[HN Gopher] Tidal energy is not renewable
___________________________________________________________________
Tidal energy is not renewable
Author : wyozi
Score : 212 points
Date : 2023-09-04 18:17 UTC (4 hours ago)
(HTM) web link (cs.stanford.edu)
(TXT) w3m dump (cs.stanford.edu)
| kepler1 wrote:
| I 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 wrote:
| Or that because they will be unevenly distributed, the planet
| might tip over.
| ggm wrote:
| Is 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?
| octacat wrote:
| Solar energy is not renewable too in the long run (very long
| run).
| qayxc wrote:
| That'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 wrote:
| But 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 wrote:
| Sadly 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).
| uoaei wrote:
| Then 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 wrote:
| Isn't wind created by temperature and pressure differentials
| between regions? How much is due to earth's rotation?
| uoaei wrote:
| Quite 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 wrote:
| A lot.
|
| Look up Hadley cells. 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 wrote:
| Hadley cells determine wind _patterns_ but not the _energy
| content_ of the wind, to any appreciable degree, which
| comes from solar flux.
|
| Wind energy is solar energy once removed.
|
| Wave energy is solar energy _twice_ removed (solar - > wind
| -> waves).
| dredmorbius wrote:
| No, wind is ultimately fed by solar energy and is driven by
| differential heating of Earth's atmosphere and surface.
|
| That is, there's a constant incoming energy flux. That's not to
| say that there isn't some maximum amount of available wind
| energy, or some maximum amount of energy that can be extracted
| from wind without causing other effects (even excepting, say,
| bird strikes and the like).
|
| But wind isn't "used up", there will be more wind tomorrow, so
| long as the sun shines and there's an atmosphere.
| NBJack wrote:
| Air currents have a purpose, and I actually believe large scale
| wind farming will have negative impacts on climate. Not to
| mention the impact on birds killed by the things. I would even
| go as far to say nuclear energy has less of an impact (as long
| as all goes well).
|
| The question few seem to ask is should we be this (literally)
| power hungry in the first place?
| hkt wrote:
| > The question few seem to ask is should we be this
| (literally) power hungry in the first place?
|
| Nobody asks because the answer is "no" - huge parts of our
| lives are absurdly inefficient, wasteful, or just gratuitous
| when it comes to energy usage. Heating, transport, all of it.
| Computing, too.
| uoaei wrote:
| > The question few seem to ask is should we be this
| (literally) power hungry in the first place?
|
| Absolutely!! Reducing excess consumption will always be
| easier than making up for it later because the latter
| inevitably causes losses which become heat from which "useful
| work" can never be recovered. We can avoid those losses by
| simply never requiring them in the first place.
|
| But too many have the Myth Of Progress burrowed deep into
| their core ideologies and will fight tooth and nail to keep
| the trivial conveniences they've built their daily routines
| around.
|
| On your first point, though, I'm not sure it will be a net
| negative considering the human component in the equation, and
| anyway, outdoor cats are orders of magnitude worse for birds
| than wind turbines are, not to mention concrete jungles with
| no trees and high average noise levels.
| hedora wrote:
| Nuclear does have less impact than wind, in terms of human
| lives lost volume of waste, and land usage.
|
| However, bird strikes can be mitigated via careful placement,
| etc. Also, we are not close to the point where wind farms
| impact wind currents.
| sgu999 wrote:
| Your first paragraph really made the second one a pleasant
| surprise!
|
| No we shouldn't be this power hungry, we've effectively never
| replaced an energy source by another... we keep on stacking
| the new ones on top of more of the old ones [1].
|
| [1] https://ourworldindata.org/grapher/global-energy-
| substitutio...
| Rantenki wrote:
| It'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 wrote:
| Not 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.
| csours wrote:
| Is this satire? It seems like there's too much math in this to be
| satire.
| joelthelion wrote:
| Issues 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 wrote:
| > 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 wrote:
| Thank you!
| idlewords wrote:
| Every energy source becomes renewable on the right time scale.
| arghwhat wrote:
| And 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 wrote:
| [TESCREALism and paperclip maximizers have joined the chat]
| exitheone wrote:
| That'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]
| mcqueenjordan wrote:
| I 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.
| DFHippie wrote:
| I'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.
| tejtm wrote:
| Short story time
| https://archive.org/details/ExhalationByTedChiang
| sideshowb wrote:
| All 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 ;-)
| hn_throwaway_99 wrote:
| But 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 wrote:
| Quoting from the OP:
|
| >it will take about 10.468 billion years for Earth to lock to
| the Moon naturally.
| iamthemonster wrote:
| I 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.
| AnimalMuppet wrote:
| Neither is fission.
| blincoln wrote:
| How is fission not renewable, when one can literally make more
| of the material in the right type of reactor?
| nirse wrote:
| Did you invent something and forgot to tell us about it?
| mgiampapa wrote:
| Step 1, create the universe... Step 2, ????, Step 3, Profit?
| pdonis wrote:
| _> 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.
| alexey-salmin wrote:
| Neither is fusion (including solar and wind power). Scale
| matters
| josephcsible wrote:
| Where is the angular momentum going?
| changoplatanero wrote:
| it goes into pushing the moon's orbit further out
| pdonis wrote:
| To the Moon's orbital angular momentum. As the Earth's spin
| slows, the Moon moves further away and its orbital angular
| momentum increases.
| qayxc wrote:
| Incidentally, this also causes the tidal effects to weaken to
| a point where calculations show that tidal locking will
| actually never happen.
| pdonis wrote:
| What calculations are you referring to?
| [deleted]
| systemBuilder wrote:
| It'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 wrote:
| a few lines of css will massively improve mobile experience
| obastani wrote:
| > 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 wrote:
| That 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 wrote:
| Conflict 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://www.mdpi.com/2673-4060/4/3/32
|
| https://news.ycombinator.com/item?id=37313586 |
| https://medium.com/@samyoureyes/the-busy-workers-handbook-
| to...
|
| https://overshoot.footprintnetwork.org/newsroom/country-
| over...
|
| 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 wrote:
| > 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.'
| bbor wrote:
| You have some sources for "Sweden and France are failed
| countries"? Something tells me that's not quite an
| objective take. "Inequality exists now so it will always"
| is also not the objective scientific take I think you're
| implying it to be
| hef19898 wrote:
| At least those people moved on from raping refugees at
| German christmas markets and new year's eve celebrations.
| At least it some kind of progress...
| Nemrod67 wrote:
| just a feeling of insecurity ;)
| bbor wrote:
| Jesus fucking Christ this is depressing. You just brought
| up how you think genocide inevitable, and you imply that we
| should start it so that we'll win?
|
| I don't think there's any reason we should take "let's kill
| everyone else so we can keep our nice stuff" should make
| any more sense in 2023 than it has over the last... well,
| such arguments pop up in all of human history, I guess.
|
| To answer your question: i think it's more likely that we
| build an egalitarian global society, or at least continue
| on the path.
| toomuchtodo wrote:
| I didn't say genocide, I said violence over scarce
| resources. They are distinct motivators. I also didn't
| say to start it, I said to win.
|
| > To answer your question: i think it's more likely that
| we build an egalitarian global society, or at least
| continue on the path.
|
| Good luck with that. Hope is not a strategy, but
| hopefully the future is not as bleak as the current data
| predicts. Show me a voter cohort that will willingly give
| up substantial go forward energy or resource quality of
| life for people on the other side of the world who they
| have not nor will never meet. Do you know how many people
| are dying right now at this moment because their basic
| needs are not being met? One every 4 seconds per Oxfam.
| This is before more frequent heat events, crop failures,
| aquifers reaching terminal depletion, etc.
|
| https://www.oxfam.org/en/press-releases/humanitarian-
| organiz...
|
| Agreed it's (extremely!) depressing, but facts are
| different than a reality based on feelings. Finding truth
| is following the facts to the (sometimes) unpleasant
| places it takes us.
| JumpinJack_Cash wrote:
| > > Good luck with that. Hope is not a strategy, but
| hopefully the future is not as bleak as the current data
| predicts. Show me a voter cohort that will willingly give
| up substantial go forward quality of life for people on
| the other side of the world who they have not nor will
| never meet.
|
| Voters might never do it, but the guy who wins the
| Presidency and only has to face voters every 4 years, he
| starts thinking about Nobel Peace Prize the moment he
| sets foot in the WH, and to make a legitimate candidacy
| he needs to be a great humanitarian and/or getting some
| significant Foreign Policy victories.
|
| Bush 43 took it upon himself to fund a whole lot of
| malaria and HIV prevention campaigns, and even Trump
| pursued the defeat of ISIS and normalization of
| relationships between Israel and the Arab world.
| TheSpiceIsLife wrote:
| The future is hard to predict.
|
| I'm willing to bet our descendants will be approximately as
| irrational _and_ lucky as humans have always been.
|
| There's a good chance that at least one of those ten
| billion are going to have some radically good ideas, and an
| even better chance than a few more will have some really
| good ideas.
| JumpinJack_Cash wrote:
| Increasing the number of brains won't help if their
| mental pattern correlation also increases.
|
| People are acting more and more in unison, that means no
| variability and no room for radically good ideas
| skywhopper wrote:
| This 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.
| uxp8u61q wrote:
| I would have expected HN users to have learned their lesson
| after this superconductor fiasco. Expertise in a field grants
| you no expertise in another.
| paulmd wrote:
| Despite 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 wrote:
| 200 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 wrote:
| it'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.
| Zenst wrote:
| So 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.]
| [deleted]
| sudhirj wrote:
| This 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!
| giblfiz wrote:
| Wait, isn't most of that "tidal power" that we would be capturing
| going into grinding rocks into sand along the coast?
| dools wrote:
| Imagine the rock buildup!
| dbingham wrote:
| Can 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 wrote:
| The 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 wrote:
| One 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 wrote:
| Was 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.
| [deleted]
| FriedPickles wrote:
| Hmm 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 wrote:
| lol great minds think alike
| jaggederest wrote:
| This 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.
| hirundo wrote:
| > ... 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 wrote:
| There's an award-winning sci-fi book with a tidally locked
| planet as its premise:
| https://www.goodreads.com/en/book/show/37534907
| throwaway87543 wrote:
| But 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 wrote:
| If 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 wrote:
| You missed the part where he assumed that energy demand
| will increase 400 million times and took 1 percent of that
| wizofaus wrote:
| The 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.
| wcoenen wrote:
| I'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
| [deleted]
| thewakalix wrote:
| If we're still around in 500 years and producing that much
| energy, I don't expect we'd be limited to Earth anymore!
| more_corn wrote:
| Collecting solar power in orbit is quite reasonable.
|
| But yeah I expect we'll not make it 100 years let alone 500.
| Our ability to change our behavior to avoid obvious problems
| is poor bordering on suicidal.
| [deleted]
| empath75 wrote:
| While this is true, a lot of economists build their models
| assuming unlimited exponential growth. It does seem that we're
| going to hit a brick wall in growth in a few hundred years if
| that doesn't stop. There seems to be some idea that we can
| continue exponential growth if we can just figure out renewable
| energy and we can't. There is _no such thing_ as renewable
| energy in a regime with unlimited exponential economic growth.
| Aerroon wrote:
| Economic growth doesn't necessarily require energy
| expenditure growth. Figuring out how to do something more
| efficiently (for half the energy) is also economic growth.
| golem14 wrote:
| I found the Hans Rosling series of talks quite good and a bit
| reassuring. If we survive the next 100 years, we'll probably
| do OK for a while longer.
| WillPostForFood wrote:
| Any sort of straight line extrapolation is useless. Look at the
| US energy consumed per capita, flat or declining for the last
| 50 years. Other parts of the world will follow as they develop.
| Likely the same for population growth.
|
| http://insideenergy.org/wp-content/uploads//2017/01/historic...
|
| from:
|
| https://insideenergy.org/2017/01/12/energy-explained/
| littlestymaar wrote:
| > Look at the US energy consumed per capita, flat or
| declining for the last 50 years.
|
| This doesn't account for all the "imported energy" that comes
| when you outsource your industrial production abroad. Granted
| even then the energy consumption doesn't increase
| exponentially anymore, but it's not flat either.
| wmf wrote:
| Here you go https://ourworldindata.org/grapher/consumption-
| based-energy-...
| hgsgm wrote:
| And that shows steadily increasing usage except during
| economic recession.
| JamisonM wrote:
| Do you have some data to back up this assertion? For me
| what I see in the numbers is that Chinese domestic quality
| of living improvements correlate better with increases in
| energy consumption than does US imports (or Chinese
| exports).
|
| What is also interesting is that China's "energy intensity"
| - energy used per unit of GDP is pretty flat, if wealthier
| nations were exporting energy demand via imports I would
| expect that number to be climbing. I am at a bit of a loss
| as to how to determine exactly what is going on TBH.
| littlestymaar wrote:
| You can find data related to this phenomenon when
| searching for "imported emissions". But then it's only
| going to be related to the CO2 emissions, not energy, and
| the measure appears to vary a lot depending on the
| methodology (from a quick search, France is estimated to
| import between 117 and 750Mt of CO2 a year, quite a large
| error margin...).
|
| > if wealthier nations were exporting energy demand via
| imports I would expect that number to be climbing
|
| Why? These exports from China generates GDP in China so
| it just grow the energy consumption as well as the
| Chinese GDP, making the ratio flat.
| JamisonM wrote:
| > France is estimated to import between 117 and 750Mt of
| CO2 a year, quite a large error margin...
|
| I don't know, if your basis for your opinion is that you
| googled it and you got some very wide ranging and
| contradictory results then that seems like a poor
| foundation to start with.
|
| > Why? These exports from China generates GDP in China so
| it just grow the energy consumption as well as the
| Chinese GDP, making the ratio flat.
|
| If the ratio is flat then there isn't really much of an
| export of energy effect in my view. If you are exports
| were dominated specifically by the use of energy (over
| say human capital or laxer pollution standards) that
| intensity would rise because it would be the source of
| the economic advantage. I.e. if domestic consumption
| trade 1 unit of energy for one unit of growth but exports
| trades 2 units of energy for one unit of growth intensity
| will rise if exports dominate the energy mix. That does
| not seem to be the case.
|
| A huge proportion of US imports seem to be based on
| "assembly" from what I can tell, the dominant categories
| from China are electrical/electronic goods and industrial
| machines - most of the stuff is the assembling of US & EU
| (and Taiwan for semiconductor reasons) made parts.. the
| energy mix of the import-export dynamic seems like it
| needs a lot of analysis - I would like something
| authoritative that shows an attempt at an analysis, I
| can't seem to find it.
| Onavo wrote:
| It flattened in the midst of manufacturing outsourcing and
| globalization. Bring back the heavy industries and it would
| look much more different.
| mikeyouse wrote:
| Nope. Common belief but not true:
| https://ourworldindata.org/consumption-based-co2
|
| More specifically: https://ourworldindata.org/grapher/prod-
| cons-co2-per-capita
| eldaisfish wrote:
| the rest of the world still has to catch up to these levels.
| Granted, they won't get to the absurd wastage levels of north
| america but they will continue to consume more energy. Just
| looking at the energy levels in one country doesn't tell you
| much.
| giantrobot wrote:
| Developing countries will increase their energy usage but
| have the benefit of buying things from developed countries.
| As we've seen developing countries today have been able to
| jump right to modern technology for infrastructure.
|
| They didn't need to build massive lines of analog
| telecommunications, they just jumped right to cellular and
| satellite technology. They can jump right to solar and
| other renewables as they electrify. They can skip
| incandescent lighting and go right to LEDs.
| wmf wrote:
| This doesn't help much on the demand side but it will
| help if they go straight to clean energy.
| [deleted]
| sjducb wrote:
| I think we'll have colonized space by then, maybe even starting
| to build a Dyson sphere.
| uoaei wrote:
| Sci-fi idea: binary star system is really the remnants of an
| advanced civilization, originally orbiting a single (much
| larger) star on their own planet, that collapsed in on itself
| from the consequences of its energy generation technology.
| rich_sasha wrote:
| > Our global energy consumption in 2008 was estimated to be 474
| exajoules.
|
| If my maths is right, that's about 40,000 kcal per person per
| day, or about 15 times the energy consumption of an average
| adult.
|
| I'm trying to figure out if that's a lot or not. On the one
| hand, not: this ratio is not strictly bounded in any way, and
| the human energy consumption is an arbitrary denominator.
| Still, a very rough interpretation is to say, we consume daily,
| on average, the fruit of work of 15 people.
|
| Of course, that is very skewed. I wonder what the ratio looks
| like for an average American or European - must be much more.
|
| It goes to show what a gilded life we live (on average!!!).
| Before industrial revolution, all energy basically was muscle
| power, and it's like for every 1 person alive, we have 15
| servants turning the generator for us. I suppose some of this
| number is literal service providers, fed by food produced by
| powered agriculture.
|
| Is there a logical upper bound to this number? Is there some
| energy amount we can't use given sufficient supply? Ultimately,
| all energy we produce is spent on humans so our energy
| consumption is a yardstick for human energy needs.
|
| But that's not quite right either; a lot of energy is wasted. I
| wonder how much of this number is clothes that go straight from
| factory to landfill, AC left overnight, inefficient engines and
| energy storage.
|
| I don't really have a point, other than I think this is an
| interesting fraction to look at.
| gus_massa wrote:
| It's an interesting comparison.
|
| I got some numbers form a random result in google:
| http://www.ejolt.org/2012/12/human-energy-use-endosomatic-
| ex...
|
| Endosomatic energy (i.e. food): 3.5GJ/year/person
|
| Exosomatically energy (i.e. firewood, electricity, solar,
| fossil fuel, whatever):
|
| hunter-gatherers: 20 GJ/year/person (i.e. x6)
|
| agriculturalists using animals: 60 GJ/year/person (i.e. x17)
|
| industrial society: 200-300 GJ/year/person (i.e. x57-x86)
| messe wrote:
| > If my maths is right, that's about 40,000 kcal per person
| per day, or about 15 times the energy consumption of an
| average adult.
|
| As someone with a physics background... well... it's within
| an order of magnitude or two, so that sounds close enough to
| be probably accurate.
| cornel_io wrote:
| I was super skeptical of this article, because I was trying to
| imagine how we'd have to arrange extractors in the oceans to
| pull any meaningful amount of energy out of the rotation of the
| earth based on tides, and only at the end of the article did I
| see that assumption of 2% compounding multiplied out as far as
| needed...ugh.
|
| The implausibly is staggering, we'd run out of resources to
| build extractors way before causing any meaningful shift in the
| rotation: if the monstrous land barriers of the continents take
| millions of years to drain a small percentage of the energy, we
| have zero hope of achieving much more with the solid mass
| available to us on Earth, short of a Dyson sphere-level
| breakthrough in "moving mass around", oh, and by the way it has
| to happen deep underwater as well, and we need to channel all
| the energy somewhere useful! Way harder than just making a
| ginormous but thin solar array in space, which is almost
| certainly what we'd do instead from a "energy cost to arrange
| matter" optimization POV.
| Aerroon wrote:
| To extrapolate further on the silliness of 2% growth. Let's
| convert the entire Earth into pure energy:
|
| Earth's mass is 10^24 kg.
|
| E_earth = mc^2 = 9 * 10^40 J
|
| E_current * 1.02^x = E_earth
|
| 474 * 10^18 * 1.02^x = 9 * 10^40
|
| x = 2357.91 years
|
| At a modest 2% growth we would be using up the entire Earth's
| mass in energy _per year_ in only 2358 years.
| arnaudsm wrote:
| Your 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
| detourdog wrote:
| I think the next step is to figure how many exajoules goes to
| waste heat.
| Baeocystin wrote:
| Minus the tiny fraction embodied in global temperature
| increases, all of it.
|
| It's the same reason that the Earth radiates exactly as much
| energy as it receives from the sun, just a larger number of
| lower energy, higher entropy photons. What the sun really
| provides is a source of low entropy.
| [deleted]
| graypegg wrote:
| Wouldn't energy available to be consumed become a limiting
| factor in our rate of using that energy?
| gnfargbl wrote:
| Human energy use isn't going to continue to grow exponentially
| for the next 500 years.
|
| The world population is predicted to peak about 30% above where
| it is now and then fall back -- maybe to 7 billion people
| sustained. We seem to need about 200 GJ per person to be really
| happy [1], so let's assume 300 GJ per person.
|
| We should be able to get by, happily, on 2000 EJ per year
| sustained. By your figures, that's less than 1% of what the sun
| provides.
|
| [1]
| https://esajournals.onlinelibrary.wiley.com/doi/10.1002/ecs2...
| [deleted]
| littlestymaar wrote:
| > We should be able to get by, happily, on 2000 EJ per year
| sustained. By your figures, that's less than 1% of what the
| sun provides.
|
| Then at that rate we'd have 100,000 years of Tidal energy
| available even if we used it for the totality of our energy
| needs (and 10,000,000 years if we use it for 1% of our needs
| as taken in the paper). And that was basically the point of
| the person you're responding to: it's not so much that tidal
| energy is non-renewable, the problem is that the paper assume
| exponential consumption growth, and exponential growth is
| unsustainable no matter what.
| hkt wrote:
| We, 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.
| dduugg wrote:
| What's the theoretical max energy for other sources of energy,
| such as nuclear (fission) power?
| Nition wrote:
| Humanity needing that amount of energy seems obviously absurd,
| but then I suppose a CPU with 100 billion transistors seemed
| clearly impossible in 1960.
|
| Maybe a few hundred years from now, Internet archaeologists
| will find your comment as one of the first harbingers of the
| coming World Energy Crisis, much as we see the 1912 Rodney &
| Otamatea Times "Coal Consumption Affecting Climate" snippet
| today.[0]
|
| Then they'll find this comment...
|
| ----
|
| [0] https://paperspast.natlib.govt.nz/newspapers/rodney-and-
| otam...
| littlestymaar wrote:
| > one of the first harbingers of the coming World Energy
| Crisis,
|
| It's been well known since at least _The limits to growth_
| [1], 51 years ago.
|
| [1]: https://en.wikipedia.org/wiki/The_Limits_to_Growth
| hgsgm wrote:
| 250 years
|
| https://en.m.wikipedia.org/wiki/Thomas_Robert_Malthus
| frind wrote:
| [dead]
| 7speter wrote:
| Right now, the minds that conceive of any practical way of a
| spacecraft reaching the speed of light says we need the
| energy of multiple suns to be able to even reach that speed,
| so who knows where humans are in 500 years...
| ben_w wrote:
| Right now, most of the suggestions for going at _actually_
| the speed of light (rather than just very close) require a
| _negative_ energy, which is much much harder than even a
| huge positive energy as nobody has any idea if it 's even
| possible[0] let alone how.
|
| [0] no a Casimir cavity won't do that:
| https://kitsunesoftware.wordpress.com/2017/04/20/can-a-
| casim...
| mNovak wrote:
| A direct link to the mentioned snippet:
|
| https://paperspast.natlib.govt.nz/newspapers/ROTWKG19120814..
| ..
| giantg2 wrote:
| "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."
|
| So nuclear?
| [deleted]
| PUSH_AX wrote:
| Isn't it more likely that demand will just outgrow supply?
| Energy poverty seems like a classic "planet Earth" kind of
| thing.
| azernik wrote:
| Even more likely is that, as we're already seeing in rich
| countries, demand does _not_ continue to grow exponentially
| and economic growth mostly happens in non-energy-intensive
| sectors.
| gcanyon wrote:
| "the rotation of the Earth would lock to the Moon in about 1000
| years." -- based on unlimited exponential growth. That's not
| worthy of a high school term paper, let alone the work of a
| PhD. Thanks for saving me the read.
| almenon wrote:
| Relevant: 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 wrote:
| In 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 wrote:
| This 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.
| haskmell wrote:
| If you can slow down the Earth by consuming the tidal energy, can
| you also speed it up by correctly timing pumping water to
| reservoirs?
| blake1 wrote:
| The 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.
| bobthepanda wrote:
| The UN has revised peak projections down several times; the
| peak is now expected at 10 billion.
| coldcode wrote:
| More countries are now sub-2.0 replacement, China is down to
| 1.09 so the peak is unlikely to get much more than that.
| popol12 wrote:
| A Google search for "china children per woman" gives me
| 1.705
|
| Are you talking about something else ?
| smcin wrote:
| The Google hit China TFR 1.705 for 2023 is bogus (and
| 2023 isn't even over yet, which should have alerted you),
| it's single-sourced from macrotrends.net which is quoting
| an old (pre-pandemic) UN forecast; you can see from their
| graph their (forecasted) numbers for 2020-2 turned out
| totally wrong. Lots of other sites are quoting the Google
| and macrotrends as fact. So now the #1 Google hit on that
| is misinformation. (Always look for attributions and
| dates).
|
| As to 2022, China did briefly drop to a TFR of 1.09, like
| GP said [1]; but the moving average over several years is
| more like 1.3. You have to put the 2022 drop in context
| that their very strict lockdown went into its third year,
| and there were two cases of pregnant women losing their
| babies e.g. because the hospital denied them entry for
| having negative Covid tests but a few hours too old [2].
|
| [0]: https://www.macrotrends.net/countries/CHN/china/fert
| ility-ra...
|
| [1]: "China's fertility rate drops to record low 1.09 in
| 2022- state media"
| https://www.reuters.com/world/china/chinas-fertility-
| rate-dr...
|
| [2]: https://fortune.com/2022/01/07/china-covid-cases-
| miscarriage...
| anonylizard wrote:
| Its now dropping even lower in 2023, long after the
| lockdowns have ended.
|
| Turns out the East Asian style of hyper-competitive child
| rearing has its downsides, namely the high costs dissuade
| parents from having children altogether.
|
| China faces every antinatal problem the west does, except
| far worse.
|
| 1. Extremely high housing prices making family formation
| expensive
|
| 2. Small apartments suppress large family formation (Seen
| in Europe)
|
| 3. General collapse of marriage rates due to changing
| incentives and thus moral norms
|
| 4. Higher education decreasing fertile years.
|
| 5. Economic depression, especially for young people, euro
| debt crisis level of youth unemployment.
|
| You add to that, that China still officially has a
| 3-child policy (not that many people even have 2),
| because the birth control bureaucrats still need a job.
|
| China is probably 2nd lowest in the world behind South
| Korea, and will stay there, if not
| happymellon wrote:
| Normally it requires two people to make a baby. So 1.7 is
| less than the number of people requires to create it.
|
| Rates are normally calculated by couples. 0.85 per person
| is a decline.
| paulmd wrote:
| Leave it to HN to be unaware of the physical or social
| mechanics of reproduction
| jl6 wrote:
| The trends are _mostly_ encouraging but there are still 102
| countries with a fertility rate above replacement rate, so
| we're not out of the woods yet:
|
| https://en.wikipedia.org/wiki/List_of_countries_by_total_fe
| r...
| ido wrote:
| You mean less than that? But more importantly, after that
| peak comes a long and steady decline (as far as we can
| tell).
| quotemstr wrote:
| Almost every human population is under strong selection
| pressure towards having more people. This dip in fertility
| cannot and will not last.
| deepsun wrote:
| Unless external factors kick in, like depletion of
| resources and soils. There's no any law of nature that says
| homo sapiens must be able to survive. Smaller scale
| examples are:
|
| 1. Easter island -- we, humans, deforested the island, that
| degraded and depleted human population significantly even
| before the first european ships discovered the island. From
| what I've heard, "Rapa Nui" movie is unusually historically
| correct on the events.
|
| 2. St. Matthew Island -- 29 introduced reindeer rapidly
| overpopulated the island and ate all the available food
| there, so the whole population died.
|
| Same thing can happen on planet Earth.
| RetroTechie wrote:
| > The single most important assumption in this paper is that
| energy consumption will increase by 2% per year.
|
| There's a 2nd big assumption:
|
| That tidal energy extracted is additional Earth's rotational
| energy loss _above_ what Earth does by itself.
|
| According to the paper, tidal energy is dissipated through
| friction between ocean water & the seafloor. This dissipated
| energy subtracts from Earth's rotational energy. And some
| rotational energy is transferred to the moon (which makes the
| moon move further out). Ok so far.
|
| Author's 2nd assumption is that as tidal energy is tapped, this
| is _extra_ energy that subtracts from Earth 's rotation.
|
| But is it? It might also be that tidal energy extracted by
| humans, comes out of some fixed 'budget', and the remainder is
| dissipated naturally. More tidal energy extracted by humans ->
| less tidal energy dissipated through ocean vs. seafloor
| friction.
|
| Kind of like solar influx: it's a huge but (apart from
| fluctuations) fixed amount. We can tap some % of that
| potential, but what's available doesn't increase. And what
| humans don't tap, gets absorbed / radiated out by other natural
| processes.
|
| I won't even hazard a guess. But it would be interesting to
| figure out which of those applies.
| ricardobeat wrote:
| Yes, the assumption seems to be that any energy extracted is
| in addition to the friction with the ocean floor and
| continental plates, as those will continue to exist.
| pmontra wrote:
| Your observation seems to make sense.
|
| Intuitively, if we extract energy from the tides, tides will
| be less tall and the speed of water will be smaller. Ocean
| currents will slow down too.
|
| What I don't know is, less friction on the seafloor means
| that we would actually make Earth slow down less faster than
| it would do if left alone?
| hollerith wrote:
| >Author's 2nd assumption is that as tidal energy is tapped,
| this is extra energy that subtracts from Earth's rotation.
|
| Not so. The calculation of the 1031 years is equation 19 and
| assumes the decrease in rotational energy all goes to human
| purposes. It is the assumption that human consumption keeps
| rising at .02 per year for 1031 years that is unrealistic: we
| would probably boil the oceans away because of the waste heat
| from using that much electricity.
| api wrote:
| 20000X the energy of a current human shows how absurd it would
| be for growth and energy use to not decouple. I can't even
| imagine what I could do on Earth using that much power. Fly my
| own 737 to a new city every day?
|
| I suppose spacefaring humans might use that kind of power but
| if they are living in space they are no longer part of the
| biosphere of Earth.
| rodgerd wrote:
| > Fly my own 737 to a new city every day?
|
| That's literally the billionaire lifestyle.
|
| Meanwhile cryptocurrency is seeing decades of power
| efficiency undone as miners bring old power plants online and
| want to burn tyres to power their scams.
| ben_w wrote:
| > I can't even imagine what I could do on Earth using that
| much power. Fly my own 737 to a new city every day?
|
| Sure, why not?
|
| It's absurd _today_ for the average person, but it 's the
| kind of thing rich people get to do already, and looking at
| the rich today is a decent (though imperfect because
| inflation and invention don't work like that) hint for what
| normal people can afford in a richer future.
| mattmaroon wrote:
| Aviation historically, has not gotten cheaper overtime. If
| anything, it is more expensive. Only rich people had planes
| 100 years ago and only rich people own them now and the
| trend line doesn't indicate it'll be different in another
| hundred.
| ben_w wrote:
| Nobody owned a 747 a hundred years ago.
|
| Cheapest flight I've ever taken was 9.99 from Berlin to
| London -- not sure if pounds or euros, but does it matter
| when either way it is less than I used to spend on a week
| of school lunches nearly 20 years earlier?
| [deleted]
| [deleted]
| codethief wrote:
| > The single most important assumption in this paper is that
| energy consumption will increase by 2% per year. [...] How much
| energy will we consume in 1,000 years
|
| I keep posting this link here on HN but, once again, it seems
| very appropriate:
|
| > The upshot is that at a 2.3% growth rate (conveniently chosen
| to represent a 10x increase every century), we would reach
| boiling temperature in about 400 years.
|
| https://dothemath.ucsd.edu/2012/04/economist-meets-physicist...
| casparvitch wrote:
| If HN was reading Murphy the front page would look very
| different every day
| joak wrote:
| This boiling temperature conclusion makes the assumption that
| we continue using thermal power (steam engines, etc...),
| where waste heat is around 60%.
|
| However photovoltaic and wind does not produce much waste
| heat. Arguably solar and wind cannot scale 1000x but then you
| could have non thermal fusion like Helion's
| https://www.helionenergy.com/technology/.
|
| Btw, thermal power is already showing limits (rivers
| overheating in summers), we don't have to wait 400 years to
| see its failure.
| midasuni wrote:
| Where does the energy go then? EM radiation leaving the
| planet?
| svnt wrote:
| > gets us to about 150 trillion humans in 1,000 years
|
| I realize the big issue is settled here but just to scope this
| detail: the total land area of earth is coincidentally
| approximately 150 million km^2
|
| At 150 trillion humans each human would get just about a square
| meter. Many of those square meters are uninhabitable.
| midasuni wrote:
| That's about the density of Kowloon walled city. And ignores
| the available space in the ocean.
| dredmorbius wrote:
| The lesson that constant percentage (that is, exponential)
| growth _cannot_ continue endlessly is the fundamental message
| behind the concept of Limits to Growth. That is, _there exist
| intractable limits to growth_ , and that no matter how
| convenient it may be to pretend otherwise, humans ignore this
| fact at their extreme peril.
|
| Long-term ongoing economic growth, expressed as a constant
| percentage, is baked in to most current orthodox economics and
| economic policy. Even apparent mavericks such as Thomas Piketty
| assume that growth will continue interminably (noted in
| _Capital in the Twenty-First Century_ ).
|
| Rather than being a critique of Liu, you've actually written a
| criticism of those he himself is generally addressing.
| rwoerz wrote:
| Let 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 wrote:
| Even 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.
| callalex wrote:
| More quality science coming out of Stanford as usual.
| crazygringo wrote:
| Tons 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 wrote:
| According 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 wrote:
| Thanks 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 wrote:
| Any 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.
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