10 replies to this topic

[Pete31]

Hello

I have a small question about windturbines.
Turbines of the same park usually turn in the same direction. Because the wind direction is the same for all turbines of the same park. And I guess there are some electronics onboard of these windturbines which let the blades turn into the direction of the wind. But there are some noticeable irregularities. Sometimes some of the turbines are not turning, or when they are, they are turning in another direction compared with most of the other turbines. I just wondered what could be the reason for this. To be more precise: I see more large windfarms  with 2-3 windmills simply not operating for some reason than large windfarms with fully working ‘members’. It could be there is some kind of defect of the incentive electronics. But in that case there are lots, lots of windmills that are dysfunctional, which seems unlikely.

[Hayden]

Hello Pete. First of all welcome to our green community. Great question! I could be wrong but I believe there is a specific science behind the placement of multiple windturbines so that wind that is funneled through one turbine is used by another turbine deliberately positioned to feed off the first.

To confirm this did some research and found that when a system expels or accelerates air in one direction, the accelerated air will cause a proportional but opposite force on that system. A single rotor wind turbine causes a significant amount of tangential or rotational air flow to be created by the spinning blades. The energy of this tangential air flow is wasted in a single-rotor propeller design. Thus, to make use of this wasted effort, the placement of a second rotor behind the first takes advantage of the disturbed airflow. Contra-rotation wind energy collection with two rotors, one behind the other, can gain up to 40% more energy from a given swept area as compared with a single rotor.

Hope this helps.

[Pete31]

Hayden

Thank you very much for your quick reply. I'm afraid my English isn't good enough to comprehend your fully technical explaination  (i am dutch). But if i comprehend well, you suggest some windmills are there to obstruct the other ones turning. It could be the case, but it seems odd.

I will pose the question in another fashion. When you've got a windpark with 30-40 windmills and the windforces are ideal, is it a normal situation that all windmills spin together in the same direction at the same time? But the larger the windpark seems to be, the bigger the chance of windmills not working. With smaller windparks this seems lesser the case.

[still learning]

Hayden, on 13 March 2012 - 01:16 PM, said:

....behind the placement of multiple windturbines so that wind that is funneled through one turbine is used by another turbine deliberately positioned to feed off the first.....

I'm pretty sure that's not true.
A second turbine does not "feed off the first." Not the ones you see in windfarms, the three bladed horizontal axis ones..
Wind turbines are normally set apart so that one doesn't interfere with another.
Think about what a wind turbine does: It extracts energy from moving air.
To do that it slows down some of that moving air. Some of the kinetic energy of a moving mass of is converted into the kinetic energy of rotating windmill parts and much of that that energy is in turn converted to electrical energy by the windmill's generator.
Putting a second turbine in the path of that now slowed down piece of air would tend to make the second turbine less effective.

That bit about the counter-rotating setup, looks like you copied from wikipedia here: http://en.wikipedia....l_wind_turbines
There are quite a few unconventional wind turbine designs, and I expect that many of those can be more efficient in converting wind energy into electrical energy, sure enough, but with increased construction cost and/or decreased reliability.
If the object were to remove as much energy as possible from a given amount of moving air you could gang together several sets of blades on one shaft, increasing in size downwind, enclosing the whole thing in a conical duct to keep that tangential flow from escaping outward. Greatly increased cost though. End up with something very like what's inside a steam turbine.

As to the original questions by Pete31, I don't know the answers.
Speculating though: Could be some are down for maintenance. Could be that there isn't enough demand right then for all the electricity that all the windmills can produce, so the operator might put some in idle mode.
Rotating the other way? Just depends on how the thing is built. Design the rotor blades mirror image then they want to run the other way, same net capability. Might be bettter to run some clockwise and others counter-clochwise to reduce downwind turbulence, don't know.

[Pete31]

Still learning, thx for your suggestions. I've read somewhere else windmills are sometimes shut down because the energy cannot be stored. It has to be consumed right away. So when there isn't enough demand, they shut some windmills down. Tis makes me wonder. Because why can't electricity from wind energy be stored like electricity from other origins? I mean, electricity is electricity right? Normally it could be stored. And when it could be stored, why should someone shut down some of the generators? Those mills are quite an investment. Therefore the 'controller' should be happy there is enough wind to make every mill of the same farm running when no maintenance issues are involved.

Concerning the rotating direction: i thought that with the latest models of mills the blades can rotate 360 grades into every direction: south, north, east, west, depending from where the wind is coming. The blades of the ones 'that are shut down' are usually turned in an opposite direction to the ones that are rotating. There, it seems, the blades are used to turn in such a way the mill cant be moving, no matter how much wind there seems to be.

[Shortpoet-GTD]

I found a few links for you Pete, that may be helpful.

"Many wonder about the wind turbines. Why are some turning and others aren't?
The wind turbines may not be fully installed, or fully constructed or they may not be connected to the grid and producing power.
The electrical network or grid where the energy goes could also be full, so turbines have to stop so the grid doesn't overheat.
Turbines may also halt when undergoing maintenance.
They can't function when the wind is too strong, when the wind is too weak, the wind is gusty, things like that really
inhibit energy production."
http://www.wlfi.com/...es-from-turning
General wind turbine info here:
http://www.explainth...ndturbines.html
Individual "ask" question here:
http://www.bwea.com/ref/faq.html

Hope that helps.

[Hayden]

Thanks for clearing it up. The beauty of community forums.

[still learning]

Pete31, on 15 March 2012 - 01:45 PM, said:

. Because why can't electricity from wind energy be stored like electricity from other origins? I mean, electricity is electricity right? Normally it could be stored.

Normally electricity isn't stored.

Not in grid-significant quantities anyway.
With one major exception, which is called "pumped storage."

Not being able to store electricity inexpensively in significant amounts is a headache in planning for a renewables based electricity grid.
Finding an inexpensive way of storing electricity in grid-useful amounts would be a huge advance.  A person who invented a way could get rich.
There are lots of ways grid electricity can be stored, but most ways are too expensive for actual use: http://en.wikipedia...._energy_storage

Batteries?  Costly.  For portable applications you put up with the cost.  Used in some specialized grid situations like :  http://www.wired.com.../dayintech_0827

[jasserEnv]

To date, the only cost effective means of storing electricity that I know of is in the form of homopolar motors and flywheels and these are barely cost effective. in many cases, they are not. I have seen some work about pumping air into bags underwater to store in compressed form and the people creating these say it is cost effective but I have not actually seen independent analysis to confirm that that is true. The storage of the power presents similar challenges as does the use of alternatives.

[still learning]

jasserEnv, on 20 March 2012 - 11:32 AM, said:

To date, the only cost effective means of storing electricity that I know of

Found a paper dealing with the costs of electricity storage.  Published in IEEE Transactions so it's peer-reviewed stuff but It's from 2008, so maybe there's been significant change.  Or maybe not.  At  http://fgamedia.org/...ity Storage.pdf

Take-home is that storing electricity (in other than pumped storage setups) adds considerable cost, $0.15 to $0.60 per kWh, in this 2008 analysis.  This is added to the ordinary cost of electricity, $0.095 per kWh, US residential average in 2008.

[apprenticeneed]

tacnically various reasons to do not proper work of turbine like gear oil, barings grease etc.