24 ms·
Rain Panels: Harvesting the energy of falling raindrops
- ilyt 3y agoI'm sure that 20W the whole panel generates every few days for an hour or two will offset the cost
- JadeNB 3y ago> I'm sure that 20W the whole panel generates every few days for an hour or two will offset the cost You can—and it's usually safe to, in the translation from actual researchers to PR departments—ceertainly doubt the viability of this claim, but the whole article is devoted to at least explicitly claiming that they're aware of the obvious problems, and can overcome them: > … the efforts to collect energy from falling raindrops have faced a technical hurdle that has made the concept inefficient and impractical. … as one might expect, the amount of power per raindrop is incredibly small. … > Now, a team of researchers says they have found a design and configuration that greatly reduces the coupling capacitance issue and one they claim could make energy-harvesting rain panels a practical reality. One key seems to be that, although you're obviously meant to think of rooftop panels, it seems more to be about large-scale installations: > “The peak power output of the bridge array generators is nearly 5 times higher than that of the conventional large-area raindrop energy with the same size, reaching 200 watts per square meter,” Li explained, “which fully shows its advantages in large-area raindrop energy harvesting.” (I do notice on re-reading that it says "… may lead to the development of rooftop, power-generating rain panels", but (1) one can freely claim that anything may lead to something else, and (2) one can claim that anything may lead to anything else, so I prefer to go by quotes from the researchers themselves.)
- Retric 3y agoRaindrops fall at 10m/s or less. The absolutely rainiest place on earth revives 12 meters of rain per year. A 1x1x12 meter block of water weighs 12,000kg going 10m/s it has KE = 1/2 M * V^2 = 6 * 10 ^ 5j. 200 watts per meter is 200j/second… So your hypothetical 200 watts per square meter at 100% efficiency assuming spherical cow types of ideal conditions could possibly provide that power for 50 minutes per year under ideal circumstances or average 0.02w/m2 over a year. And average roughly 0.002w/m2 in extremely rainy though not world record setting locations. Now, you ignore the kinetic energy in rainfall and try and harvest the potential energy when it lands at a high altitude, allowing a large collection area and large differences in altitude. But we call those things dams.
- ilyt 3y agoRight, so why they are bothering ? The technical limit is known and it is making it barely acceptable if it was free (because you still need to have dedicated inverter channel for the power conversion as characteristics are much different than what solar panels generate). And if it wasn't free or near-free it's competing with putting one more panel or adding one more battery to the system. Or... just big, cheap funnel that is feeding water generator Sure you lose some of the velocity but it is so much simpler system Like, generating energy from tiny movements have its niches (like sensors powered by piezoelectrics from vibrations of machine they monitor), but using it for raindrops just feels like a waste of time, most areas don't even get enough rain for that to matter. Now if they figured out to do it to airflow with few moving parts, that would be more interesting.
- feoren 3y agoPeak output doesn't matter: you cannot get more energy out of rain than rain has. You could build a turbine that can theoretically generate 10MW at its max speed, but if it's being pushed by ants, who cares what its max theoretical output is? Look at the top comment of this thread. Even at 100% efficiency, there is nowhere near 200 W/m^2 of energy to possibly extract from rain. Four orders of magnitude less.
- willcipriano 3y agoIn the UK it would probably look a lot better, rainforests as well.
- konschubert 3y agoA factor 3 doesn’t compensate a factor 1000
- willcipriano 3y agoThere is a sort of reverse time value of money[0] but for energy. When it's raining, it's often cloudy so solar isn't as efficient and the cost of energy goes up. Things like this become more attractive under certain conditions and I could see a use as the technology is improved and commercialized. Energy is never going to be a single technology, we will probably end up with dozens of sources in the end. https://en.m.wikipedia.org/wiki/Time_value_of_money https://en.m.wikipedia.org/wiki/Time_value_of_money
- stephen_g 3y agoIt's good to think outside the box, but unfortunately the theoretical amount of energy available (that others have calculated in the comments here) just make it a non-starter. For comparison, even on the rainiest day I've measured in the last year from my 6.6 kW photovoltaic array on my house, I made 8 kWh of energy (on a good summer's day I get around 40 kWh), with the lowest output across most of the day being 450W (less at sunrise and sunset obviously). Other have posted calculations of the maximum energy that can be expected to be collected from raindrops, and from those calculations, I doubt that with a raindrop capture device as large as my PV array you could make 8 kWh in a month.
- Brusco_RF 3y agoEven the most optimistic reading has these "rain panels" well under 1W/m^2. For comparison, peak solar irradiance is something like 1400W/m^2. This webpage has already burned more energy than that panel will ever produce.
- 3y ago
- kevinlinxc 3y ago200W/m^2 is what it says at the end right? Regardless, the tech will improve and get cheaper and this will be a nice sell for countries with less sun. Maybe eventually we could get hybrid panels powers by Sun or rain?
- angry_moose 3y agoThen their math is off by nearly 4 orders of magnitude somewhere (see other comments in the the thread). "Technology improvements" can't get around the fundamental limit in the amount of energy available to harvest. Edit: Oh, that's horribly misleading. They seem to be reporting the theoretical maximum output of this harvesting technology - e.g., how much energy could be recovered if they started blasting the panel with a firehose. The amount available in rain is on the order of .2-.4 W/m^2. At that rate you'd never recover the amount of energy as was used to produce the panel.
- jacquesm 3y ago200 mW at best... seriously, this is bunk.
- NuSkooler 3y agoI would imagine these could ultimately be combined with solar. insert why not both? meme here
- koala_man 3y agoThis is already the case according to The Guardian. Imagine solar panels that generate 200W/m2 at night when it rains. https://www.theguardian.com/environment/2018/mar/13/rain-or-shine-new-solar-cell-captures-energy-from-raindrops https://www.theguardian.com/environment/2018/mar/13/rain-or-...
- Brusco_RF 3y agoYou're off by 4 orders of magnitude. These "rain panels" generate <<1W/m2 even in heavy rain.
- deleted 3y ago[deleted]
- monero-xmr 3y agoWouldn’t it be better to have some underground cistern and as water flows down it passes through a turbine? A roof solution will generate a tiny amount of electricity.
- leetnewb 3y agoCould theoretically put a wheel/turbine in downspouts from the roof.
- chucksta 3y agoI forget the ending but I think its milliwatts https://www.youtube.com/watch?v=S6oNxckjEiE https://www.youtube.com/watch?v=S6oNxckjEiE
- BizarroLand 3y agoXKCD did a What If about this very scenario: https://what-if.xkcd.com/23/ https://what-if.xkcd.com/23/ If the generator cost $100 to buy and install, it would take nearly a century to pay back its install cost even in one of the rainiest locations in America.
- lesuorac 3y agoI found the bottom of that page much more interesting. >> What if you strapped C4 to a boomerang? Could this be an effective weapon, or would it be as stupid as it sounds? > Aerodynamics aside, I’m curious what tactical advantage you’re expecting to gain by having the high explosive fly back at you if it misses the target.
- BizarroLand 3y agoDeath before dishonor. Or at least put a remote trigger on it so you can get some splash damage on your target.
- ramesh31 3y ago> Wouldn’t it be better to have some underground cistern and as water flows down it passes through a turbine? Congrats, you've invented the hydroelectric dam.
- WesolyKubeczek 3y agoWhy not make panels that do both? Also make them harvest energy from the wind at the same time somehow. “Come Rain or Come Shine”™
- PaulKeeble 3y agoThese need a conductor to touch the raindrop which ends up in a capacitor for the charge stealing to work. Any conductor you put on top of a solar panel will block the sunlight so it will decrease efficiency. The rain collectors equally need as much surface area as possible for the conductors with their underlying capacitor area close to them. It's more likely to be effieicent to have separate panels as a result. Also rain panels can face away from the sun and suffer no ineffiencies from that. So the optimal strategy is solar facing the sun and rain on roof that is not.
- _jplc 3y agoBetween sun and rain, guess which one is there more regularly nowadays.
- Razengan 3y agoDo we also have to guess where?
- taftster 3y agoDepends on your area. Both conditions are trending towards extremes. Some areas are seeing more rain that are traditionally sunny and vice versa even.
- timbit42 3y agoThis year we've had 3 times the rain we usually have. My municipality puts a foot bridge in the river each spring and we're at the end of July and they haven't been able to put it in yet because the river is still too high. We're also getting more heat which increases how much water the sun draws up into the atmosphere creating clouds.
- lygaret 3y agoI was very surprised these weren't piezo or turbine based, but rather harvesting voltage differences in the water droplets itself. Could a piezo collect current like this, on a solar panel sized sheet? I'd imagine it's not an insignificant amount of power during a downpour.
- ragebol 3y agoWhat's the velocity and mass of a single rain drop? And how many fall in a square meter in an average year? Can't do this homework at the moment...
- mcdonje 3y ago1. Is a triboelectric nanogenerator similar to a piezoelectric component? 2. Would this work any better than a downspout turbine? I suppose that could also be wired in series.
- qbrass 3y agoIt's a miniaturized version of this: https://en.wikipedia.org/wiki/Kelvin_water_dropper https://en.wikipedia.org/wiki/Kelvin_water_dropper The actual device is: https://arxiv.org/pdf/1309.2866.pdf https://arxiv.org/pdf/1309.2866.pdf
- mcdonje 3y agoThat's super interesting and not at all what I thought. Thank you.
- mabbo 3y agoIt's just such a miniscule amount of power. Do you want to know why you don't see power dams below a certain size and height? Because gravitational potential energy is not very much. And I say this as someone who gets more excited by the Niagara falls power station than by the actual waterfall. I also question their math claiming 200w per sq meter. https://www.insidescience.org/news/how-much-power-can-we-get-raindrops https://www.insidescience.org/news/how-much-power-can-we-get...
- angry_moose 3y agoI tracked it down in another comment, the 200 w/m^2 is the maximum output of the harvester, e.g. if you started spraying the panel with a firehose. In this case, the input energy available is ~4 orders of magnitude lower than that.
- Brusco_RF 3y agoSeems misleading to even mention 200W in any capacity at all.
- powera 3y agoThis is a bad idea and cannot possibly work as well as the commenters here are imagining it. But it is easy to say "this would be big if true" and difficult to prove "these cannot make anything close to enough electricity to be useful". So, we have a comments section filled with blind hype and hope, and little actual knowledge.
- deleted 3y ago[deleted]
- angry_moose 3y agoSo 25mm/hour (1") is a fairly heavy sustained rain. Terminal velocity of rain drops is on the order of 10 m/s. Volume of a rain drop is on the order of .5ml. Total rainfall volume per m^2 is .025 m^3/hour. This is approximately 500,000 randrops/hour or about 14 drops/second. Each drop has 1/2 * m * V^2 = 25 mJ of energy. So putting it all together, this is generating 25 mJ/drop * 14 drops/second = .35 W/m^2, and that's only when its raining. (Edit: and this is assuming 100% conversion efficiency, which....no. Don't know anything about this technology, but probably cut that number in half again). Sounds a lot like Solar Freakin Roadways. Edit: Just a sidenote; back in college the best course I took was billed as a "Renewable Energy" but was really just a weekly set of unit conversion problems like this that proved how absolutely stupid most energy proposals are. We did focus a fair amount on real technologies like Wind and Solar (and analyzing the shortcomings like storage, which haven gotten better since ~2009). The professor took a lot of joy in shooting down ideas like this though.
- slashdev 3y agoAnd way more intermittent than solar. Seems like a really dumb idea.
- jurassicfoxy 3y agoNot in the PNW! > A tourist arrives in Vancouver on a rainy day. He gets up the next morning and it's still raining. In fact, it's still raining three days later. He goes out to supper and spies a young kid. Out of despair, he asks, "Hey kid, does it ever stop raining around here?!" The kid says, "How should I know, mister? I'm only six."
- irrational 3y agoI live somewhere where it rains almost constantly for 9 months out of the year. Solar panels are really only effective for the other 3 months. It would be fantastic if this was a real thing.
- LegitShady 3y agoits not. this is solar roadways level shenanigans
- notyoutube 3y agohttps://www.pv-magazine.com/2023/05/04/construction-begins-on-solar-cycling-path-in-netherlands/ https://www.pv-magazine.com/2023/05/04/construction-begins-o... I saw the construction of this thing by chance the other day. Is it so obvious it's a "shenanigan" if they're still researching it?
- LegitShady 3y agothere have been other tests of solar roadways - the costs are abysmal, the durability sucks, the efficiency is abysmal. https://www.sciencealert.com/the-world-s-first-solar-road-has-turned-out-to-be-a-disappointing-failure https://www.sciencealert.com/the-world-s-first-solar-road-ha... https://www.sciencealert.com/solar-roads-have-finally-been-tested-and-the-results-are-dissapointing https://www.sciencealert.com/solar-roads-have-finally-been-t... https://interestingengineering.com/innovation/solar-roadways-engineering-failure https://interestingengineering.com/innovation/solar-roadways... I think its someone pocketing grant money, or stupid bureaucrats spending tax money/grants for green headlines that has allowed those grifters to continue bullshitting people into building these poor decisions as "tests".
- timbit42 3y agoIt would likely make more sense to put turbines on the downspouts of your roof gutters.
- 3y ago
- bobthepanda 3y agoIt would probably be better if you had a roof for solar panels that also collected rainwater for storage.
- yuumei 3y agoAm I missing something or does this generate on the order of 3 nano watts? (They show charging a 4.7uF capacitor in 25s to 2v)
- ejz 3y agoSeems like not that much power. I guess you could build this into solar panels (some kind of coating?) so that they generate power when it rains too so that the percentage of time the panel generates power is higher. But would the decrease in efficiency justify it or would it decrease the overall wattage produced? Maybe in places where it rains a lot, like Seattle, that would be worth it to increase the percentage of time it is producing power?
- HelloNurse 3y agoHow can the huge and expensive panels required to intercept a meaningful amount of rain possibly compete with harvesting the energy of the same rainfall with small and inexpensive bronze age technology? Ridiculously high efficiency doesn't seem likely.
- barbariangrunge 3y agoThat page has so many ads I actually got confused about what I was reading and what was an ad
- abeppu 3y agoEven looking at the actual paper [1] I think no raindrop ever touched such a device during their experiments? In their extremely brief experiments section, they say "The water droplet was generated by the commercial infusion sets" which I think means ... they sprayed one of their devices with a hose? There's nothing which seems to indicate anything about droplet size, or rate of simulated rain. Did they use a pressure washer? Not describing the actual amount of "rain" they sprayed on the device also makes it unclear whether their "5 times higher" number is an apples to apples comparison, esp since 200W is a _lot_. > When the area of the raindrop energy harvesting device is 15 × 15 cm2, the peak power output of BAGs is nearly 5 times higher than that of the conventional large-area raindrop energy with the same size, reaching 200 W/m2 I think perhaps the most important sentence on the posted article is (emphasis mine): > Christopher Plain is a _Science Fiction and Fantasy novelist_ and Head Science Writer at The Debrief. [1] https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=10185664 https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=101...
- johnea 3y agoFuget aboud it...
- jacquesm 3y agoI've seen this idea in different guises many times by now, there should be one of those standard 'why your energy idea based on rain/VAT/resonance/sound/cold fusion/vacuum fluctuations won't work' checklists for this one by now.
- teeray 3y agoIsn’t this ultimately just a really inefficient way of harvesting solar power?
- wilg 3y agoBasically the exact opposite of free energy.
- expertentipp 3y agoThe energy from rain panels could be used to collapse solar panels and expand the rain panels during the rain.
- tb_technical 3y agoThis sounds like it right out of Against the Storm
- jeffreyander 3y ago[dead]