May 17, 2010
Wind Turbine Arrangement Boosts Efficiencies
Turbulence caused by wind turbines forces large gaps between turbines and therefore lowers efficiency and raises the cost of wind farms. Some Caltech researchers got inspired by patterns of swimming by schools of fish that suggested smaller gaps should be possible. Vertical turbines combined with alternating rotation patterns should allow much closer turbine placement.
Vertical turbines—which are relatively new additions to the wind-energy landscape—have no propellers; instead, they use a vertical rotor. Because of this, the devices can be placed on smaller plots of land in a denser pattern. Caltech graduate students Robert Whittlesey and Sebastian Liska researched the use of vertical-axis turbines on small plots during a class research project supervised by Dabiri. Their results suggest that there may be substantial benefits to placing vertical-axis turbines in a strategic array, and that some configurations may allow the turbines to work more efficiently as a result of their relationship to others around them—a concept first triggered by examining schools of fish.
In current wind farms, all of the turbines rotate in the same direction. But while studying the vortices left behind by fish swimming in a school, Dabiri noticed that some vortices rotated clockwise, while others rotated counter-clockwise. Dabiri therefore wants to examine whether alternating the rotation of vertical-axis turbines in close proximity will help improve efficiency. The second observation he made studying fish—and seen in Whittlesey and Liska's simulation—was that the vortices formed a "staircase" pattern, which contrasts with current wind farms that place turbines neatly in rows.
The researchers expect to be able to increase wind energy extraction in an area by several times.
Whittlesey and Liska's computer models predicted that the wind energy extracted from a parcel of land using this staggered placement approach would be several times that of conventional wind farms using horizontal-axis turbines. Once they've identified the optimal placement, Dabiri believes it may be possible to produce more than 10 times the amount of energy currently provided by a farm of horizontal turbines. The results are sufficiently compelling that the Caltech group is pursuing a field demonstration of the idea.
Looks like wind power costs have the potential to fall considerably.
Wouldn't that kind of require that the wind always be blowing in the same direction, or at least quite close to it?
I thought the reason no one used vertical turbines anymore (they used to) was that they were very poor in low-wind conditions and required assistance to start rotating; both factors killed their economics.
No, a vertical rotor is like the exhaust vents on houses, they're axially symmetrical, so wind from any horizontal direction will drive them. And VAWTs have lower wind startup speeds than HAWTs. There are directions which make the "staircase" pattern back into a row pattern, though.
However there are a number of downsides which have kept Vertical-Axis Wind Turbines(VAWTs) from being used as widely as Horizontal-Axis Wind Turbines (HAWTs).
1. VAWTs are very difficult to mount high on a tower to capture the higher level winds.
2. Each blade sees maximum lift (torque) only twice per revolution, making for a huge torque (and power) sinusoidal output -- just like cranking on a bicycle -- that is not present in HAWTs. And the stress in each blade due to wind loading changes sign twice during each revolution as the apparent wind direction moves through 360 degrees. This reversal of the stress increases the likelihood of blade failure by fatigue.
3. And the long VAWT blades have many natural frequencies of vibration which must be avoided during operation.
What about 80m altitude? What is the cost per swept area?
There is a lot of necessary arithmetic to be done here.
Vertical turbines, new? Some article author (Weiner?) is utterly clueless; the Darreius turbines east of Sacramento were too small and needed too much maintenance, so IIRC they are no longer there (I saw some around 1994).
Not only are the units in the article pathetically small (6 turbines totalling 15 kW?), the horizontal bars would attract roosting birds whenever they were still. What really galls me about this is that the mistake is so completely obvious if you know recent history.
Okay, maybe vertical turbines can extract more energy from a given flow of wind. We're not short of wind, or land; we're starved for capital to build and install machines. This is a solution in search of a problem.
Thanks, Larry -- that makes sense; I've no idea why I remembered otherwise.
52 week high $79.80...52 week low 46.55 current price 47.30,
As european socialism runs out of money and bankrupts itself, affirmative action energy goes with it.
Vesta is a European company whose major market is Europe so shouldn't you use Krone or Euro numbers which may be a significant part of the price drop?
I'm pretty sure it was mainly economics that favored the horizontal axis wind turbines. Vertical axis wind turbines are much less efficient and this increases their cost/watt. Recent large horizontal axis turbines on the market are like 50% plus efficient, close to theoretical maximum (about 60%). Combined with higher maintenance, reliability issues etc this further increased the levelised cost of the vertical axis designs.
Maybe a really big vertical axis wind turbine could be efficient, but I doubt it.