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Posts Tagged ‘wind farms’

Wind farms are still fairly new technology. In resource assessment, you see this when you look back at the sort of analysis that was done about 5-10 years ago, on older wind farms. To generalise, at the beginning of our industry we greatly underestimated the variability and complexity of the wind. This mostly resulted in an overestimation of the yield.

Differences compared to current best practice include having too few masts; making masts too small and then vertically extrapolating the wind flow to hub height; underestimating uncertainty on the whole procedure and the output prediction; a lack of understanding on how the landscape features would interact with the turbines.

The trouble is that this means that the wind farms which have been designed according to current best practice are pretty new. If it takes 4-5 years to get a wind farm from the stage of measuring the wind through all the technical and non-technical surveys, calculations and checks that have to be done and then through construction, then the best practice of 4 years ago is only just becoming operational. This makes it challenging to compare the actual output with the prediction and thus demonstrate that the current best practice works.

Of course, there are improvements that can be made, and there are several interesting developments of the last few years which are feeding back into best practice.

  • Lidar technology: This is based on radar technology and can measure wind speed using a laser pulse rather than a physical device actually sitting in the wind. That means you can put a lidar on the ground and measure up to 200m up (some models go further than this). While this technology has been around for decades and has been used in the wind industry for at least five years, it’s only relatively recently that the wind industry has really taken the opportunities this presents to heart. The reason for this, to my mind, is about understanding. Lidar measures the wind in a completely different way, averaging over a large area rather than at a tiny point the way previous anemometer technology did. This is a very fundamental difference on what the data are telling you, and frankly none of our tools really understand how to make best use of this. The difference gets most notable as the terrain gets more complicated — so hills and forestry; both of which are often found near proposed wind farms.
  • Computation Fluid Dynamics. Lay English considers a “fluid” to be a synonym for “liquid” but in fact gases are also fluid and therefore the movement of air is best described by fluid dynamics. Computational fluid dynamics or CFD is a way to solve the predictions for the movement of air in an environment which takes in as much information as we can manage about the complexity of the real world. This has become much more important with the rise of offshore, where, we discovered, the wakes of wind turbines behave very much differently than they do on land. Previous models, which were extrapolation and approximation to limit computing time (and which, I should add, do fairly well most of the time and are still both relevant and extensively used), couldn’t provide a reasonable approximation of wind farm wakes offshore. I don’t think CFD is being used much onshore at present, but given how complex the newest wind farms are it won’t surprise me if we begin to see CFD models being performed more often for onshore sites over the next few years.
  • Models: Virtual Met Masts created by meteorologists seem to be very popular at present. These use large scale climate measurements, such as satellite data, to feed into local models and provide detailed predictions of various aspects of the local climate such as wind speed and direction. What I’ve seen of these has been very positive, generally these predictions align well with mast measurements. Still, no scientist worth their salt would ever suggest that real world data could be removed in favour of model outputs: especially with weather and climate the world is complex and the only way to really see what happens out there is to be there measuring it. Where these models come into their own is in trying to establish what the long term climate is like. Anemometers degrade over time, and the landscape itself changes around a mast which has been there for decades. These two facts mean it’s hard to get long term wind measurements with the sort of accuracy the wind industry demands that can give confidence in how the wind at a particular site is likely to be over the lifetime of a proposed wind farm. Models have the potential to be perhaps more consistent.

I suspect that when we look back in five or ten years on the industry now we’ll still see it as a teething period when a lot of initial problems in analysis, measurement, modelling and prediction, let alone actually operating large scale wind farms, still had to be resolved. I don’t know which of these technologies, or perhaps something else entirely, will become the normal face of wind analysis in ten years time. And I find that uncertainty rather exciting.

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Wind farm layouts are pretty controversial. The bare fact is that putting turbines in the most lucrative positions which catch the most wind generally means putting them on top of hills. Which makes them visible for miles around.

There’s not really much that can be done about this conflict.

Besides, developers of wind farms don’t, as a general rule, actually buy the land they’re building on. Usually they rent it under contract from the landowner. And although the area of the wind farm is usually large, there’s usually a fair bit of spare ground around the turbines which can continue to be used for livestock or crops. In Scotland, we have laws protecting the right to access land; this means that if you want to go mountain biking at an operational wind farm the law is on your side (up to the point where you do any malicious or criminal damage etc obviously).

Once a contract has been drawn up with the landowner or landowners for a particular wind farm, it’s time to design a layout. This remains a challenging issue.

There are a number of criteria which are likely to restrict your options before the wind can be taken into account. These will include bird and wildlife surveys; land use and availability for roads; waterways and steep valleys which restrict access to heavy plant; planning restrictions on tip height; noise considerations; nearby residents; ground suitability; and local considerations such as archaeology, sites of scientific interest, and so on.

From there, the best practice is to use actual wind measurements to model how the wind flow changes across the site. Because you need at least a year’s worth of data from a met mast before you can really use the data (to cover all seasons), the reality of this part will vary substantially depending on how far into the project we are. If the project has two years’ of measurements at one or more masts on site, then great. Otherwise there are other sources of wind information we can use: bought data from a Met office measurement station; a virtual met mast built from a model; reanalysis data based on satellite measurements; extrapolation based on a combination of measurements. If the worst comes to the very worst the rule of thumb that “higher elevation = windier” would provide at least a guide.

Once you have an idea of the wind flow, you need to decide where to put the turbines. There are a number of things to take into consideration when doing this.

Each individual turbine removes a little of the energy from the wind it encounters, resulting in a slower wind speed for those turbines behind it. It also increases the turbulence, which further reduces the effectiveness of the turbines behind: it’s harder to extract energy from turbulent air. The combination of these is called the “wake” effects in the industry. To reduce the impact, it’s considered best practice to leave between 4 and 7 rotor diameters’ worth of gap between the turbines. Larger spacing is generally left in the predominant wind direction so that the overall wake effect is lower. (Offshore the spacing is larger, because wakes travel further offshore for reasons to do with atmospheric effects. Best practice will also vary from region to region based on the appropriate climate drivers.)

Trees and slopes will have several impacts on your positions. The top of a hill will be the windiest location, but steep slopes can provide huge challenges for accessing the turbines for construction or maintenance. Steep slopes also tilt the wind to an angle, and above 17° or so start to cause real problems for accurate wind flow or turbine performance modelling. Forestry increases turbulence directly above the forest, and can have other effects on the wind flow (increased change in wind speed with height, for instance, and boundary effects at the edge of the forest) which reduce the efficiency of the turbines.

Dwellings should generally be avoided as far as possible. I think the guideline in Scotland is 500m (note: there are experts on these constraints, and I’m not one), but a much larger buffer zone is wise. The issues of noise and shadow flicker are only relevant with regards to nearby homes. The danger of ice throw from blades or of blade throw is not thought to be a risk beyond tip height of the turbine (so if the turbine is 160m tall and you’re more than 500m away the risk to your property from these things is vanishingly small). To be honest I think the main driver here is the good will of the community. Big wind farms are generally built by bespoke developers, and there is much to be lost in appearing to trample over communities.

You want to maximise both the number of turbines and their output. Developers (or the banks who lend to them) take on the financial risk of a project when they sink their money into constructing the wind farm; they get nothing back until they start to produce electricity. If the costs of building and maintaining the wind farm turn out to be more than the wind farm can generate, the project is a failure. So the energy output is actually critical to project success.

Ultimately, then, from an industry perspective, the challenges of layouts are as follows:

  • Comply with all planning restrictions
  • Keep the local community on-side as far as possible
  • Space the turbines 5 by 3 rotor diameters, which for an 82m rotor diameter machine (about average for large wind farms at present) is 410m by 246m
  • Keep the turbines away from steep slopes, forestry, and dwellings as far as possible
  • Install as many turbines as you can to increase your maximum production
  • Put your turbines as high up as you can manage

I’ve often seen the accusation “poorly sited” levied at wind farms in newspaper letters. Reading between the lines, I suspect that this is because the writer objects to wind farms on hills where they can be seen, rather than that they know a secret way of establishing the best place to put wind farms that the industry hasn’t stumbled on yet.

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I’m starting to get really worried about the wind industry. I think it’s an important industry, for several reasons:

  • It brings jobs to Scotland, even in a time of recession,
  • It allows for our dependence on imports for electricity supply to be reduced,
  • It reduces the carbon intensity of our energy,
  • It serves as a point of learning on the road to making real use of our renewable resources: solar, wave and tidal, and whatever new technology comes after.

What worries me is that the debate on wind energy, from the pro-wind side, is totally dominated by three voices: the economists/business leaders, the politicians and the green activists.

The way I see the world, politicians are there to tell us if something should be done; economists tell us if people will pay for it; and activists are there to lobby for a pre-existing set of ideas. When it comes to “can something be achieved”, that’s where you need the geeks: specifically the scientists and the engineers. And the scientists and engineers are very, very quiet on the issue of wind power.

Part of the reason for this is that wind energy for large-scale electricity is still very much in its infancy. Ten years ago, the procedure for installing a wind farm was completely unrecognisable compared to what happens today: masts were smaller, turbines were smaller and closer together, and the softer requirements like bird surveys and protection for peat lands weren’t as well established. Ten years in a career is a long time; but it’s hardly any time at all when you look at how quickly the onshore wind industry has grown. (Offshore wind has barely begun its journey yet, so I’m not talking about that.)

Within that huge rate of growth, large companies have grown from small groups of tinkering engineers, and somehow the managers, the politicians and the economists have become the dominant voices. And they say: protect our IP, don’t say anything which will bring the industry into disrepute, keep to the party line. It’s scientists who say, share data, do best practice and let people see it’s being done. But somehow the scientists and the engineers aren’t making the decisions in this industry. And where they’ve risen to the top, they seem to do so by falling in line with the industry position. Don’t question, don’t talk about any issues, don’t ever suggest there’s anything wrong. And so they become the business leaders, the economists, the politicians.

One result of this is that an industry which employs hundreds, perhaps thousands of highly-qualified engineers, and a fair few scientists too, doesn’t seem to have the geeks on their side.

I’m talking about this blog. The author of the blog is Colin R McInnes, a professor of engineering at the University of Strathclyde. As a citizen, he’s been writing to newspapers fairly often lately. His letters tend to be good engineering, as you’d expect, but they tend to come down on the anti-wind side.

He’s not correct. But, and this is important: IT IS NOT HIS FAULT THAT HE’S WRONG.

He’s an engineer. More than that, this guy researches into solar sails for a living. If you asked him about whether solar sails were worth investing public money in, presumably he’d say yes. This is frontier research: it can’t fund itself without huge subsidies. Yet this same man is essentially arguing that if offshore wind farms, a very new attempt at large-scale deployment of technology to an extremely challenging environment, can’t fund themselves commercially then they should be scrapped. So what’s the difference?

He doesn’t know that we’re here. The scientists and engineers who are tasked with building wind farms and actually making them work. He’s not in the industry, doesn’t go to conferences or meetings. He’s only engaging with the public discourse. Which is, as I stated earlier, dominated by politics, activists and the party line. He is operating in a complete vacuum of technically-literate information on wind farms.

We need to start talking in a language that the technical people can understand. That means demonstrating good practice and actually letting the numbers out there. How much are wind farms generating? Why are they being installed where they are? What are the measured capacity factors? How do we determine the layouts? What actions do we take to mitigate public concerns? How do we re-power or decommission a wind farm at the end of its life? Are we held to account if we breach our planning?

I don’t know if I can make this happen. This blog is a start, I suppose. Perhaps you can. The time for secrecy is ending; if anything I’m very concerned that we’re already too late. What might have been good for an individual company is threatening to doom an entire industry. And that industry matters.

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As I said earlier, I’ve been reading the Geek Manifesto lately. This is the sort of thing you don’t read if you want a quiet life of rolling your eyes when people are wrong rather than gathering friends to overdose on homeopathic remedies outside a chemist.

It has come to my attention that one Mr Griff Rhys Jones has recently weighed in on the wind farm question. He has been quoted as claiming that wind farms are “green tokenism”, and being “randomly deposited” across the country. (Apparently this is from a column in the Radio Times, which is not online.)

Fresh from my perusal of the Geek Manifesto, it occurs to me that there are some parallels between this occurence and the British Chiropractic Association vs Simon Singh libel case. In the BCA case, Simon Singh had claimed Chiropracters made bogus claims; the BCA then sued for libel claiming damage to their reputation. In the case of Mr Rhys Jones, a celebrity has similarly made comments which are highly damaging to the reputation of an industry.

Only I can provide all sorts of evidence that wind farms are not “randomly distributed”, and that far from being “green tokenism” they actively contribute to our electricity networks saving on fossil fuels.

(I’ve not linked to much for the first statement about not being randomly distributed because to be honest it’s a bit of a blog post in itself and I don’t think anyone’s written it yet. Basically I need to demonstrate that there are financial incentives to build in the windiest places, that there are well established procedures in the industry for establishing windiness before construction, and that these procedures are generally followed. Some of the evidence may be commercially sensitive, but certainly there’s a solid case there.)

Has the reputation of the wind industry been libelled? Well, let’s be honest, Mr Rhys Jones is no more guilty of that than dozens of journalists, editors and commentors in print and even more random people online. But maybe they are all guilty of libel. Because I see far more accusations of bad practice from random people than I’ve seen any evidence of it. I’m not saying that the industry as a whole should start suing for libel when critics make rash statements which aren’t backed up by even a modicum of evidence. Neither am I saying that the wind industry is perfect. But no industry is perfect.

I do wish that celebrities, whose opinions are magnified in today’s culture, would try to remember that if it isn’t backed up by evidence it’s only an opinion.

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“The Geek Manifesto” is a book by Mark Henderson which has been making quite a splash with a few science-minded people I know: I think I’ve had it recommended to me about four times by different people. So I bought it for my kindle and I’m now about half way through.

Because I’ve been following a lot of science people on twitter for a while, a lot of the issues raised by the book aren’t new to me. I followed the sacking of David Nutt for commenting on his scientific findings on drugs, I followed the libel reform case between Simon Singh and the BCA, and I also saw the birth of the Science is Vital campaign as a response to the 2010 Spending Review. These issues, and other similar ones are covered in the manifesto. I’m sure there’ll be others as I work my way through the book.

As a scientist, these issues do matter to me. I want decisions to be based on evidence, and I want politicians to try to compile high-quality evidence where it’s needed. It is true that it is easier in general to find examples of policy-driven evidence than evidence-driven policy; for instance, the War in Iraq was not justified by the evidence available at the time.

If there was evidence to show that wind farms don’t work — that they don’t produce power that can be used, that they fail to reduce CO2 emissions, or that they are ultimately more polluting than they save — I would want to know about it. I would want to say to my colleagues, look, it’s not working, let’s find another way, some other technology. I don’t want to bet my career on something that doesn’t work.

Of course, wind power may not be the best long-term solution to all our energy needs. That’s different, and fine by me. I’m not trying to build a panacea for all humanity’s ills, I just want to change the world a little bit to be a better world.

The truth is that the evidence /doesn’t/ say that. Wind farms produce more electricity than they use and they save enough in carbon to balance their construction costs in only a few months of their 20-year lifetime (also see here.

I wonder if part of the reason that the wind industry has failed to engage with its detractors is that most of our talking comes from the CEOs and lobbyists that are a crucial part of our industry, but who aren’t actually scientists or trained in assessing evidence objectively. That’s one reason why I set up this blog; I wanted someone to be presenting the balanced viewpoint that the energy debate demands.

Scientists are good at that, and we need to be here; we need to be heard.

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I talked here about the job that myself and my colleagues actually do, in terms of why it would be complex to predict how the wind will flow across a potential site. I’d like to continue that topic a little and talk about how we actually measure the wind.

The first rule of good science is to make good measurements. In the wind industry, that means we want to know as much as possible about the wind which will encounter the rotors of the planned turbines. The most common instrument to use for this is a cup anemometer, which is actually a fairly simple mechanical device. Most commonly it’s made up of three cup-shaped objects which sit horizontally in the wind and spin round a central axis. By counting the number of spins we get a measurement of the wind speed. You’ll most likely have seen them; you see small ones quite commonly by the roadside, near small wind vanes.

Of course, a cup anemometer can only measure the wind speed that it’s actually sitting in. To measure at the heights of a wind turbine we need to mount it on a mast, preferably one which reaches to the turbine hub height. We also need several instruments at different heights, so that we can see how the wind flow changes with height. Then there’s the wind vanes, which give the wind direction, generally we want two of them. Multiple instruments have several advantages: they provide measurements at different locations, they can be used to sanity check measurements, and there is redundancy built in if something fails.

In fact the wind industry has generally had far higher requirements for measurement accuracy than the Met Office when it comes to wind speeds. There are wind industry professionals who visit masts in various locations and assess how accurate the measurements are, how consistent across the dataset and whether the data could be used as a reliable indication of how the wind behaves. The accuracy of the eventual dataset will depend on whether the mast is correctly sited, how the instruments are mounted on the mast, what sort of instruments are used and at what height, and whether the data are regularly checked and maintained.

Recently, lidar and sodar technology have started to really take off in the wind industry. These are alternatives to a mast, to an extent, and they work in a similar way to radar: by bouncing a wave off a moving target and looking for the reflection. Lidar units use light, generally infrared wavelengths, and sodar units use a sound-based wave. They’re collectively termed “remote sensing”, because they can sense the wind speed without sitting in the wind flow.

As it turns out, met masts with their instruments and the less intrusive remote sensing units are complementary technology rather than competitors. Met masts are large and unwieldy and cost a lot to install, but once they’re properly installed they continue to take data and require very little maintenance or additional expense. Temporary met masts which are installed for a wind project often take data for three years or even longer. Lidar and sodar can be bought outright or hired. Their huge strength is that they’re comparatively portable: lidar units in particular can generally be moved across a muddy field by two people, and they are not generally mentioned in planning requirements. A resource analyst might have two or three places on a site where the wind will be challenging to model or which are a long way from the mast but a mast can’t be installed there — in this case a short lidar deployment can really help in forming a full overview of how the wind is behaving.

Met masts are relatively simple things. Wind industry met masts are generally much smaller and less intrusive than the big telecommunications masts you see. However they have their challenges. They can be deployed in incredibly remote locations, which can make getting the required construction vehicles to the required location challenging; sometimes helicopters are required to transport the mast to site. (Note that one of the first things done when constructing the wind farm itself is building the roads. The turbines can then go along the roads. The met mast pre-dates this step, though.)

Remote sensing is obviously also a huge advantage offshore — the wind can be measured from the surface of an oil rig or even on a nearby shore rather than expensive and time consuming offshore met masts being required. The taller wind turbines of today, and the challenging terrain they’re sited in onshore, also benefit from remote sensing measurements which can be made far higher than a mast would support without any increase in cost.

There are technical differences between met masts measurements and remote sensing measurements which the wind industry as a whole are starting to get a handle on. It’s one of the more interesting elements of my job, watching the techniques and the technology changing and evolving. In many respects the wind remains something of a mystery to us.

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Come, walk wi’ me on Scottish hills,
Or by her comely lochs,
And see the footprint in the peat
Whaur ancient farmers walked.
Stop to drink fae water fresh,
Sae cauld it chills your hand,
And think o’ ancient fisherfolk
Who fed thus fae this land.

Born o’ you in ancient days, in ancient days were we,
Wi’ life fae you in many ways, and many ways to be.

Come, walk wi’ me on Scotland’s roads,
and to her busy heart
Whaur city folk ha’ toiled long
Through daylight and through dark.
Walk through halls o’ industry
Whaur working folk did tread,
Or ponder wi’ the thinking men
Who changed the world wi’ lead.

Drawn by you through history, through history were we,
And thus we grew in industry, in industry were free.

Come, walk wi’ me whaur pylons stride
across the misty hill
And tether thus each hame and hearth
to coal plant or wind-mill.
Ride on electricity
Throughout our thriving land
And feel the pulse o’ life and worth
You’re holding in your hand.

Guided now through modern days, through modern days are we,
And much we learn through modern ways, in modern ways to see.

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