Tuesday, October 5, 2010

Vinalhaven turbine update and noise science corrections

The New York Times has an OK article today about the Vinalhaven turbines and the noise problems with wind power plants in general.

I say OK. It has a terribly biased headline but that's just the usual yellow journalism. But it was interesting in places.

The primary substantive failing of the article is that it is an incomplete study of a difficult problem.

In particular, it aims to describe Maine's noise problems with turbines, but fails to accurately state why we have a noise problem with turbines, and fails to reference two concerns that we should be able to address, going forward, in other Maine wind power proposals: wind power noise modeling, and the particular noisiness of the Vinalhaven turbine make and model (and mark number).

The rest was fine, although the article also did a less than adequate job of trying balance the views of the few residents of Vinalhaven not in favor of the turbines adequately with those very many, a great majority, who are in favor. The attached video does a better job because you get to actually hear the low-grade clash of cultures that is taking place on the island in the voices of the folks that are being interviewed. As a person who studied environmental justice for some of my graduate work, with several field studies under my belt in more deprived places like Baltimore row house neighborhoods and Maryland eastern shore fishing communities, I have to say, I find this situation slightly ironic.

But let's get the science right before we start on the social science.

First up: the high noise levels of wind power plant at Vinalhaven or Beaver Ridge were unexpected. You can't get the companies involved to admit this because they face possible lawsuits, but I can tell you what I think happened, an educated guess. This unexpected noise was because we essentially took wind farm design approaches out of the midwest and Europe, where terrain is more open and less forested, and applied them in our woodsy Maine hills and dales.

It wasn't unreasonable or stupid to bring in midwestern expertise and use midwestern models. Ordinary common sense says that if you want to do a thing right, you bring in the guys who've done it before, or at least copy their ideas and systems. But in this case it backfired somewhat in terms of noise.

Not in terms of power production. If anything, these wind farms make more power than expected.

And for the same reason they make more noise than expected, which is high wind shear.

Specifically, expectations that ground level wind would be noisy enough to drown out turbine noise were not met.

Wind shear is the concept that wind speeds change as height above ground level changes, the wind layers shear, creating a laminar flow pattern.

The wind nearly always speeds up as you get farther from ground level interference. The more it speeds up, the higher the wind shear. The normal wind shear factors used for wind farm planning top out at levels of 0.3 (this is a factor or exponent in the Power Law equation, so, for once in science, no units are appropriate to state). But we have measured actual wind shear factors as high as 0.5 or 0.6 in Maine.

This throws all the design models off. You'll essentially hear noise pollution at further distance from the turbine than you otherwise would, although not all of the time and not under all atmospheric conditions, but definitely some of the time. This is because the wind at the ground level is low or non-existent, while the wind at higher elevation is turning the turbines just fine.

In the midwest it was generally a given that you couldn't hear a GE 1.5S model turbine at all once you got a thousand feet or so from the base because there'd be plenty of noise in the trees or grass or buildings. Here in Maine, especially in summer when wind shear is higher, you can hear the turbines, some of the time at least.

The other thing is that the GE 1.5S model turbine is noisier than some other turbines, although not noisier than all turbines and perhaps not even noisier than the average.

But there are quieter turbines, some made by GE even, some even later models of the 1.5 series, that might have been used.

It's a moderately big turbine, for one, and that makes it noisy. But it also has a gearbox, and that makes a lot of noise. Direct drive turbines make less noise. It also has a monopole tower. Lattice towers, available for smaller turbines up to a fraction of the capacity of the GE model, make less blade noise.

So to avoid the problems we've had at Vinalhaven and Beaver Ridge and Mars Hill, we should plan out our turbine noise models using expectations of higher wind shear, and work hard to not put turbines so closely upwind of houses, considering carefully the wind rose data that tells you where the wind comes from that is strong enough to turn the turbine. And we should consider using direct drive turbines for large scale wind farms and lattice-tower turbines for small scale community or private wind turbines.

This is of course probably too much pragmatism and common sense for our local anti-wind activists, who won't be at all happy with this kind of thinking.

I distinctly remember one encounter with such a person in a public meeting in which I tried as carefully and as moderately as I could to explain wind shear and even drew a picture of laminar flow, while all the time this person's voice was raised, talking way too fast and not at all listening.

The Tea Party of wind?

I don't say that they should necessarily be satisfied with this kind of thinking. That's a personal choice and a matter of conscience.

But since we can use this technology to do good things like reduce greenhouse gas emissions and begin to reduce oil consumption, reasoned analysis of our efforts so far should probably be considered.

By the way, our local wind activists will also dispute that wind power reduces climate emissions or oil consumption.

They're mostly wrong on the first, and partly right on the second.

When you connect a wind turbine to the grid and the wind blows, if it's just one turbine or even a small farm like Vinalhaven, what happens is that one or more natural gas powered "peak load" plants are throttled back to keep voltages stable throughout the grid.

That reduces GHG emissions, although not by quite as much as they would have been reduced if we'd been able to take a coal-fired power plant off-line.

Twelve twenty-thirds (12/23), to be exact. That's the ratio of GHG emissions between natural gas and coal. It's a bit more complicated than that due to differences in plant efficiency and the power curve of the natural gas generators, but that's a good number to start with.

You still have to have the GHG-emitting plants, you can't get rid of them because the turbine doesn't run all the time. But the more wind you have in your system, the less GHGs per unit electricity are produced.

If we could turn off a coal-fired plant, we'd obviously save more GHG emissions.

But coal-fired plants are very different, especially older dirtier ones. They like to run at full blast, because of the way coal burns: long, slow and hot. A coal plant is generally run at it's rated output all the time that it's running.

This isn't quite true for more modern combined cycle, fluidized bed systems, which are also about a third more efficient as older steam turbine plants. These can be throttled up or down a little. But they still are generally kept operating at stable outputs, not continuously variable outputs.

So we would need to be able to know exactly when wind power was going to come online if we wanted to specifically reduce GHG emissions from coal plants. This would be a good thing to do, because coal is damaging to the environment in other ways than just producing GHGs. There's also mountaintop removal mining to consider. Or acid rain, to name just two of many.

There are two ways to do this. One is to forecast the wind and change the number and distribution of coal plants you have turned on at any given time accordingly. The other is to have wind farms in the most consistent winds, which are generally offshore.

Europeans have succeeding in using both to reduce climate emissions from electrical power production. But as with the wind shear example above, it requires a little more complex thinking on the part of both power plant engineers and the folks they are making power for.

Engineers, who can be surprisingly fragile when it comes to some kinds of complexity, need a little help to appreciate a less consistent but still very green power source. Consumers need a little help to understand a more complex set of questions and choices than is normally encountered in consumer life, such as the trade off between the damaging effects of GHG emissions versus the damaging effects of wind power plants.

The other claim our anti-wind activists are making is that wind power doesn't reduce dependence on foreign oil. This is certainly true as long as you plan to drive a gas or diesel powered vehicle for the rest of your life, and pay the price of fuel at whatever rate it will be then. But I'm interested in plug-in hybrid and battery-electric vehicles, and society should be too. I might like to consider, for instance, putting a medium scale, grid-tied turbine like a recycled Vestas V-15 on my property, and using the power for electrical resistance heat in winter and for vehicle charging.

I'd try to get my neighbor's cooperation by offering them free power through net-metering, a local power cooperative. I'd do this myself. I'd enjoy the engineering challenge, and I've seen a Danish farmer on TV who did much the same kind of thing.

Unfortunately, this would no longer be legal in many Maine towns because of the restrictive ordinances that have been passed.

(Funnily enough, despite an otherwise restrictive ordinance, a relatively large private turbine like a V15 could be made legal in my town of Jackson. You see, when our local anti-wind activists rallied for their restrictive ordinance, they made the ordinance apply only to grid-tied turbines. So if instead I just run the power into home heat and car-charging, I can put up my V15, or even a much bigger turbine, even one that would be totally offensive to my neighbors. Obviously I'm not going to do this because that would not be polite, but that's the way the ordinance is written. Go figure. I did explain this to the anti-wind group and the planning board at the time, very carefully. After all, if you're going to have an ordinance, you'd better understand the technology and it's various possible applications, and plan for contingencies, right? But I guess they weren't listening.)

At a much larger scale, we could, and probably will, consider feeding wind and solar energy into battery electric cars. We would do this just for reasons of developing green transportation, but as I've mentioned elsewhere, it wouldn't be a bad thing to have some more storage in our grid system for reasons of evening out intermittent solar and wind power production, and battery electric cars could provide some of this ability.

1 comment:

Robert Rand, INCE said...

Hi Mick,

Well said, on your discussion of wind shear. I would like to see a conservative noise correction factor used in permitting applications for the elevated wind shear measured at sites in Maine.

I wanted to indicate that the noise levels at Vinalhaven were expected by this independent investigator. Similar noise level data have been readily available at the 3,GE-1.5MW wind turbine facility in Freedom, Maine which has been operating for some time prior to permitting at Vinalhaven- a similar facility. The sound levels versus distance are similar under similar wind conditions.