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Archive for the ‘risk’ Category

If I ask you what colour the sky was, you’d say blue. If I asked what colour it was right now where you are, the only way for you to answer correctly would be to go and look. That’s science: the go and look bit. Science is where we try and get past the rote answer and use evidence to understand what’s going on.

There have always been people who don’t like the go-and-look philosophy. Most of the time they’re the same people who would prefer we all take on the listen-to-them philosophy. It rankles with a certain type of person that they can’t just say anything they like without being fact-checked. It used to be religious authority who were most guilty of this; now it seems to be marketers & PR people working for rich corporations, billionaires and politicians. Or at least so the documents about the Heartland Institute released this week would lead us to conclude. (I’ll not go through this, you can read more about it here if you’re interested.

I don’t like this war. To me, if you want to know what colour the sky is, you go and look. If you can’t do that, you use the scientific method to find the most probable answer. You don’t ask yourself, what is the most beneficial answer? And then shout out to everyone who’ll listen that the sky is in fact black-and-white-stripes, punching anyone who disagrees with you in the mouth. The trouble is that in human affairs, what matters most isn’t what you can prove, it’s what you can get people to believe. And the anti-climate-change lobby have been very, very effective at getting the public to accept the idea that there’s any scientific controversy. There isn’t. Human action is causing the climate to change. (The graph in that last link is particularly compelling.)

Over and over again, I encounter the idea that renewables are only being developed for the subsidies; like there are fat cats putting up useless wind farms and then laughing at us all the way to the bank. I’ve seen no evidence for this. Firstly the subsidies are generally paid out alongside the electricity being generated, so that if you build a wind farm in a bad location or if you don’t maintain it you get far less in terms of subsidies. Secondly the expense of building the project and the risk of failure all fall on the developer, and many wind farms do fail at various points after significant time and money has been invested in them; not really something that encourages risky development and then running off with the cash. Thirdly, the renewables lobby, like the climate change lobby, are nowhere near as effective as their various counterparts. And fourthly, electricity prices are driven by gas prices. Renewables aren’t driving profits or costs to any large extent, and a lot of their profits goes back into the next development. Profits which are being invested in infrastructure aren’t lining fat cat pockets.

If there are powerful people with lots of spare money about, they’re not coming from the renewables industry. They’re more likely to be coming from the oil and gas sector. Those are the people who don’t want us to invest in renewable energy which doesn’t require a constant fuel source. Those are the people with both the motivation and the money to actually get their voice heard. And the evidence seems to suggest that they’re using that voice: they’re using it to lie to you.

The worst thing about it is that if we don’t know the facts we make poor decisions. We all want our grandchildren to live on a planet that’s at least as good as the one we have. No-one wants the luxury of a private jet if the direct cost is watching their grandchildren starve in a climate-change induced drought. If we change things now, we can do it slowly, keep the level of technology we have. If we don’t…

Well, the way I see it, if we don’t reduce our reliance on oil and gas we face much bigger problems than just climate change. We face the increasing instability of the Middle East, and hugely fluctuating prices. We face increasingly desperate technologies (like fracking) used in increasingly unsuitable environments. We face dwindling global supplies and perhaps even wars over what remains (the question of who owns North Sea oil if Scotland gains independence will seem tame in comparison). On a human level there could be a global crisis of a level not seen since the second world war. And on top of that we could have hurricanes, tornadoes, droughts and monsoons, rising sea levels and dwindling water supplies.

Unless we work to avert it. Now. Little by little.

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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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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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