Wind turbines not turning?
July 27, 2011 7:20 AM   Subscribe

Why do you see so many wind turbines stopped - even on a windy day? (What constitutes good or bad wind turbine running conditions?)

I'm seeing more wind turbines around (including this new one at our local VA hospital) but hardly ever see them turning! Why is that? What constitutes good running conditions for a wind turbine? What are bad running conditions for a wind turbine? Do they need a significant amount of maintenance causing them to be stopped often?

This is partly prompted by an acquaintance of mine who drives truck and is all "HURF DURF I never see those turbines spinning in Iowa or [some other state] where there are fields full of them!"
posted by jillithd to Science & Nature (13 answers total) 4 users marked this as a favorite
I had a similar question when I was driving out east of San Francisco where there are a huge amount of turbines. I was told that its because they have some issues and if they were spinning it would cause further damage and could even break apart rather dangerously. Plus wind turbines are expensive and if there's no need for the energy or an issue on the line, stopping them spinning helps prevent wear and tear.
posted by Carillon at 7:25 AM on July 27, 2011

I once read that a lot had to be turned off because on a very windy day they produced too much juice - the grid couldn't handle it.
posted by missmagenta at 7:26 AM on July 27, 2011

Wind turbines can collapse violently if the brakes fail, which can happen in very strong winds:
The blades should be locked down in high winds, else, well, this happens. I thought that was counter-intuitive when I first heard it, too, but my guess is that the brakes simply failed. (I was tangentially, briefly, involved in a wind turbine project for nPower a few years ago. I got this from a project engineer. He also said they still don't break even, but they get closer with every farm they build. For example the stuff I was working on would have reduced maintenance costs.)
posted by griphus at 7:32 AM on July 27, 2011 [1 favorite]

The same reason all kinds of electricity generation facilities aren't always running 100% of the time- there isn't always anywhere for the electricity to go. Just that nobody hurf durfs when they see a smoke stack not smoking.

IE, the grid doesn't need it. Or the winds are too heavy and it will wreck the turbines. Or the interconnect equipment is offline for maintenance. Or the winds are too gusty and the the equipment can't handle the variable nature of the wind.

Too many wind "skeptics" approach it from the false assumption that all types of electricity generation need to be 100% useful and available 100% of the time. It would be nice if wind was, but it's not necessary that they are. The grid managers turn on the various generation facilities as needed, based on the cost. (Whether it is positive cost or negative cost. Meaning, they run the nukes as much as possible because it is the cheapest, but slowest to react to demand, on down to the nat gas "peaker" plants that are really expensive to run, but it is necessary to have something that rides the wave of demand and matches it in real time. So if running the turbines means having to also turn the nuke plant down, and run a peaker, it doesn't make sense to "save" money with the turbines that they have to pay back by running the more expensive one.)
posted by gjc at 7:40 AM on July 27, 2011 [1 favorite]

Funny thing. If a turbine that can deal with "really strong winds" costs 10x what a "light breeze" turbine does, but "really strong winds" only turn up for a few hundred hours per year, you don't make the investment back. It's better to put up the light breeze turbine, and lock it down when things get bad.

Learnt that when I did some software that went into a wind turbine. Cool gig. (for nPower, a few years ago, and I got this from a project manager. Hmm. griphus, was there any really cool gearbox monitoring tech in your project?)
posted by Leon at 7:40 AM on July 27, 2011 [1 favorite]

(HAH! griphus was, in fact, quoting me. I spend too much time on this damn website.)
posted by Leon at 7:41 AM on July 27, 2011 [3 favorites]

I think I've heard 7-40 as acceptable wind speeds (some can function at higher (60s?)), but higher that they turn off because of possible failures and breakage.
posted by zombieApoc at 7:42 AM on July 27, 2011

Also, in wind farms with lots of older turbines (like the one in Altamont Pass that Carillon mentioned), when an old one breaks they just leave it sitting there instead of fixing or dismantling it.
posted by zsazsa at 7:45 AM on July 27, 2011

Though blades can often spin at a relatively low wind speed, a gust of as much as twice their minimum rotation speeds may be required for each to start up from a standstill. Also, many good sites for turbines have significant daily wind changes due to the microclimates around mountains, coasts, etc. -- so that quite typically much of the output is at night (or at least peaking around dawn and dusk) or even seasonal as the weather shifts.
posted by glibhamdreck at 8:02 AM on July 27, 2011

That VA one has a factsheet that says: "The turbine operates in wind speeds of approximately 8 mph to 55 mph." 8 mph is a pretty decent wind: Weather Underground doesn't show sustained winds above that at any point in the next week.

The 8 mph is called the cut-in speed, when the turbine is generating enough power at a good enough voltage to feed it into the system. Below that will be a start-up speed, maybe 3-5 mph, where there is enough wind energy to start the blades turning. Below that the turbine will just be sitting there. OTOH, the cut-out speed is that 55 mph, where it actually stops generating any power at high wind speeds to protect the equipment.
posted by smackfu at 8:03 AM on July 27, 2011

Yeah, the problem isn't generating the electricity, it's moving it out of there. The turbines that aren't moving have been turned off, because there simply isn't enough of a backbone to handle the energy.
posted by Gilbert at 8:20 AM on July 27, 2011

A wind turbine will typically be producing power for about 85% of its online life (ie the blades would be expected to be turing for 85% of the time). It will not be going flat out for most of this, but will be producing some fraciton of the total while it is turning. A typical large turbine will cut in at about 3m/s, have a fairly steady power increase up to about 12 m/s and then have flattish output to its cut out speed, which will be somewhere between 20-25m/s. This is when it cuts out completely and doesn't turn to prevent damage occurring to the turbine. Going above the cut out point would generally account for less than 1% of the turbine life. You would lose a few more percent to maintenance, less for the early life (once properly set up), more in later life.

I have come across turbines that have been poorly sited for one reason or another and were operational a lot less than the average, usually for greenwash or becasue the owner had more money than sense. I did see one in Stockholm once that I think was being powered to turn (hub below the tree line, steady speed in low wind) but that is very rare.

The total time a turbine is operational will produce energy equivalent to about 20-35% of the figure if it was going flat out all the time. This is the capacity factor. The 20% would represent a fairly poor onshore turbine, 25-30% would be a fairly typical onshore, 30-35% a fairly typical offshore turbine.
posted by biffa at 11:16 AM on July 27, 2011 [1 favorite]

Was going to chime in - I'm a wind farm designer/operator - but biffa pretty much got it.

In North America, we're pretty much in the "maintenance months"; winds tend not to be very high, so you can really get working on the maintenance without losing too much revenue. Your turbines have to have to be available and running in January, when the winds are screaming and you don't want to be out there. Wind turbines don't need much maintenance - of the order of 30 hours in the first year, and 8-15 in subsequent years.

If a large chunk of a wind farm isn't running but the rest of the farm is, there could be maintenance on the collector system - the internal distribution grid that gets power from the turbines to the substation. It's cheaper to wire a bunch of turbines together than have each one go out to the main distribution/transmission system.

The thing about cut in and cut out wind speeds is that they're measured at the turbine hub. It's much less windy on the ground. 8mph at the hub is frequently 4mph or less (far less in summer, with thermal effects) near the ground. Weather stations measure the wind at 10m height, so even they are higher than what we generally experience.

For the projects I work on, we only lose <8 hours per year on wind speeds being too high. That Danish turbine link that griphus posted could only have happened under manual and incorrect intervention, where interlocks had been deliberately removed. And Leon, we are very happily more than breaking even now.

Wind turbines in urban setting generally don't work too well, as people tend to choose to live in sheltered locations. Buildings cause all sorts of turbulence - which feels windy, but doesn't have a ton of useful energy - and urban heat islands cause the wind to come from odd directions. F'rinstance, we full expected the majority of the wind for the Toronto wind turbine to come from the lake. Who knew that most of the time it'd be facing up Dufferin?
posted by scruss at 1:14 PM on July 27, 2011 [3 favorites]

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