Serious question from a beginner in electronics. For reasons I do not fully understand, I have become fixated on the idea of collecting small amounts of electricity from “interesting” sources. I don’t mean “free energy”, instead, I mean things like extracting a few mV from being so close to a AM radio tower using two tuned loop antennas in phase with each other, or getting a few mV from the rain’s kinetic energy with PTFE and using two electrodes which are shorted when a drop of rain hits it. In short, I’ve done small experiments to confirm that I can get a few mV and enough to get me excited but not much more. I know I’m not going to get much power out of this, but I’ve been able to charge a NiMH battery a few mV by being a quarter mile from an AM radio station with my antenna setup. It would be fascinating to me if I could store these small charges in something like a 5V USB power brick eventually.
The smarter idea would be for me to harvest energy with the sun or from the wind or a stream. I’m tinkering with this as well, but larger amounts of electricity scare me for right now. I guess I’ve seen enough experimental sources of harvesting electricity and I’ve gotten the itch to invent, which is a dangerous itch for a newbie like me to have.
The best advice I’ve seen online (ok, it was ChatGPT) is that it’s just not worth it to work with such small amounts of electricity, because the equipment required is too expensive and sophisticated (e.g, devices to read the charge of a capacitor without discharging it) to make anything that’s efficient enough to be worthwhile. Would you agree? Do you know of some other fascinating source of gathering electricity that I should also waste lots of time on?
I just have all these electronic components and magnets and when I move them together the numbers on multimeter get bigger. it’s neat.
Depends on the use case. It is a very good idea to harvest small amounts of energy for example to use it in a calculator or a clock or a remote control or button or light switch. This way you never need to replace batteries or have them leak and destroy the thing.
Apart from that. There aren't many use cases for those very small amounts of energy. You have to ask yourself what you're going to use that small amount of energy for. Because batteries and wires are way cheaper. And they store amounts of energy you'd need 20 years of harvesting with equipment that costs a lot more. It just depends on the use case. And for little amounts of energy, the use-cases are severely limited.
You're allowed to do this as a hobby, however ;-)
Inspiration for building something hit me when the following things happened:
I figured that I could create a small, maybe 1cm x 1cm device that could harvest 200mV when a drop of water hits it. 200mV isn’t much, but if I had 100 of them hooked together in a 10cm x 10cm square, that could be somewhere between 1-100x that voltage (though, more likely lower than that unless it’s a downpour).
Then I got thinking, well it’s water, so after the kinetic energy and whatnot has been harvested it could go into a large bucket at the top of the slope. That large bucket could then be connected to a tube that’s connected to this mini 12v dc hydro generator I bought off amazon. Of course then I could use the energy generated/harvested during the day to pump water back up to the bucket at night.. (ok, would have to be a large bucket and I realize this is still small amounts of electricity)..
I guess the reason we don’t see commercial systems like this has to do with energy density. After printing and prototyping and hours of trial and error, I may arrive at a device that can harvest/generate 0-15v depending on the weather. I imagine if I were to buy some TI energy harvesting devices and put them all together, I would be able to get enough energy to charge my phone in a day, but it may set me back the price of a house and may take up the size of a room to do so.
I guess my realisitic-use case would be to take something like what I just described and use it to power some outside LEDs. Then, everytime it rains, the LEDs would twinkle, and that would kind of be neat to see. Especially if these devices were installed in something like a raingutter system with individual LEDs, sort of lighting up roughly wherever rain drops were hit. No energy stored, just used as it’s harvested. It sounds like if it did work, it would be a big undertaking and would require quite a lot of time and money to build.
But still. twinkles!
https://youtube.com/watch?v=S6oNxckjEiE
I’ve seen that one before. Robert Murray-Smith shows a different approach which I’ve also experimented with. https://youtu.be/WYUwBGQS5_E?si=P_H8JJpeeSMnJKg-
Wow. Thanks for the link. Unfortunately this video isn't very scientific. You don't measure electrical energy in millivolts but in Jules (or watt-hours). Or in an experiment like this you would measure electrical charge (Coulomb) generated by a certain amount of water.
And I would expect the charge to come from the clouds or air or something. That would mean the water wheel shouldn't generate any electricity in his experiment.
Measuring Voltage is kind of wrong. You also get a reading of a few hundred millivolts if you randomly stick your multimeter somewhere. Or take the probes in your hands and squeeze them. That also generates a few hundred millivolts. But it isn't energy.
I'd love to see his experiments repeated in a bit more scientific way. And someone to figure out how to do that at scale. How to connect a square meter of those electrodes. And how to arrange them.
If you actually build something, make sure to document that in a blog with pictures or video for us. I kind of want to know if it's really 50W per square meter of free energy in the rain drops.
I have aluminum foil and a spray can at home :-)
Here’s the best resource I can find on the tech he’s using. https://onlinelibrary.wiley.com/doi/full/10.1002/eom2.12116
Hopefully I picked the right video here, he has hundreds. In one of the videos robert measures mA with some of these in series and powering some LEDs, I believe, or I’ve confused that with another video.
From the paper, I just skimmed but it seems that most of the energy is kinetic, then possibly converted into static? I’ll obviously need to do some actual reading.
Thx. I think it's a variant of the Kelvin water dropper
(Derek from Veritasium explains it here. At the end he explains how much energy is generated.)