Greencarcongress had an interesting bit about using undersea air bags as a means of storing energy from peak production to be used for generating power. In the discussion about it the idea of capturing power from the floatation force the bag would create each time it was filled pulling against its moorings was questioned. (Yes, I am the maligned “Don” there.)
Now it just got me wondering - what is the general possibility of using piezoelectric generation for electricty generation from incidental loadings? Is the thought of capturing incidental loadings with something like mats placed under areas that regularly experience high pressure forces totally crazy or doable?
Force alone won’t generate any energy; what you need is both force and motion, in non-perpendicular directions. Otherwise you could generate power just by sitting a boulder on top of a piezoelectric crystal.
Undersea airbags probably have a sizeable force, but crystals are notorious for not stretching very far, so the motion would probably be minuscule. If you wanted to get practical use out of a system like that, you’d moor it to cables attached to a winch and a generator, which would let it move a significant distance while generating power. But I think this would be at cross-purposes with the compressed-gas method they’re proposing, since changes in buoyancy would come from a change in volume of the bag, which they’d want to minimize to keep the pressure storage as efficient as possible.
In a circumstance in which say a boulder was repetitively dropped and picked up off of a surface (a surface subject to repeated compessive forces) could significant energy be harvested?
You could presumably use a piezoelectric motor “in reverse”, i.e. using it as a generator. I sincerely doubt that it would be as efficient as a normal electrodynamo. In general piezoelectrics are not especially efficient in terms of their conversion of electricity into kinetic energy; their main advantage is very compact size and low inertia (hence, why they are used in cameras and electronic equipment). Piezoelectric materials are typically very stiff and somewhat brittle, too.
Nanoscale generators might end up being extremely efficient in terms of processing thermal or kinetic energy (like vibrations) into electricity or chemical potential energy; however, they do so on such a tiny scale that it would be difficult–at least at any realistic projection of the technology–to organize this for gross use on a large scale, at least more efficiently that already done by natural nanomachines, i.e. the cellular organelles of living organisms.
Doable, but as Chronos notes you won’t get much energy out of it. That said, piezo power generation has been tested at ticket gates in Japanese train stations, and there have been experiments in implanting piezo devices in shoes to “harvest” some of the energy in your stride. (Note that the average rate of power generation in the shoes is less than 10 mW — not even enough to light up a standard LED.)
Why store the air in underwater bags rather than just in airtight compartments above ground or underground?
My father, who was ahead of his day in many ways, liked the idea of using compressed air to store excess energy from hydro-electric dams, and then releasing it to power turbines during times of peak load.
>the idea of using compressed air to store excess energy from hydro-electric dams
Doesn’t the dam already do that by adjusting the flow to increase during high demand? They already have an immense energy storage device (the upstream body of water) and generators set up to use it.
And there’s ‘pumped storage’ as well… Near Niagara Falls are two vast lagoons. When demand for hydroelectric power is low, they use the excess power from the plants to pump water upwards into the lagoons. When demand for power is high, they release the stored water back through the turbines that pumped it to get extra power. It works just like the battery storage in a hybrid car, but with water.
Plenty magazine has an article about using rain and piezo to generate electricity. Apparently you can get up to 12.5 milliwatts of instantaneous power from a large droplet. The original work was done at Grenoble and published in February’s Smart Materials and Structures journal.