Are there any wind farm experts here on BAUT? Todays UT blog post made me wonder, how long does a typical farm take to recoup the cost of construction? Also, I've heard that people complain about land based farms, claiming they are an eyesore (I think they're pretty) and that the emit a constant low frequency noise. Is that true? They seem pretty quiet to me.

Hi, I should think that the only problem we face with good windmills is
with Severe Ice Storms and Hurricanes. In many places, these are not concerns , and therefore windfarms have sprung up quickly. These sites should be experimenting with the much larger cousins, the really big windmills.
Size does matter, and with the larger swept area comes more and more power.
So long as severe weather doesn't threaten the investment, big is a good thing.
Here in New England, they are starting to apply wind technology, considering that we have in many places a high average wind speed.
The problems come when certain insensitive individuals want to take coastal areas (which they take for nothing and for granted ....in view of increasingly
intense protests .....hmmmmm...) and make navigational hazards for
marine interests. Perhaps they would serve better in very shallow areas
which already present hazards to navigation. Also....you need to consider the loss of an blade ( a fifty foot blade slinging through the air packs a wallop
that will do some damage....hmm...) in the viscinity of homes .
There simply has to be thoughtfull consideration of windmill sighting which
meets with sensible facts and serves that community well.
But the positives are many....

1. Clean Power
2. Jobs .....hey, let's build something made in america...heh???
3. Less line loss and better efficiency for local consumers.
4. Every KW generated with wind is a KW not spent on foreign oil....
and friends...that IS a very good thing indeed.

We are capable of generating 1/3 of our electricity ....when we can...
from wind. It is a wind....win....win situation if it's done right.
But....I don't even want to see windmills built over seas. Those jobs and that quality technology should ,must needs, be ours. We are talking some really big bucks hear , and we need to spend our money at home, now and in the future. When these dollars are spread around, they make taxpayers and put roofs over our heads. It is as simple as that.
Good engineering, good jobs and good power.

Best regards, Dan

I certainly don't pretend to be an expert on wind farms. Here's an article that points out that certain aspects of depending on wind farms for large scale wind generation are problematic, to say the least.

One of the most frequent criticisms levelled at wind power is variability. That is, when the wind drops (or blows too hard) the windmills stop spinning and you get no power. To begin with, Oswald simulates the output rises and falls that might result from a lot of windfarms distributed around the UK by using Met Office archived data from different points up and down the land. Many wind advocates have argued that with enough windfarms, widely enough distributed, you would get more reliable power output as some windmills would always have wind.

Oswald's analysis says this isn't true, with calm conditions across pretty much all the UK being fairly regular events.

Analysis from 1996 to 2005 shows similar results: large, rapid, and frequent changes of power output being common occurrences ... any national power system has to manage under the worst case conditions likely to occur ... These are not extreme cases, whose frequency is so low as to render the events negligible. Rather, these are representative ...

The point of the analysis is that for many areas, the wind isn't blowing hard enough or can be blowing too hard. During those times, the electricity produced isn't sufficient to meet the needs. The likely way to make up for the shortfalls is something that can rapidly adjust to changing conditions such as gas turbine generators. The problem is that the most efficient and long lasting gas turbines are designed to operate at an essentally steady level. Throttling them up and down causes stress on the turbines and shortens their operational life.

http://www.eagleworldnews.com/2008/0...est-wind-farm/

I lived about 60 miles NW of Pampa. I don't remember a time when the wind didn't blow.

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Hi, I'll be back next week. I love this subject.
See you soon.
Best regards, Dan

I'm not a wind farm expert (I'm a controls geek), but I work with a bunch of them.

Modern wind farm economics depend on three main factors:
1) Capacity Factor
2) Distance to transmission lines
3) Tax incentives

Sites with high capacity factor (ie lots of wind and reliable turbines) that don't have to build transmission lines are generally pretty cost effective. Those are the sites that will generally be developed first. Some of them are cash cows even without tax incentives. With the incentives, they're Green gold. Plus, costs are still coming down on the turbines and their operating costs. The 2.5MW and larger models improve on economy of scale (we're selling 1.5MW in massive quantities these days because the technology is proven), and new windfarm management techniques make them easier to integrate with the power grid.

All of the major wind turbine manufacturers are completely maxed out on capacity right now. We're literally selling them faster than we can build them--customers are paying for the rights to turbines years in advance.

Last farm I visited it was amazing to watch--two or three crews could put up a string of 20 turbines in a week (not counting waiting for the concrete in the foundation to set or commissioning). I'm amazed at the people who climb up those things to work on them--a 350 foot ladder (usually with multiple landings and a safety cage) sounds like an adventure until you're looking up it. I chickened out on my chance.

As for noise, well, I could barely hear them even standing right under them. Nobody is generally going to be close enough to hear them--most sites keep the public well away, both to prevent vandalism and to protect people from falling debris (ice is a killer, literally, when flung off of a blade at near the speed of sound).

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It depends on the wind and grid characteristics where it's built. But the simple answer is about seven years. This is because without subsidies private enterprise tries not to build things they can't get their money back on within seven years. Otherwise they'd be better off investing their money in ice cream stores or bulldozer manufacture or developing computer games.

Most wind turbines built today are quite large and so hard to hear over the wind itself.

There is nothing special about wind turbines that results in more jobs than other forms of manufacturing.

The US currently generates almost no electricity from oil.

It is irrelevant where the wind turbines are manufactured. This is because if they are purchased from overseas the US dollars spent on them can only be used to purchase US goods. If they are not used to purchase US goods, then the US recieved the wind turbines for free. With the current decline in the US dollar it is probably quite worthwhile to build wind turbines in the US.

Most gas turbines are peakers and designed to vary output. The cost of the turbine itself is also much less than the cost of the fuel per kilowatt-hour generated.

Exactly - the ones that can't be throttled quickly or easily are the baseload coal and nuclear.

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If wind turbines didn't emit noise, I don't think they'd have an annual conference on the subject. http://www.windturbinenoise2007.org/

The best that this source can say http://www.bwea.com/ref/noise.html is that wind turbines aren't as noisy as "normal road traffic", and you can stand next to a turbine and have a conversation without having to "raise your voice". Well I can stand next to the 4-lane road outside my office and have a conversation without having to raise my voice most of the time, provided it isn't raining or something (why does rain make roads so much noisier?).

I don't live in the countryside on a very little trafficked lane to have to put up with the sound of "normal road traffic" 24/7. As you can see from the decibel list, it delivers a level of noise that would add up to 10 dB to my "quiet bedroom" if it was my neighbour.

Having stood next to the Penistone wind farm http://www.photographersdirect.com/b...mageid=1230246 comprising 13 turbines in a small field on the top of a hill right next to a public road, on a moderately windy day, I can tell you I wouldn't want to live near there.

Wind turbines are no more an ornament to our cherished wilderness and rural landscapes than the electricity pylons they need to take the power away. They may not be very noisy, but they are not noiseless, and hence are an intrusion. I don't mind them being installed in factory-farm landscape as you see in Germany, but I'd really rather they didn't ruin the nicer places of our countryside. Building them off-shore is a very good idea.

Few concerns of mine. A few years ago a low settled over the UK. Pretty much everywhere dead in the wind department. It lasted around a week.
Next would be some snippet that may be a load of old baloney but turbines are not effective below and above certain speeds? Like to have that one cleared up.

No, there would be constant work on it world wide trying to solve the mystery.

Penistone has puny 500 kW turbines.

I have to admit that the thought of anyone living close to wind turbines sounds odd to me, although I have seen pictures of people living not far from them in Europe.

Next would be some snippet that may be a load of old baloney but turbines are not effective below and above certain speeds? Like to have that one cleared up.

A wind turbine is designed to produce peak power at a specified wind speed. If the wind speed is less than that, the power output falls sharply. It isn't a linear function where doubling the speed doubles the output. It's a cubic function - doubling the wind speed increases the output by a factor of 8. Conversely, halving the wind speed cuts the output by a factor of 8. From this source:

The "rated wind speed" is the wind speed at which the "rated power" is achieved and generally corresponds to the point at which the conversion efficiency is near its maximum. In many systems, the power output above the rated wind speed is mechanically or electrically maintained at a constant level, allowing more stable system control.

Note that at lower wind speeds, the power output drops off sharply. This can be explained by the cubic power law, which states that the power available in the wind increases eight times for every doubling of wind speed (and decreases eight times for every halving of the wind speed).

Using the power curve, it is possible to determine roughly how much power will be produced at the average or mean wind speed prevalent at a site. In the example above, the turbine would produce about 20% of its rated power at an average wind speed of 15 miles per hour (or 20 kilowatts if the turbine was rated at 100 kilowatts). This is somewhat lower than most modern wind turbines.

Below a certain speed, the wind turbine produces no energy. The graph shows that on a typical wind turbine, that speed is about 10 MPH. As the wind speed increases, the turbine produces more energy until it gets to its rated power output. At some high speed (I've seen the figure of 45 MPH in some articles), the wind turbine is often shut down to prevent damage.

The effectiveness of wind power depends on the strength and constant nature of the wind in a particular area. I live in Colorado where it can get quite windy but there are plenty of times (such as right now) where the winds are below 10 MPH. During certain times of the year, the winds can easily exceed 45 MPH. During those times, wind turbines would produce no electricity. The air is less dense here which could also reduce the lift on the blades, cutting output. Add to that the effects of icing on the blades in the winter (reduces lift and increases chances of dangerous vibrations) that must be delt with in some manner (perhaps electric heaters in the blades). The state is going to wind power in a big way but it remains to be seen how effective it'll be in producing usable amounts of commercial electricity here.

I live close enough to a Naval Air Station and an Air Force Base that once in a great while, an errant sonic boom can be heard. The interesting thing is, they are so far away that you can't actually hear them if you're standing outside. You can only hear them inside the house, and then not as a bang, but as a tremor.

I wonder if it's possible that wind farms create very low frequency sound waves that actually cannot be heard except inside a house some distance away.

It was more or less the first windfarm in the country, probably didn't have the bigger ones available yet. If that's what small ones are like...
Could this be to do with the fact that the EU population density is about 3 times that of the US (excluding Alaska)? And Britain 6 times, England 10 times? Also US population tends to be more concentrated into cities with large open spaces (eg deserts) in between.

USA (exc Alaska) about 7,500,000 km2, 300m people, ca 40 people/km2
EU 4,300,000 km2, 500m people, ca 115/km2. (Sweden and Finland help keep the average down.)

UK: about 225,000 km2, 60m people, ca 270 people/km2
of which:
England: about 130,000 km2, 51m people, ca 400 people/km2
Scotland: about 79,000km2, 5.1m people, ca 65 people/km2

We just don't have many places in Britain where there aren't people living close by. Those we have are largely in Scotland, which despite being one of the few remaining wildernesses in Europe is on average more densely populated than the US ex Alaska. And those few places without too many people in them are generally our few, remaining cherished beautiful places.

I have very little objection to wind-turbines being placed in fields in the extensive factory farm flat arable land that is, for example, much of the eastern lowlands of England. I didn't expect to have much of a nice view there in the first place. This is largely similar to the areas with large densities of wind turbines I have seen in similar unprepossessing agricultural scenery in Germany, outside Dortmund for example. But this is not where they want to put them, they want to put them on the top of hills in our scarce uncultivated land in the west of the country. Though even lowland E England is probably windier than central Germany. Renewable energy has a large subsidy in Germany. They are subsidy-farming, not wind-farming.

It's the small ones that are noisy. The modern large ones are quiter.

It's not a remaining wilderness, it's a manufactured one. In any case, the windfarms around here - of which there are far, far too many and they are despised by virtually all who live here - tend to be close to where people live anyway.

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Noise reduction requires proper blade design with very complex calculations, so of course there are conferences. A poorly designed turbine can get pretty loud, but most modern systems are pretty quiet. Most countries regulate wind turbine noise, typically to 30 or 40 db at night in residential areas.

There are two main noise categories: mechanical and aerodynamic. Aerodynamic noise is further divided into low frequency noise from turbulence caused by the tower itself, turbulent inflow noise (the “swishing” noise), and air foil noise (usually a continuous whine or tone arising from turbulence or vortex creation along different parts of the blade).

Mechanical noise has been reduced about 2:1 since the late 80s