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)
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.
Maybe Elon Musk has a wacky idea to inverse this problem and build tunnels below lakes to make this work.
The is a special case of the culture of repetitive, unimaginative, formulaic humor threads in which a series of people pretend to engage in a conversation in earnest, but the entire thread is satire, or meta, or fake invention, etc.
Edit: It seems to me that there is a correlation between the users who participate in these kinds of threads, and the users who damage the culture of HN in other ways. I'm not speaking of the specific users in this particular humor thread, but what I've seen in the past of humor threads in general. Clicking on their profile and viewing past comments, I've found that humor-thread participants often also engage in ideological battle, rely heavily on emotionally manipulative rhetoric, make low quality fallacious arguments, etc.
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.
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/
Anything that is either out of range on scale, or that ducks the question, is worthy of further evaluation and at least some mild skepticism. Theranos promising hundreds of blood tests out of a thimble of blood would be the former. The article referring to Volts of electricity is like a car salesman replying to 'how many seats does it have?' with 'The seats are upholstered in Fine Corinthian Leather' the statement isn't incorrect, it is just useless and, in context, intentionally misleading. Salesmen do it to sell cars, scientists to sell research, journalists to sell papers, and conspiracy theorists for, whatever reasons, I guess.
 A few examples: How many piano tuners are in New York City? How many ping pong balls could fit in a school bus?
I really don’t get when people bemoan these. Do they not get that it’s supposed to be an estimation, and it’s not actually a quiz of whether you’ve memorized a seemingly useless bit of trivia? Do they not see how it can be a useful skill to have, especially in an engineering field where you frequently deal with many orders of magnitude? (If acquiring this lock takes 100 ns, am I doing this often enough for this to cause a user-perceivable delay longer than doing it single-threaded?)
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).
In this particular case, there's the knowledge of the first basic law of thermodynamics (You can't win, the limiting case on energy conversion) and Kinematics, typically taught as the first half/third of physics. (Broadly: Mechanics/Kinematics, E/M, Optics and Waves)
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.
If I'm not mistaken, the technical term for these broad-area drainage systems is "river"
In some area's/countries - yes. What I was referring to would be your towns/cities and heck in the UK, we have most accomodation plumbed for water going in and out.
Some countries/area's have what they call storm drains.
Yes they all end up at the river, ideally for the sewage - after it is treated, though again mileage may vary from country to country.
The potential energy of a municipal sewage system, while not zero, since there is flow, is so small as to be useless, unless your city is bisected by a 400 foot cliff.
I really doubt that generators in individual houses drain pipes would be viable.
Warm clouds full of evaporated water would hit it, be forced up into colder air, and release the water.
It would then run down the rockpile and freeze, but the ice would flow down to warmer air closer to the surface, where it would melt amd you could harness the energy of the aggregated raindrops as they flow back to the sea.
If “building the wall” is politically unfeasible due to liberal tears, you could find some drifting continent and get it to smash into another continent. Wait a while, and the continents smashing together will make the wall for you.
No need for balloons, just be patient.
the purpose of a gutter is to direct the water to areas where it can seep into the ground without damaging the house (while carrying away leaves and other things that would rot and damage the roof), at least where I live, a motor in the drain pipe would slow down the gutters in its function, which you don't want to slow down in some of the rain you get in Denmark, and finally would leave it open to more easily blocking the drain. Of course one could put a guard up on the gutter to keep large things from coming down but as I understand it gutter guards aren't really a good idea https://www.cleanproguttercleaning.com/are-gutter-guards-wor... (from a company trying to sell gutter cleaning services so maybe should be taken with grain of salt but the arguments sound pretty reasonable) and at any rate I believe would still have to let things through that would be problematic for the motor to have through.
So essentially having a motor in the gutter for generating energy would mean the gutter could no longer be able to perform its function as a gutter and a new way to handle that would need to be devised.
1. How to Harvest Free Energy From Your Roof with a Hydro Electric Generator! https://youtu.be/S6oNxckjEiE
2. 3D Printed Alternator vs. DC Generator for More POWER From the Rain! https://youtu.be/YLb4enCgnP4
3. Fidgeting With Turbines! https://youtu.be/vify0k2sHlQ
4. Charge a Smartphone With The RAIN!!! https://youtu.be/amu5LJaDUPY
The mine drainage system was later gradually replaced with steam engines, however there is a ~megawatt hydropower electrical plant still functional.
The problem with these is terrible efficiency as you scale down, due to fluid dynamics and the added redundancy from having multiple small units rather than one large one. This is why generators are huge.
Back of the envelop calculations would have break even after about 100 years...
It was started awhile back, then stopped. Recently a dear friend of mine  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.
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.
The Hover Dam for example collects water across 167,800 square miles.
So while dams may catch rain efficiently, if they were 10x higher perhaps the extra potential energy usable is more than 10x
On the flipside, there's the question of how far down you can get the water to drop, before feeding it to your generator. This is something already taken advantage of - https://en.wikipedia.org/wiki/K%C3%B6lnbrein_Dam#Reisseck-Kr...
I guess considering that, the only way to make it viable is if there isn't much rainfall, or if the terrain is very flat/porus, or if you can make the collection devices very cheap (for example a kite that flies into a cloud and can collect a few tens of liters per second 1km up could generate 100 kilowatts, which is a lot less than a big wind turbine, so needs to be a lot cheaper to compete)
Sure potential energy is linear with height, but energy conversion efficiency is I think non-linear. You can I think collect more than 10x useful energy from an object that is 10x as hot. Equally I suspect you can get more than 10x useful energy from a column of water 10 miles high than from a column of water 1 mile high.
I'm pretty sure your idea won't work but that doesn't mean it can't possibly work. It's more likely harvesting wind energy via kites (as has been proposed) is more realistic, but still, I don't like dismissing dumb ideas. Sometimes they can be made useful.
For a given flow rate, no.
High pressure water can be fairly efficiently converted to electrical energy, which itself can fairly efficiently be converted between low voltage+high current to high voltage+low current.
All the conversions are linear and well understood - there is no magic squared here to make this idea magic.
> High pressure water can be fairly efficiently converted...
And lower pressure less efficiently converted? Therefore the higher the column, the higher the pressure and the better the efficiency of the conversion?
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.
I'm not bullish on the future of tidal power--there may be some use case for it, but the reality of the engineering challenges associated with putting hardware in a marine tidal zone for years at a time presents serious obstacles with limited advantages over versus a wind turbine or solar array of the same capacity.
I'm curious, do you know if your friend ended up investing?
He was looking specifically to invest in Gujarat, because of family ties. However, the government decided the project wasn’t worth it and binned it. IIRC they were more interested in developing solar. I tried googling around for articles related to it, this the best I could find: https://energy.economictimes.indiatimes.com/news/renewable/i...
Australian government wasn’t super interested in developing tidal resources because of the coal special interest groups, but also because solar resources are lower hanging fruit. The UK project was very legitimate and institutionally mature, but was more of a science project for proving the technology than an investment opportunity.
It was also the largest for 45 years until a bigger one opened in South Korea: https://en.wikipedia.org/wiki/Sihwa_Lake_Tidal_Power_Station.
Not sure if someone has an analysis about why those aren't more widespread ? It seems like the existing ones are pretty massive and in very specific spots, maybe smaller installations aren't cost-effective enough.
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?
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.
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.
Maybe I should rephrase my original to be "the important point of journalism is speaking truth to power".
Seeing what a farce the UK media is making of Assange's trial (sorry, extradition hearing), it seems we're nowhere near that at the moment.
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.
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.
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.
And of course solar thermal in the desert can do quite a bit better than that.
A Drop of Water can light up 100 LEDS LightBulbs.
Sparks from Falling Water: Kelvin's Thunderstorm
It's complicated cheating physics.
> Can the teardrops that fall after reading bad science writing generate renewable electricity? Yes, they can.
(But it is not very much energy.)
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.
(Sidenote: Huh, a snickers bar can power a home for longer that I expected.)
Can a salad power a home longer than a snickers bar? Or what about a potato.
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.
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?