Gravity Battery!

Long story short, I ended up crossing paths with Charlotte is Creative recently and that ultimately led to a conversation with a Charlotte artist for which I agreed to co-pitch a fairly improvisational art installation grant with- mostly because it sounds fun with potential for something more aligned with my interests in innovation. This is an environmental themed piece involving illuminated/animated/dynamic light features powered by sustainable (solar) electricity. To take the theme a step further and leverage the fact that this is a stationary exhibit that doesn’t necessarily require a portable chemical battery (the type commonly used in devices and EV’s). Instead, it converts sunlight to electricity which is used to power a motor & gearset and then a pulley to lift a ballast (eg. a 400lb rainbarrel or boulder, or it could just pump some water. Still TBD)

Ultimately energy is stored as potential energy against gravity instead of in a battery. The overall output is a primarily a function of weight & height. This energy can get converted back to electricity, and this can happily happen after the sun sets. I thought it would be a fun teaching opportunity to scale it down as a proof of concept, so that’s what we did.

As an overview, D explains what’s going on with the conservation of energy below:

In my grant pitch I cited a boulder or (water?) barrel as ballast, but here we’re using a little tin bucket with a billiard ball in it. I pulled a couple of dead AA batteries out of the trash to use as opposing ballast so that my drive cord will get some friction applied to it. I turned an acrylic pulley which is just barely wide enough to keep a cord on track with a bit of luck. I didn’t want to get too crazy with the load since we’re just single side loading the output axle and it’s just a cheap plastic assembly. This seems to be the right balance. For the cord, I simply pulled out a length of black TPU filament (85A I think) which is pretty ideal for strength, cost, and especially friction. It’s nice also that if I want to make it into a belt you just melt the ends and stick them together.

With all that in place, I just mounted it all to a board and stuck it out the back of my office like a diving board into the stairwell below. This corner has a nice long drop and gets good sun in the morning to afternoon. One momentary switch completes the circuit to drive the motor/pulley and lift the ballast. At the top we can stop and enjoy the marvel of stored potential energy. For maximum effect, you can now either cover the solar cells or just wait for the sun to go down. Releasing the billiard bucket draws the cord back over the pulley and drives that motor (now a generator) reversing the polarity through the system. I have a diode in there along with a pair of LED’s to help illustrate what’s happening. A yellow LED illuminates while the solar is engaged and powering the motor. A Green one illuminates while the ballast/gravity is engaged. For lack of a better idea, I just threw another DC motor on there with a little red flag- that turns during the gravity power stage- if you have a better idea of what to do with it please do let me know. So, in conclusion everything worked out. I’m not sure how well this scales for the art installation but we’ll cross that bridge if & when we get there. I hope it illustrates the point- which is especially topical in the context of a stationary art installation.