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Archive for December, 2011

Wind resource assessment is something of a dark art. It’s not taught in schools, you can’t study it in university: it’s handed down from one professional to their trainee bit by bit. In fairness, that’s mainly because the growth of the wind industry is still a fairly recent phenomenon and it takes a bit of time for schools and universities to catch up.

Still, it does mean that when people are asked to comment on a met mast planning application on some prospective wind farm site, they don’t really know much about why it is needed, what benefit it brings to the developer, or what it is attempting to measure. What will it look like? How much space will it take up?

I’m going to begin by thinking about the wind. Chances are that the wind is considerably more challenging and complex than you realise, unless you are an atmospheric scientist or an expert in fluid dynamics. In fact, the wind is a constantly-changing phenomenon, interacting with itself and with the ground in interesting and difficult-to-predict ways.*

An example I particularly like which illustrates this is a pedestrian walking through a town centre with an umbrella on a windy day. Town centres are full of right angles, rarely found in nature, which redirect gusts of wind in strange directions, sometimes providing shelter and at others channeling a powerful blast. Such a pedestrian would find that they need to keep changing the position of the umbrella as they walk, to avoid it being blown inside-out.

On a bigger scale, that happens with even relatively simple landscapes. Hills force the wind upwards and around, making for more wind at the top of the hill than the bottom. Buildings block the wind, diverting it around themselves and creating a turbulent wake behind themselves. Forestry provides a very challenging environment for the wind, resulting in shelter within the trees and turbulence above them. The ground itself slows the wind, so that as you move away from the ground it gets windier.

We are small fry to the wind. It covers the whole landscape, and our tiny area is relatively small. We experience only a tiny fraction of it at a time (unless we’re carrying an umbrella…) Buildings, bridges, lorries and wind turbines are far larger and more likely to feel its devastating effects.

Considering all this, it’s perhaps not surprising that there is a dark art to measuring the wind. Deciding where to make the measurements, working out how the wind will vary across the landscape, establishing the best positions for turbines, and providing a confident estimate of how windy the site can be expected to be over the next ten or twenty years are all genuine challenges faced by wind farm developers. It plays a crucial role in establishing whether the money spent on building the wind farm can be recouped, and how long it might take. This in turn helps to convince investors to provide loans, and insurance companies to provide insurance.

It’s an art, and a science, yes. But there’s no need for it to be a dark art. I’ll share some of it with you over the next few months.

* In this case I’m simply talking about the wind as we experience it near the ground. There are large scale atmospheric winds higher up, but these are not really of much interest or use to the wind industry at present, save perhaps as a potential future resource. (Back)

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Disclaimer to start with: I don’t work in planning, I work in the data-evaluation end of wind farm development. I need an awareness of planning issues in my job but I don’t need to know the details.

One thing I do know about planning is that the public consultation is an essential part of the process. In fact almost the entire point of requiring planning permission is to keep the local community involved with any development and changes to said community. I can’t speak for the industry as a whole, but my experience has been that companies generally bend over backwards to ensure they go through the planning system properly. If they don’t use the system then the system should hold them to account, naturally — that’s how the legal system works. It’s also in the interests of the industry to work with local communities and get them on-side.

I’m seeing this sort of article occasionally now, though. Often people in local communities who object to wind farms have very strong feelings about them. But somehow, objecting to a met mast because you can’t yet object to the wind farm seems a little unfair.

I can understand it. This development is happening near you, and you’d do anything to register your protest. Object to the met mast and, firstly, you’re sending a message that you intend to use your voice in the matter, and secondly you make the project more difficult and expensive for the developers. You see a company, perhaps a large one, with a fair amount of clout. You perhaps fear that, next to the company, your voice will count for little. You want a megaphone to make sure your objections are heard. If there’s no met mast, then there will be no wind farm, right?

I know all that, and it still doesn’t quite seem fair. There’s a process involved in the development of wind farms, and jumping in to object to a met mast even though you may not actually even notice the mast itself just in case the development goes ahead feels a bit like the adult version of saying “bagsies*” to get what you want. Each structure which is to be built will go through planning. There is ample scope for people to object to whichever item they find objectionable. There’s even scope for compromise: I’ve seen planning permission processes which have removed whole turbines, which have restricted the heights of some or all of the turbines, or which have required the turbines to shut down or moderate their output at certain times of the day or year or under particular wind conditions. I’ve also seen companies pledge to keep some of the benefits in the local community.

I think the reason I find this irksome is simply that it smells like people manipulating a system for their own ends — lying about their true opinion so that they are more likely to get the result they want. In the main, they don’t really care if there’s a met mast erected. It’s the wind farm they dislike and they want all debate on the matter shut down immediately, regardless of anyone else’s opinion in the matter. They’re not interested in compromise, in benefits to the community, in job creation, or in any of the advantages to humankind and energy balance wind farms can offer. They’re not even open to hearing of any benefits. They have made up their mind, and are not open to negotiation.

It’s probably also worth pointing out that in the last five to ten years, new “remote sensing” devices have come on to the market which allow wind speeds to be measured without requiring a large permanent structure like a met mast. Where planning is refused for a met mast, these devices can still be installed and the development, though hampered, is not yet dead in the water.

If you don’t like wind farms, say so. That’s fine, you don’t need to like them. There’s even a process for it. You may even be worried by some of the myths of wind farms which have little to no scientific evidence behind them — if you’re willing to listen, we might be able to put your mind at ease. But please, play fair.

And if we don’t, then hold us to account.

*This may be a local term… (Back)

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Last Thursday, December 8th, was a particularly windy day across most of Central Scotland. You might have heard about it, it trended on twitter as #hurricanebawbag. It was the windiest day across Scotland at least since 2006 with gusts of over 100mph.

It’s often said rather disparagingly by people who don’t like wind turbines that they need to be switched off when it’s windy. And of course that’s true, and for a very good reason. The amount of energy available in the wind which a turbine could potentially extract is proportional to the cube of the wind speed — so when the wind speed doubles, the energy available is eight times as much. Theoretically we could design wind turbines which operated in the sort of wind speeds that we saw in Scotland, but most of the time they’d be useless. We need to choose the energy range we want to work in, and we choose the one, unsurprisingly, which lets us harvest the most energy.

It was extensively reported, in Scotland at least, that a turbine caught fire during the storm. Dramatic pictures captured by amateurs went viral on the web; you can see them at the stv news site linked above. Infinis have released a statement (pdf), and New Scientist attempted an explanation on their blog, but it’s clearly been tackled by someone who is a scientist rather than someone who works with wind turbines. So I thought it was worth looking at it in more detail.

There are a few comments that can be made about this. Firstly, wind turbines very rarely catch fire. There are currently over 2.5GW of wind turbines generating in Scotland. Since the current onshore wind turbines only really go up to about 2.5 MW that’s at least 1000 turbines. That means that in the wind conditions experienced last week, only 1 turbine in a thousand caught fire. So it’s not a high risk event; if you’re near a turbine and it’s very windy, chances are you’re pretty safe. That’s what those unnamed “experts” quoted in the media as calling it a “freak event” were probably getting at. Although I would still recommend that you don’t stand near a turbine if it’s very windy.

So what went wrong with this one? Well, Infinis, who own the site in question, don’t yet know what happened but shut down the whole site and notified the grid operator, Scottish Power, immediately. They will be slow to comment as they go through the data from the turbine. There are a few things we can think about though:

  • What components are there in a wind turbine that involve naked flame?
    Well, none, as a matter of fact. Turbines don’t use fire.
  • What components are there in a wind turbine that can generate heat?
    Now we’re on to something. Just about any moving component can generate heat if there’s excess friction involved. Brakes slow down moving parts with friction, which releases most of the energy as heat. So there’s the brakes. Any other moving components could be a risk if there’s not enough lubrication on the joints. And then there’s the electricity itself in the generator; there could be a fault or a short circuit.
  • What was happening to the turbine immediately before it caught fire?
    In this case we’re rather lucky because someone video’d it. Without that, we would have no way to narrow down the list of things which can cause heat and potentially start a fire.

It’s this third point that I want to look into in a bit more depth. Notice in the photographs, how this turbine is pointing a different way to it’s neighbours? That’s not a good sign. Smoke trailing out in front of it, horizontal in the wind, is also a bad sign. Wind turbines (of this 3-blade design, at least) are only designed to harvest energy from the wind if they’re pointing at it. Unless they’re completely switched off (rather than simply under shut down through the automatic control system) the turbine should be tracking the wind direction. From the video you can see that the turbine in question is turning its head, so to speak — the technical term is yawing — away from the wind. That means something crucial has failed.

I’m not going to say that I know what caused the fire. But you’ve got a turbine that can no longer control its direction, and a hurricane. You’ve got gyroscopic forces from the rotor spinning at relatively high speed (because it’s windy), you’ve got a turbine facing the wrong way which means the blades are very likely trying to spin in the wrong direction, putting forces on the wrong components in the wrong way. The brakes, if they haven’t failed already, are under tremendous forces. So you’ve got an event which is the culmination of a number of unusual circumstances contributing to a fire.

How dangerous is it if wind turbines can catch fire?

This is an important question. But actually it’s not as bad as it might seem. Generally hot air from a fire spreads upwards more easily than downwards and most of the moving parts of a wind turbine are already at the top. Turbines need to be placed in clear air, so generally they’re well spaced out. Unless a turbine is in an urban area or a forest, both of which are comparatively rare for a turbine of this size, the chances of the fire spreading beyond the one turbine is very small. There are also generally no people inside a turbine except for maintenance.

Scotland’s Right to Roam laws mean that the general public are allowed to walk within wind farm grounds. So although wind farms are generally remote that doesn’t mean that general members of the public are completely safe. However, risk from falling debris is very small if the distance is further than tip height (the total height of the turbine including the top blade).

There are warning signs that dangerous failure is imminent, and to be honest they’re fairly obvious. If you’re near a large turbine, you can generally hear a sort of low-pitched “whoosh” as the blades go by. Even in a high wind, the rate of the blades passing is generally less than a fast heart beat. If a turbine is freewheeling, something critical has failed. Get away from the turbine as fast as you safely can, and if you can get in touch with the operator to let them know (although by that point there’s not much that can be done — the safety systems have already failed and it’s far too dangerous to approach the turbine until the wind drops. Still they can at least close access). A turbine that is turning and isn’t facing the wind direction is also a danger, as we saw in this case.

The thing is that catastrophic failure is incredibly unlikely to ever happen when the wind speed is low. What risk exists is at its maximum when the turbine is being bombarded with lots of energy from gale force winds. It bears saying that no general member of the public should be within the height of a turbine from its base when the winds are that extreme. If you are, then keep away from any turbine which is behaving differently from its companions. Do this and you’re pretty much as safe as you can be.

If you live near a turbine, the risk of debris is very small if you’re further away than the total height of the turbine, generally somewhere between 100 and 150m. In the conditions seen last week, obviously the biggest risk is downwind, and in any other direction you will most likely be fine. There is no harm in leaving your property if you feel at risk, however. Nor in confirming with your insurance company that you’re covered in the event of a problem with your nearest wind turbine.

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Let’s talk some sense

People fear change. Those who fear it the most are perhaps the ones with the most to lose; those who have benefitted from the status quo. Worst of all, perhaps, is the fact that those same people who have benefitted often have the money and the influence to disproportionately shape public discourse. What they say isn’t always true.

There are those who will tell you that wind farms are without benefit. They will claim they are ugly and that they despoil the countryside, as though the countryside were a pretty picture to be admired rather than a place where resources have to be carefully balanced. As though there is no room for those of us who believe that wind turbines have a dignity and elegance of their own. They will claim they are polluting, that they keep energy barons rich on subsidies, that they are imposed on an unwilling public without due process… the list is endless.

There is very little a single voice can do in this society, it seems. But I work in the wind industry because I believe that wind power takes society in the direction it should be heading: towards a better use of resources. And so I will use my voice, so that those who are interested can hear a more balanced view.

My intent is to post once per week in 2012, taking a single incident or article about wind power and trying to provide a balanced viewpoint within the fog of propaganda. Wind farms have their faults: they are not The Answer. For today, they are a way forward. It is dangerous to society, to discourse, and to the planet to let the lies go unchallenged. Let’s challenge them.

Let’s talk some sense.

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