Rain Panels: Harvesting the energy of falling raindrops

https://thedebrief.org/forget-solar-panels-here-come-rain-panels/

by MadcapJake • 3 years ago

112 135 3 years ago

thedebrief.org

ilyt3• 3 years ago

I'm sure that 20W the whole panel generates every few days for an hour or two will offset the cost

JadeNB• 3 years 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• 3 years ago

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.

ilyt3• 3 years ago

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.

feoren• 3 years ago

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.

willcipriano2• 3 years ago

In the UK it would probably look a lot better, rainforests as well.

konschubert• 3 years ago

A factor 3 doesn’t compensate a factor 1000

kevinlinxc• 3 years ago

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?

angry_moose4• 3 years ago

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.

jacquesm2• 3 years ago

200 mW at best... seriously, this is bunk.

NuSkooler• 3 years ago

I would imagine these could ultimately be combined with solar.

insert why not both? meme here

koala_man• 3 years ago

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-...

Brusco_RF5• 3 years ago

You're off by 4 orders of magnitude. These "rain panels" generate <<1W/m2 even in heavy rain.

WesolyKubeczek• 3 years ago

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”™

PaulKeeble• 3 years ago

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.

monero-xmr• 3 years ago

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.

leetnewb• 3 years ago

Could theoretically put a wheel/turbine in downspouts from the roof.

chucksta• 3 years ago

I forget the ending but I think its milliwatts https://www.youtube.com/watch?v=S6oNxckjEiE

BizarroLand2• 3 years ago

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.

ramesh31• 3 years 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.

gardenfelder• 3 years ago

Heck! For many of us, that cistern would help cover for our many drought periods, electricity notwithstanding...

SoftTalker3• 3 years ago

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.

foobiekr• 3 years ago

EROI for that is almost certainly negative and it's more likely to just be a source of clogs and maintenance.

Sirikon• 3 years ago

Between sun and rain, guess which one is there more regularly nowadays.

Razengan• 3 years ago

Do we also have to guess where?

taftster• 3 years ago

Depends on your area. Both conditions are trending towards extremes. Some areas are seeing more rain that are traditionally sunny and vice versa even.

timbit423• 3 years ago

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.

lygaret• 3 years ago

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.

ragebol• 3 years ago

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...

mcdonje2• 3 years ago

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.

qbrass• 3 years ago

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

mcdonje2• 3 years ago

That's super interesting and not at all what I thought. Thank you.

mabbo• 3 years ago

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...

angry_moose4• 3 years ago

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.

Brusco_RF5• 3 years ago

Seems misleading to even mention 200W in any capacity at all.

powera• 3 years ago

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.

angry_moose4• 3 years ago

So 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.

slashdev2• 3 years ago

And way more intermittent than solar. Seems like a really dumb idea.

jurassicfoxy• 3 years ago

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."

geph2021• 3 years ago

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...

angry_moose4• 3 years ago

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.

MadcapJake2• 3 years ago

Yes, the TENG that they refer to in the paper is TriboElectric NanoGenerators https://en.m.wikipedia.org/wiki/Triboelectric_effect

jrockway2• 3 years ago

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.

dieselgate• 3 years ago

Heck it feels like the majority of my whole engineering degree was unit conversions

standardUser• 3 years ago

"The professor took a lot of joy in shooting down ideas like this though."

Gatekeepers of domain knowledge usually do.

bathMarm0t• 3 years ago

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.

mrguyorama2• 3 years ago

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.

SoftTalker3• 3 years ago

Yes it's just very, very inefficient solar power.

mrguyorama2• 3 years ago

I mean this is true of nearly every single form of power available to us, maybe excepting nuclear.

MadcapJake2• 3 years ago

No this is more like each raindrop shimmying down the sky carpet and then poking the panel to deposit the collected static charge.

zie• 3 years ago

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.

lackinnermind• 3 years ago

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'.

dojomouse3• 3 years ago

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.

eesmith• 3 years ago

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.

K0balt2• 3 years ago

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.”

pc2g4d• 3 years ago

Perhaps an unrealistic test environment?

billbr2• 3 years ago

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 …

billbr2• 3 years ago

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 ?

dojomouse3• 3 years ago

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.

itake• 3 years ago

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,

playa1• 3 years ago

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/

sacnoradhq• 3 years ago

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

amluto• 3 years ago

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.

Animats• 3 years ago

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/

chongli• 3 years ago

Thank you. Collecting rainwater in a barrel is useful for gardening if you want to save a bit of water. This nonsense? Total bunk!

LeonB2• 3 years ago

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.

benj111• 3 years ago

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.

irrational• 3 years ago

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.

LegitShady2• 3 years ago

its not. this is solar roadways level shenanigans

notyoutube• 3 years ago

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?

timbit423• 3 years ago

It would likely make more sense to put turbines on the downspouts of your roof gutters.

nerdbert• 3 years ago

That doesn't make sense either. You need a vast land area to collect water for you before you can generate enough electricity from it to be worth the cost of your equipment.

bobthepanda• 3 years ago

It would probably be better if you had a roof for solar panels that also collected rainwater for storage.

yuumei• 3 years ago

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)

ejz• 3 years ago

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?

HelloNurse• 3 years ago

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.

barbariangrunge• 3 years ago

That page has so many ads I actually got confused about what I was reading and what was an ad

abeppu• 3 years ago

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...

johnea• 3 years ago

Fuget aboud it...

jacquesm2• 3 years ago

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.

teeray• 3 years ago

Isn’t this ultimately just a really inefficient way of harvesting solar power?

wilg• 3 years ago

Basically the exact opposite of free energy.

expertentipp• 3 years ago

The energy from rain panels could be used to collapse solar panels and expand the rain panels during the rain.

tb_technical• 3 years ago

This sounds like it right out of Against the Storm

Rain Panels: Harvesting the energy of falling raindrops

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