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I've been wondering if roads and stairways laced with piezoelectric generators be a viable method in clean energy generation?

I'm currently unfamiliar with all engineering aspects of piezoelectricity except for the fact that it generates electricity given differences in pressure. We generate pressure all the time using our bodies, dropping our feet downstairs, and our automobiles generate pressure on our roads all the time.

Q1. So I'm wondering if current piezoelectrical generators could be able to generate electricity through the transmitted pressure of our paved roads?

Q2. If that is possible, would the generators be able to stand such pressures casually?

Q3. How much electrical generation could I expect from a 50 step stair ladened with such a device?

Q4. If it's plausible in terms of engineering, is it economically viable?

I would love to hear an answer, thanks!

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  • $\begingroup$ See this paper on 'staircase Power Generation Using Piezo-Electric Transducers' $\endgroup$ – atom44 Aug 16 '16 at 9:55
  • $\begingroup$ Wow thanks! I skimmed over the paper, and it's fantastic! $\endgroup$ – Caprica Aug 16 '16 at 10:19
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    $\begingroup$ TINSTAAFL . The only way to get "free" energy from moving objects such as cars or people is to reclaim waste heat somehow, or use clever gadgets like the regenerators which charge batteries while applying braking force in EVs and hybrids. $\endgroup$ – Carl Witthoft Aug 16 '16 at 18:40
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Q1: Yes.

Q2: Yes.

Q3: It depends but generally not much.

Q4: No.

Without getting into the technical details of how you recover the energy, consider it from a conservation of energy perspective.

Yes, you can generate energy from roadways or stairs in a number of ways, but that energy has to come from somewhere. If you make the road generate energy from the cars traveling over it, then you will reduce the fuel economy of the cars driving on it. If you take energy from stairs, you will make them harder to walk up. By the time you've collected enough energy to be useful, you've normally had a significant impact on the practicality of the road/stairs you are using.

Roads do heat up a small amount when driven on; this is a mixture of heat generated in the road surface and heat transferred from the tires, which heat up when driven. This heat is effectively wasted and and so could in theory be used to generate usable energy with no penalty. That gives you a theoretical upper limit on the "free" energy that you could collect. However the total heating effect is only a few degrees and spread over a huge area, the inefficiencies involved gathering this energy (either before or after it becomes heat) and making use of it mean it's simply not a practical idea from an economic point of view.

Anything you do to gain more energy than that will make it harder for the cars to roll on the road and so reduce their efficiency. At that point, you are burning fuel to generate electricity, you may as well cut out the middle man and use a generator.

There is one time when cars want to lose energy, when they are slowing down. Conventional cars throw the extra energy away as heat in the brakes. If you could come up with a road surface that only tried to remove energy from the car while it is slowing, then that would be a potentially practical energy generation system. So far the most practical system for doing this has proven to be to build the equipment to do this into the car rather than the road and call it a hybrid car.

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  • $\begingroup$ Curious to know. What kind of force would be induced or deducted from that would cause more inefficiencies in cars with piezoelectricity? $\endgroup$ – Caprica Aug 16 '16 at 11:29
  • $\begingroup$ The piezoelectric effect is that a voltage is caused due to stresses in the material. That requires that the material moves slightly, unless it has an infinite youngs modulus it must move when under stress. In other words the car has to push the road down a tiny amount. If the road the car is on is pressed down and the road in front of it isn't then the car is effectively constantly driving uphill. $\endgroup$ – Andrew Aug 16 '16 at 11:36
  • $\begingroup$ Oh I see. So there isn't much practicality with cars. $\endgroup$ – Caprica Aug 16 '16 at 11:41
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    $\begingroup$ Just to be clear, piezoelectricity is generated by strain. Strain is the motion that is caused by stress (force). $\endgroup$ – Dave Tweed Aug 16 '16 at 12:03

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