Piezoelectricity and roads.

[Sorcerer]

Would it be possible to develop a road surface with peizoelectric crystals embedded in it, or just embedded in the base of the light poles on the side of the road and use the vibrations given off by traffic to generate electricity?

 

If so this could be fed into the mains or assist in powering the road lighting directly, especially since modern lighting is LED and much more efficient.

Would the cost of doing this be worth it? For example Quartz is piezoelectric and relatively abundant, do the crystals need to be of a quality that makes them expensive? Would there be a need for wiring if embedded in the carriageway itself, which would make it too expensive?

Would it reduce vehicles fuel efficiency? ie would it not only use the normal waste vibrational energy, but drain more energy.

Would it reduce road noise?

How much power could be generated this way? If you assume some numbers for a high volume highway, what kind of power could be generated, how would the cost compare to other power sources?

Edited August 16, 2015 by Sorcerer

[swansont]

They've done this with walkways. Thus far, it's pretty much been for show. At the Olympics in 2012, they generated a few dollars' worth of electricity

http://blogs.scienceforums.net/swansont/archives/12292

 

The only way I can think of where this is cost-effective is if it's a remote site and running the cable there is more expensive, and you ca't put up a solar panel and battery to do the job.

 

Would it reduce vehicles fuel efficiency? ie would it not only use the normal waste vibrational energy, but drain more energy.

 

Yes, by a small amount. You don't get this energy for free.

[Sorcerer]

I thought as much, so in addition to the waste energy vehicles give off in vibrations it would drain a little extra?

 

Let's say if we put piezoelectrics and a battery in lamp posts with LED lights would the cost of not having to wire them up off set the cost of the crystal and battery?

 

Also I notice these posts sway in the wind, could that be used to create electricity piezoelectricly.

 

Is the lower cost of solar panels due to the actual resource cost or because the infrastructure is already available for production?

[swansont]

I thought as much, so in addition to the waste energy vehicles give off in vibrations it would drain a little extra?

 

You aren't tapping waste energy. Vibrations in the road come from work the car does, and if you tapped into that, you would be adding to the frictional force the car feels.

[Moontanman]

They've done this with walkways. Thus far, it's pretty much been for show. At the Olympics in 2012, they generated a few dollars' worth of electricity

http://blogs.scienceforums.net/swansont/archives/12292

 

The only way I can think of where this is cost-effective is if it's a remote site and running the cable there is more expensive, and you ca't put up a solar panel and battery to do the job.

 

Yes, by a small amount. You don't get this energy for free.

 

 

I disagree, the energy is not coming for free but you are converting pressure that would normally bleed off into waste heat and turning it into electricity, no reason it should drain extra energy from moving cars they are already giving up that energy...

Edited August 16, 2015 by Moontanman

[swansont]

 

 

I disagree, the energy is not coming for free but you are converting pressure that would normally bleed off into waste heat and turning it into electricity, no reason it should drain extra energy from moving cars they are already giving up that energy...

 

No, you aren't draining off waste heat. You are doing work on the tiles that normally you wouldn't be doing. The pavement tiles compressed by 5mm. Roads don't do that. If we had 1 tile per meter, that would be like going uphill at an angle of 5 milliradians. It's not big, but it's also not zero.

 

It's the same reason why running on sand requires more effort than running on solid ground. The ground "gives" and you do work pushing it out of the way, which isn't available to make you move.

[Moontanman]

 

No, you aren't draining off waste heat. You are doing work on the tiles that normally you wouldn't be doing. The pavement tiles compressed by 5mm. Roads don't do that. If we had 1 tile per meter, that would be like going uphill at an angle of 5 milliradians. It's not big, but it's also not zero.

 

It's the same reason why running on sand requires more effort than running on solid ground. The ground "gives" and you do work pushing it out of the way, which isn't available to make you move.

 

 

Ok, I didn't read about the "tiles" I was thinking of more or less converting pressure that was already being generated into electricity instead of waste heat. Driving on a road does indeed heat it up, significantly enough to notice in the winter. I was generalizing from that heat build up, my bad....

[Sorcerer]

I was thinking not of any mechanism in the road that moves or adds extra friction, but simply something that absorbs that road noise/vibrations which are normally there.... the house can shake when a big truck 2 blocks away goes by fast.... why can't that energy be useful?

 

Also there are some places where it could be used and slow down traffic, for instance speed bumps, I know I feel them when I hit them, surely the speed bump feels it too why couldn't that energy be used?

Edited August 17, 2015 by Sorcerer

[jajrussel]

What if they put the crystals inside the tire? The weight compresses and locks the spring, then as the tire rounds the spring lock is released through expansion. A lot of engineering might have to go into the tire, but could it work if they designed the right kind of tire?

[swansont]

What if they put the crystals inside the tire? The weight compresses and locks the spring, then as the tire rounds the spring lock is released through expansion. A lot of engineering might have to go into the tire, but could it work if they designed the right kind of tire?

 

How would this help? You're just robbing the car of energy in a different way. Unless this is more efficient than running a generator, why do it?

[jajrussel]

 

How would this help? You're just robbing the car of energy in a different way. Unless this is more efficient than running a generator, why do it?

Actually I was thinking more along the line of returning energy to the cars battery, or using the spark to fire the spark plugs, or both. Maybe running the on board computer,or radio. It probably wouldn't make any more sense than adding solar panels to the roof of the house when all I really have to do is pay the electric bill, but then probably a few well placed thermal piles throughout the car might do the same thing.

[dimreepr]

A little off topic but I think this new type of thermionic generator could be a more efficient way to go.

[swansont]

Actually I was thinking more along the line of returning energy to the cars battery, or using the spark to fire the spark plugs, or both. Maybe running the on board computer,or radio. It probably wouldn't make any more sense than adding solar panels to the roof of the house when all I really have to do is pay the electric bill, but then probably a few well placed thermal piles throughout the car might do the same thing.

 

You increase the work the engine has to do, only to return some of that to the battery. Unless it's more efficient than a generator, it's not better.

[jajrussel]

 

You increase the work the engine has to do, only to return some of that to the battery. Unless it's more efficient than a generator, it's not better.

I admit to being easily confused, but truthfully I can not figure out how this increases the engines work load. Gravity cocks the mechanism, the tire returning to its round state releases the striker. The car does have to move which would involve the engine, but how is it doing anything extra? Except for the piezo mechanism everything is a natural state normally associated with a car. It's the how the piezo mechanisms presence is adding to the work load of the engine that I do not understand.

 

My experience is that as soon as you get rid of something you find that you need it, desperately. As far as I am concerned that generator with the fly wheel attached to the engine isn't going anywhere no matter how efficient a different style generator turns out to be.

[swansont]

I admit to being easily confused, but truthfully I can not figure out how this increases the engines work load. Gravity cocks the mechanism, the tire returning to its round state releases the striker. The car does have to move which would involve the engine, but how is it doing anything extra? Except for the piezo mechanism everything is a natural state normally associated with a car. It's the how the piezo mechanisms presence is adding to the work load of the engine that I do not understand.

 

(emphasis added)

 

That's the part you have to worry about. You have to depress the piezo, which is a different situation than for a normal tire. That's additional work. It's going to behave like a tire with additional friction.

 

Put another way, if you rolled a device with these tires with some initial KE alongside one with regular tires, would they roll the same distance? No. The energy you extract with the PZTs is extracted from the KE, so it won't roll as far.

[jajrussel]

 

(emphasis added)

 

That's the part you have to worry about. You have to depress the piezo, which is a different situation than for a normal tire. That's additional work. It's going to behave like a tire with additional friction.

 

Put another way, if you rolled a device with these tires with some initial KE alongside one with regular tires, would they roll the same distance? No. The energy you extract with the PZTs is extracted from the KE, so it won't roll as far.

Ah, so the potential energy stored in the devices by gravity isn't going to compensate for the additional fuel needed to move the car?

[ACG52]

A fairly exhaustive study on piezoelectric roads was done in California

www.energy.ca.gov CEC-500-2013-007

[swansont]

Ah, so the potential energy stored in the devices by gravity isn't going to compensate for the additional fuel needed to move the car?

 

Gravitational potential energy isn't part of the analysis. You generate energy with a PZT by exerting pressure on them and having them compress, which means you are doing work. The energy to do that work has to come from somewhere, and it's not gravitational PE — that's a one-off (something drops). If you raise it up again, you're doing work there. You can't get away from the fact that you are doing extra work to generate the electricity.

___

 

Two parts of the car where you have waste energy you could harvest would be the brakes and the shock absorbers. The brakes bleed the KE of the car away as heat, and shock absorbers dampen the vertical motion, also ultimately dissipating it as heat.

[dimreepr]

Not to mention the heat of the engine.

 

A little off topic but I think this new type of thermionic generator could be a more efficient way to go.

 

[swansont]

Not to mention the heat of the engine.

 

 

Right. I was thinking only of two obvious mechanical systems.

[jajrussel]

 

Gravitational potential energy isn't part of the analysis. You generate energy with a PZT by exerting pressure on them and having them compress, which means you are doing work. The energy to do that work has to come from somewhere, and it's not gravitational PE that's a one-off (something drops). If you raise it up again, you're doing work there. You can't get away from the fact that you are doing extra work to generate the electricity.

 

Okay, I'll have to remember this next time I try to reinvent the wheel.

[Moontanman]

 

You aren't tapping waste energy. Vibrations in the road come from work the car does, and if you tapped into that, you would be adding to the frictional force the car feels.

 

 

If you lased a solar cell it would produce waste heat, if you collected that head and used it instead of letting it radiate away would that diminish the efficacy of the solar cell? I have given this a lot of thought and I can't see how harvesting waste heat would require the tire to work harder...

 

Like harvesting the wasted energy of a braking vehicle, as long as all you are doing is harvesting waste heat how could it make the vehicle work harder.

[swansont]

 

 

If you lased a solar cell it would produce waste heat, if you collected that head and used it instead of letting it radiate away would that diminish the efficacy of the solar cell? I have given this a lot of thought and I can't see how harvesting waste heat would require the tire to work harder...

 

Like harvesting the wasted energy of a braking vehicle, as long as all you are doing is harvesting waste heat how could it make the vehicle work harder.

 

PZTs don't harvest waste heat.

[Moontanman]

 

PZTs don't harvest waste heat.

 

 

Ok, I think I see your point now, thanks Swansont.