Rain Panels: Harvesting the energy of falling raindrops(thedebrief.org)
thedebrief.org
Rain Panels: Harvesting the energy of falling raindrops
https://thedebrief.org/forget-solar-panels-here-come-rain-panels/
139 comments
Love you for this! I had exactly the same “solar freaking roadways” thought, although at least that idea qualified by basic theoretical analysis of available energy and area for harvesting and conversion efficiency. It was an obviously terrible idea for other reasons :-) yet it still got a prototype…
I wasn’t sure about the droplet analysis so took your same numbers (25mm/h, 10m/s) and just worked out aggregate mass: 25mm over 1m^2 = 0.025m^3 = 25kg
0.5mv^2 => 1250J/h… so looks like we agree.
And to add a simple economic analysis of why this is such a dead-end idea:
Mawsynram, in India, is apparently the rainiest city in the world with roughly 10,000mm of annual rainfall - 10x the global average.
A given rain energy harvesting panel, deployed there, would generate 500,000J/yr… or 0.138kWh. That’s significantly less than what a typical rooftop 1m2 solar panel would generate in an hour on a sunny day. 0.138kwh is worth around 1.3cents at 10c/kWh.
A big roof might get you $1-$2/year. You couldn’t pay to clean your roof for that. You couldn’t even pay someone to answer an email enquiry about the install costs for your system for that. This solution would have to be VASTLY cheaper than paint to stand a chance of being viable.
There is a reason our existing systems to collect power from rainfall rely on vast existing landscapes and aggregation mechanisms (rivers) to concentrate the rainfall for us.
It is - in my view - a dead idea.
I wasn’t sure about the droplet analysis so took your same numbers (25mm/h, 10m/s) and just worked out aggregate mass: 25mm over 1m^2 = 0.025m^3 = 25kg
0.5mv^2 => 1250J/h… so looks like we agree.
And to add a simple economic analysis of why this is such a dead-end idea:
Mawsynram, in India, is apparently the rainiest city in the world with roughly 10,000mm of annual rainfall - 10x the global average.
A given rain energy harvesting panel, deployed there, would generate 500,000J/yr… or 0.138kWh. That’s significantly less than what a typical rooftop 1m2 solar panel would generate in an hour on a sunny day. 0.138kwh is worth around 1.3cents at 10c/kWh.
A big roof might get you $1-$2/year. You couldn’t pay to clean your roof for that. You couldn’t even pay someone to answer an email enquiry about the install costs for your system for that. This solution would have to be VASTLY cheaper than paint to stand a chance of being viable.
There is a reason our existing systems to collect power from rainfall rely on vast existing landscapes and aggregation mechanisms (rivers) to concentrate the rainfall for us.
It is - in my view - a dead idea.
If the raindrops were caught with a funnel, so the actual surface area of the device is very small, but the funnel is large, would that improve the economics? Maybe add in a water tank + hydro power to capture more gravitational potential energy from the water,
Catch them with a patch of ground and use a river as the funnel and you’re really on to something.
Maybe you could like block the river just a bit to build up like a reservoir.
It wouldn’t help with kinetic energy harvesting from the raindrops as that would go into the funnel as heat.
It might provide a way to harvest the remaining gravitational potential energy of the rain (possible funnel being your roof and guttering) but the only upside is that you could concentrate the energy with something that’s already there (and hence harvest over a smaller area). The amount of energy (and hence value) available would be even lower - unless you had a really high roof.
This is also the reason I abandoned my high school scheme of hydro turbines at the bottom of downpipes.
As the comments below say - you need to be working at the scale of a few major geographic features as a funnel before it starts to get really interesting.
It might provide a way to harvest the remaining gravitational potential energy of the rain (possible funnel being your roof and guttering) but the only upside is that you could concentrate the energy with something that’s already there (and hence harvest over a smaller area). The amount of energy (and hence value) available would be even lower - unless you had a really high roof.
This is also the reason I abandoned my high school scheme of hydro turbines at the bottom of downpipes.
As the comments below say - you need to be working at the scale of a few major geographic features as a funnel before it starts to get really interesting.
Given the explanation above, it would need to be a funnel that is cheaper than paint. If the analysis above
Is accurate (I can’t vouch for it either way) then it’s hard to imagine a material strong enough at such a low price point.
It’s possible too that the proposed mechanism is related to electrostatic charge in which case funnelling would probably interfere.
It’s possible too that the proposed mechanism is related to electrostatic charge in which case funnelling would probably interfere.
I'm wondering if the charge generated by a rain drop could be from its static charge, rather than kinetic energy conversion?
Clearly storm systems can accumulate a large charge differential with the ground (i.e. lightning), but I don't know if that's the principle behind rain drop charge harvesting. Cursory googling[1] tells me electrostatic charge may be the source?
1 - https://onlinelibrary.wiley.com/doi/abs/10.1002/smll.2023015...
Clearly storm systems can accumulate a large charge differential with the ground (i.e. lightning), but I don't know if that's the principle behind rain drop charge harvesting. Cursory googling[1] tells me electrostatic charge may be the source?
1 - https://onlinelibrary.wiley.com/doi/abs/10.1002/smll.2023015...
I'm getting well outside of my depth here, but some starting points:
Rain drops have been calculated to charge up to about 1/50 of an esu (electrostatic charge unit): https://agupubs.onlinelibrary.wiley.com/doi/10.1029/TE040i00...
Their paper is reporting 70V, so Joule/drop is on the order of 3.7E-11 J https://www.wolframalpha.com/input?i=%282.65E%E2%88%9211%29%...
(many, many orders of magnitude below the kinetic energy per drop)
It's important to note most of the research they've published is not using real rain, but laboratory generated droplets that is intended to push the harvester to the maximum.
Rain drops have been calculated to charge up to about 1/50 of an esu (electrostatic charge unit): https://agupubs.onlinelibrary.wiley.com/doi/10.1029/TE040i00...
Their paper is reporting 70V, so Joule/drop is on the order of 3.7E-11 J https://www.wolframalpha.com/input?i=%282.65E%E2%88%9211%29%...
(many, many orders of magnitude below the kinetic energy per drop)
It's important to note most of the research they've published is not using real rain, but laboratory generated droplets that is intended to push the harvester to the maximum.
I feel like if we want static charges there must be some sort of potential difference between the top of a large building and the bottom during a thunderstorm. Probably not, though.
While we're at it, can we extract any energy from lightning? Not sure if the blocker is being able to store energy delivered over a short period of time, or if it's the unlikeliness of a purpose-built structure being hit by lightning. Probably both.
While we're at it, can we extract any energy from lightning? Not sure if the blocker is being able to store energy delivered over a short period of time, or if it's the unlikeliness of a purpose-built structure being hit by lightning. Probably both.
> While we're at it, can we extract any energy from lightning?
Wikipedia has you covered.
https://en.wikipedia.org/wiki/Harvesting_lightning_energy
Wikipedia has you covered.
https://en.wikipedia.org/wiki/Harvesting_lightning_energy
Yes, the TENG that they refer to in the paper is TriboElectric NanoGenerators https://en.m.wikipedia.org/wiki/Triboelectric_effect
And way more intermittent than solar. Seems like a really dumb idea.
Not 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."
> 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."
This was true 20 years ago. Nowadays, we joke about Juneuary and this year we had Maygust. Our summers are hotter and longer, winters bringing weeks of freezing and snow where I grew up expecting a single day of snow. The calm weeks-long drizzles of my childhood are gone, replaced with days-long "atmospheric rivers" called "monsoon" in warmer climes.
Is Juneuary June in January or the other way around?
June in January, and August in May. As a kid, we wouldn't expect to even see the sun until late May.
noooo i'm sure it's the opposite here. January in June. (very accurate in 2023)
An amusing joke, but while rain is frequent in the winter in the PNW (Pacific Northwest USA) the rain is often light. Seattle residents tend not to use umbrellas unless the rain is particularly heavy. It might not be a very good power source.
All it took was a year and a half in Bellevue and I've never needed protection from the rain ever since.
Now that I'm back in California I get a lot of weird looks in the office when I go out into the rain on purpose. It's a lot easier to appreciate the rain here when it's not raining nonstop for nine months.
Now that I'm back in California I get a lot of weird looks in the office when I go out into the rain on purpose. It's a lot easier to appreciate the rain here when it's not raining nonstop for nine months.
Come spend some time in the Gulf Coast! Rain here actually physically hurts, sometimes. Big droplets (though probably not as big as the ones in the Alaskan Panhandle[0]), falling at a very rapid pace, looks and feels like a curtain of water. It's not unusual to have an inch an hour.
[0]: https://en.wikipedia.org/wiki/Ketchikan,_Alaska#/media/File:...
[0]: https://en.wikipedia.org/wiki/Ketchikan,_Alaska#/media/File:...
I get the same puzzled bemusement here in Idaho. Originally from the Oregon Coast I now relish a good rain and love a long walk through it.
Seattle actually gets less rainfall per year than any major city east of the Mississippi. It's just overcast and misty/drizzly a lot in the winter. Summers are bone dry.
Yes and: Foggy. When I was a kid, typical day was foggy til noon.
As a fun data point, the capital of Sierra Leone gets more rainfall in a single month than the PNW gets in an entire year.
I was there in the rainy season, it rained harder than I ever imagined possible for ten hours a day, every day.
I was there in the rainy season, it rained harder than I ever imagined possible for ten hours a day, every day.
You sent me down a rabbit hole. Holy crap! The AVERAGE rainfall in Sierra Leone in August is over 600mm... 23 inches!
According to Wikipedia, the average August rainfall in the capital, Freetown, is over a meter (~42")[0]. Tropical wet-and-dry climates, they're wild!
[0]: https://en.wikipedia.org/wiki/Freetown#Climate
[0]: https://en.wikipedia.org/wiki/Freetown#Climate
Freetown gets more rain in one August week than my town (Scottsdale) gets in a full YEAR
It was seriously, seriously impressive to live in that environment.
I wound up finding mould on my clothes, on my fridge, inside my Jeep, etc. etc. It was extremely hard, so after a month I drove north into Mali where the rainy season was basically over :)
I saw rain staggeringly heavy more times than I can count on the West Coast of Africa - it was truly incredible. Now that I think about it, I'm not sure I ever got it on film.
I wound up finding mould on my clothes, on my fridge, inside my Jeep, etc. etc. It was extremely hard, so after a month I drove north into Mali where the rainy season was basically over :)
I saw rain staggeringly heavy more times than I can count on the West Coast of Africa - it was truly incredible. Now that I think about it, I'm not sure I ever got it on film.
Funny, but also very inaccurate for large parts of the PNW? Maybe it is always raining in Vancouver, but summer is remarkably dry in large parts of the area.
Edit: Granted, the time of the year that solar is likely too spotty, we do have rain.
Edit: Granted, the time of the year that solar is likely too spotty, we do have rain.
I was visiting a friend in the PNW and we went for a walk. Shortly after we started, the drizzle started. Honestly, it felt great, the drizzle on the face. My clothes didn't really seem to be getting wet, either, that's how slight it was. Then, he mentioned "the rain" and I looked at him. Dude, you think this is rain? He said, yeah, it rains harder, but they consider this rain. I questioned him a bunch and it seems much of the time the rain was at drizzle level.
Now, this was in the 90s. I don't know if the rain is harder now, due to, you know, the changin' weather.
Now, this was in the 90s. I don't know if the rain is harder now, due to, you know, the changin' weather.
I think this is still very accurate. I tell folks from the south that ask if it rains a lot here, that they likely wouldn't call what we get rain. It definitely looks wet all the time in the winter. As if it always recently rained.
A drizzle is pleasant when it's warm but part of grim and cold weather when the temperature dips down (below 15-10°C?)
The other fun thing of the PNW is that it really doesn't get too cold that often. :D
Average daily high stays under 15ºC (~60ºF) from about November to April. Definitely cold enough that being damp is unpleasant, especially with any kind of breeze.
Depends on the rain. We don't have the cold rain I was used to from the south. Such that I'm perfectly fine biking in all year and basically all weather.
So you aren't wrong that it can certainly be unpleasant. But it isn't as bad as rain from where I grew up. By a long shot.
So you aren't wrong that it can certainly be unpleasant. But it isn't as bad as rain from where I grew up. By a long shot.
I lived in Vancouver for a number of years. I sure don’t miss the winter. Otherwise it’s a lovely part of the world. But the clouds and the rain really got to me.
Seattle rain festival; January 1st to December 31st.
100% it's always raining here it's especially bad in the summer.
Seattle has 156 rainy days per year, Vancouver has 168.
Honestly doesn't sound like that much to me. >150 is typical for most cities here in Germany. Munic has 193 rainy days per year.
So it just seems like the people living in the PNW are exaggerating a bit.
Honestly doesn't sound like that much to me. >150 is typical for most cities here in Germany. Munic has 193 rainy days per year.
So it just seems like the people living in the PNW are exaggerating a bit.
How are they claiming 200w/ meter^2?
That seems like an utterly fanciful figure for kinetic harvesting, and AFAIK the droplet charge also wouldn’t be enough? What am I missing here?
“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.”
That seems like an utterly fanciful figure for kinetic harvesting, and AFAIK the droplet charge also wouldn’t be enough? What am I missing here?
“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.”
Placing the rain power panel under a waterfall might generate a useful amount of energy, eventually. The key feature is some sort of vertical conductive channel that gets the charges away from each other quickly. Maybe the idea is that if they can produce power in a worst case, they can improve solar panel efficiency in low light condition. Anyway, it sounds like useful research that got into the hands of the marketing department. Lost in several layers of translation ?
It may be on some level a culture issue. Grand announcements in unreproducible results are more common in societies with a profound respect for learning. Think Dr. Pangloss …
I was just thinking the same thing. xD This is a totally useless idea (outside of Florida). If you wanted to harvest some energy reliably, there's plenty in wind and tides and ocean currents.
.35 W/m^2 vs 250 W/m^2 (after conversion losses) for solar, 2 solid orders of magnitude more energy. Even in cloudy conditions, solar is still going to deliver 15 W/m^2.
You'd be better off harnessing the power of wildlife to turn hamster wheels than spend money for the occasions to harvest a few joules when it rains. I imagine the operational costs and idle losses swamp any gains this system could ever hope to realize.
"Solar Roadways: When failure is worth 30 MILLION Dollars!"
https://youtu.be/ff-3MhQ7ri8
"EEVblog 1534 - Solar Freakin' RAILways!"
https://youtu.be/7vItnxhWRqw
.35 W/m^2 vs 250 W/m^2 (after conversion losses) for solar, 2 solid orders of magnitude more energy. Even in cloudy conditions, solar is still going to deliver 15 W/m^2.
You'd be better off harnessing the power of wildlife to turn hamster wheels than spend money for the occasions to harvest a few joules when it rains. I imagine the operational costs and idle losses swamp any gains this system could ever hope to realize.
"Solar Roadways: When failure is worth 30 MILLION Dollars!"
https://youtu.be/ff-3MhQ7ri8
"EEVblog 1534 - Solar Freakin' RAILways!"
https://youtu.be/7vItnxhWRqw
Speaking of Florida…
There are apparently something like 30M lightning strikes per year (about 1 per second!), and random sources I found suggest the average strike has an energy north of 1GJ.
1GW is somewhat respectable. Good luck collecting it.
There are apparently something like 30M lightning strikes per year (about 1 per second!), and random sources I found suggest the average strike has an energy north of 1GJ.
1GW is somewhat respectable. Good luck collecting it.
At least some research and experimentation has gone into the idea[1]. Doesn't seem like much has come from it to date, for good reason(s). But who knows, maybe somebody clever will come up with a mechanism for this that works, somewhere down the line.
[1]: https://en.wikipedia.org/wiki/Harvesting_lightning_energy
[1]: https://en.wikipedia.org/wiki/Harvesting_lightning_energy
> Sounds a lot like Solar Freakin Roadways.
Worse, power-generating sidewalks.[1]
"Our kinetic energy solutions are inspiring brands all over the world to create a meaningful and lasting connection with stakeholders around sustainability and ESG practices. Our award-winning kinetic technology uniquely uses the renewable energy generated by a footstep, with the excitement of highly engaging experiences, to educate and inspire stakeholders."
Virtue signalling monetization as a business. They've been at this for 13 years now. "Crowdfunding soon".
[1] https://www.pavegen.com/
Worse, power-generating sidewalks.[1]
"Our kinetic energy solutions are inspiring brands all over the world to create a meaningful and lasting connection with stakeholders around sustainability and ESG practices. Our award-winning kinetic technology uniquely uses the renewable energy generated by a footstep, with the excitement of highly engaging experiences, to educate and inspire stakeholders."
Virtue signalling monetization as a business. They've been at this for 13 years now. "Crowdfunding soon".
[1] https://www.pavegen.com/
I was really thrown by this parenthetical
> and analyzing the shortcomings like storage, which haven gotten better since ~2009
But then realised: it makes no sense. You’ve written “haven” — and I can’t tell if you meant to type “have” or “haven’t” … I mean “haven” falls right in between the two, your meaning is completely lost.
Overall the lecturer who relishes demolishing an idea… I grew up with that kind of intellectual attitude and had to do a lot more growing up before I realised that it’s a terrible habit in an educator. Taking actual joy in the debunking alone - that’s not the kind of joyful curiosity that a great educator would pass on, and it’s an abuse of young minds to act as if it is.
> and analyzing the shortcomings like storage, which haven gotten better since ~2009
But then realised: it makes no sense. You’ve written “haven” — and I can’t tell if you meant to type “have” or “haven’t” … I mean “haven” falls right in between the two, your meaning is completely lost.
Overall the lecturer who relishes demolishing an idea… I grew up with that kind of intellectual attitude and had to do a lot more growing up before I realised that it’s a terrible habit in an educator. Taking actual joy in the debunking alone - that’s not the kind of joyful curiosity that a great educator would pass on, and it’s an abuse of young minds to act as if it is.
Wow, I totally forgot about solar fricken roadways. That video was 2014.
Looks like they ended up getting over $6m in funding. I can’t tell how alive they are but they received some FCC approval for the wireless connectivity in Jan 2022.
“So you are saying there’s a chance?”
https://solarroadways.com/faq-funding/
Looks like they ended up getting over $6m in funding. I can’t tell how alive they are but they received some FCC approval for the wireless connectivity in Jan 2022.
“So you are saying there’s a chance?”
https://solarroadways.com/faq-funding/
I'm surprised you even bothered to do the maths.
A turbine on a down pipe isnt really worth it, so there's no way this will be.
The only plausible thing I can think of is some extremely low power rain sensor.
A turbine on a down pipe isnt really worth it, so there's no way this will be.
The only plausible thing I can think of is some extremely low power rain sensor.
Thank you. Collecting rainwater in a barrel is useful for gardening if you want to save a bit of water. This nonsense? Total bunk!
Heck it feels like the majority of my whole engineering degree was unit conversions
Yes it's just very, very inefficient solar power.
I mean this is true of nearly every single form of power available to us, maybe excepting nuclear.
It's still stellar power, but not from sol.
Yeah true. Geothermal I guess is another one.
Geothermal is nuclear with extra steps.
No this is more like each raindrop shimmying down the sky carpet and then poking the panel to deposit the collected static charge.
But if you could combine it with a solar panel, using the same footprint somehow, then you at least get some output while the sun isn't shining, which would be better than now.
I'm sure that's a huge BUT for an engineer currently, I'm not trying to say it's easy or even doable, but that's the only reasonable use I could see, if it's just a touch extra energy for a solar panel, I could see it as a value-add, if the added cost is low enough.
I'm sure that's a huge BUT for an engineer currently, I'm not trying to say it's easy or even doable, but that's the only reasonable use I could see, if it's just a touch extra energy for a solar panel, I could see it as a value-add, if the added cost is low enough.
First engineering is an iterative process.
Which means something that's engineered is made better by successive improvements from previous work.
2nd this is failing to consider different environment conditions and applications may make gathering energy from the environment in creative ways practical and useful.
Not saying this particular technology will eventually be practical from a commercial standpoint, only wishing to state it's more than just 'will this technology easily solve global energy demands'.
Which means something that's engineered is made better by successive improvements from previous work.
2nd this is failing to consider different environment conditions and applications may make gathering energy from the environment in creative ways practical and useful.
Not saying this particular technology will eventually be practical from a commercial standpoint, only wishing to state it's more than just 'will this technology easily solve global energy demands'.
Correct, but what the parent here presents is a theoretical upper bound. A working product wouldn’t even get close. When the theoretical upper bound shows that something could never aspire to more than a vastly inferior alternative to existing proven technologies, the correct approach is to abandon it rather than invest in iterative improvements.
I agree we should keep an open mind regarding creative ways of collecting energy from the environment. But we should also abandon those which are quickly demonstrated to have no meaningful potential even if we were to perfect them.
I agree we should keep an open mind regarding creative ways of collecting energy from the environment. But we should also abandon those which are quickly demonstrated to have no meaningful potential even if we were to perfect them.
> successive improvements from previous work
The first iteration produces 0.5 units. The next produces 0.75. The third produces 0.875, then 0.9375 and so on. Each iteration improves on the previous, but no engineering will surpass the 1.0 limit set by fundamental physics.
> may make gathering energy from the environment in creative ways practical and useful.
There's no end of crappy ways to produce electricity. Get electricity from walking across the floor? Yep [1]. Get electricity from exercise bikes at the gym? Yep. Get electricity from plants? Yep [2]. "Solar Freakin Roadways"? Yep. [3]
[1] https://en.wikipedia.org/wiki/Pavegen#Criticism
[2] https://www.sciencedaily.com/releases/2018/12/181212093308.h...
[3] https://en.wikipedia.org/wiki/Smart_highway#Solar_road_panel...
> it's more than just 'will this technology easily solve global energy demands'.
You know how I know it's not a "potentially game-changing breakthrough in energy harvesting"? The best place to use this is not in extracting power from rainfall but in ultra-low-head hydropower energy production. Let the water fall on the panel as drops, and extract power.
The energy involved corresponds to a head of about 3m, so it needs to be more efficient than other ULH methods, which already exist.
Yet there's no mention of that application in the article. It's not like I'm an expert on the topic, so I conclude this is a solution in search of a problem.
The first iteration produces 0.5 units. The next produces 0.75. The third produces 0.875, then 0.9375 and so on. Each iteration improves on the previous, but no engineering will surpass the 1.0 limit set by fundamental physics.
> may make gathering energy from the environment in creative ways practical and useful.
There's no end of crappy ways to produce electricity. Get electricity from walking across the floor? Yep [1]. Get electricity from exercise bikes at the gym? Yep. Get electricity from plants? Yep [2]. "Solar Freakin Roadways"? Yep. [3]
[1] https://en.wikipedia.org/wiki/Pavegen#Criticism
[2] https://www.sciencedaily.com/releases/2018/12/181212093308.h...
[3] https://en.wikipedia.org/wiki/Smart_highway#Solar_road_panel...
> it's more than just 'will this technology easily solve global energy demands'.
You know how I know it's not a "potentially game-changing breakthrough in energy harvesting"? The best place to use this is not in extracting power from rainfall but in ultra-low-head hydropower energy production. Let the water fall on the panel as drops, and extract power.
The energy involved corresponds to a head of about 3m, so it needs to be more efficient than other ULH methods, which already exist.
Yet there's no mention of that application in the article. It's not like I'm an expert on the topic, so I conclude this is a solution in search of a problem.
"The professor took a lot of joy in shooting down ideas like this though."
Gatekeepers of domain knowledge usually do.
Gatekeepers of domain knowledge usually do.
Ah yes. Physics, the ultimate gatekeeper.
If an idea doesn't work on the back of a napkin, it's done. Think about other approaches to the problem and get another napkin. I think that's what he's getting at. Analysis from first principles is hardly gatekeeping.
If an idea doesn't work on the back of a napkin, it's done. Think about other approaches to the problem and get another napkin. I think that's what he's getting at. Analysis from first principles is hardly gatekeeping.
If you think a system not passing the sniff test because basic physics shows it to be mediocre, your problem is with reality, not a physics professor.
It'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...
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...
I 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.
In this case, the input energy available is ~4 orders of magnitude lower than that.
Seems misleading to even mention 200W in any capacity at all.
Even 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=101...
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=101...
I'm sure that 20W the whole panel generates every few days for an hour or two will offset the cost
> 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.)
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.)
Raindrops 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.
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.
Right, 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.
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.
Peak 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.
200W/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?
Then 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.
"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.
200 mW at best... seriously, this is bunk.
In the UK it would probably look a lot better, rainforests as well.
A factor 3 doesn’t compensate a factor 1000
There 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
It'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.
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.
Even 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.
This webpage has already burned more energy than that panel will ever produce.
Right. So mount a wind turbine instead of this garbage
I'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.
I 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.
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.
What'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...
Can't do this homework at the moment...
This 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.
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.
I 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.
It would likely make more sense to put turbines on the downspouts of your roof gutters.
its not. this is solar roadways level shenanigans
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?
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?
there 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-ha...
https://www.sciencealert.com/solar-roads-have-finally-been-t...
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".
https://www.sciencealert.com/the-world-s-first-solar-road-ha...
https://www.sciencealert.com/solar-roads-have-finally-been-t...
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".
Wouldn’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.
> 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.
Congrats, you've invented the hydroelectric dam.
EROI for that is almost certainly negative and it's more likely to just be a source of clogs and maintenance.
Heck! For many of us, that cistern would help cover for our many drought periods, electricity notwithstanding...
I've thought about it, but water in my area is so cheap the payback would be forever.
I pay about $30/month for local utility water. It's metered, but I rarely exceed the minimum billing amount.
I pay about $30/month for local utility water. It's metered, but I rarely exceed the minimum billing amount.
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Could theoretically put a wheel/turbine in downspouts from the roof.
I forget the ending but I think its milliwatts
https://www.youtube.com/watch?v=S6oNxckjEiE
XKCD did a What If about this very scenario:
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.
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.
I 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.
>> 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.
Death before dishonor.
Or at least put a remote trigger on it so you can get some splash damage on your target.
Or at least put a remote trigger on it so you can get some splash damage on your target.
Seems 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?
1. 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.
2. Would this work any better than a downspout turbine? I suppose that could also be wired in series.
It's a miniaturized version of this:
https://en.wikipedia.org/wiki/Kelvin_water_dropper
The actual device is: https://arxiv.org/pdf/1309.2866.pdf
https://en.wikipedia.org/wiki/Kelvin_water_dropper
The actual device is: https://arxiv.org/pdf/1309.2866.pdf
That's super interesting and not at all what I thought. Thank you.
It would probably be better if you had a roof for solar panels that also collected rainwater for storage.
How 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.
I would imagine these could ultimately be combined with solar.
insert why not both? meme here
insert why not both? meme here
This 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-...
https://www.theguardian.com/environment/2018/mar/13/rain-or-...
You're off by 4 orders of magnitude. These "rain panels" generate <<1W/m2 even in heavy rain.
[deleted]
Am 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)
The energy from rain panels could be used to collapse solar panels and expand the rain panels during the rain.
That page has so many ads I actually got confused about what I was reading and what was an ad
Isn’t this ultimately just a really inefficient way of harvesting solar power?
[deleted]
Between sun and rain, guess which one is there more regularly nowadays.
Depends on your area. Both conditions are trending towards extremes. Some areas are seeing more rain that are traditionally sunny and vice versa even.
This 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.
Do we also have to guess where?
This sounds like it right out of Against the Storm
Basically the exact opposite of free energy.
Why not make panels that do both?
Also make them harvest energy from the wind at the same time somehow.
“Come Rain or Come Shine”™
Also make them harvest energy from the wind at the same time somehow.
“Come Rain or Come Shine”™
These 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.
So the optimal strategy is solar facing the sun and rain on roof that is not.
Fuget aboud it...
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.