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More renewable is good.. but there is always one fear in my crazy mind about these: This isn't actually renewable but taking energy out of a huge reservoir (Sam

More renewable is good.. but there is always one fear in my crazy mind about these: This isn't actually renewable but taking energy out of a huge reservoir (Same for solar if pea counting, but solar is really endless until the end of the solar system).. and if we'd scale it massively the result could be another catastrophe. (Same btw. with geothermal?). (Btw.. I maybe got tidal wrong, so if it is just taking energy from waves via wind this counts as endless solar. Still, consider systems which would really break the tides and take energy out of the earth<=>moon system). The answer to this fear is that this reservoirs are so massive they are quasi endless in regard to what we ever could take out? It is hard to find numbers for these crazy thoughts :)

lm28469 3y ago
> (Same btw. with geothermal?). Not a chance, we're barely scratching the surface > More renewable is good.. but there is always one fear in my crazy mind about these It depends a lot on the rate of maintenance, materials used, &c. For example small windmills are next to useless: https://solar.lowtechmagazine.com/2009/04/small-windmills-put-to-the-test/ https://solar.lowtechmagazine.com/2009/04/small-windmills-pu...
zakary 3y ago
You’re right that nothing is unlimited. Luckily in this case, the energy of waves and tides is given to the oceans mostly by the gravity of the moon pulling the water as it passes overhead. Also a little bit by the wind which is fed by solar heat energy. The moon is slowly moving away from earth and eventually, in hundred of millions of years, it will impart significantly less energy into the tides. The energy that the moon gives the tides is essentially the same as how the sun gives energy to the ground with light. That is to say: If we don’t collect it, it just gets turned into another kind of energy that is absorbed by the environment. For tides and waves that would be mostly heat, and a little sound. And most of that heat would eventually be radiated back out into space. So suffice it to say, while there is a finite pool of energy stored in the tides, it is so massive we could never make a difference, and it gets recharged everyday by the moon.
HPsquared 3y ago
There's also ocean thermal energy conversion, which exploits the temperature gradient in the ocean. https://en.m.wikipedia.org/wiki/Ocean_thermal_energy_conversion https://en.m.wikipedia.org/wiki/Ocean_thermal_energy_convers...
opeon 3y ago
the tidal systems are insanely vast and powerful. the gravitational pull of the moon and the sun is so large that even if you deploy a massive amount of kits on a small surface, you're unlikely to have an impact on the tides. theoretically it's possible, but it'd require an implausible scale of deployment
ben_w 3y ago
Tidal energy comes from the moon (and the sun) pulling the oceans as the Earth spins. Extracting energy from this effectively increases the drag between the ocean and the land, which slows down the rotation of the Earth. This effect even occurs without extracting tidal energy, and some of the dinosaurs (IIRC) had 19 hour days. The amount of energy in the rotation of the Earth is so huge that this basically doesn't matter, 10 TW for 660 million years, which is into the realm of "will too much carbon be subducted for photosynthesis to continue?" timescales.
- Y-bar 3y ago
  I propose two possible solutions: A. Build some huge-ass rockets on the moon to accelerate it to offset any slowdown from changes in tidal energy. B. Divert a few billion tonnes of asteroids to crash into the moon's aft, adding both to the moon's velocity and mass. I believe that if we begin working on any of these solutions within a hundred thousand years or so from now we should be able to offset most of the projected long-term lengthening of the day.
  - ben_w 3y ago
    You'd have to put the rockets/target the asteroid impacts on the Earth, the effect on the Moon from this interaction is to push it into a higher orbit to conserve angular momentum of the combined Earth-Moon system.
- Mistletoe 3y ago
  > "will too much carbon be subducted for photosynthesis to continue?" Great, you gave me a new fear. :)
jacquesm 3y ago
You're edging on the laws of thermodynamics there: on a long enough time scale all energy is non-renewable, every little bit of consumption gets you that much closer to the heat death of the universe. But given the vast reserve in that system for once humans won't be able to meaningfully affect it unless we start consuming far more than we do today. Interesting aside: that momentum is a giant energy reserve and conceivably you could rob some of it to create a means of escaping the gravity well even if there had not been any other.
card_zero 3y ago
Some numbers here: https://en.wikipedia.org/wiki/Tidal_power#Principle https://en.wikipedia.org/wiki/Tidal_power#Principle (last paragraph). Tidal energy is wasted by natural coastlines all the time, being converted into heat and erosion. If this effect is constant, it looks like the day gets longer by 7 minutes 12 seconds every 36.5 million years. (I calculated that because it's a 1% reduction in rotational energy.) Human extraction of tidal energy is much smaller than the energy wasted by tides acting on all the world's coastlines, I assume. To some extent it takes energy away from coastal erosion, which also seems fairly benign.
- whatisyour 3y ago
  Erosion is not always wastage.
  - mft_ 3y ago
    Could you expand? I'm interested in what you're getting at.
    - Eddy_Viscosity2 3y ago
      I think he's referring to nature making less florida.
      - actionfromafar 3y ago
        OTOH there's a case to be made for keeping florida diluted.
    - idontknowifican 3y ago
      erosion actually creates nests for various sea birds
    - wongarsu 3y ago
      Erosion makes gravel and sand, which are quite useful. It also makes minerals and nutrients accessible to life. But we spend a lot of time and money managing erosion, and at the same time (often accidentally) create lots of erosion in other places. I doubt extracting tidal energy will have effects on a global scale, though it might cause some local changes
piaste 3y ago
It's good that you are aware it's a crazy thought :) Nothing wrong with looking into it though. Wikipedia offers: > Movement of tides causes a loss of mechanical energy in the Earth-Moon system: this results from pumping of water through natural restrictions around coastlines and consequent viscous dissipation at the seabed and in turbulence. This loss of energy has caused the rotation of the Earth to slow in the 4.5 billion years since its formation. During the last 620 million years the period of rotation of the Earth (length of a day) has increased from 21.9 hours to 24 hours;[10] in this period the Earth-Moon system has lost 17% of its rotational energy. While tidal power will take additional energy from the system, the effect is negligible and would not be noticeable in the foreseeable future. and there is some simple math in the [Tidal acceleration] page [0] that you may want to read. Basically, the tides slow the rotation of the Earth, with some of the energy being transferred to the Moon but most of it going into friction. The natural friction is estimated at a (surprisingly low, IMO) 3.64 TW, and at this rate the Earth will stop rotating in 50 billion years, long after the Sun has blown up. So if we want to keep the Earth spinning (albeit slowly) until the Sun goes red giant, we can afford to cut that time down to a tenth, meaning we can produce 36 TW (before conversion to electricity, i.e. ignoring efficiency). If we are being reckless and just want to use power until we figure out nuclear fusion or something better, let's say a million years or so, we can make some 180 PW from tides. But since it would almost all turn to heat, and since that is more energy than the Earth gets from the Sun, that would probably be unwise unless we find a way to get it off-planet with very high efficiency. (Global electrical energy production is currectly about 28 PWh per year, equivalent to a constant 3TW or so.) [0] https://en.m.wikipedia.org/wiki/Tidal_acceleration https://en.m.wikipedia.org/wiki/Tidal_acceleration
- lloeki 3y ago
  > If we are being reckless and just want to use power until we figure out nuclear fusion or something better, let's say a million years or so, we can make some 180 PW from tides. But since it would almost all turn to heat, and since that is more energy than the Earth gets from the Sun, that would probably be unwise unless we find a way to get it off-planet with very high efficiency. I think you're touching on the problem very nicely here: the problem is not "how much raw energy is there" (because there's an absolute fuckton of it) but "when does the impact of capturing this energy - thus removing it from a complex ecosystem whose stability may depend on it - and turning it into something else - thus adding to a complex ecosystem in other ways - becomes a problem", which may or may not come well before the theoretical raw energy cap.
LM358 3y ago
"Tidal Energy Is Not Renewable": https://cs.stanford.edu/people/zjl/pdf/tide.pdf https://cs.stanford.edu/people/zjl/pdf/tide.pdf Previous discussion on HN: https://news.ycombinator.com/item?id=37383283 https://news.ycombinator.com/item?id=37383283
- dogtimeimmortal 3y ago
  Thanks for this! Something has always bugged me when I hear about big plans for tidal energy. TLDR, the 1000 year estimate is is derived from the geometric series proof(i needed a refresher). Wolfram explains it pretty well: https://mathworld.wolfram.com/GeometricSeries.html https://mathworld.wolfram.com/GeometricSeries.html ...then i needed a refresher on exponents and logarithms: https://wou.edu/mathcenter/files/2015/09/Exponents-and-Logarithms.pdf https://wou.edu/mathcenter/files/2015/09/Exponents-and-Logar... It's good to do the math and think about the big picture sometimes. ;) p.s. i tend to feel somewhat skeptical about a lot of renewable projects i read about in the news. And even if the math all works out and it really IS The Best Solution i cant help feeling we are ignoring the elephant in the room(population growth). Maybe human beings should start preparing themselves to live with less(and be happy with that).
  - ComputerGuru 3y ago
    Population growth is effectively over.
    - Cthulhu_ 3y ago
      Even if that were true (and it won't be for another 5-6 decades using current predictions at least), energy consumption is anything but. And if there is a risk of electricity usage plateauing, they'll just find something new like training AI models or spinning GPU's to churn out digital money (where said churning is entirely artificial).
  - dogtimeimmortal 3y ago
    Little addition, couldn't resist sry: After reading a bit of the comments thread above, i couldn't resist adding a bit more. > The single most important assumption in this paper is that energy consumption will increase by 2% per year. Quick reality check: 1.02^1000years = 398,264,652x increase! This could potentially be an unrealistic projection. Let's consider what we know from the article(and google). Here's a few numbers pulled from the article for reference: ~1.73 x 10^20 J tidal energy lost per year naturally 5.67x10^20 J was the total global energy consumption in 2013(10^18 is 1%) So 398,264,652 x 5.67x10^18 J = 2.258 x 10^27 J! That does seem like a lot. In comparison total sunlight absorbed on earth's surface each year is roughly 3.85 x 10^24 J.[1] > It might also be that tidal energy extracted by humans, comes out of some fixed 'budget' So lets compare that to what is already being consumed and think about what amount of energy generated might be realistic. Top google result tells me global energy consumption is about 5.80 x 10^20 J2 these days.[2] I guess the next question is what would be a realistic upper limit for the amount of energy we could harvest globally from the tides? Referencing the Stanford article again, we have an estimated annual energy loss of 1.73 x 10^20 J total from natural friction of the tides globally. Is it realistic to think we can harvest an equivalent amount of energy for the grid? I wonder what sort of impact a turbine project that size would have on the earth? Is it even possible? For sake of being rational, let's say we think a network of turbines 1% of that size(10^18J) is potentially possible. How many turbines might you need to make for something that size? So lets take the kite-turbines from the article at the top. Each one of the produces 1.2MW. Does that mean it produces 3.78×10^13 J annually? Or is it closer to half that(1.89×10^13J)? In a 10^13 J ballpark we would need to produce about 10^17 to approach our max limit 10^20 J harvested. Correspondingly a project 1% the size still needs 10^15(a quadrillion) of these turbines globally. That seems like a lot and it just sort of seems in my mind(maybe i'm wrong) that there would be some sort of environmental impact. Also, now that you have shrunk your project the total energy produced is now a fraction of 1% of the current total global annual energy consumption, and grows more insignificant every year consumption rises. Not sure I agree that population growth is over, but isn't it true that energy consumption per capita is also increasing? Either way I think we still have the realistic expectation of continued 2% growth in global energy consumption for the next few decades at least, doubling every 35 years. Unless we can find ways to harvest larger quantities of tidal energy without breaking the ocean it just doesn't seem like a silver bullet to me as far as climate goes. Assuming we could harvest 25% the quantity of what occurs naturally, that only gives us 0.4325x10^20J annually, which is only 7% current global consumption - in 35 years that number will only equal 3.5% of the total consumption. I guess it's a question of how much you want to screw up the environment in order to save it. TLDR, saving the planet with tidal energy seems kind of misrepresented imho. Build wooden megaliths instead. ;) [1] https://www.ucdavis.edu/climate/definitions/how-is-solar-power-generated https://www.ucdavis.edu/climate/definitions/how-is-solar-pow... [2] https://www.theworldcounts.com/challenges/climate-change/energy/global-energy-consumption https://www.theworldcounts.com/challenges/climate-change/ene...
lloeki 3y ago
> Same for solar if pea counting, but solar is really endless until the end of the solar system Imagine you wrap the Earth inside a sphere of perfectly efficient solar panels, that would be energetically troublesome! Every bit of solar panel we lay removes a bit of that overall energy flux; the question is then how much can we afford without detrimental impact. Essentially we dampen tides with these devices. Windmills are slowing the wind. How much can we afford before it has an actual detrimental effect? Also, pedantically, "renewable" is a fun word. The question of "renewable" is whether the energy/matter somehow gets back in some way... Of course there's entropy and such. Say you cut wood (CHO) and burn it. If you grow enough wood it'd recapture H2O+CO2 and you have a nice endless loop (plus entropy). That would presumably be renewable. In that sense (again, pedantically): - nuclear (and so the sun) is not renewable: reversing U/Pu/whatever fission is a teeny bit out of our league so someday the supply will dry out. Fusion as we do it (and the sun too, being main sequence) is H->He and we don't exactly know how we could reverse that so someday the supply will dry out. - fossil fuel is renewable... on a geological timescale, which is not really practical; we can't exactly grow big enough forests and bury them for millions of years to get fuel back. So someday the supply of humans surviving will dry out. - tides/wind is not renewable: we get mechanical energy but don't return it to the original place (or maybe extremely indirectly in the form of heat) So it's all named backwards! Or really there's no renewable... Essentially it all pans out because the Earth is not a closed system, there's loss in every transformation but it's balanced by the energy influx from our nearby star. So I guess the "renewable" thing is not really, it's more like "capturing energy from an astoundingly immense and complex system in a way that doesn't throw it in a runaway catastrophe one way or another before the sun exits its main sequence".
- IanCal 3y ago
  I think you're assuming renewable means infinite. > - nuclear Nuclear isn't renewable, but there's a huge amount of it and it doens't have the same problems. > (and so the sun) is not renewable: The energy we get from it is. It's not a fixed resource that we're depleting. When we burn all the coal, it's gone. Tomorrow there will be more sunlight. We're not cutting chunks off of the sun to get energy for solar. > - fossil fuel is renewable... on a geological timescale, Only some of them, and only if we change the definition of renewable. Coal is there because there weren't fungi that could break down lignin at the time. > Imagine you wrap the Earth inside a sphere of perfectly efficient solar panels, that would be energetically troublesome! Every bit of solar panel we lay removes a bit of that overall energy flux; the question is then how much can we afford without detrimental impact. We could probably benefit significantly with reducing the energy flux right now.
amelius 3y ago
And most electricity eventually turns into heat. So there's a limit there too.
dsign 3y ago
Alien archeologists from the future: "Earthlings caused a catastrophe by trying to suck every bit of tidal energy. Via tidal acceleration[^1], they made their natural satellite fall into their planet. The curious thing is that the kind of planetary technology level they deployed to extract energy from the tides was more than enough to build huge rotating habitats, which they even knew of and called O'Neill cylinders[^2]. But Earthlings called names anybody proposing the idea, and it never really took off before their moon fell on their heads. This is a textbook case of how a civilization's culture affects their development." [^1]: https://en.wikipedia.org/wiki/Tidal_acceleration https://en.wikipedia.org/wiki/Tidal_acceleration [^2]: https://en.wikipedia.org/wiki/O%27Neill_cylinder https://en.wikipedia.org/wiki/O%27Neill_cylinder
- jvanderbot 3y ago
  Yeah I sometimes wonder about our use of energy. Like two whole percent goes to cracking puzzles, and if you prove you crack those puzzles we let you buy things. Those puzzles? Guessing hashes for Blockchain. Not cancer or science or engineering, just automated planet wide gambling. Then how much is used for ads? Like top to bottom, serving ads. Must be a ton. As a planetary anthropologist, seeing how much infra we built to watch people do silly dances or say things on TikTok... Like we're so addicted to ourselves that we built all this to watch ourselves do things.
  - MRtecno98 3y ago
    I get your point with blockchain(altough i'd like a source for 2% of the entire human energy production going into it) but ads are useful actually, they make people know about what other people do which drives economy, and economy is basically a fancy word for the system that distributes each human's limited time into the various tasks society needs(which do include large scale planetary development but also for example, your local supermarket which makes you eat). As for tiktok and silly dances, humans don't need only food and water to work reliably, they also need mental health. So leisure, amenities, relationships etc.(yeah tiktok included) are an addiction in the same sense food water and oxygen are an addiction, we just need them to work.(obviously while "addiction" to leisures is in general not a real problem, addiction to a specific thing in this list is, just like addiction to a specific food is a problem. I'm not saying tiktok addiction is a good thing) If you think humanity's purpose is to develop their knowledge of the universe and techonological grasp, then i reassure you that(almost) everything we do on this spinning ball is a cog in the machine that ultimately sustains that development
usrusr 3y ago
How would solar be the same? That "reservoir" is emptying wether we hold silicon into the photon flow or not. Tides and wind aren't quite as far from just taking what is already disappearing, but even there: the natural drag of land and sea floor shapes is not only so many more orders of magnitude larger than anything we could ever build, there's also the nonlinearity of drag, if we slow down the natural flow a tiny little but the effect of natural drag will decrease accordingly and the total difference to natural flow will be much smaller than it would be if drag was linear to speed.
doubloon 3y ago
in the past twenty years the plains states like kansas and oklahoma began having earthquakes due to injection of petroleum wastewater into the ground. The government had to stop them because private industry literally does not care what gets destroyed
friend_and_foe 3y ago
Yes, you're right. What you're doing when harvesting tidal energy is introducing a friction like resistance on the moon as it revolves around the earth and on the rotation of the earth, and taking energy from it's energy of motion, that is, slowing it down. But I'd expect with the masses and velocities involved that this amount is miniscule and not even close to being measurable. That said, we didn't think we could impact the earth by burning fuel, and if something like this were adopted large scale the impact could surprise us and be a real problem. Solar isn't as limitless as you'd think. It is limited to the surface of the earth, more precisely, the surface area of the 2 dimensional disk from the perspective of the sun. And on earth, that's what drives life, so harvesting solar energy on the surface is something that, if deployed beyond what we think we need right now, can have a negative impact on the earth. Harvesting it in space and beaming it down would heat the earyy up too, as the energy is used it produces waste heat which means on a large scale even using the energy on earth would have a negative impact.

lm28469 3y ago

> (Same btw. with geothermal?). Not a chance, we're barely scratching the surface > More renewable is good.. but there is always one fear in my crazy mind about these It depends a lot on the rate of maintenance, materials used, &c. For example small windmills are next to useless: https://solar.lowtechmagazine.com/2009/04/small-windmills-put-to-the-test/ https://solar.lowtechmagazine.com/2009/04/small-windmills-pu...

zakary 3y ago

You’re right that nothing is unlimited. Luckily in this case, the energy of waves and tides is given to the oceans mostly by the gravity of the moon pulling the water as it passes overhead. Also a little bit by the wind which is fed by solar heat energy. The moon is slowly moving away from earth and eventually, in hundred of millions of years, it will impart significantly less energy into the tides. The energy that the moon gives the tides is essentially the same as how the sun gives energy to the ground with light. That is to say: If we don’t collect it, it just gets turned into another kind of energy that is absorbed by the environment. For tides and waves that would be mostly heat, and a little sound. And most of that heat would eventually be radiated back out into space. So suffice it to say, while there is a finite pool of energy stored in the tides, it is so massive we could never make a difference, and it gets recharged everyday by the moon.

HPsquared 3y ago

There's also ocean thermal energy conversion, which exploits the temperature gradient in the ocean. https://en.m.wikipedia.org/wiki/Ocean_thermal_energy_conversion https://en.m.wikipedia.org/wiki/Ocean_thermal_energy_convers...

opeon 3y ago

the tidal systems are insanely vast and powerful. the gravitational pull of the moon and the sun is so large that even if you deploy a massive amount of kits on a small surface, you're unlikely to have an impact on the tides. theoretically it's possible, but it'd require an implausible scale of deployment

ben_w 3y ago

Tidal energy comes from the moon (and the sun) pulling the oceans as the Earth spins. Extracting energy from this effectively increases the drag between the ocean and the land, which slows down the rotation of the Earth. This effect even occurs without extracting tidal energy, and some of the dinosaurs (IIRC) had 19 hour days. The amount of energy in the rotation of the Earth is so huge that this basically doesn't matter, 10 TW for 660 million years, which is into the realm of "will too much carbon be subducted for photosynthesis to continue?" timescales.

Y-bar 3y ago
I propose two possible solutions: A. Build some huge-ass rockets on the moon to accelerate it to offset any slowdown from changes in tidal energy. B. Divert a few billion tonnes of asteroids to crash into the moon's aft, adding both to the moon's velocity and mass. I believe that if we begin working on any of these solutions within a hundred thousand years or so from now we should be able to offset most of the projected long-term lengthening of the day.
- ben_w 3y ago
  You'd have to put the rockets/target the asteroid impacts on the Earth, the effect on the Moon from this interaction is to push it into a higher orbit to conserve angular momentum of the combined Earth-Moon system.
Mistletoe 3y ago
> "will too much carbon be subducted for photosynthesis to continue?" Great, you gave me a new fear. :)

jacquesm 3y ago

You're edging on the laws of thermodynamics there: on a long enough time scale all energy is non-renewable, every little bit of consumption gets you that much closer to the heat death of the universe. But given the vast reserve in that system for once humans won't be able to meaningfully affect it unless we start consuming far more than we do today. Interesting aside: that momentum is a giant energy reserve and conceivably you could rob some of it to create a means of escaping the gravity well even if there had not been any other.

card_zero 3y ago

Some numbers here: https://en.wikipedia.org/wiki/Tidal_power#Principle https://en.wikipedia.org/wiki/Tidal_power#Principle (last paragraph). Tidal energy is wasted by natural coastlines all the time, being converted into heat and erosion. If this effect is constant, it looks like the day gets longer by 7 minutes 12 seconds every 36.5 million years. (I calculated that because it's a 1% reduction in rotational energy.) Human extraction of tidal energy is much smaller than the energy wasted by tides acting on all the world's coastlines, I assume. To some extent it takes energy away from coastal erosion, which also seems fairly benign.

whatisyour 3y ago
Erosion is not always wastage.
- mft_ 3y ago
  Could you expand? I'm interested in what you're getting at.
  - Eddy_Viscosity2 3y ago
    I think he's referring to nature making less florida.
    - actionfromafar 3y ago
      OTOH there's a case to be made for keeping florida diluted.
  - idontknowifican 3y ago
    erosion actually creates nests for various sea birds
  - wongarsu 3y ago
    Erosion makes gravel and sand, which are quite useful. It also makes minerals and nutrients accessible to life. But we spend a lot of time and money managing erosion, and at the same time (often accidentally) create lots of erosion in other places. I doubt extracting tidal energy will have effects on a global scale, though it might cause some local changes

piaste 3y ago

It's good that you are aware it's a crazy thought :) Nothing wrong with looking into it though. Wikipedia offers: > Movement of tides causes a loss of mechanical energy in the Earth-Moon system: this results from pumping of water through natural restrictions around coastlines and consequent viscous dissipation at the seabed and in turbulence. This loss of energy has caused the rotation of the Earth to slow in the 4.5 billion years since its formation. During the last 620 million years the period of rotation of the Earth (length of a day) has increased from 21.9 hours to 24 hours;[10] in this period the Earth-Moon system has lost 17% of its rotational energy. While tidal power will take additional energy from the system, the effect is negligible and would not be noticeable in the foreseeable future. and there is some simple math in the [Tidal acceleration] page [0] that you may want to read. Basically, the tides slow the rotation of the Earth, with some of the energy being transferred to the Moon but most of it going into friction. The natural friction is estimated at a (surprisingly low, IMO) 3.64 TW, and at this rate the Earth will stop rotating in 50 billion years, long after the Sun has blown up. So if we want to keep the Earth spinning (albeit slowly) until the Sun goes red giant, we can afford to cut that time down to a tenth, meaning we can produce 36 TW (before conversion to electricity, i.e. ignoring efficiency). If we are being reckless and just want to use power until we figure out nuclear fusion or something better, let's say a million years or so, we can make some 180 PW from tides. But since it would almost all turn to heat, and since that is more energy than the Earth gets from the Sun, that would probably be unwise unless we find a way to get it off-planet with very high efficiency. (Global electrical energy production is currectly about 28 PWh per year, equivalent to a constant 3TW or so.) [0] https://en.m.wikipedia.org/wiki/Tidal_acceleration https://en.m.wikipedia.org/wiki/Tidal_acceleration

lloeki 3y ago
> If we are being reckless and just want to use power until we figure out nuclear fusion or something better, let's say a million years or so, we can make some 180 PW from tides. But since it would almost all turn to heat, and since that is more energy than the Earth gets from the Sun, that would probably be unwise unless we find a way to get it off-planet with very high efficiency. I think you're touching on the problem very nicely here: the problem is not "how much raw energy is there" (because there's an absolute fuckton of it) but "when does the impact of capturing this energy - thus removing it from a complex ecosystem whose stability may depend on it - and turning it into something else - thus adding to a complex ecosystem in other ways - becomes a problem", which may or may not come well before the theoretical raw energy cap.

LM358 3y ago

"Tidal Energy Is Not Renewable": https://cs.stanford.edu/people/zjl/pdf/tide.pdf https://cs.stanford.edu/people/zjl/pdf/tide.pdf Previous discussion on HN: https://news.ycombinator.com/item?id=37383283 https://news.ycombinator.com/item?id=37383283

dogtimeimmortal 3y ago
Thanks for this! Something has always bugged me when I hear about big plans for tidal energy. TLDR, the 1000 year estimate is is derived from the geometric series proof(i needed a refresher). Wolfram explains it pretty well: https://mathworld.wolfram.com/GeometricSeries.html https://mathworld.wolfram.com/GeometricSeries.html ...then i needed a refresher on exponents and logarithms: https://wou.edu/mathcenter/files/2015/09/Exponents-and-Logarithms.pdf https://wou.edu/mathcenter/files/2015/09/Exponents-and-Logar... It's good to do the math and think about the big picture sometimes. ;) p.s. i tend to feel somewhat skeptical about a lot of renewable projects i read about in the news. And even if the math all works out and it really IS The Best Solution i cant help feeling we are ignoring the elephant in the room(population growth). Maybe human beings should start preparing themselves to live with less(and be happy with that).
- ComputerGuru 3y ago
  Population growth is effectively over.
  - Cthulhu_ 3y ago
    Even if that were true (and it won't be for another 5-6 decades using current predictions at least), energy consumption is anything but. And if there is a risk of electricity usage plateauing, they'll just find something new like training AI models or spinning GPU's to churn out digital money (where said churning is entirely artificial).
- dogtimeimmortal 3y ago
  Little addition, couldn't resist sry: After reading a bit of the comments thread above, i couldn't resist adding a bit more. > The single most important assumption in this paper is that energy consumption will increase by 2% per year. Quick reality check: 1.02^1000years = 398,264,652x increase! This could potentially be an unrealistic projection. Let's consider what we know from the article(and google). Here's a few numbers pulled from the article for reference: ~1.73 x 10^20 J tidal energy lost per year naturally 5.67x10^20 J was the total global energy consumption in 2013(10^18 is 1%) So 398,264,652 x 5.67x10^18 J = 2.258 x 10^27 J! That does seem like a lot. In comparison total sunlight absorbed on earth's surface each year is roughly 3.85 x 10^24 J.[1] > It might also be that tidal energy extracted by humans, comes out of some fixed 'budget' So lets compare that to what is already being consumed and think about what amount of energy generated might be realistic. Top google result tells me global energy consumption is about 5.80 x 10^20 J2 these days.[2] I guess the next question is what would be a realistic upper limit for the amount of energy we could harvest globally from the tides? Referencing the Stanford article again, we have an estimated annual energy loss of 1.73 x 10^20 J total from natural friction of the tides globally. Is it realistic to think we can harvest an equivalent amount of energy for the grid? I wonder what sort of impact a turbine project that size would have on the earth? Is it even possible? For sake of being rational, let's say we think a network of turbines 1% of that size(10^18J) is potentially possible. How many turbines might you need to make for something that size? So lets take the kite-turbines from the article at the top. Each one of the produces 1.2MW. Does that mean it produces 3.78×10^13 J annually? Or is it closer to half that(1.89×10^13J)? In a 10^13 J ballpark we would need to produce about 10^17 to approach our max limit 10^20 J harvested. Correspondingly a project 1% the size still needs 10^15(a quadrillion) of these turbines globally. That seems like a lot and it just sort of seems in my mind(maybe i'm wrong) that there would be some sort of environmental impact. Also, now that you have shrunk your project the total energy produced is now a fraction of 1% of the current total global annual energy consumption, and grows more insignificant every year consumption rises. Not sure I agree that population growth is over, but isn't it true that energy consumption per capita is also increasing? Either way I think we still have the realistic expectation of continued 2% growth in global energy consumption for the next few decades at least, doubling every 35 years. Unless we can find ways to harvest larger quantities of tidal energy without breaking the ocean it just doesn't seem like a silver bullet to me as far as climate goes. Assuming we could harvest 25% the quantity of what occurs naturally, that only gives us 0.4325x10^20J annually, which is only 7% current global consumption - in 35 years that number will only equal 3.5% of the total consumption. I guess it's a question of how much you want to screw up the environment in order to save it. TLDR, saving the planet with tidal energy seems kind of misrepresented imho. Build wooden megaliths instead. ;) [1] https://www.ucdavis.edu/climate/definitions/how-is-solar-power-generated https://www.ucdavis.edu/climate/definitions/how-is-solar-pow... [2] https://www.theworldcounts.com/challenges/climate-change/energy/global-energy-consumption https://www.theworldcounts.com/challenges/climate-change/ene...

lloeki 3y ago

> Same for solar if pea counting, but solar is really endless until the end of the solar system Imagine you wrap the Earth inside a sphere of perfectly efficient solar panels, that would be energetically troublesome! Every bit of solar panel we lay removes a bit of that overall energy flux; the question is then how much can we afford without detrimental impact. Essentially we dampen tides with these devices. Windmills are slowing the wind. How much can we afford before it has an actual detrimental effect? Also, pedantically, "renewable" is a fun word. The question of "renewable" is whether the energy/matter somehow gets back in some way... Of course there's entropy and such. Say you cut wood (CHO) and burn it. If you grow enough wood it'd recapture H2O+CO2 and you have a nice endless loop (plus entropy). That would presumably be renewable. In that sense (again, pedantically): - nuclear (and so the sun) is not renewable: reversing U/Pu/whatever fission is a teeny bit out of our league so someday the supply will dry out. Fusion as we do it (and the sun too, being main sequence) is H->He and we don't exactly know how we could reverse that so someday the supply will dry out. - fossil fuel is renewable... on a geological timescale, which is not really practical; we can't exactly grow big enough forests and bury them for millions of years to get fuel back. So someday the supply of humans surviving will dry out. - tides/wind is not renewable: we get mechanical energy but don't return it to the original place (or maybe extremely indirectly in the form of heat) So it's all named backwards! Or really there's no renewable... Essentially it all pans out because the Earth is not a closed system, there's loss in every transformation but it's balanced by the energy influx from our nearby star. So I guess the "renewable" thing is not really, it's more like "capturing energy from an astoundingly immense and complex system in a way that doesn't throw it in a runaway catastrophe one way or another before the sun exits its main sequence".

IanCal 3y ago
I think you're assuming renewable means infinite. > - nuclear Nuclear isn't renewable, but there's a huge amount of it and it doens't have the same problems. > (and so the sun) is not renewable: The energy we get from it is. It's not a fixed resource that we're depleting. When we burn all the coal, it's gone. Tomorrow there will be more sunlight. We're not cutting chunks off of the sun to get energy for solar. > - fossil fuel is renewable... on a geological timescale, Only some of them, and only if we change the definition of renewable. Coal is there because there weren't fungi that could break down lignin at the time. > Imagine you wrap the Earth inside a sphere of perfectly efficient solar panels, that would be energetically troublesome! Every bit of solar panel we lay removes a bit of that overall energy flux; the question is then how much can we afford without detrimental impact. We could probably benefit significantly with reducing the energy flux right now.

amelius 3y ago

And most electricity eventually turns into heat. So there's a limit there too.

dsign 3y ago

Alien archeologists from the future: "Earthlings caused a catastrophe by trying to suck every bit of tidal energy. Via tidal acceleration[^1], they made their natural satellite fall into their planet. The curious thing is that the kind of planetary technology level they deployed to extract energy from the tides was more than enough to build huge rotating habitats, which they even knew of and called O'Neill cylinders[^2]. But Earthlings called names anybody proposing the idea, and it never really took off before their moon fell on their heads. This is a textbook case of how a civilization's culture affects their development." [^1]: https://en.wikipedia.org/wiki/Tidal_acceleration https://en.wikipedia.org/wiki/Tidal_acceleration [^2]: https://en.wikipedia.org/wiki/O%27Neill_cylinder https://en.wikipedia.org/wiki/O%27Neill_cylinder

jvanderbot 3y ago
Yeah I sometimes wonder about our use of energy. Like two whole percent goes to cracking puzzles, and if you prove you crack those puzzles we let you buy things. Those puzzles? Guessing hashes for Blockchain. Not cancer or science or engineering, just automated planet wide gambling. Then how much is used for ads? Like top to bottom, serving ads. Must be a ton. As a planetary anthropologist, seeing how much infra we built to watch people do silly dances or say things on TikTok... Like we're so addicted to ourselves that we built all this to watch ourselves do things.
- MRtecno98 3y ago
  I get your point with blockchain(altough i'd like a source for 2% of the entire human energy production going into it) but ads are useful actually, they make people know about what other people do which drives economy, and economy is basically a fancy word for the system that distributes each human's limited time into the various tasks society needs(which do include large scale planetary development but also for example, your local supermarket which makes you eat). As for tiktok and silly dances, humans don't need only food and water to work reliably, they also need mental health. So leisure, amenities, relationships etc.(yeah tiktok included) are an addiction in the same sense food water and oxygen are an addiction, we just need them to work.(obviously while "addiction" to leisures is in general not a real problem, addiction to a specific thing in this list is, just like addiction to a specific food is a problem. I'm not saying tiktok addiction is a good thing) If you think humanity's purpose is to develop their knowledge of the universe and techonological grasp, then i reassure you that(almost) everything we do on this spinning ball is a cog in the machine that ultimately sustains that development

usrusr 3y ago

How would solar be the same? That "reservoir" is emptying wether we hold silicon into the photon flow or not. Tides and wind aren't quite as far from just taking what is already disappearing, but even there: the natural drag of land and sea floor shapes is not only so many more orders of magnitude larger than anything we could ever build, there's also the nonlinearity of drag, if we slow down the natural flow a tiny little but the effect of natural drag will decrease accordingly and the total difference to natural flow will be much smaller than it would be if drag was linear to speed.

doubloon 3y ago

in the past twenty years the plains states like kansas and oklahoma began having earthquakes due to injection of petroleum wastewater into the ground. The government had to stop them because private industry literally does not care what gets destroyed

friend_and_foe 3y ago

Yes, you're right. What you're doing when harvesting tidal energy is introducing a friction like resistance on the moon as it revolves around the earth and on the rotation of the earth, and taking energy from it's energy of motion, that is, slowing it down. But I'd expect with the masses and velocities involved that this amount is miniscule and not even close to being measurable. That said, we didn't think we could impact the earth by burning fuel, and if something like this were adopted large scale the impact could surprise us and be a real problem. Solar isn't as limitless as you'd think. It is limited to the surface of the earth, more precisely, the surface area of the 2 dimensional disk from the perspective of the sun. And on earth, that's what drives life, so harvesting solar energy on the surface is something that, if deployed beyond what we think we need right now, can have a negative impact on the earth. Harvesting it in space and beaming it down would heat the earyy up too, as the energy is used it produces waste heat which means on a large scale even using the energy on earth would have a negative impact.