13 ms·
Which way a wind turbine turns might not seem to matter, but it does
- nrki 6y agoOutline link: https://outline.com/GTwkCb https://outline.com/GTwkCb
- floatrock 6y agoFun-fact pot-shot time! The first paragraph states the thesis that there's something about wind patterns in the northern hemisphere that make windmill directionality important. The first paragraph also says: > It is convenient to have all clock hands turn in the same direction, but it is an accident of history which direction that is. Clockwise is not a random coin-flip of history. Ironically, clockwise is clockwise also because something about the northern hemisphere: the shadows on a sundial move clockwise in the northern hemisphere, so when europeans first started making clocks, they continued the sundial convention!
- Demiurge 6y agoThat's a really good point, and comes up in first result to a google query: https://www.google.com/search?q=why+is+clockwise+to+the+right https://www.google.com/search?q=why+is+clockwise+to+the+righ... ...
- thoraway1010 6y agoBeat me to this. Water also drains clockwise and foucault pendulums process clockwise in northern hemisphere. These are somewhat less likely to have a bearing on the matter than a sundial.
- Angostura 6y agoThe coriolis effect is too weak to have any appreciable effect on the way that water drains in any sink or bath.
- jcims 6y agoDefinitely has an effect - https://www.youtube.com/watch?v=mXaad0rsV38 https://www.youtube.com/watch?v=mXaad0rsV38 Whether or not it meets the standard of 'appreciable' is subjective i suppose.
- Jedd 6y agoThis is poor science, and very weak support for 'definitely'. I didn't watch this all the way through this time, but I do recall watching it back in 2017 when it was posted -- IIRC he did this experiment <sic>, asserting all variables were controlled for, but in a garage with leaky walls, on a poorly insulated floor, with no control test and only once, in one location. Consider that hurricanes don't form within 5 degrees (~ 550km) of the equator - which gives a good indicator of just how strong (or not) the Coriolis effect is.
- emmelaich 6y agoThere has been experiments, published in Nature in the 60s that did confirm an effect. I personally know one of the authors. The tub they used was something like 60cm deep and 3 or 4m in diameter. I can pull up the reference if you like. It wasn't perfectly reproducible though; in classic fashion when they demonstrated for a local newspaper (Sydney Morning Herald) the water went the "wrong" way. I have given the url / details here in HN a few years back.
- Jedd 6y agoThat it's not perfectly reproducible should be setting off alarm bells, even for people who would really like this effect to work at the scale of a few metres.
- emmelaich 6y agoI'm not sure that any experiment is perfectly reproducible. Though I would be very surprised to see a hurricane going the wrong way at mid-latitudes! Anyway, we're in agreement that it is a thing, and we just need a big enough tub to demonstrate it, correct? The force is perfectly calculable, and we can compare that to the effect of, say, a breeze across the top. ps. the reference https://www.nature.com/articles/2071084a0 https://www.nature.com/articles/2071084a0 "Published: 01 September 1965 The Bath-Tub Vortex in the Southern Hemisphere LLOYD M. TREFETHEN, R. W. BILGER, P. T. FINK, R. E. LUXTON & R. I. TANNER pps. my earlier mention https://news.ycombinator.com/item?id=15122988 https://news.ycombinator.com/item?id=15122988 Nature volume 207, pages1084–1085(1965)"
- jjtheblunt 6y agotypo: process -> precess
- bvandewalle 6y agoThis must be one of the most misunderstood pieces of popular science. The Coriolis effect is WAY too weak to affect the direction the water is flowing. Typically the way the water moves initially and the shape of the container will have an outsized impact in the final direction.
- kbenson 6y agoI think the issue is between people who interpret the statement as "water is predisposed to drain in a particular direction depending on hemisphere" or as "water will drain in a particular direction depending on hemisphere". Does it have an effect and can it sometimes be seen? Yes. Is it often swamped by other factors and rendered irrelevant? Also yes. That doesn't mean it's false, but it does mean that some statements that rely on it as a factual basis are at best mistaken.
- marcosdumay 6y agoWhen you have a large reservoir with a drain, keep it still, and the water reaches the level where it starts to rotate, the Coriolis effect is the dominant influence. It is something large enough to be plainly visible, but not something that appear on every drain.
- nostromo 6y agoYou just made me spend 5 minutes wondering if sundials would work on the equator, and if so, do they go counter-clockwise or clockwise during which parts of the year. Also, a fun fact: even if you have a wall-mounted sun dial (which was common in the ancient era) it still moves clockwise in the northern hemisphere, even though noon would be near the bottom of the clock.
- jaggederest 6y agoOf course they do. On the equinox it would follow a straight line through the middle of the pointer with times marked on it. At other times of the year, they behave Northerly in the northern summer and Southerly in the southern summer. Always west-to-east, though, obviously.
- minikites 6y agoAnd around noon near the equinox, there's no shadows at all: https://en.wikipedia.org/wiki/Lahaina_Noon https://en.wikipedia.org/wiki/Lahaina_Noon https://boingboing.net/2017/04/13/lahaina-noon-when-the-sun-is.html https://boingboing.net/2017/04/13/lahaina-noon-when-the-sun-...
- yencabulator 6y agoEven an approximation of that is quite convincing. In the right time of year, palm trees in Los Angeles have their shadows pretty darn perfectly centered, and if the top of the tree is narrow the shadow is nearly invisible.
- colanderman 6y agoA sundial on the equator has a horizontal gnomon (oriented north-south), and the shadows move underneath it from west to east. (There is of course a slight curve in one direction or the other based on the seasons.) See e.g. https://en.wikipedia.org/wiki/Sundial#/media/File:Sundial,_Singapore_Botanic_Gardens.jpg https://en.wikipedia.org/wiki/Sundial#/media/File:Sundial,_S...
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- teraflop 6y agoYou could argue that the fact that we use clock face designs derived from sundials built in the northern hemisphere, rather than the southern, is itself an accident of history.
- abraae 6y agoYou could argue that the bulk of the world's landmass and hence people being in the northern hemisphere is itself an accident of history.
- CydeWeys 6y agoBut that we call it the "north" hemisphere is itself an accident of history. We could've easily called it the south hemisphere instead. /s
- ajuc 6y agoThat's just English. In my language directions are named from where the sun is at given time, so it wouldn't change. East is "sunrise", south is "midday", west is "sunset" and north is "midnight". Context and grammatical case differentiate between midnight as time vs midnight as direction.
- ashtonkem 6y agoThat’s both true and not. Yes, it’s true that once clock makers started adding dials they used clockwise because they mostly lived in the northern hemisphere, and decided to mimic the design of sundials. What’s less obvious is the inclusion of dials at all. While in popular imagination the road from sundial to clock is clear, in reality some of the first modern clocks had no faces at all. The initial responsibility of medieval clocks was actually chiming, first in “liturgical hours” and then eventually regular hours. Their weight, cost, and inaccuracy meant that they were more commonly used to call monks to pray (hence liturgical hours) than for economic activity. Jumping from chiming to circular clocks was actually a pretty significant leap for clock makers, and one that only seems obvious in retrospect. Especially since sundials typically trace semi-circular paths and not the full circle that a clock uses, and the installation of clocks into tall, prominent locations took a few centuries.
- close04 6y agoSeems like the turbines rows should be positioned in alternating CW and CCW rows in order to benefit from a potentially substantial (up to 23%) increase in efficiency in the downwind turbine(s) during the night. But I wonder is the tradeoff is worth it. There would definitely be increased costs with always building 2 mirror versions of the same turbine blades. The logistical effort would also likely increase. This [0] is the cost breakdown for manufacturing blades. Unfortunately it's hard to tell how much "up to 23% at night" translates to in real life gains. 100 turbines' worth of tooling costs $250K-$1.5M. Two sets of these being recouped from the efficiency improvement alone is a tough sell. Building 10% more "regular" turbines might be cheaper and provide more output. Unless you really need to get the max efficiency out of the lowest number of turbines. Perhaps as manufacturing gets cheaper, turbines get more popular, we run out of good places to put them and need to max out efficiency, and we get decent energy storage options for night-time generated power this will make more sense. [0] https://windpower.sandia.gov/other/031428.pdf https://windpower.sandia.gov/other/031428.pdf
- ninju 6y agoAny initial additional costs during construction/installation should be easily recouped in short period of usage allowing for net gains after that point for rest of the lifetime of the turbine
- Someone 6y agoI think that, at the scale we will be building wind turbines, and given the relative scarcity of areas with good wind, having separate production lines will be worth it, even if the difference is ‘only’ about 5%.
- close04 6y agoI agree, it will make more sense when we run out of improvements and upgrading turbines is the only way to squeeze more. It's a very high hanging fruit.
- starpilot 6y agoThere are some massive simulations to determine turbine siting, check it out: https://www-gs.llnl.gov/energy-homeland-security/windpower/technology https://www-gs.llnl.gov/energy-homeland-security/windpower/t... Terrain, weather, etc. all affect power capture.
- scrooched_moose 6y agoPreprint of the full paper here: https://www.researchgate.net/publication/338882074_Should_wind_turbines_rotate_in_the_opposite_direction https://www.researchgate.net/publication/338882074_Should_wi... It's cool work. Some things I've picked out from a quick skim: - Only the downstream turbines gets a boost, cutting gains of a pair in half* - The boost only occurs at night, cutting gains approximately in half again. - Veering winds only occur 75% of the time This already cuts the gains from an ideal 23% to roughly 4.5% real world. I don't see any treatment of incoming wind direction - it appears to only consider pure West to East wind with turbines precisely aligned with the wind. I suspect the effect would disappear as the wind shifted from other directions. While wind is generally westerly in the US, it varies a lot hour-to-hour. Combine this with the above and I'd suspect real-world benefit is in the 1-2% range, at which point the added complexity of maintenance and production probably cancels out the benefit. Not a knock on the research, because it is great work, but it is incomplete. *This may be unfair, as it's unclear what affect multiple in a row would have. But the power production of multiple turbines in a row when the wind is blowing precisely parallel to the row drops off pretty quickly. Commercial turbines are something like 45% efficient these days, so turbine 3 only has ~30% of the original power available.
- csours 6y agoA 5% gain is worth it when you have some severe constraints. If you can just plop down another wind turbine, that 5% almost certainly won't pay off. If you can imagine some scenario where you absolutely have to get the most energy out of the wind in a specified footprint, then it would make more sense (and cents). As a counter-example, consider internal combustion engines (ICEs): they have had to get more efficient and cleaner, so you see more and more abstruse dingusses and doohickeys added to them. A 4.5% improvement in ICE efficiency is beyond amazing these days, and would justify well more than a 4.5% increase is cost for the engine.
- statictype 6y agoI’m kind of surprised that this research wasn’t already done decades ago. I just assumed the placement and positioning of turbines within a cluster was already subject to rigorous modelling, seeing as these turbines are huge and likely very expensive
- dbuder 6y agoIt probably was, many times over.
- qsolo 6y agoWake effects are studied extensively and automated systems exist that will optimize the turbines' yaw direction to maximize power output (and / or keeping loads in check) of the entire plant instead of just a single turbine. For example: https://www.siemensgamesa.com/en-int/newsroom/2019/11/191126-siemens-gamesa-wake-adapt-en https://www.siemensgamesa.com/en-int/newsroom/2019/11/191126... What's novel here is the effect the counter-clockwise rotation has on the power output of the down stream turbines... I think it hasn't really been a point to research as the costs of blades, maintenance, etc... are assumed to far outweigh the potential gains. Something else to keep in mind is that it's not as pleasant to look at a park full of turbines spinning in different directions.
- marvin 6y agoHuh. Seen in retrospect, it's sort of obvious. Propeller efficiency can be increased by mounting them in pairs, one behind the other, where the two are rotating in different directions. This reduces the "twisting" movement of the airflow behind the propeller, which is a sign of energy that's lost and not used for propulsion. Stands to reason that the same thing would be the case with wind turbines, and maybe a little surprising that it hasn't been on anyone's radar before now.
- mannykannot 6y agoThe way this effect works, however, is dependent on a Coriolis-force-induced veer in the atmospheric boundary layer, something that is not an issue in contra-rotating propellers. Unless one understands the mechanism, one will be unaware that, for any given location, it matters which way the first turbine rotates. At best, an arrangement based on an analogy to contra-rotating propellers would be a lucky guess, right for the wrong reasons.
- kevin_thibedeau 6y agoPretty much the same as the reason why stacking fans adds little benefit unless they rotate in different directions.
- phkahler 6y agoStacking identical fans that run at similar speed is probably not effective. Jet engines seem to use many compressor stages though - none of them the same.
- londons_explore 6y agoBut every 2nd one is stationary, effectively meaning the air sees counter-rotating fans...
- Proven 6y agoIt doesn't matter if the cost is subsidized
- deleted 6y ago[deleted]
- 0xfaded 6y agoI was once curious about if in a line of propellors, having the propellors rotating in the same direction (line wheels on a shared belt) or counter rotating (like interlocking gears) would produce any difference in thrust. I made a rig to test this https://www.youtube.com/watch?v=SJ7BVa8Ol1I https://www.youtube.com/watch?v=SJ7BVa8Ol1I. Unfortunately it seems I didn't upload the strain gauge measurements, but I remember the net difference was negligible.
- sourcesmith 6y agoI am guessing vertical axis turbines do not have this bias but they only seem to be used in smaller designs?
- mannykannot 6y agoI would guess that their awake is asymmetrical (though in a different way) and so there might be a favored way to arrange them, but as they are inefficient compared to conventional turbines, and because the blades undergo a large cyclic variations of wind load with each rotation, they are not cmpetitive for large-scale commercial use.