ALTERNATIVE DESIGN: Vertical axis wind turbines and other alternative designs still have kinks to work out.
Image: Joanne and Matt/Wikimedia
Propeller wind turbines are the most common way of using one of the most abundant energy sources on Earth to generate electricity. The tall three-bladed fans are the ubiquitous symbol of wind energy, but they aren't the only design on the market.
Vertical axis turbines, where the rotating axis stands upright, have been around as long as their horizontal brethren but have failed to catch on at large scales. "The simple story is that the companies that were commercializing [vertical turbines] were unable to make the inherent advantages exceed the inherent disadvantages," said Paul Veers, chief engineer at the National Renewable Energy Laboratory's Wind Technology Center.
The turbines come in two main varieties of rotors -- the part of the generator that catches the wind and spins -- and share many of the same advantages. The Darrieus rotor uses arced narrow blades anchored at both ends of a shaft, akin to a whisk or an eggbeater. The blades have a cross section similar to an airplane wing and generate force in similar fashion.
Savonius rotor turbines are another design, where air scoops are mounted on the shaft of the generator, forming a spinning cylinder. Where the Darrieus turbine spins by generating lift, the Savonius rotors spin from drag.
Since the turbines are vertical, the generators can be placed on or close to the ground, lowering maintenance costs. Their narrower vertical footprint allows them to be placed closer together, though spacing is limited by how much energy is extracted from passing breezes and by support structures like guy wires. Vertical turbines also tend not to be as tall and have a steady gravity load, meaning the effects of gravity don't change as the turbine spins, unlike in horizontal axis turbines. They can also accept wind from any direction with equal efficiency.
More mass, less power
"It's a technology that works, but it has some problems," said Veers. "The design is complicated. It's got very dynamic loading, and it's a very dynamic structure." Though the effects of gravity are constant, forces from wind change on various parts of the structure as it spins, said Veers. He noted that the frequency of the shifting forces can create a phenomenon known as resonance, where the effective force is amplified and the rotor ends up tearing itself apart. This limits the size of individual turbines.
In addition, the designs have an inherently higher mass-to-power ratio and an inherently lower efficiency, said Veers. Because the rotors tend to be shorter, vertical turbines only have access to lower wind speeds and are more vulnerable to turbulent air flows from buildings and trees. "There's a bit of an uphill climb to make them work," he said.
Mick Sagrillo, an independent consultant for small wind energy companies, agreed with this assessment. "The rotors themselves are actually less efficient," he said. "The successful technologies that are out there are horizontal. It's Darwinian economics. It would be nice if this weren't the case, because then we'd have other options, but unfortunately, that's where we're at."
Because of the lack of investment, there hasn't been much progress in improving vertical turbines as there has with horizontal windmills. "There are several decades of a growing knowledge base for horizontals," said Veers. "There's a lot of investing by knowledge, learning by failing."
Nonetheless, some engineers have tweaked the vertical turbine designs to improve their efficiency and cost-effectiveness. One method is to arrange the scoops or blades in a helix, thereby ensuring a constant level of force from wind, minimizing oscillations.
Fishing for better configurations
Another approach is to rearrange how the turbines are placed. John Dabiri, a professor of engineering and applied science at the California Institute of Technology, studied how schools of fish maneuver in water and extrapolated his findings to wind turbines. From computer models, he found that counter-rotating vertical turbines could be arranged in such a way that a vertical wind farm has a higher power output per unit of area than a horizontal farm, upward of 10 times the energy density.
See what we're tweeting about
9 Comments
Add CommentOn a discovery program that I can't remember the name off it showed a type of turbine I thought was really clever. It was a vertical type and looked like those spinning things you get on top of flues but was much larger. It turned with wind from any direction. The radical thing was that the spinning part floated on magnets in a ring on the base so that there was no friction. The magnets also formed part of the generator. I have no idea if this was ever pursued commercially but looked like it had a lot of potential.
Reply | Report Abuse | Link to thisSounds really interesting. As I understand (what little that is) turbulence is the enemy of efficiency.
Reply | Report Abuse | Link to thisI saw that show also. I'm surprised I haven't seen more of it, though it could be due to patents and lack of capital to make it more mainstream. As I remember it was much more efficient than today's 'standards' and even worked as rooftop generators for homes and factories.
Reply | Report Abuse | Link to thisThere are a bunch of manufacturers of vertical axis wind turbines. The model that resembled a flue rotor was being marketed by Platek in Canada, and had great promise. For some reason no longer on the site.
Reply | Report Abuse | Link to thishttp://www.ecobusinesslinks.com/vertical_axis_wind_turbines.htm
Overall, verticals have several benefits that outweigh their inconveniences, namely they're much quieter than horizontals, the heavy bits are on the base, and they can be run in much higher wind speeds.
Because the technology is somewhat immature, there is a lack of hard data. But data that has been coming in after wind tunnel testing has shown that the VAWT models have exceeded predicted outputs by up to 40%. Cleanfield's model is a notable one for this.
In an urban/suburban setting, where turbulence and noise would be the enemy of traditional units, small wind VAWT units are ideal for meeting local loads.
PTripp said
Reply | Report Abuse | Link to this" As I remember it was much more efficient than today's 'standards' and even worked as rooftop generators for homes and factories."
That's the one. It was indeed shown on a buildings roof.
VAWT's are the tools of scammers and others who don't really have a clue about physics, economics or how to make cost effective power from the wind.
Reply | Report Abuse | Link to thisWhy is because of their slow speeds, they can't get enough energy from the wind. Since energy is rpmx's torque, you always need 5-10x's size, weight of machine in a VAWT to produce what a good 3blade HAWT does.
How do I know? Because I've built both sereral times and you won't catch me building an overpriced, low output, overweight VAWT when for 10-20% of the cost, I can get it from a HAWT.
It really makes me mad seeing all the scammers ruin wind's reputation with their what can only be called lies about how much their units put out. I watched them in the 70's destroy solar and wind with their scams, delaying our energy independence from big oil, coal.
A great 2kw in 20mph windgen designed well need only cost $500 in parts and labor so why are they selling for $5-10K+? Because of this, Late this I'm building a new improved version of my old design which should sell for about $2k.
RE is fairly simple cheap machines that are not rocket science. Less complicated than a moped. A HAWT is just 3blades, an alternator, some bearings, brushes mounted on a 40-100' pole.
A heat engine is no more than an A/C run in reverse which could use solar, boimass or waste heat to run. They too should cost no more than $2k/kw including the solar collector and/or bioburner.
PV panels are now under $1.50/wt retail if you shop well. Mount them yourself and hire an electrician to wire them up to the inverter/grid for under $2.5k/kw.
If you want to do RE, it really pays to research it well. Their is no reason an eff home can't make all their own power for $5-10k for 25-50 yrs of energy.
Reply | Report Abuse | Link to this@Lazarus
Maybe you were thinking of this:
Mazur's Regenedyne wensite
http://www.regenedyne.com/
Four videos of Mazur's prototype in live test.
http://www.maglevwindturbine.com/HD.htm
The handheld device that you see in the test is a Prova AVM-03 Thermo Anemometer (that measures wind velocity (looks like 50 meters per second in one frame) and air temperature in degrees Celsius.
My impression from many months ago was that Mazur was out to get investors, but was not responsive to technical questions or questions of his cost to build estimates.
I have been studying many diferent designs for wind generators and have been considering a possibility of combining a turbine type generator on one side with a verticle generator offset on the opposing or back side of the turbine generator, thus optimizing the wind at any given speed, if you are intrigued by this design idea let me know at your soonest and I would be willing to work with you on a proportionately balanced design. Respectfully, Kirk Francis
Reply | Report Abuse | Link to thiskirkcb1@hotmail.com
wind technolgy is now technology at particular location (s)etc. using the exsisting means of this wind turbin priencible of its form to but rather bringing the wind to wind turbin can be disiredable if [ veiw of landscape in not dramatilly allterd) I come up with this practicallty and some simplitcation and every aspect those envoled directly and indirectly will gain corbon credits from americas green initave act. [taking the soure to the technology] may qualify as substaible energy]... is what i have drafted. only little enginering needed. perrymanbrian@rocketmail.com implentation means needed
Reply | Report Abuse | Link to this