Harvesting Mechanical Energy From Falling Rain

Collecting energy from various small mechanical processes has always been something that’s been technically possible, but never done on a large scale due to issues with cost and scalability. It’s much easier to generate electricity in bulk via traditional methods, whether that’s with fossil fuels or other proven processes like solar panels. That might be about to change, though, as a breakthrough that researchers at Georgia Tech found allows for the direct harvesting of mechanical energy at a rate much higher than previous techniques allowed.

The method takes advantage of the triboelectric effect, which is a process by which electric charge is transferred when two objects strike or slide past one another. While this effect has been known for some time, it has only been through the advancements of modern materials science that it can be put to efficient use at generating energy, creating voltages many thousands of times higher than previous materials allowed. Another barrier they needed to overcome was how to string together lots of small generators like this together. A new method that allows the cells to function semi-independently reduces the coupling capacitance, allowing larger arrays to be built.

The hope is for all of these improvements to be combined into a system which could do things like augment existing solar panels, allowing them to additionally gather energy from falling rain drops. We’d expect that the cost of this technology would need to come down considerably in order to be cost-competitive, and be able to scale from a manufacturing point-of-view before we’d see much of this in the real world, but for now at least the research seems fairly promising. But if you’re looking for something you can theoretically use right now, there are all kinds of other ways to generate energy from fairly mundane daily activities.

40 thoughts on “Harvesting Mechanical Energy From Falling Rain

  1. The amount of energy that can be harvested is so tiny, it’s not worth building the infrastructure to harvest it. For things that are far away from a regular source of power, we already have solar panels.

    1. If I had not joined the institute of naysayers, I would say this is an exiting development with significant potential, but the other members would disprove. Oh why did the wright brothers not make provision for trolley dollies on their first flight. nay nay nay.

        1. To be fair, solar roadways is one of the less crazy ideas on the planet. In hindsight they font work, but I would assume that a majority of tech savvy folks did not immediately see problems there.

          Compare that to self filling water bottles or – what was the rebreather thing called? – cyberlungs?

          1. No.

            It was obviously a terrible idea to anybody who’s mind isn’t ‘so open their brain fell out’. Maybe worth considering when _all_ the roofs are covered in solar, but a moments consideration says it won’t be needed then. Just dumb gofundme bait.

            You can find discussions archived on places like slashdot (Used to be a decent tech discussion site, 20 or so years ago. Now the only people left are the _same_ assholes, apparently their egos live there)…Only credulous fools EVER thought it was a good idea.

            Still a fool and their money were lucky to get together in the first place. Taking money from solar road believers and putting it into the pockets of solar road scammers increased it’s utility.

        2. Bad ideas will inevitably fail, few developments are the product of a single mind, ideas begat more ideas and eventually perhaps, success.
          I have now been suspended from the institute, Oh nay nay and thrice nay.

          1. All ideas should be funded and left to possibly fail?

            There is plenty of grey between believing anything and naysaying everything. This (TFA) is an example of an idea where the Venn diagram people calling it dumb and people who aren’t scared of numbers is a circle.

            ‘Naysayer’ has historically been the cry of credulous fools. Which is fine, for credulous fools outside government. Their funds.

    2. The original paper claims:

      “ When the area of the raindrop energy harvesting device is 15 × 15 cm^2 , the peak power output of BAGs reached 200 W/m^2”

      Unclear whether they used a firehose or actual rain to achieve that.

      PS: Hackaday writers, for science news please link to the original papers instead of the PR fluff pieces or journalistic interpretations thereof.

      1. Reading a bit further into the paper, 200W/m^2 seems to refer to the instantaneous power when a drop hits a BAG cell. So divide by a big number to get realistic continuous power.

        1. “ At the dripping frequency of 10Hz (The test method for frequencies is described in Note S4 in the ESM), the BAGs with 5 × 5 cm2, 7.5 × 7.5 cm2, 15 × 15 cm2 AS takes about 24 s to charge the 4.7 µF capacitor to 2 V, l.7 V, and 0.7 V respectively, which shows that the smaller the sub-electrode is, the more favorable for charging”

          Not too shabby for some energy harvesting applications. Though 10 drops per second is quite the downpour.

          1. But we do have downpours. Think of it maybe as a contribution to the whole electric source instead of the main. Power obtained from diversifying sources rather than one main one.

          1. What if I want to measure stalagmite growth with my solar-powered calipers?

            Anyways, the paper seems to be very reproducible, if the FEP film is the same stuff as sold for SLA 3D printers.

          2. If you can make this an easy to make system practically scaleable and slip it into other systems like solar seamlessly doesn’t really matter what the power output rates are very much. In the same way those multi layer solar panels that harvest a wider spectrum to bump up overall efficiency, or the combined water pre-heat PV panel may one day really become common in the wild and give the average solar panel a pretty significant bump in functional efficiency should the manufacturing become scalable and cheap.

            Though this does clearly have some way to go before it gets there (if it does). I wonder what the terminal velocity of the varied sizes of rain drop are as to what the upper ceiling for the rain impact derived power could be. Though it seems the better placement would be along sea defence walls – those always get ‘rain’ and if the system is tough enough to take the wave action directly…

          3. >doesn’t really matter what the power output rates are

            As long as you exceed the self-discharge rate of your storage capacitors. Larger electrolytics tend to leak microamps per microfarad, and you need very large storage because it doesn’t actually rain that often.

  2. LED’s are the favorite demo device for triboelectric power research, because they will turn on visibly with less than a microamp of current and appear to remain on for much longer than the actual duty cycle, thanks to persistence of vision. Note the use of green LEDs which humans perceive to be brighter per watt than the other colors.

    Even if you have a hundred LEDs like that on a board, making them appear visibly “on” only takes about 1-2 nanoWatts of power on average, which is a million times less than what it takes to run a pocket calculator. A tiny solar under direct sunlight will provide you with 1 mW/cm^2

  3. The frequency and density of rain drops at terminal velocity seems a bit unreliable. The amount of energy wasted by typical human activity, however, seems to have global effects!

  4. Never mind: “cost of this technology would need to come down . . . and be able to scale from a manufacturing point-of-view”. Where do people live that the rain falls so torrentially this would be feasible? Harry Harrison’s Deathworld? Ireland?

    Research is great, but good reporting has a duty to impart a sense of scale grounded in reality; not just breathlessly fawn.

    I admit I’m jaded, 30 years of reading Popular Science and Popular Mechanics has shown how much vaporware and pipe dreams mean in day to day life.

    Meanwhile I was noting just last night that evem in this age of google connected Doom playing thermostats I can’t recall the last one that monitored internal and external humidity to open and close the windows and save you money on air conditioning.

    Somewhere there is a crossroads between low hanging fruit and pie in the sky experimental science. I guess like Dirk Gently I would like to see a holistic approach with the “interconnected-ness of all things” considered.

  5. I live in an area that is powered by falling snow.

    Of course it has to fall on some mountains, melt, be captured behind a series of dams then run through turbines, but why let a little complexity get in the way of a great headline?

  6. I haven’t done the math, but I suspect you could get more energy by using the weight of the water running off a roof to get more energy than this. The higher the roof the better.

    That of course assumes you actually have rain. I live in southern Arizona and we haven’t had a single rain storm at our house yet this monsoon season. A few rare squalls have been seen in the area, but it is very localized.

  7. i refuse to be the naysayer so let’s do math:

    Total rainfall over the earth (yearly):
    505,000 cubic kilometres

    Terminal velocity of the average raindrop: 5m/s

    100% coverage of the landmass gives us 107,000 cubic kilometres of precipitation that could be harvested without just blanketly saying voer the earth in an umbrella.

    That gives us: 1.3375e+15 Joules.

    Not inconsiderable that’s for sure but then you can use your own average coverage vs transmission vs impacts on soil and plants vs production cost before you decide if it’s feasible at all even with 100% efficiency.

    1. Consider what people who were ‘promised no math’ would make of your post. All they’d see is a number they don’t know how to read, google tells them that’s a buttload of energy though.

      Is ‘credulous fool’ the opposite of naysayer? ‘Fraud victim’?

    1. Not nearly cheap enough.
      Not in the rainiest environment.
      Not during Indian Monsoon, ignoring the rest of the year’s losses.

      also: Complications. Lots and lots of complications.

      1. I was refering to the individual tinkerer, when it rains the average person can more easily get a simple generator in the drain than to cover his roof with this experimental stuff.
        And of course you lose the space for solar panels if you do a rain-drop power thing, even if it was working as well as suggested and available to joe average for a doable price.

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