22 ms·

How much power can we expect from rainfall?

175 points by avoidboringppl 6y ago

hirundo 6y ago
"Shockingly, and inexcusably in my opinion, the researchers only state the instantaneous power (50 W/m2) of their device..." That's not entirely fair. If Nature demanded that articles be written defensively, anticipating possible misinterpretations from non specialists, they would be very different articles with lower bandwidth for the target audience, who already know the difference between average and instantaneous power. The journal would not be improved by writing for endgadget instead. It would be nice to have an implications section that put the effects in scale, but hardly inexcusable not to.
- bastawhiz 6y ago
  "Shockingly, and inexcusably in my opinion, the manufacturers only state the clock speed (3.2ghz) of their CPU..." I suppose it depends on the intent. If the intent is to impress you with numbers by giving you a seemingly "good" number, then they're being intentionally deceptive for the sake of getting published in Nature. Does instantaneous power actually matter in context, even to knowledgeable experts?
- acidburnNSA 6y ago
  I think it is pretty misleading if they just gave the peak device power density. As in the car analogy given in TFA, if you were to burn all 270 Calories of a single Snickers bar in a thousandth of a second, your device would have a peak power of about 1 gigawatt, comparable to a large nuclear power plant. Yet if your publication said you had made a 1 GW device instead of saying that your device could power a single average home for 17 minutes, you reasonably be accused of misleading. Surely a subtext of the research was that energy sources are important to humanity. (Sidenote: Huh, a snickers bar can power a home for longer that I expected.)
  - aetherspawn 6y ago
    I would be interested to see a food chart that described how long various things can power a home in minutes. Can a salad power a home longer than a snickers bar? Or what about a potato.
    - saagarjha 6y ago
      While I don’t have numbers, your questions are easy to answer: foods with more calories in them can power your home longer. A typical 700 calorie meal can, if used 100% efficiently, can power a 10 W LED lamp for about three days.
  - wiredfool 6y ago
    Yeah, Dietary Calories are actually Kilocalories in engineering terms, so it's a pretty energy dense material.
- zentiggr 6y ago
  Actually, having read the Engadget end of things, I can see exactly what the professor is saying in his blog post. The potential energy capture from any rain-related technique is trivial, negligible is a better word. The article sounds completely clueless to anyone who understands the energy flow involved. The fact that it was written should be a professional embarrassment for that author. The fact that the original paper was treated with any respect is yet another level of embarrassment. A high school science project sounds more believable. None of the original ink / bits should have been wasted. But I suppose some sort of nanoscale power supply could be some potential use, so maybe, maybe, there's some redeeming value. But not the way the paper or the article tried to spin it.
Zenst 6y ago
I looked at this area a few decades ago and two approaches stood out as potential, though not stand out. 1) Roofs already collect a large surface area and funnel into a single point via roof guttering - so tapping the flow from the gutter run off would enable a viable volume of water turn a motor in the drain pipe as it descended and generate power. 2) Piezo electric generating from the roof, though was looking at a form of artificial grass format that would capture the wind as well as the rain hitting it, generating the vibrations to the base which would be a piezo element. The first idea, maybe has some traction, though the volume of water (yearly rainfall) with roof surface area and the napkin maths didn't show a huge gain and bit of a limited market due to rainfall you would need to generate anything noticeable. Second idea, kinda got mooted as roofs solar panels did better with the real-estate, and whilst for non south facing or some area's it may well been useful. Then the area's were solar is not as good due to latitude, well, then you have snow. So I kinda self-killed that avenue off as well. Figured that tapping the drainage flow of water from a whole area combined would work better and for that need a organised drainage system all connected and yes you do get those. Though they are also the sewage system and with that, the cleanish flow of rainwater would be less common once you factor in the rest of the mix. But I'm all for micro based generation, like a wall of small wind turbines instead of one large one and more aesthetic and palatable to add to existing buildings and area's.
- chrischen 6y ago
  Wouldn't the water back up and then you'd have to somehow contain a ton of water on your roof?
- hannasanarion 6y ago
  >Figured that tapping the drainage flow of water from a whole area combined would work better and for that need a organised drainage system all connected and yes you do get those. If I'm not mistaken, the technical term for these broad-area drainage systems is "river"
  - SlowRobotAhead 6y ago
    I think you’re on to something there. What if we made on very large, and collected lots of water at a central point and could control how much of it we use for electricity? It’s a damn good idea.
goldenkey 6y ago
I don't even have to read this article to know that the best way to harvest rainfall is already being done: rain flows into rivers and we already use hydroelectric dams!
jemski 6y ago
If you're at all interested in useless research (and not necessarily anything to do with ecology or the environment) I strongly urge you to check out the podcast "Improbable Research"[1]. I'm a long time lurker, but this felt so perfectly relevant I had to make an account and chime in. It was started awhile back, then stopped. Recently a dear friend of mine [2] became involved in re-editing the episodes and releasing them again. I know they'd appreciate the support from like-minded individuals. Hope to see more submissions like this one. It's a great thought experiment. [1]: https://www.improbable.com/category/the-weekly-improbable-research-podcast/ https://www.improbable.com/category/the-weekly-improbable-re... [2]: https://sethgliksman.wordpress.com/ https://sethgliksman.wordpress.com/ EDIT: formatting.
m463 6y ago
Tears are a higher form of power than raindrops. They can indicate joy, or solve intractable problems or eliminate traffic tickets.
jerzyt 6y ago
I'm surprised that tidal energy is not yet a big player. The amount of potential energy is massive, and it's very reliable, unless the moon falls of its orbit.
- gen220 6y ago
  I have a friend who was very interested in investing in this space, and did some research. TLDR, even though the tech is probably mature enough, the economics just aren’t there for private industry yet. It’s require major state-level funding to get it off the ground at this point, IMO. Very similar to how solar used to be. First, tidal turbines are very specialized pieces of hardware (compared to wind turbines), that have to survive corrosive brine for a decade to pay for themselves. There are not many competing manufacturers, and they are expensive. The wires connecting them to land are also expensive, both in installation but especially in maintenance. So the up front and ongoing capital expenditures are relatively high, and there isn’t an economy of scale like there is for wind turbines and solar panels. Second, there aren’t as many places that are well situated for tidal as you think. You need a basin of relatively shallow ocean, close to metropolitan power grids. There are only a handful of places like this in the world (around the UK, India, Australia), and developers would require a lot of work to get approval to develop this space, compared to solar or wind, where permit-seeking has relatively well-trodden path. That would be fine, and we’d still be in business, but third, when you compare it to the opportunity cost of investing in a more traditional (or even “renewable”) power plant of a similar output, the story really falls apart. The ROI for the builder just isn’t there, and it makes way more sense to build solar or wind farms. Some forward thinking governments are trying to help the ROI angle by providing subsidies on the generated electricity, but as a developer this is sketchy, because you still aren’t breaking even until 5-10 years, even with subsidies, and subsidies themselves can be politically fickle. When you combine this with the uncertainty attached to the turbines being relatively bespoke technology (compared to the commodity of wind turbines and solar panels), it makes sense why we haven’t seen more development here.
  - jerzyt 6y ago
    Thanks for sharing - great info. I still think that the potential energy (no pun intended) is huge, so if the engineering challenges are solved, it may not compete with solar, but should be competitive with wind.
nstart 6y ago
I absolutely love the gist of the article: interpreting quantitative research is something most of us are fundamentally illiterate on. That's definitely how I feel about it at least. Others might feel differently. That said, how does one actual build skills in this area. It feels like the author is able to do this here because it's a research paper in an area they have knowledge in. How does one build up a general ability to critically evaluate numbers in a case like this? Does one have to know how to go look up formulas? I recall an article from some time ago where authors released a paper about chocolate and health benefits or something similar but they intentionally gamed the numbers to find something that correlated. The press ate it up before the authors revealed the truth. How does one go about becoming more literate in evaluating those kinds of papers and conclusions? I'm willing to put in the time to read carefully and calculate. I just wish I knew what skills to acquire.
- knzhou 6y ago
  To evaluate stuff like this, you just need basic physics knowledge (enough to do dimensional analysis with) and estimation skills. One fun read along these lines is "The Art of Insight in Science and Engineering". For stuff like the bad social science you mentioned, often you can catch it if you know basic statistics along with the common tricks people use to p-hack. See, for example, "The garden of forking paths" by Gelman. Even if the statistical analysis is not given explicitly, or the issue is more subtle, for social science that touches on everyday life, you can usually tell if it'll hold up just with common sense. Try yourself using this quiz: https://80000hours.org/psychology-replication-quiz/ https://80000hours.org/psychology-replication-quiz/
- GuiA 6y ago
  As the author notes in the article, all this takes is basic knowledge of physics units, and the only math required is addition and multiplication. So it’s a matter of basic skills to some extent, but that’s not really the key. The way you get better at this is by doing it, a lot. Every time you read such an article, or some one relays such information to you, run the math through your head as much as you can. Make notes of the things you don’t know that prevent you from pushing the thinking further, and methodically learn about those. Don’t think of yourself in terms of particular labels - eg “I’m not much of a physics person” or “I’m a software guy” - your job is to understand the world, solve problems, answer questions. It’s a constant effort and it’s not easy. It helps to surround yourself with others with the same drive. It helps to teach, as it forces you to constantly reassess the fundamentals, and the common mistakes beginners make (see Feynman’s writing on that topic).
Animats 6y ago
Remember the "pavement that generated electricity"? [1] Raised £2.6m by crowdfunding. Turns what they really power is "exciting brand activation". By this they mean something you step on which interrogates your cell phone and ships the identity data off for marketing purposes. [1] https://pavegen.com/ https://pavegen.com/
- saagarjha 6y ago
  But you can click on the demo on their website and generate 3 Ws (wouldn’t it be nice if there was a convenient unit for this?) of energy fit each triangle you interact with!
  - leghifla 6y ago
    1 Ws is just 1 J (1W = 1J/s). Just for comparison with a more widely used unit, you need 3.6 million J to make one kWh.
porlw 6y ago
There is an interesting series of videos on Youtube about harvesting energy from gutter flow: https://www.youtube.com/watch?v=S6oNxckjEiE https://www.youtube.com/watch?v=S6oNxckjEiE
- dalemyers 6y ago
  I've been watching this and I'm quite impressed at the lengths he has gone through to make this work. Designing and creating a custom alternator is definitely one of the more impressive things I've seen in engineering videos on YouTube.
- TamDenholm 6y ago
  ive been enjoying this video series, i especially liked the video where he built his own alternator from scratch, i found it extremely educational.
alpb 6y ago
I'm having trouble understanding what the article's title actually means right now. Can HN parse this down for me, please: > Can the teardrops that fall after reading bad science writing generate renewable electricity? Yes, they can.
- mohn 6y ago
  A text is written on a scientific topic and it is so poorly written that when people read it, they cry. Can we harvest the kinetic energy in those falling teardrops and turn it into electricity? Yes. (But it is not very much energy.)
londons_explore 6y ago
This raises a question in my mind... Current hydroelectric systems rely on building a dam, say 50m high, and generating electricity from a large mass of water falling that 50m. Might another approach be to build a tower as high as possible, say 500m, and catch rain up there. You might catch less rain, but you'd have a lot more height. Obviously the challenge with this is getting a large catchment area very high up. I guess you'd need some kind of aerodynamic design like a kite to allow a massive square meter-age to stay aloft during storms.
- Retric 6y ago
  Rivers collect water over thousands of square miles. Thus turning inches of rainfall into serious amounts of water. Going 10x as high, but collecting 1/1,000,000th the water is not going to provide much power as energy is linear with height. https://en.wikipedia.org/wiki/Drainage_basin https://en.wikipedia.org/wiki/Drainage_basin The Hover Dam for example collects water across 167,800 square miles.
- steerablesafe 6y ago
  One can argue that these dams are already catching rainfall indirectly, from a very large area with very high efficiency.
  - throwaway_pdp09 6y ago
    I suspect theoretical energy generation efficiency is in disproportion to the difference in potentials (IIRC the hotter something is, the more efficiently you can extract energy from it - not more energy, but more in proportion - but IANAexpert). So while dams may catch rain efficiently, if they were 10x higher perhaps the extra potential energy usable is more than 10x
- jdietrich 6y ago
  Dams are very efficient to construct, because you take advantage of natural valleys - erosion has done most of the heavy construction work for you. The catchment area isn't just the surface area of the reservoir, but huge areas of surrounding land. Major hydroelectric reservoirs are unimaginably vast. https://en.wikipedia.org/wiki/List_of_reservoirs_by_volume https://en.wikipedia.org/wiki/List_of_reservoirs_by_volume
jzer0cool 6y ago
I had come across these videos in past: A Drop of Water can light up 100 LEDS LightBulbs. https://www.youtube.com/watch?v=fhj2BN-cbvg https://www.youtube.com/watch?v=fhj2BN-cbvg Sparks from Falling Water: Kelvin's Thunderstorm https://www.youtube.com/watch?v=rv4MjaF_wow https://www.youtube.com/watch?v=rv4MjaF_wow
Someone 6y ago
Before it starts falling, a rain drop of mass m has potential energy of mgh, with g earth’s constant of gravity, and h the height of the drop above ground. Let’s pick a drop height of 1 km (low for cloud cover). That would make the kinetic energy about 10⁴m (where m is the mass of the raindrop) At time of impact, potential energy is gone, and the drop has a kinetic energy of ½mv². Taking the (high) impact speed of the rain drop of 10m/s of the article, that’s 50m (where m again is the mass of the raindrop) So, at least 99.95% of energy is lost, heating the air or accelerating air downwards. ⇒ We could build a huge vacuum tube and let rain fall into that :-) in real life, the alternative way of not letting air take much energy from the falling water is easier to build: make larger “droplets”, and have them tailgate each other really closely (also called a waterfall)
- fnord123 6y ago
  >in real life, the alternative way of not letting air take much energy from the falling water is easier to build: make larger “droplets”, and have them tailgate each other really closely (also called a waterfall) To make this "aqua electricity" viable in the real world you would need huge bodies of water penned up and ready to be released at the appropriate time. Like the size of a lake. Pretty ridiculous.
  - gherkinnn 6y ago
    That body of water also needs to be placed high enough for it to release a waterfall. I can’t think of something. Some large geological structures, perhaps? I dunno. Maybe Elon Musk has a wacky idea to inverse this problem and build tunnels below lakes to make this work.
    - bathtub365 6y ago
      Coquitlam Lake actually has a tunnel leading to Buntzen Lake for the purposes of supplying it with water for power generation. Pipes then carry the water down to a generating station on the ocean shore. https://curiocity.com/vancouver/wp-content/uploads/2019/08/powerhouse.jpg https://curiocity.com/vancouver/wp-content/uploads/2019/08/p...
acqq 6y ago
I have also read one estimate about how fast the water would have to fall during 40 days and 40 nights of Noah flood to cover the "highest mountain" on Earth -- apparently that speed alone would kill everything on Earth and also destroy any ark made of wood. It's complicated cheating physics.
marcus_holmes 6y ago
The point of science journalism is not to report on great science, or "speak truth to power" (the point of journalism). It is (like all other online publications) to get people to click on titles so they get shown adverts. It's not really got anything to do with how educated the readers are, it's just the business model. I read this after reading the article about banning "persuading" advertising. In my head the two are related. If we remove "supported by advertising" as a viable business model for journalism, then it has to go back to being paid for by readers. We would get much better journalism if this happened. In fact, if we removed "supported by advertising" for everything, we'd get much better everything. But, as TFA says, it's worrying that Nature published this crap. Nature is supported by a non-advertising business model, and although there are lots of problems with their business model, it should in theory produce good results. I wonder what happened for this article?
- zdragnar 6y ago
  > "speak truth to power" (the point of journalism) I think that might be a bit of wishful thinking. An "investigative journalist" might take that on as a motto, but it certainly isn't true of all journalism as a general goal.
  - marcus_holmes 6y ago
    Interesting. What is the point of journalism then?
    - zdragnar 6y ago
      Obviously, that depends on where in the world you are. Assuming a press that is relatively free from government and adversarial editorial oversight, journalism can likely be summed up as "obtaining newsworthy information and publishing it to the public". According to Wikipedia, at least, there are at least 242 ethics standards for journalism worldwide, with something of a general consensus on truthfulness, accuracy, impartiality and fairness. "truth to power" may be a very narrow aspect (if, perhaps, an important one), but the simple fact is that there is plenty of newsworthy information that is fundamentally unrelated to struggles against powerful people, bureaucracies, political entities and companies. The "point" of journalism, then, is much simpler: gather information, attempt to filter it through a lens of accuracy and impartiality, and disseminate it. Not quite tautological, but there you have it.
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stevage 6y ago
I'm really skeptical about the claim that a monkey could generate 100W with a hand-crank. Serious human cyclists only produce 250-350W with their legs, and a monkey is tiny compared to that - and with only one or two hands?
- r_parthasarathy 6y ago
  The monkey number was a very rough order of magnitude comment, and shouldn't be taken too seriously. But: You’re technically correct — I didn’t actually look up the metabolic rate of monkeys. The average value for humans (2000 Calories / 24 hours) is approximately 100 Watts. Very quickly looking into it, rhesus monkeys are around 30-50 Watts average power (https://www.merckvetmanual.com/management-and-nutrition/nutrition-exotic-and-zoo-animals/nutrition-in-primates https://www.merckvetmanual.com/management-and-nutrition/nutr...), converting kcal/day into Watts. I don't know what their peak power is. Anyway, you'd need a few monkeys, but not hundreds!
ctdonath 6y ago
One sentence that should have been elaborate on a bit more to mirror/complete the article’s approach: “For a sense of scale, a solar panel gets around ten thousand times this, or 100 Watts per square meter.” Solar power has the same problem of terminal optimism as the proposed raindrop energy harvesting: in short, the source 1300W/m^2, all factors considered, becomes a real world 13W/m^2. Better than raindrops falling on my head, but still way less than most people comprehend.
- smaddox 6y ago
  Do you have a source for 13W/m^2? That looks about an order of magnitude low to me.
  - ctdonath 6y ago
    Math. Once you account for night, impingement angle, weather, atmospheric absorption, panel efficiency, dirt, seasons, storage efficiency, etc it averages out around 13W/m^2 long term. Experience. I run my “office” all summer on solar. 1m^2 panel gives 70W max; usable light about 8 hours, average over a day is 23W. Halve that for winter, overcast, etc.
    - smaddox 6y ago
      Gotcha. That still seems a bit low for where I live, assuming 18% efficient panels. Roughly 5kW.hr/m^2 averaged over the year, so 5000/24*0.18 = 37.5 W/m^2. And of course solar thermal in the desert can do quite a bit better than that.
pierrebai 6y ago
Wrong. One can harvest power from raindrop. It's called an hydro-dam. Seems to be working pretty well from what I know.
- djrogers 6y ago
  Not sure why the snark is called for - FTA explicitly calls this out: “ (There is, by the way, a very good way to harness rain for renewable electricity: let geography concentrate the water into a river, then build a dam and a hydroelectric plant!)”
  - deleted 6y ago
    [deleted]
murftown 6y ago
I didn't read the article, and I know it's more about math than an actual plan, but as a tangent I wanted to say that there's a cost to preventing rain from reaching the earth - even if we eventually returned the water there and didn't pollute or reduce the water. I think by altering this age-old cycle, we would lose some of the impact on the soil, and plants, the way it rolls downwards into increasing rivers. We've caused a lot of damage with pavement and structures. The benefit of the power generated would have to be weighed against this cost.
steve76 6y ago
People need encouragement. Criticism can also provoke destructive reactions. Weather is a source of tremendous energy. It just needs to be concentrated from the size of coastlines into something applicable to humans. Here are some ideas: 1. Industrial processes which release particulates in the air go through a scrubber to produce nano capacitors. The particulates fall to earth recovering energy. The world's water now serves as the electrical grid. Produce the right digital signal and capacitors in the water release power. 2. A normally closed solenoid opens a cistern for water collection. After rainfall, the collector closes to prevent evaporation. 3. Rain water falls on a flywheel with magnetic bearings to reduce magnetic levitation and engage a clutch to a water wheel. Put on buoys in the water, or make something really large like a rail system. 4. Fertilizers and genetics recover the energy to turn the rain water into sugar or oil. 5. Mobile towers receive a rain sensor. Content changes to adjust human behavior, like slow down messages on the highway. Or limit wildfires in times of drought, such as raising the prices of lighters and matches. Sometimes the best source of power is removing mistakes.

"Shockingly, and inexcusably in my opinion, the researchers only state the instantaneous power (50 W/m2) of their device..." That's not entirely fair. If Nature demanded that articles be written defensively, anticipating possible misinterpretations from non specialists, they would be very different articles with lower bandwidth for the target audience, who already know the difference between average and instantaneous power. The journal would not be improved by writing for endgadget instead. It would be nice to have an implications section that put the effects in scale, but hardly inexcusable not to.

bastawhiz 6y ago
"Shockingly, and inexcusably in my opinion, the manufacturers only state the clock speed (3.2ghz) of their CPU..." I suppose it depends on the intent. If the intent is to impress you with numbers by giving you a seemingly "good" number, then they're being intentionally deceptive for the sake of getting published in Nature. Does instantaneous power actually matter in context, even to knowledgeable experts?
acidburnNSA 6y ago
I think it is pretty misleading if they just gave the peak device power density. As in the car analogy given in TFA, if you were to burn all 270 Calories of a single Snickers bar in a thousandth of a second, your device would have a peak power of about 1 gigawatt, comparable to a large nuclear power plant. Yet if your publication said you had made a 1 GW device instead of saying that your device could power a single average home for 17 minutes, you reasonably be accused of misleading. Surely a subtext of the research was that energy sources are important to humanity. (Sidenote: Huh, a snickers bar can power a home for longer that I expected.)
- aetherspawn 6y ago
  I would be interested to see a food chart that described how long various things can power a home in minutes. Can a salad power a home longer than a snickers bar? Or what about a potato.
  - saagarjha 6y ago
    While I don’t have numbers, your questions are easy to answer: foods with more calories in them can power your home longer. A typical 700 calorie meal can, if used 100% efficiently, can power a 10 W LED lamp for about three days.
- wiredfool 6y ago
  Yeah, Dietary Calories are actually Kilocalories in engineering terms, so it's a pretty energy dense material.
zentiggr 6y ago
Actually, having read the Engadget end of things, I can see exactly what the professor is saying in his blog post. The potential energy capture from any rain-related technique is trivial, negligible is a better word. The article sounds completely clueless to anyone who understands the energy flow involved. The fact that it was written should be a professional embarrassment for that author. The fact that the original paper was treated with any respect is yet another level of embarrassment. A high school science project sounds more believable. None of the original ink / bits should have been wasted. But I suppose some sort of nanoscale power supply could be some potential use, so maybe, maybe, there's some redeeming value. But not the way the paper or the article tried to spin it.

Zenst 6y ago

I looked at this area a few decades ago and two approaches stood out as potential, though not stand out. 1) Roofs already collect a large surface area and funnel into a single point via roof guttering - so tapping the flow from the gutter run off would enable a viable volume of water turn a motor in the drain pipe as it descended and generate power. 2) Piezo electric generating from the roof, though was looking at a form of artificial grass format that would capture the wind as well as the rain hitting it, generating the vibrations to the base which would be a piezo element. The first idea, maybe has some traction, though the volume of water (yearly rainfall) with roof surface area and the napkin maths didn't show a huge gain and bit of a limited market due to rainfall you would need to generate anything noticeable. Second idea, kinda got mooted as roofs solar panels did better with the real-estate, and whilst for non south facing or some area's it may well been useful. Then the area's were solar is not as good due to latitude, well, then you have snow. So I kinda self-killed that avenue off as well. Figured that tapping the drainage flow of water from a whole area combined would work better and for that need a organised drainage system all connected and yes you do get those. Though they are also the sewage system and with that, the cleanish flow of rainwater would be less common once you factor in the rest of the mix. But I'm all for micro based generation, like a wall of small wind turbines instead of one large one and more aesthetic and palatable to add to existing buildings and area's.

chrischen 6y ago
Wouldn't the water back up and then you'd have to somehow contain a ton of water on your roof?
hannasanarion 6y ago
>Figured that tapping the drainage flow of water from a whole area combined would work better and for that need a organised drainage system all connected and yes you do get those. If I'm not mistaken, the technical term for these broad-area drainage systems is "river"
- SlowRobotAhead 6y ago
  I think you’re on to something there. What if we made on very large, and collected lots of water at a central point and could control how much of it we use for electricity? It’s a damn good idea.

goldenkey 6y ago

I don't even have to read this article to know that the best way to harvest rainfall is already being done: rain flows into rivers and we already use hydroelectric dams!

jemski 6y ago

If you're at all interested in useless research (and not necessarily anything to do with ecology or the environment) I strongly urge you to check out the podcast "Improbable Research"[1]. I'm a long time lurker, but this felt so perfectly relevant I had to make an account and chime in. It was started awhile back, then stopped. Recently a dear friend of mine [2] became involved in re-editing the episodes and releasing them again. I know they'd appreciate the support from like-minded individuals. Hope to see more submissions like this one. It's a great thought experiment. [1]: https://www.improbable.com/category/the-weekly-improbable-research-podcast/ https://www.improbable.com/category/the-weekly-improbable-re... [2]: https://sethgliksman.wordpress.com/ https://sethgliksman.wordpress.com/ EDIT: formatting.

m463 6y ago

Tears are a higher form of power than raindrops. They can indicate joy, or solve intractable problems or eliminate traffic tickets.

jerzyt 6y ago

I'm surprised that tidal energy is not yet a big player. The amount of potential energy is massive, and it's very reliable, unless the moon falls of its orbit.

gen220 6y ago
I have a friend who was very interested in investing in this space, and did some research. TLDR, even though the tech is probably mature enough, the economics just aren’t there for private industry yet. It’s require major state-level funding to get it off the ground at this point, IMO. Very similar to how solar used to be. First, tidal turbines are very specialized pieces of hardware (compared to wind turbines), that have to survive corrosive brine for a decade to pay for themselves. There are not many competing manufacturers, and they are expensive. The wires connecting them to land are also expensive, both in installation but especially in maintenance. So the up front and ongoing capital expenditures are relatively high, and there isn’t an economy of scale like there is for wind turbines and solar panels. Second, there aren’t as many places that are well situated for tidal as you think. You need a basin of relatively shallow ocean, close to metropolitan power grids. There are only a handful of places like this in the world (around the UK, India, Australia), and developers would require a lot of work to get approval to develop this space, compared to solar or wind, where permit-seeking has relatively well-trodden path. That would be fine, and we’d still be in business, but third, when you compare it to the opportunity cost of investing in a more traditional (or even “renewable”) power plant of a similar output, the story really falls apart. The ROI for the builder just isn’t there, and it makes way more sense to build solar or wind farms. Some forward thinking governments are trying to help the ROI angle by providing subsidies on the generated electricity, but as a developer this is sketchy, because you still aren’t breaking even until 5-10 years, even with subsidies, and subsidies themselves can be politically fickle. When you combine this with the uncertainty attached to the turbines being relatively bespoke technology (compared to the commodity of wind turbines and solar panels), it makes sense why we haven’t seen more development here.
- jerzyt 6y ago
  Thanks for sharing - great info. I still think that the potential energy (no pun intended) is huge, so if the engineering challenges are solved, it may not compete with solar, but should be competitive with wind.

nstart 6y ago

I absolutely love the gist of the article: interpreting quantitative research is something most of us are fundamentally illiterate on. That's definitely how I feel about it at least. Others might feel differently. That said, how does one actual build skills in this area. It feels like the author is able to do this here because it's a research paper in an area they have knowledge in. How does one build up a general ability to critically evaluate numbers in a case like this? Does one have to know how to go look up formulas? I recall an article from some time ago where authors released a paper about chocolate and health benefits or something similar but they intentionally gamed the numbers to find something that correlated. The press ate it up before the authors revealed the truth. How does one go about becoming more literate in evaluating those kinds of papers and conclusions? I'm willing to put in the time to read carefully and calculate. I just wish I knew what skills to acquire.

knzhou 6y ago
To evaluate stuff like this, you just need basic physics knowledge (enough to do dimensional analysis with) and estimation skills. One fun read along these lines is "The Art of Insight in Science and Engineering". For stuff like the bad social science you mentioned, often you can catch it if you know basic statistics along with the common tricks people use to p-hack. See, for example, "The garden of forking paths" by Gelman. Even if the statistical analysis is not given explicitly, or the issue is more subtle, for social science that touches on everyday life, you can usually tell if it'll hold up just with common sense. Try yourself using this quiz: https://80000hours.org/psychology-replication-quiz/ https://80000hours.org/psychology-replication-quiz/
GuiA 6y ago
As the author notes in the article, all this takes is basic knowledge of physics units, and the only math required is addition and multiplication. So it’s a matter of basic skills to some extent, but that’s not really the key. The way you get better at this is by doing it, a lot. Every time you read such an article, or some one relays such information to you, run the math through your head as much as you can. Make notes of the things you don’t know that prevent you from pushing the thinking further, and methodically learn about those. Don’t think of yourself in terms of particular labels - eg “I’m not much of a physics person” or “I’m a software guy” - your job is to understand the world, solve problems, answer questions. It’s a constant effort and it’s not easy. It helps to surround yourself with others with the same drive. It helps to teach, as it forces you to constantly reassess the fundamentals, and the common mistakes beginners make (see Feynman’s writing on that topic).

Animats 6y ago

Remember the "pavement that generated electricity"? [1] Raised £2.6m by crowdfunding. Turns what they really power is "exciting brand activation". By this they mean something you step on which interrogates your cell phone and ships the identity data off for marketing purposes. [1] https://pavegen.com/ https://pavegen.com/

saagarjha 6y ago
But you can click on the demo on their website and generate 3 Ws (wouldn’t it be nice if there was a convenient unit for this?) of energy fit each triangle you interact with!
- leghifla 6y ago
  1 Ws is just 1 J (1W = 1J/s). Just for comparison with a more widely used unit, you need 3.6 million J to make one kWh.

porlw 6y ago

There is an interesting series of videos on Youtube about harvesting energy from gutter flow: https://www.youtube.com/watch?v=S6oNxckjEiE https://www.youtube.com/watch?v=S6oNxckjEiE

dalemyers 6y ago
I've been watching this and I'm quite impressed at the lengths he has gone through to make this work. Designing and creating a custom alternator is definitely one of the more impressive things I've seen in engineering videos on YouTube.
TamDenholm 6y ago
ive been enjoying this video series, i especially liked the video where he built his own alternator from scratch, i found it extremely educational.

alpb 6y ago

I'm having trouble understanding what the article's title actually means right now. Can HN parse this down for me, please: > Can the teardrops that fall after reading bad science writing generate renewable electricity? Yes, they can.

mohn 6y ago
A text is written on a scientific topic and it is so poorly written that when people read it, they cry. Can we harvest the kinetic energy in those falling teardrops and turn it into electricity? Yes. (But it is not very much energy.)

londons_explore 6y ago

This raises a question in my mind... Current hydroelectric systems rely on building a dam, say 50m high, and generating electricity from a large mass of water falling that 50m. Might another approach be to build a tower as high as possible, say 500m, and catch rain up there. You might catch less rain, but you'd have a lot more height. Obviously the challenge with this is getting a large catchment area very high up. I guess you'd need some kind of aerodynamic design like a kite to allow a massive square meter-age to stay aloft during storms.

Retric 6y ago
Rivers collect water over thousands of square miles. Thus turning inches of rainfall into serious amounts of water. Going 10x as high, but collecting 1/1,000,000th the water is not going to provide much power as energy is linear with height. https://en.wikipedia.org/wiki/Drainage_basin https://en.wikipedia.org/wiki/Drainage_basin The Hover Dam for example collects water across 167,800 square miles.
steerablesafe 6y ago
One can argue that these dams are already catching rainfall indirectly, from a very large area with very high efficiency.
- throwaway_pdp09 6y ago
  I suspect theoretical energy generation efficiency is in disproportion to the difference in potentials (IIRC the hotter something is, the more efficiently you can extract energy from it - not more energy, but more in proportion - but IANAexpert). So while dams may catch rain efficiently, if they were 10x higher perhaps the extra potential energy usable is more than 10x
jdietrich 6y ago
Dams are very efficient to construct, because you take advantage of natural valleys - erosion has done most of the heavy construction work for you. The catchment area isn't just the surface area of the reservoir, but huge areas of surrounding land. Major hydroelectric reservoirs are unimaginably vast. https://en.wikipedia.org/wiki/List_of_reservoirs_by_volume https://en.wikipedia.org/wiki/List_of_reservoirs_by_volume

jzer0cool 6y ago

I had come across these videos in past: A Drop of Water can light up 100 LEDS LightBulbs. https://www.youtube.com/watch?v=fhj2BN-cbvg https://www.youtube.com/watch?v=fhj2BN-cbvg Sparks from Falling Water: Kelvin's Thunderstorm https://www.youtube.com/watch?v=rv4MjaF_wow https://www.youtube.com/watch?v=rv4MjaF_wow

Someone 6y ago

Before it starts falling, a rain drop of mass m has potential energy of mgh, with g earth’s constant of gravity, and h the height of the drop above ground. Let’s pick a drop height of 1 km (low for cloud cover). That would make the kinetic energy about 10⁴m (where m is the mass of the raindrop) At time of impact, potential energy is gone, and the drop has a kinetic energy of ½mv². Taking the (high) impact speed of the rain drop of 10m/s of the article, that’s 50m (where m again is the mass of the raindrop) So, at least 99.95% of energy is lost, heating the air or accelerating air downwards. ⇒ We could build a huge vacuum tube and let rain fall into that :-) in real life, the alternative way of not letting air take much energy from the falling water is easier to build: make larger “droplets”, and have them tailgate each other really closely (also called a waterfall)

fnord123 6y ago
>in real life, the alternative way of not letting air take much energy from the falling water is easier to build: make larger “droplets”, and have them tailgate each other really closely (also called a waterfall) To make this "aqua electricity" viable in the real world you would need huge bodies of water penned up and ready to be released at the appropriate time. Like the size of a lake. Pretty ridiculous.
- gherkinnn 6y ago
  That body of water also needs to be placed high enough for it to release a waterfall. I can’t think of something. Some large geological structures, perhaps? I dunno. Maybe Elon Musk has a wacky idea to inverse this problem and build tunnels below lakes to make this work.
  - bathtub365 6y ago
    Coquitlam Lake actually has a tunnel leading to Buntzen Lake for the purposes of supplying it with water for power generation. Pipes then carry the water down to a generating station on the ocean shore. https://curiocity.com/vancouver/wp-content/uploads/2019/08/powerhouse.jpg https://curiocity.com/vancouver/wp-content/uploads/2019/08/p...

acqq 6y ago

I have also read one estimate about how fast the water would have to fall during 40 days and 40 nights of Noah flood to cover the "highest mountain" on Earth -- apparently that speed alone would kill everything on Earth and also destroy any ark made of wood. It's complicated cheating physics.

marcus_holmes 6y ago

The point of science journalism is not to report on great science, or "speak truth to power" (the point of journalism). It is (like all other online publications) to get people to click on titles so they get shown adverts. It's not really got anything to do with how educated the readers are, it's just the business model. I read this after reading the article about banning "persuading" advertising. In my head the two are related. If we remove "supported by advertising" as a viable business model for journalism, then it has to go back to being paid for by readers. We would get much better journalism if this happened. In fact, if we removed "supported by advertising" for everything, we'd get much better everything. But, as TFA says, it's worrying that Nature published this crap. Nature is supported by a non-advertising business model, and although there are lots of problems with their business model, it should in theory produce good results. I wonder what happened for this article?

zdragnar 6y ago
> "speak truth to power" (the point of journalism) I think that might be a bit of wishful thinking. An "investigative journalist" might take that on as a motto, but it certainly isn't true of all journalism as a general goal.
- marcus_holmes 6y ago
  Interesting. What is the point of journalism then?
  - zdragnar 6y ago
    Obviously, that depends on where in the world you are. Assuming a press that is relatively free from government and adversarial editorial oversight, journalism can likely be summed up as "obtaining newsworthy information and publishing it to the public". According to Wikipedia, at least, there are at least 242 ethics standards for journalism worldwide, with something of a general consensus on truthfulness, accuracy, impartiality and fairness. "truth to power" may be a very narrow aspect (if, perhaps, an important one), but the simple fact is that there is plenty of newsworthy information that is fundamentally unrelated to struggles against powerful people, bureaucracies, political entities and companies. The "point" of journalism, then, is much simpler: gather information, attempt to filter it through a lens of accuracy and impartiality, and disseminate it. Not quite tautological, but there you have it.

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stevage 6y ago

I'm really skeptical about the claim that a monkey could generate 100W with a hand-crank. Serious human cyclists only produce 250-350W with their legs, and a monkey is tiny compared to that - and with only one or two hands?

r_parthasarathy 6y ago
The monkey number was a very rough order of magnitude comment, and shouldn't be taken too seriously. But: You’re technically correct — I didn’t actually look up the metabolic rate of monkeys. The average value for humans (2000 Calories / 24 hours) is approximately 100 Watts. Very quickly looking into it, rhesus monkeys are around 30-50 Watts average power (https://www.merckvetmanual.com/management-and-nutrition/nutrition-exotic-and-zoo-animals/nutrition-in-primates https://www.merckvetmanual.com/management-and-nutrition/nutr...), converting kcal/day into Watts. I don't know what their peak power is. Anyway, you'd need a few monkeys, but not hundreds!

ctdonath 6y ago

One sentence that should have been elaborate on a bit more to mirror/complete the article’s approach: “For a sense of scale, a solar panel gets around ten thousand times this, or 100 Watts per square meter.” Solar power has the same problem of terminal optimism as the proposed raindrop energy harvesting: in short, the source 1300W/m^2, all factors considered, becomes a real world 13W/m^2. Better than raindrops falling on my head, but still way less than most people comprehend.

smaddox 6y ago
Do you have a source for 13W/m^2? That looks about an order of magnitude low to me.
- ctdonath 6y ago
  Math. Once you account for night, impingement angle, weather, atmospheric absorption, panel efficiency, dirt, seasons, storage efficiency, etc it averages out around 13W/m^2 long term. Experience. I run my “office” all summer on solar. 1m^2 panel gives 70W max; usable light about 8 hours, average over a day is 23W. Halve that for winter, overcast, etc.
  - smaddox 6y ago
    Gotcha. That still seems a bit low for where I live, assuming 18% efficient panels. Roughly 5kW.hr/m^2 averaged over the year, so 5000/24*0.18 = 37.5 W/m^2. And of course solar thermal in the desert can do quite a bit better than that.

pierrebai 6y ago

Wrong. One can harvest power from raindrop. It's called an hydro-dam. Seems to be working pretty well from what I know.

djrogers 6y ago
Not sure why the snark is called for - FTA explicitly calls this out: “ (There is, by the way, a very good way to harness rain for renewable electricity: let geography concentrate the water into a river, then build a dam and a hydroelectric plant!)”
- deleted 6y ago
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murftown 6y ago

I didn't read the article, and I know it's more about math than an actual plan, but as a tangent I wanted to say that there's a cost to preventing rain from reaching the earth - even if we eventually returned the water there and didn't pollute or reduce the water. I think by altering this age-old cycle, we would lose some of the impact on the soil, and plants, the way it rolls downwards into increasing rivers. We've caused a lot of damage with pavement and structures. The benefit of the power generated would have to be weighed against this cost.

steve76 6y ago

People need encouragement. Criticism can also provoke destructive reactions. Weather is a source of tremendous energy. It just needs to be concentrated from the size of coastlines into something applicable to humans. Here are some ideas: 1. Industrial processes which release particulates in the air go through a scrubber to produce nano capacitors. The particulates fall to earth recovering energy. The world's water now serves as the electrical grid. Produce the right digital signal and capacitors in the water release power. 2. A normally closed solenoid opens a cistern for water collection. After rainfall, the collector closes to prevent evaporation. 3. Rain water falls on a flywheel with magnetic bearings to reduce magnetic levitation and engage a clutch to a water wheel. Put on buoys in the water, or make something really large like a rail system. 4. Fertilizers and genetics recover the energy to turn the rain water into sugar or oil. 5. Mobile towers receive a rain sensor. Content changes to adjust human behavior, like slow down messages on the highway. Or limit wildfires in times of drought, such as raising the prices of lighters and matches. Sometimes the best source of power is removing mistakes.