11 ms·
Tidal energy is not renewable
- systemBuilder 3y agoIt's probably much worse than this. Once the earth stops rotating IMHO it's likely the magnetic core stops rotating. Then the solar wind strips our aosphere in only 1000 years ...
- foderking 3y agoa few lines of css will massively improve mobile experience
- hirundo 3y ago> ... if we were to extract the rotational energy just to supply 1% of the world's energy consumption, the rotation of the Earth would lock to the Moon in about 1000 years ... and most life on Earth could be wiped out. Important safety tip.
- caesil 3y agoThere's an award-winning sci-fi book with a tidally locked planet as its premise: https://www.goodreads.com/en/book/show/37534907 https://www.goodreads.com/en/book/show/37534907
- Vecr 3y agoThe City in the Middle of the Night by Charlie Jane Anders if the link does not work for you either.
- throwaway87543 3y agoBut is it possible to extract that much energy from the tides with current techniques? That starting point in their math may be invalid. But it is good to know that not very much energy is available from the tides.
- PaulKeeble 3y agoIf its not possible then we really shouldn't be very interested in it because it can't get us very far, 1% is a rounding error towards solving the CO2 PPM causing climate change.
- alexey-salmin 3y agoYou missed the part where he assumed that energy demand will increase 400 million times and took 1 percent of that
- wizofaus 3y agoThe difference any individual (or even a single small to medium sized business) can make is never more than a rounding error either - I'm not convinced that means we shouldn't be interested in such changes.
- uoaei 3y agoThen technically neither is wind, since it slows down surface air currents and widens the effective boundary layer of the atmosphere. Technically-technically, no forms of energy "generation" (technically just conversion) are 100% efficient so something is always lost to heat. I guess the important question is, what is the net effect in changing that kind of energy into purely thermal energy?
- jval43 3y agoIsn't wind created by temperature and pressure differentials between regions? How much is due to earth's rotation?
- uoaei 3y agoQuite a lot because of thermal expansion/contraction of air and differentials in incident sunlight heating the surface at different points at different times. Albedo, thermal mass of the objects being heated, etc., all contribute to a complex system of air and energy transport via air currents. It would take quite a lot of planning and work but maybe there are ways to mitigate these losses by balancing out the effects between different processes. Typically nature finds such dynamic equilibria as a matter of course -- I suspect anything humans attempt to control will not be as resilient or sound.
- btilly 3y agoA lot. Look up Hadley cells. https://groups.seas.harvard.edu/climate/eli/research/equable/hadley.html https://groups.seas.harvard.edu/climate/eli/research/equable... Warm air rises near the tropics, rotating with the Earth. It then goes towards the temperate zone, still rotating with the Earth to form the jet stream. It then falls, creating the trade winds as it slows down. It then is sucked back towards the tropics, creating a reverse trade wind because it is only going as fast as the temperate zone. And then it rises, completing the cycle. The prevailing wind in both temperate zones and the tropics is therefore due to the Earth's rotation.
- dredmorbius 3y ago
- idlewords 3y agoEvery energy source becomes renewable on the right time scale.
- arghwhat 3y agoAnd every energy source becomes non-renewable on the right time scale. Post humanity, post-earth time scales might not be relevant to most discussions.
- kmeisthax 3y ago[flagged]
- exitheone 3y agoThat's not actually true. The conditions for the formation of coal and oil may likely never happen again because the bacteria to break decompose trees did not exist then but exist now, making oil formation impossible because trees decompose now. Unless they all die out, we won't get any new oil ever.
- deleted 3y ago[deleted]
- DFHippie 3y agoI'm curious about this. We certainly won't get any more coal, but a whole lot of carbon gets subducted into the mantle regularly. Some gets turned into diamonds. Some gets blown out of volcanoes. Is the oil we pump out of the ground produced directly in the continental crust or is it generated from some of this carbon subducted with oceanic crust that has been transformed by some process and then made its way back into continental crust? I'm lazy, so I'm hoping some geologist will stop by and educate me.
- mcqueenjordan 3y agoI think it's a joke about how all finite sequences will repeat during infinite time. But it doesn't really add anything to the discussion.
- haskmell 3y agoIf you can slow down the Earth by consuming the tidal energy, can you also speed it up by correctly timing pumping water to reservoirs?
- AnimalMuppet 3y agoNeither is fission.
- blincoln 3y agoHow is fission not renewable, when one can literally make more of the material in the right type of reactor?
- mgiampapa 3y agoStep 1, create the universe... Step 2, ????, Step 3, Profit?
- pdonis 3y ago> one can literally make more of the material in the right type of reactor? Until one runs out of the feedstock one is using to make more fissionable material. You're not recycling actually burned fission fuel. You're making more fission fuel out of isotopes that don't fission at all.
- nirse 3y agoDid you invent something and forgot to tell us about it?
- alexey-salmin 3y agoNeither is fusion (including solar and wind power). Scale matters
- josephcsible 3y agoWhere is the angular momentum going?
- pdonis 3y agoTo the Moon's orbital angular momentum. As the Earth's spin slows, the Moon moves further away and its orbital angular momentum increases.
- changoplatanero 3y agoit goes into pushing the moon's orbit further out
- obastani 3y ago> So, the 2% growth rate for world energy consumption should be a conservative assumption. An important caveat: this article assumes that energy consumption will continue to increase exponentially to get the 1000 year timeline of draining the rotational energy of the Earth.
- JumpinJack_Cash 3y agoThat better be the case , we are already seeing that if the pie can't grow then we start fighting each other violently to enlarge one's piece of it.
- toomuchtodo 3y agoConflict over scarce resources is inevitable. When the violence starts, you should be prepared to win (from a nation state perspective). https://news.ycombinator.com/item?id=37122796 https://news.ycombinator.com/item?id=37122796 | https://www.mdpi.com/2673-4060/4/3/32 https://www.mdpi.com/2673-4060/4/3/32 https://news.ycombinator.com/item?id=37313586 https://news.ycombinator.com/item?id=37313586 | https://medium.com/@samyoureyes/the-busy-workers-handbook-to-the-apocalypse-7790666afde7 https://medium.com/@samyoureyes/the-busy-workers-handbook-to... https://overshoot.footprintnetwork.org/newsroom/country-overshoot-days/ https://overshoot.footprintnetwork.org/newsroom/country-over... https://en.wikipedia.org/wiki/Planetary_boundaries https://en.wikipedia.org/wiki/Planetary_boundaries There are 8 billion people in the world, and we’re on track to have 10 by end of century. Which is more likely? Everyone lives like a European (from a consumption perspective)? Or a bunch of people don’t or die while some do?
- adventured 3y ago> Which is more likely? Everyone lives like a European (from a consumption perspective)? Or a bunch of people don’t or die while some do? There are no systems that can ever be created to actually balance out / eliminate inequality, outside of very small communities operated via extreme authoritarianism. See: modern Sweden. A formerly highly effective welfare state, increasingly brought to its knees by poor immigrants (and it's going to get a lot worse over the coming decades). They can't remotely handle what's happening to their country in terms of inequality, despite how good they have been historically at managing it. France - also historically effective at managing a high quality of life welfare state - has entirely failed at managing a similar scenario, and for the same reasons. The exact same principle applies globally as it does locally. It can't be done under any scenario. So yes, vast inequality will persist forever, as it has forever. The end of inequality is when there are one or fewer humans remaining. We don't have to guess at likelihoods (will everyone live like a European). The answer is known and certain. Even within Europe half the population can't afford to 'live like a European.'
- skywhopper 3y agoThis is a CS professor doing some naive math and assuming that the energy usage patterns of the past 50 years (an increase of 2% usage each year on average) could or would keep going for the next 1000 years.
- paulmd 3y agoDespite all the scoffing in this thread, they’ve gone on at about that rate for 200+ years now. Expecting a deviation from this is kinda “climate change will slow down in the 2000s and 2010s from green energy” level magical thinking.
- uxp8u61q 3y ago200 years is, what, a thousandth of the duration humans have been on this Earth? 44 billionths of the age of the Earth? It's a blip.
- paulmd 3y agoit’s 1/5th of the period under consideration, which is a pretty reasonable basis for extrapolation not sure how any of those numbers have any relevance to projecting the growth of energy usage under industrialized society lmao. yes, if we extinctify ourselves in the next few decades, or return to an agrarian, pre-industrial existence, the earth will be fine and will eventually return to an equilibrium.
- uxp8u61q 3y agoI would have expected HN users to have learned their lesson after this superconductor fiasco. Expertise in a field grants you no expertise in another.
- dbingham 3y agoCan someone with more experience in the field comment on whether this paper is well founded or off base? The abstract sounds... lets go with "not completely implausible" but the assertion that extracting 1% of the Earth's energy from the tidal sloshing would slow the earth and tidally lock it in 1000 years feels extreme. Of the extreme assertions require extreme evidence variety.
- c1ccccc1 3y agoThe post assumes a 2% annual rate of growth in energy consumption. So, due to the nature of exponential functions, most of the energy loss would concentrated towards the end of the 1000 years, as the energy consumption approaches 400 million times present day energy usage. The first two centuries of use would not have a noticeable impact.
- archi42 3y agoOne thing I notice is the assumption of unlimited exponential growth by 2% per year. That's a huge fallacy. Quick check, yeah, 1.02^1031 = 735,829,316. I'm pretty sure we will be using magnitudes more energy than today because we're more people and hopefully with better living standards for everyone. But even then that's a lot. And on that scale I'm not entirely sure where the whole energy should go to... Maybe produce mass/objects out of it? If we reach peaked our energy consumption in merely 250 years, that's less than 150 times our current consumption. I didn't do the math, but would date to suggest this gives us a few years more time on this planet.
- Guvante 3y agoWas curious so did the math backwards assuming the previous 1000 years had a 2% growth rate. The world used 9,717 million tons of oil equivalent in 2017. Plugging in our growth rate that would mean the world used the equivalent of 13 tons of oil in 986 which is 515.84 million BTU. US residents making <$20k and having wood as their primary heating fuel source use 50 million BTU of wood a year. While we can argue specifics 10 households worth of fuel sounds a little low for a world with a population of 390 million.
- FriedPickles 3y agoHmm so if we pump water to amplify the tides we can speed up the Earth's spin and get rid of the leap second.
- jcims 3y agolol great minds think alike
- jaggederest 3y agoThis has already happened, actually. Some leap seconds have been skipped iirc due to faster rotation from all the impounded water in reservoirs in northern regions.
- kps 3y agoWe should draw tidal power until there are exactly 360 days in a year, to make the arithmetic nice, and incidentally give us 24 minutes extra sleep.
- alwayslikethis 3y agoThe other way of doing this is just pushing the earth a bit off its orbit. Better to do it in the other direction though to stop global warming. Let's make it 400 days instead.
- datadrivenangel 3y agoBetter yet, slow down the earth to 25 hours so that we're 1-1 with Mars!
- wcoenen 3y agoI'm not sure the author realized this, but they're actually making a statement about how crazy exponential growth is. Not about the sustainability of tidal power. This becomes obvious once you look closer at what that 2% growth rate (as assumed in the post) implies. Our global energy consumption in 2008 was estimated to be 474 exajoules. The total energy received by the earth from the sun during a year is about 5 million exajoules, a fraction of which reaches the surface. 5 million is much more than 474. But at a seemingly modest 2% per year growth rate (as it was between 1980 and 2006), our energy consumption will match those 5 million exajoules in less than 500 years! Think about that: if energy consumption growth continues at the current pace, then in 500 years we'll either be using ALL solar energy received by the earth (leaving none for the biosphere), or we'll have figured out some magic technology to produce 5 million exajoules of energy per year. Assuming the magic technology, where are we going to get rid of all that extra heat? It would effectively be like having a second sun on earth, cooking us in place. edit: I copied the numbers above from a post I wrote in 2010, so it may be a bit out of date. But Sabine Hossenfelder recently made a video where she talked about a similar timescale, i.e. boiling oceans in 400 years: https://www.youtube.com/watch?v=9vRtA7STvH4 https://www.youtube.com/watch?v=9vRtA7STvH4
- deleted 3y ago[deleted]
- arnaudsm 3y agoYour idea sounds similar to the Kardashev scale [1], and we seem to be at 0.733. The concept of the Dyson sphere emerged from that theory. [1] https://en.wikipedia.org/wiki/Kardashev_scale https://en.wikipedia.org/wiki/Kardashev_scale
- hkt 3y agoWe, or those of us who by chance survive the worst case scenarios, will just end up learning that maybe huge amounts of socially useless investment isn't compatible with life on earth. It is just not possible unless we carefully plan and ration energy - something the market simply won't do.
- PUSH_AX 3y ago
- almenon 3y agoRelevant: https://physics.stackexchange.com/questions/6400/are-tidal-power-plants-slowing-down-earths-rotation https://physics.stackexchange.com/questions/6400/are-tidal-p... This theory is very interesting, although the author presents it with too much confidence for such big claims.
- Aachen 3y agoIn that link: > The Earth's rotational kinetic energy is about 10²9 J, and the world uses something like 10²² J/year, so you could power the entire world for millions of years before you'd run out of rotational energy. (my phone somehow has a ² but not a ^9; the first number is supposed to be 1e29)
- jccooper 3y agoThis is mostly based on the assumption of a 2% growth rate in overall energy consumption, with tidal power as an ever-growing 1% of that. The effect of covering 1% of our current energy usage would be minimal. And, likely, the ability to exploit tidal power will plateau at some (fairly small) amount, due to geographic constraints.
- blake1 3y agoThe single most important assumption in this paper is that energy consumption will increase by 2% per year. This kind of exponential growth leads to outlandish estimates for the amount of tidal energy that society will demand. Energy consumption has decoupled from population growth rates and economic growth. How much energy will we consume in 1,000 years? Most projections of the population have it stabilizing at around 15 billion. But continuing at its current growth rate (an optimistic assumption I think), gets us to about 150 trillion humans in 1,000 years. And at 2% growth rate, each of those humans will consume 20,000 times more energy than a circa 2023 human. Now state of the art technology wastes about 80% of the energy consumed, so this is equivalent to 100,000 times more useful energy consumed per human. So the physics in this page is a good examination of the surprisingly large compounding effects of unchecked exponential growth.
- deleted 3y ago[deleted]
- bobthepanda 3y agoThe UN has revised peak projections down several times; the peak is now expected at 10 billion.
- coldcode 3y agoMore countries are now sub-2.0 replacement, China is down to 1.09 so the peak is unlikely to get much more than that.
- callalex 3y agoMore quality science coming out of Stanford as usual.
- joelthelion 3y agoIssues with exponential growth set aside, does wind power suffer from the same problem? If I understand correctly, wind mostly caused by the coriolis force, which is a consequence of the earth's rotation. Would building too many wind turbines slow down earth's rotation?
- hn_throwaway_99 3y ago> If I understand correctly, wind mostly caused by the coriolis force, which is a consequence of the earth's rotation. You understand incorrectly. Wind is largely a form of solar energy. The sun heats the earth and its atmosphere at different rates depending on the location, and wind is primarily the result of temperature differentials. The Coriolis effect can definitely affect how wind behaves, but it doesn't provide the energy. E.g. a hurricane's winds travel in a circle/spiral due to the Coriolis effect, but a hurricane is a heat engine that gets its energy from the sun heating the oceans.
- joelthelion 3y agoThank you!
- Rantenki 3y agoIt's a neat thought experiment, but the underlying assumption: The world's energy consumption was about 5.67x1020 Joules in 2013.[18] This number has increased by more than 2% per year on average in the last 50 years. The average world economic growth rate in the last 50 years is about 3%, which requires a corresponding increase in the energy supply. So, the 2% growth rate for world energy consumption should be a conservative assumption. ... is a bit naive. If we're consuming (does some math) `1.02^1000 = 398264651` ... Four billion times as much energy as we do today. I don't think there's much risk of us growing our population to that degree, nor of us being that power hungry if our population stabilizes. We'll be either extinct or back to a sustainable agrarian population far before we reach that upper limit. Honestly, if we produced that much power, I suspect we'd have long since boiled the oceans, making the whole argument moot. TL;DR: Don't extrapolate FAR into the future based on a small (relatively) set of data points.
- qayxc 3y agoNot only that. The paper is only even remotely plausible if the author assumes 100% efficiency. Otherwise waste heat alone would turn Earth into Venus long before any tidal locking could take effect.
- sideshowb 3y agoAll this doom and gloom, I say let's go for it though, most of us would benefit from a few extra hours in the day right? We can switch off the tidal power once it gets to 26 hours or so ;-)
- Zenst 3y agoSo they postulate how the moon will in 1000 years become stationary in orbit due to the tidal energy extraction as to why tidal energy is not renewable. Sorry but I'd need a few more than one institution to be backing this. Otherwise, it seems a bit too reaching to be anything other than a great plot for some cheesy disaster movie that they have phases of doing. [EDIT - Reversed AI's rewrite of my humble English, raw best with all its flaws, and whilst AI version good, just had an air of sterility and not me.]
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- sudhirj 3y agoThis is the old my kid was two feet tall a year ago and three feet tall this year, so by the time she's an adult she's going to be as tall as a house!
- _ugfj 3y agohttps://xkcd.com/605/ https://xkcd.com/605/
- crazygringo 3y agoTons of comments here highlighting that 2% annual growth rate in energy consumption is ludicrous. But so what if we made a more reasonable assumption that annual energy usage will stabilize at, say, 5X of what it is currently, and the (unreasonable) assumption that we get 100% of that energy from tides. Then how much of a rotational slowdown do we get after 1000 years?
- MichaelDickens 3y agoAccording to the paper, tidal energy has a total capacity of 10^29 Joules, and current global energy consumption is 10^21 Joules per year, so if we converted 100% of current energy consumption to tidal energy and didn't increase it at all, it would last 10^8 = 100 million years (rounded to the nearest power of 10). Equivalently, after 1000 years, we'd see a rotational slowdown of around 0.001%.
- crazygringo 3y agoThanks so much. That feels much more in line with intuition. So maybe not technically renewable, but many orders of magnitude more renewable than e.g. fossil fuels...
- zamadatix 3y agoAny useful interpretation of renewable energy has to do with purely human timeframes as thermodynamics doesn't allow for any energy source to be endlessly renewable. "If I use this source today will more of it naturally be there tomorrow" type consideration, otherwise you end up with a definition which either includes things like fossil fuels as renewable because you can wait millions of years or excludes things like sunlight because it won't be there in 10 billion years.
- Jweb_Guru 3y agoWell, there is a more important sense in which solar is renewable but not tidal energy. The sun does not burn out appreciably more quickly if we use a larger percentage of the available solar energy, it's there whether we use it or not. This is not the case for tidal energy.
- octacat 3y agoSolar energy is not renewable too in the long run (very long run).
- qayxc 3y agoThat's not what renewable means. Renewable energy means that the source is naturally replenished within a human lifetime. In other words, the source isn't permanently depleted by tapping into it. This is the case with solar energy: the Sun's energy output doesn't change depending on whether we use it or not. Renewable doesn't mean perpetual - that'd be physically impossible for all we know.
- nirse 3y agoBut also the sun is burning fuel and eventually that will run out and we don't really have any means of renewing that fuel (I don't know where to order intergalactic hydrogen).
- octacat 3y agoSadly it is not even means of intergalactic hydrogen. The game is over once the hydrogen in the core is fused :( Tidal energy would probably never go mainstream to cause major issues (too easy to break during the storms, not all places are good to build it, other types of energy sources are more attractive). The whole article sounds like something that fuel companies would sponsor to make the renewable energy look bad (look, tidal is not renewable too, so buy our gas/oil).
- tejtm 3y agoShort story time https://archive.org/details/ExhalationByTedChiang https://archive.org/details/ExhalationByTedChiang
- giblfiz 3y agoWait, isn't most of that "tidal power" that we would be capturing going into grinding rocks into sand along the coast?
- dools 3y agoImagine the rock buildup!
- hn_throwaway_99 3y agoBut don't the tides naturally dissipate a lot of that energy anyway? E.g. whenever you go to the beach and see waves crash upon the shore, that's tidal energy being dissipated as heat. If you stick a turbine in the mix to extract useful work before it turns into heat, isn't it still turned into heat regardless?
- hollerith 3y agoQuoting from the OP: >it will take about 10.468 billion years for Earth to lock to the Moon naturally.
- dre85 3y agoThat's exactly what I was wondering as well. I didn't really understand how tapping into the power source could possibly cause an additional loss that wouldn't otherwise happen.
- timmaxw 3y agoYes, tides do naturally dissipate energy. The main source of tidal dissipation is friction between the moving seawater and the seabed. [1] Current tidal generators work either by inserting a turbine into the moving water; or by a dam that captures the high tide, then releases it through a turbine at low tide. Depending on the exact details, it could slow down the rate at which the current later flows over the seabed, which would reduce the energy dissipated from friction with the seabed. But, there's no guarantee that this would compensate for the energy taken by the tidal power generator. You could imagine a different type of tidal power generator: covering the seabed with a giant treadmill. As water flows past, it drags the surface of the treadmill, generating power. My guess is this would dissipate less total energy than the natural friction of the seabed does. But, it doesn't sound very practical. (Anyway, all of this is a moot point. As other commenters have noted, if human energy consumption actually were to grow 2% annually for 1000 years, we'd have way bigger problems than the moon becoming tidally locked.) [1] https://en.wikipedia.org/wiki/Tidal_acceleration#Angular_momentum_and_energy https://en.wikipedia.org/wiki/Tidal_acceleration#Angular_mom...
- kepler1 3y agoI think out of embarrassment, the student also decided not to showcase his proof that in 1000 years, the mass of human beings will outweigh the Earth. Eh, who am I to criticize? They say that your early grad school years are a time to publish large amounts of papers that you don't think are likely to stick. This is a little bit out there even by this standard though.
- SoftTalker 3y agoOr that because they will be unevenly distributed, the planet might tip over.
- csours 3y agoIs this satire? It seems like there's too much math in this to be satire.
- luxcem 3y agoIt seems like https://what-if.xkcd.com/ https://what-if.xkcd.com/, absurd hypothesis and correct maths
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- rwoerz 3y agoLet me nitpick: The headline alone is right: Tidal energy cannot be renewed. But that is true for all renewables like wind and solar, because "renewable" is a misnomer. Real renewal would violate thermodynamic's 2nd law. What the author actually seems to doubt is the ABUNDANCE of tidal energy (but supports that with questionable assumptions (cf. other comments here))
- ricardobeat 3y agoEven then conflating them makes no sense. Solar and wind power are both coming from an external source, the sun, which we might as well consider infinite; whereas tidal energy is not. It can be depleted.
- ggm 3y agoIs it not the case that the moon-earth system may become locked, irrespective? I mean if we're worried about future decades.. As long as this happens before the sun expands to make the earth uninhabitably hot, it's a risk for .. some intelligence?
- iamthemonster 3y agoI really love this kind of thinking and explanation - it may not be correct per se, but it's the TYPE of thinking we need. Rather than fluffy repetitions of the slogans of in-groups, it's an attempt to explore long term impacts using fundamental scientific principles, none of which are individually too complex. And if we don't agree with the 2% annual energy growth rate for 1000 years then that's fine, we can fiddle the numbers for what we believe, and the same analysis can be valuable even if it ends up supporting a different conclusion. I'm interested by the language style as well, it reads like they put it through a filter to generate "simple English" as a deliberate choice.
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- avodonosov 3y agoA related question I think about from time to time. If our energy consumption grows, how soon we will destabilize the Earth? Even 100% clean energy, if infused into the system may increase temperature, or speed up circulation of currents, and other effects. Of course, it's not nesessary all energy goes into temperature. Some can be conserved, e.g. as chemicals. But in general, the more energy we have in our disposal, the more potential for damage. We will dig deeper, smelt more ore, etc, etc.
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- yalogin 3y agoThe comment here focus on the exponential growth of energy needs assumed. However that is besides the point, unless I am missing something. If the increase doesn’t happen in 1000, may be 10000. The main point for me is that by using the tidal energy we are slowing down the earth rotation. That just sounds intuitively wrong to me. This energy is already released because of the rotation, how can converting that impact the earth’s rotation?
- ajross 3y ago> Based on the average pace of world energy consumption over the last 50 years, if we were to extract the rotational energy just to supply 1% of the world's energy consumption, the rotation of the Earth would lock to the Moon in about 1000 years. This is bananas. I stopped right there and closed it. I see somewhere else in this thread that they tried to do that by extrapolating an exponential growth curve through an outlier (the industrial revolution!) for a thousand years. Maybe that explains it. But... that's not an error. That's just bananas. Absolutely insane. Some quick googling, FWIW, gives the earth's rotational kinetic energy as a quite plausible 2.1e29 J (though a little of this will not be extractable tidally, as the earth will lock to the moon at a few percent of rotation speed), and the total world energy consumption as 22.8 TWh/year. So the back of my envelope says that at current consumption we have a hair over... two trillion years.
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- romusha 3y agoNow do wind
- everybodyknows 3y agoNeeds (1998).
- jiggawatts 3y agoThe author makes the point that the slow-down of the day is non-linear, and then he uses a linear equation to estimate the time until the Earth is locked to the Moon! His doomsday scenario of total tidal locking would never occur -- as energy is removed from the rotation of the Earth, the maximum power level that can be extracted would decrease. Also, the cost-efficiency would also drop. There would be a point where the day is "merely" longer, the Earth is not yet tidally locked to the Moon, but extracting more tidal energy is no longer worth the trouble. The original point however is still valid. Even if the rotation was slowed to just 1/2 of what it is now, the Earth would have a 48-hour day and that would obviously cause absolute havoc with the environment.
- layer8 3y agoEveryone is commenting on the unreasonable exponential-growth assumption. But regardless of growth, the article is still technically correct that tidal energy is not renewable.
- esjeon 3y agoThe time limit of 1000 years is the worst part of this paper. If the energy consumption literally grows 2% every year, in 3013, the humanity will be consuming 3.98x10^8 times more energy than now. If it's really the case, the dissipation heat from the use of such a large amount of energy alone will kill us all, long before the tidal lock b/w the earth and the moon.
- somat 3y agoRegarding the "How Are Tides Formed?" section with a nice neat diagram and some math" But that is not really correct. it would be but there are large land masses interfering with the process. Ocean tides are better conceptualized as water sloshing in a bathtub. https://www.youtube.com/watch?v=PSJRymZ5bJs https://www.youtube.com/watch?v=PSJRymZ5bJs