Posted on 02/05/2007 7:07:18 AM PST by 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.
I suppose he means horizontal SHAFT, as most turbines have the shaft horizontal, and the blades are vertical.
There are a lot of potential advantages, including fewer moving parts. For example, it's not directional, so you don't have to include a swivel behind the rotor blades.
The biggest issues would have to do with getting sufficient "wetted area" on the airfoils.
They'll have boundary layer and turbulence problems, then.
I think the turbine blades are elevated with the generator being on the ground. But then I thought the generator on current windmill types was also on the ground.
I take it by the link you provided that you think this won't work, at least in the sense that any wind powered electric generator "works".
I think the generators on the big turbines are just behind the blades, so there must be a design aspect there -- perhaps they don't want to spend energy turning a big drive shaft.
Seems to me that the same design issues would be in play for this system, unless the thing in its entirety is sitting closer to the ground.
"What I find particularly interesting is the eventual underwater version."
Deep underwater please. We don't need no stinking navigation hazards.
There are a couple of pics at the link that are helpful in regards to your questions. You can see by the men standing next to the test model that it's quite small compared to the current windmill type generators. I'm sure the 500 KW version would be substantially larger though. The second pic is taken inside the generator room and it appears the drive shaft is very short and is coupled directly to the bottom of the turbine section.
This is what it looks like?
As #10 shows, it's indeed a savonius rotor type. That close to the ground, it'll indeed suffer from boundary layer and turbulence effects.
ping
The ones that will go around Martha's Vineyard will be very near the surface, but out of sight.
Please Freep Mail me if you'd like on/off
That ought to be good enough to rip the hulls out of John Kerry's and the Swimmer's sailboats.
Don't ya just hate verticle axis windmills?
That will be overcome in the same way they are overcoming the resistance to the present windmills. In the midwest farmers are lined up wanting to place windmills on their own property. How? They own them, and sell the electricity to the power company.
The waiting list is long, and constraind by the number of windwills the factories can manufacture.
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