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.

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Water drop on rose leaf.

Groundwater: Management Of A Much Neglected Lifeline

It seems obvious that if you dig or drill into the soil, at some point you will hit groundwater. Drill deep enough and you will reach an aquifer containing enormous amounts of fresh water. After this you can just pump water out of these wells and you will have fresh water aplenty. Or so was the thinking among many for the longest time. As enormous the fresh water reserves in the form of groundwater are – with most liquid fresh water being groundwater – we can literally empty them faster than that they’ll refill.

As the Dust Bowl disaster painfully showed in the 1930s and drought along with surface subsidence issues as in e.g. California’s Central Valley shows today is that we cannot simply use the soil and groundwater and expect no consequences. While the 19th century saw many fresh settlers to the West’s arid and semi-arid regions like California believe in the ‘Rain follows the plow‘ mysticism, the 20th century and these first few decades of the 21st century taught us that tilling the soil and drawing groundwater for irrigation does not change an arid climate into a lush one.

Perhaps ironically, even with increasing droughts, most human settlements use stormwater drainage and combined sewage systems to carry rainwater away, rather than letting the groundwater recharge naturally. Fortunately, more and more regions these days are seeing the necessity of managing groundwater.

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Is Cloud Seeding Good, Bad, Or Ugly?

The Chinese Communist Party celebrated its centenary on the 1st of July, 2021. For such a celebration, clear skies and clean air would be ideal. For the capable nation-state, however, one needn’t hope against the whims of the weather. One can simply control it instead!

A recent paper released by Tsinghua University indicated that China had used cloud seeding in order to help create nicer conditions for its 100-year celebration. Weather modification techniques have been the source of some controversy, so let’s explore how they work and precisely what it was that China pulled off.

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Failed: Air Umbrella

About five years ago, a Kickstarter popped up for the air umbrella. It wasn’t long before the project fell apart and the company made at least some refunds. Old news, we know. But [The Action Lab] recently explored the physics behind the air umbrella and why it wouldn’t be very practical. (Video, embedded below.)

Notice we said not very practical, not unworkable. It is possible to shoot rain away from you by using pressurized air. The problem is you need a lot of air pressure. That means you also need a lot of battery. In particular, [The Action Lab] used a leaf blower and even with that velocity, there was only minimal water deflection. In other words, you are still going to get wet.

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Weather Station Gets Much-Needed Upgrades

Weather stations are a popular project, partly because it’s helpful (and interesting) to know about the weather at your exact location rather than a forecast that might be vaguely in your zip code. They’re also popular because they’re a good way to get experience with microcontrollers, sensors, I/O, and communications protocols. Your own build may also be easily upgradeable as the years go by, and [Tysonpower] shows us some of the upgrades he’s made to the popular Sparkfun weather station from a few years ago.

The Sparkfun station is a good basis for a build though, it just needs some updates. The first was that the sensor package isn’t readily available though, but some hunting on Aliexpress netted a similar set of sensors from China. A Wemos D1 Mini was used as a replacement controller, and with it all buttoned up and programmed it turns out to be slightly cheaper (and more up-to-date) than the original Sparkfun station.

All of the parts and code for this new station are available on [Tysonpower]’s Github page, and if you want to take a look at a similar station that we’ve featured here before, there’s one from three years ago that’s also solar-powered.

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Rainy Day Fun By Calculating Pi

If you need a truly random event generator, just wait till your next rainstorm. Whether any given spot on the ground is hit by a drop at a particular time is anyone’s guess, and such randomness is key to this simple rig that estimates the value of pi using raindrop sensors.

You may recall [AlphaPhoenix]’s recent electroshock Settlers of Catan expeditor. The idea with this less shocking build is to estimate the value of pi using the ratio of the area of a square sensor to a circular one. Simple piezo transducers serve as impact sensors that feed an Arduino and count the relative number of raindrops hitting the sensors. In the first video below, we see that as more data accumulates, the Arduino’s estimate of pi eventually converges on the well-known 3.14159 value. The second video has details of the math behind the method, plus a discussion of the real-world problems that cropped up during testing — turns out that waterproofing and grounding were both key to noise-free data from the sensor pads.

In the end, [AlphaPhoenix] isn’t proving anything new, but we like the method here and can see applications for it. What about using such sensors to detect individual popcorn kernels popping to demonstrate the Gaussian distribution? We also can’t help but think of other ways to measure raindrops; how about strain gauges that weigh the rainwater as it accumulates differentially in square and circular containers? Share your ideas in the comments below.

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Shapeshifting Material For Weather Adaptive Structures

Where [Isaac Newton] had his apple (maybe), [Chao Chen] found inspiration in a pine cone for a design project that lead to a water-sensitive building material. He noticed the way some pine cones are sensitive to water, closing up tight when it rains, but opening up with dry conditions. Some dissection of a pine cone revealed [Mother Nature’s] solution – different layers that swell preferentially when exposed to moisture, similar to how a bimetallic strip flexes when heated. [Chao Chen’s] solution appears to use balsa wood and a polystyrene sheet laminated to a fabric backing to achieve the same movement – the wood swells when wet and pulls the laminate flat, but curls up when dry.

As [Chao] points out, the material is only a prototype, but it looks like a winner down the road. The possibilities for an adaptive material like this are endless. [Chao] imagines a picnic pavilion with a roof that snaps shut when it rains, and has built a working model. What about window shutters that let air and light in but close up automatically in that sudden summer storm? Self-deploying armor for your next epic Super Soaker battle? Maybe there are more serious applications that would help solve some of the big problems with water management that the world faces.

Make sure you check out the video after the break, with a more decorative application that starts out looking like an [M.C. Escher] print but ends up completely different.

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