Saturday, February 28, 2009

How noisy are wind turbines and wind farms?

This came up recently in response to a question from a resident involved in the wind power debate currently underway in several local towns.

Industrial wind turbines are large pieces of electrical generating equipment with moving parts, particularly swishing blades and humming gearboxes and generators, and so no-one should ever imagine, or try to get away with saying that there won't be noise.

The question is, how much noise will be created?

It's also important to ask where the noise will occur.

When is irrelevant. Although Maine's Site Location of Development Law allows for higher noise from new developments during the day than at night, you can't turn a wind turbine off at night.

The Site Location of Development law on noise boils down to one requirement, after you strip away a lot of fine print, and apply it to turbines which cannot be shut off at night: wind turbine noise may not regularly exceed 45 dBA at any location where the owners have a reasonable expectation of quietness, ie, any home in the countryside in Maine that wasn't built next to an already noisy industrial plant that existed before the home as built.

The GE 1.5 MW models currently used for all major wind power developments in Maine produce about 100+ decibels (dBA) at the turbine head at full-out operation, and about 54 decibels at the base of the tower. The sounds are reduced the further you get from the tower, until they blend into the background noise and can no longer be detected.

Because wind itself produces noise in trees and around buildings, while the turbine speed doesn't increase much after the peak operating speed of 8 or 9 meters per second is reached, the windier it gets, the more background noise there is, while the noise of the turbine remains the same. On a breezy day, woods and trees can produce 54 dBA quite easily, leading to the paradox that turbines are effectively less noisy at higher wind speeds than medium ones.

However, in Waldo County, Maine, we have primarily medium wind speeds of Class 2 and 3, leading to the paradox that turbines are effectively more noisy here than better or worse wind power sites.

Go figure. But it's true.

How quickly the noise reduces as the distance from the tower increases will also depend on the reflective or absorbent qualities of the terrain. Trees are better than open ground. The graph above is for a wind farm in wooded land in New York state.

If you place one or more wind turbines close together in a wind farm, there will be more noise than there would be from just one turbine. The manufacturer publishes data on the noise of just one turbine. The developer must mathematically model the noise from several turbines to predict the noise level at any given site. If a developer is proposing a wind farm, Maine jurisdictions and communities should look to see that the modeling has been done, so folks can be sure that the developer's noise impact predictions in planning applications are not based on just one turbine.

Based on the New York study above, the likely distance or setback that will meet these requirements is probably somewhere between 300 and 400 feet for GE 1.5 MW wind farms in woody sites. This is not to say that neighbors won't hear the turbines at 400 feet, just that the legal requirements will be met, and so the DEP will likely approve the permit, assuming all other requirements are met.

I have heard a rumor, but not had time to confirm, that GE has recently recommended a much larger setback of 650 feet for their 1.5 MW models, while the European countries tend to use an even higher standard of 500 meters.

The primary reason for these higher setback recommendations, as I understand it, is not noise, but ice throw safety. Turbine blades can accumulate ice during ice storms and other suitable weather conditions, which can get thrown off. The industry standard recommendation for ice throw safety is 1.5 times the turbine height.

Even with the 650 foot setback recommendation, it will be possible to locate turbines on sites in Waldo County and meet the requirements of the Site Location of Development Law. Towns may, however, enact stricter regulations, should they choose to do so. Care should be taken if towns decide to control turbines using noise performance standards because many agricultural and industrial operations will fall foul of the new regulations. It's probably best to require a setback specifically for large turbines instead.

Not all turbines, just the large ones.

The little camp owner or homesteader who wants to run a little Air-X or Skystream 3.7 household turbine shouldn't have to have such a big setback.


Steve said...

The noise from turbines is an issue primarily at night in rural locations when people are trying to sleep. Rural nighttime noise levels are in the 20 dB range. Maine's noise regs allow 45 dB - a 20 dB difference which studies have found are unacceptable to a majority of people.

Maine's regs are silent on low frequency turbine noise, which travels much further than noise in the dB A range. Low frequency turbine noise is a growing concern in the world medical community including here in Maine. For more information about wind power visit

Mick said...

I believe you should say "for more information about not using wind power," visit

Although you are encouraging of offshore wind. Which I agree would be more efficient.

You're incorrect, however, to state that greenhouse gas emissions are not reduced when wind turbines feed power into the electricity grid. Assuming the demand for power remains the same before and after turbines are "plugged in," the rest of the electricity grid mix of sources must therefore power down in response.

The most likely sources to power down are natural gas-burning facilities, because they do not produce base load. But they do produce greenhouse gasses.

In a comprehensive grid-scale application, such as Denmark's, large savings of GHGs have been achieved.

Somehow the notion that there are no GHG savings to wind turbines has become current among anti-wind activists in Maine.

It is not accurate.

Steve said...

I thought the topic was noise. If you want to expand the conversation to GHG impacts,
electrical generation is about 14% of overall energy use in the United States.

The grid can only accommodate 20% of demand in wind power until a cost effective solution to storing electricity is found. Got one?

20% of 14% is only 2.8% of total energy use offset by wind power. How many millions of wind turbines destroying what is left of the beautiful places on the planet do you want to see for, to put it another way, 2.8 years of additional fossil fuel supply over 100 years?

Wind power costs about $100 per MW of produced electricity (at about a 30% capacity factor to be generous) over the 20 year life of the turbines. But not all the produced electricity reduces gas generation. Wind turbines have a capacity credit of 10% of nameplate rating. That is the theoretical extent to which they displace fossil fuel use. NYSERDA wind power integration report 2005.

Electricity sells for about $40 in the ISO NE day ahead market. You are asking me to subsidize the wind industry with $60 per MW of my tax dollars, when I could use that money to insulate, conserve, improve efficiency, buy a hybrid vehicle and actually save money in the long run. Money I waste on turbines just enriches the wind industry and does nothing to solve the real problems of fossil fuel use.

If the capacity credit of 10% is used to calculate the cost of subsidizing wind power's ability to reduce fossil fuel use, the cost per MW approaches $300!

No coal mines will be closed due to wind power. More nuclear reactors must be built as demand for power grows, although the new economy might slow that growth down considerably and indefinitely.

Coal and nuclear will be the fuels of choice for developing country's electrical generation because they are cost effective.

We need the cheapest electricity we can get in the new economy. Just listen to Warren Buffet on CNBC tonight. Cap and trade is a bad policy according to people "a lot smarter" than he is.

Lets spend our money were it can make a real difference in fossil fuel consumption as mentioned above.

How about a response on the noise issue? Health impacts from turbines have been ignored by the wind industry for long enough. How many lives must be destroyed for your 2.8% solution?

Anonymous said...

August 2010 - now wind developers want more than $76.00 per Megawatt hour.

Now wind turbine noise pollution is a health issue - see Minnesota Heath study.

The real truth is that wind energy is a investment scam underwritten with tax dollars, subsidies, tax breaks, provides tax shelters, REC's, etc. There are four gigantic companies making big turbines, which are all out of scale for rural settings GE, Seimens, Furhlanger, etc. The turbines are the equivalent of 42 story buildings and emit up to 100 decibels at 1000 feet. The energy lobby and investment people are scamming us all.