Naked Science Forum
Life Sciences => The Environment => Topic started by: thedoc on 28/02/2014 16:31:30
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Wind turbines play a key role in tackling climate change, but now it seems they may also be able to mitigate hurricanes...
Read the whole story on our website by clicking here (http://www.thenakedscientists.com/HTML/news/news/1000454/)
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Apparently the current large windmills do fairly well if they are furled, or put into "hurricane mode" prior to being struck by hurricanes.
If not put into hurricane mode, they can fail quite spectacularly.
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fqph.is.quoracdn.net%2Fmain-qimg-59bb2a4501bf480189516e8a5595158e%3Fconvert_to_webp%3Dtrue&hash=f7767d6f8ff84b5b548651fc7a4a4b3f)
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.scmp.com%2Fsites%2Fdefault%2Ffiles%2Fstyles%2F486x302%2Fpublic%2F2013%2F09%2F30%2F57ca49725099aae7867e8d1cb039bad2.jpg%3Fitok%3Dww688pmZ&hash=c90096d46ea9fc60d77218ee8af2d65b)
http://barnardonwind.com/2013/12/30/wind-turbines-survive-hurricanes-what-a-blow-to-doubters/
http://www.scmp.com/business/article/1321682/typhoon-usagis-message-hong-kongs-wind-farms?page=all
According to the storm notes I'm seeing:- Cuba, Hurricane Sandy, 2 wind farms, 100% survival.
- Jersey Atlantic Wind Farm, Hurricane Sandy, 100% survival.
- China, 70% loss, 30% survival after 2 typhoons including Typhoon Usagi (collapsed photo above).
- Scotland, 1/13 windmills failed in a storm with high winds (flames above)
Anyway, the survival rate of the towers can be fairly high if the windmills are properly furled.
The paper talks about 20-50 m/s (45 to 112 mph) winds. While the windmills may be able to generate with the lower winds, they have to be shut down with the higher winds... and thus less of a "benefit" of the windmills.
Hurricane Sandy hit at least 3 windfarms and still left a wide path of destruction.
I'm not saying it couldn't be done, but the offshore windmills would have to be redesigned to actually generate power at say 200+ MPH without furling. There would also have to be many more windfarms.
The other issue is the windfarm placement.
I believe that most of the current generation offshore windfarms are placed fairly close to shore where the water is relatively shallow. In the middle of the Atlantic or Pacific oceans, the water can be a few miles deep, substantially increasing the cost of the windmill installation. Also, the further offshore, the more transmission costs increase.
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From NOAA
An average hurricane produces 1.5 cm/day (0.6 inches/day) of rain inside a circle of radius 665 km (360 n.mi) (Gray 1981). (More rain falls in the inner portion of hurricane around the eyewall, less in the outer rainbands.) Converting this to a volume of rain gives 2.1 x 1016 cm3/day. A cubic cm of rain weighs 1 gm. Using the latent heat of condensation, this amount of rain produced gives
5.2 x 1019 Joules/day or
6.0 x 1014 Watts.
This is equivalent to 200 times the world-wide electrical generating capacity - an incredible amount of energy produced![
So you'd need a heck of a lot of wind farms to mitigate one hurricane. Face it, the damn things are a con.
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A lot of friction could be generated if the brakes weren't applied properly, before the storm struck. If the blades moved only a little, that could generate a lot of power in the hub, perhaps producing the flames in the photo?
The winds at ground level are a lot less than the winds at the height of a turbine (up to 100 meters), which are much less than the winds at even higher altitudes - 500 m and above. Since the wind in a storm is continually swirling, bringing high air down to ground level, I'm not sure how much effect it would have far from the turbines.
But perhaps the Dutch could measure the effect - there is a row of turbines along some parts of the Dutch coast.
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The paper's quite interesting (the reference is at the bottom of the article if you want to follow it up). You're right, the number of turbines needed is high - they simulate from 500,000 down to about 80,000. But, interesting, with 80,000 turbines, they still get 60% of the benefit returned by 500,000.
The mechanism of action of the mitigation strategy is to extract energy from the cold air being drawn into the storm from across the planet's surface. The result is a de-powering of the storm as it develops and a slowing of the peripheral air. They suggest, according to their models, that a wind velocity reduction of up to 90mph - and a corresponding storm-surge attenuation of up to 70% - is feasible. The turbines should all be deployed off-shore. The economics are also presented in the paper; electricity via these turbines, and not having to spend money building walls around cities, prices the power at about 4c/kWh. Fossil-fuelled generation (and building defences and doing repairs) costs about 10c/kWh in comparison.
So it's an interesting proposition...
fossil fuel generation
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Seriously flawed economics and geophysics, I feel.
Building walls around cities isn't a lot of use anyway. You might keep out a few Picts and Saxons but unless the wall is as high as the tallest buildings, and the city is no more than about 10 times as wide as it is high, and the city isn't built on a hill, and the wall is at least as strong as the strongest building it is supposed to protect, and you aren't worried about flooding the buildings just inside the wall.....it isn't a good anti-hurricane strategy anyway. Better not to build new cities near the coast in the first place.
Cyclogenesis begins with a relatively small patch of rising warm air. The cold air that is drawn in comes from a very wide area, at quite low speed. So you'd have to be pretty clever to work out where to put a small ring of windmills to prevent one hurricane developing, and you'd need to distribute them over most of the western north atlantic to have a significant impact on US hurricane landfalls. But most of them would be pretty inactive most of the time: a windmill designed to extract power from 100 mph gusts isn't very efficient at 10 mph, and one that works at 10 mph would have to be grossly overengineered for most of its duty if it was to work at 100 mph.
The capital cost of storm defences, or any other civil engineering works, should surely be met by those who will benefit from them. But the attraction of new developments in Florida, Texas or Missisippi wetlands is their low cost. Adding an active hurricane defence system would surely make them less financially attractive.
And a little physics to consider. In order to abate a hurricane by 70% you need to dissipate 400,000,000 gigawatts (yes, fourhundred million gigawatts!). What are you going to do with all that electricity? It has to be transmitted (using a grid with 5,000,000 times the capacity of the entire UK national grid) and used immediately (for what?) or stored in a bigger battery than anyone has ever conceived.
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When looking at hurricane maps, many form either just west of Africa, or in the Caribbean sea.
This map was from 2012, with travel roughly northwestward.
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fupload.wikimedia.org%2Fwikipedia%2Fcommons%2Fthumb%2F4%2F4f%2F2012_Atlantic_hurricane_season_summary_map.png%2F640px-2012_Atlantic_hurricane_season_summary_map.png&hash=4bdd16d3079de49d71aad88baf84c039)
http://en.wikipedia.org/wiki/2012_Atlantic_hurricane_season
Of course, that may all be a bit North American centric of a view. Looking at the 2013 typhoons, they impact a broad area.
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fupload.wikimedia.org%2Fwikipedia%2Fcommons%2Fthumb%2F8%2F83%2F2013_Pacific_typhoon_season_summary.png%2F640px-2013_Pacific_typhoon_season_summary.png&hash=f1dc77da2c581d04936362813779e6be)
http://en.wikipedia.org/wiki/2013_Pacific_typhoon_season
Anyway, in the Atlantic, if one wished to catch several of the typhoons where they form, it would mean covering a swath of ocean, perhaps 500 miles wide from Africa to the Caribbean sea.
As far as dissipating the power of the storm. It wouldn't come in a single burst, but rather each storm would have energy removed over the life of the storm of several weeks. With a large enough grid, during the "storm season", potentially there would always be a storm somewhere feeding the grid.
Still, the logistics of building such a large grid, in deep SALT water would be a nightmare, as well as connecting thousands of miles of high energy power cables underwater. And, the system would have to be designed to be efficient over a very wide range of wind speeds.
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Alan - the idea is to slow the incoming slowly-moving air that is feeding the storm. Conservation of angular momentum speeds this slowly-rotating air to become hurricane-force by the time it meets the eye-wall. The idea of the walls around the cities of the cost of mitigation against flooding, rather than wind...
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What creates hurricanes? Tornadoes?
A standard breeze is the movement of air from a high pressure area to a low pressure area, perhaps created in part by the movement of the sun's heat across the planet's surface. Slowing the movement of air would not get rid of the potential difference between high and low pressures, and in fact it could make that difference more extreme.
So, slowing the winds of the hurricane... is that sufficient to dissipate the hurricane? Or, does the root cause of the hurricane remain?
What would be the effects of slowing the wind over the oceans on non-stormy days? Would artificially dissipating hurricanes increase the ocean temperatures?
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What about planting shrubs etc in the water, at the shores, binding the soil and creating a barrier, giving local fish wild life somewhere to dwell and hatch, as well as possibly also becoming a sort of buffer to storms? Think I read about Australian tries in that direction a little time ago? Can't find it now though. Otherwise I think I will agree with Alan. Seems a very costly and difficult solution, using the turbine construction we have today, with wings. Think I've seen some other solutions there, the wind entering a tunnel of sorts, maybe those would work better for strong winds?
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I think there was a lot of talk about maintaining swampland in Louisiana for "storm surges". It doesn't do much for the wind, but it helps provide a buffer for waves from the sea.