its generator on a high tower.)

No, you can't really put the horizontal shaft generator on the ground and run gears down to it from the hub up above. They simply have failed in use: too much stress and and too expensive for the complex gears and shafts.

[Robert A Cook PE]

the little (almost unnoticed!0 key to their entire scheme is the "pull" of the blades FORWARD as they pass into the wind, combined with the PUSH of the blades BACK (away) from the wind that you'd naturally expect. Naturally, the writer skipped right past this point, but I'll bet it's why they are more efficient at low speeds: no "drag" of the prop against the wind as the blade turns as in a conventional vertical turbine.

A sailing boat's sail do the same thing: much of the sail's pressure (forward) is from the suction of the wind passing in front of the curved sail when the boat is sailing at an angle from the wind.

That's why "wind directly astern" is not the fastest direction of sailing for anything but a square-rigged single masted, single sail boat.

[saganite]

I guess I passed over that point too but I've been reading about these folks for a couple of years and that fact is mentioned prominently in all their press releases. Guess it didn't seem new or exciting given my familiarity.

[neverdem]

thanks, bfl

[syriacus]

Thanks for posting this. I have a feeling that the appearance of wind-powered generators will change quite a bit, as the idea catches on.