California Energy Commission studies stealing energy from cars and trucks.

WTF are they smoking?

In other news, they’re investing money in perpetual motion machines (okay, not really but they might as well be).

They’re trying to get something for nothing here. If there’s energy being produced by a car driving on the road then that energy is being stolen from the car and it will use more fuel to reach it’s destination. It’s physics 101!

You end up taxing drivers for driving on the road by causing them to use part of their fuel to generate electricity. It isn’t inherently wrong to charge someone for the use of a road, but generating electricity by burning more gasoline or diesel is neither renewable nor clean.

:dubious: Um, are you under the impression that cars don’t currently transmit energy to roads that is consequently lost in vibration, sound and heat?

AFAICT, these proposals are simply suggesting capturing some of that energy that would otherwise be dissipated. Not requiring the car to transmit more energy which it could otherwise use for locomotion.

Similarly, regenerative braking captures energy that would otherwise just be dissipated as heat in the car’s brake system, and uses it to help recharge the car’s battery. This doesn’t require the car to use more energy in order to brake.

You might want to take another look at your old notes from Physics 101.

Follow-up question: davidm, can you guess what would happen if a moving car weren’t transmitting energy to the road it was traveling on?

That’s right, zero friction, and all the merry highway hijinks that that would entail. :eek: Personally, I quite like being able to stay on the road by transmitting some of my car’s energy to the road via the tires, and if some brainy boffins in California can figure out how to usefully capture some of that otherwise lost energy with piezoelectric crystals under the road surface, they are welcome to it.

Piezoelectric devices work by deformation. Deformation will increase rolling resistance. Heat is irrelevant, and vibration is probably also irrelevant except for the tiny amount of vibration that happens to be in the right direction.

I have no idea how to do the calculations but I doubt that you’d be able to economically generate a useful amount of electricity from just what is currently waste energy. Even if you could there’s the cost of installation and maintenance (like with “Solar Freakin’ Roadways”).

If you’re looking to conserve energy from traffic you’d do much better to install regenerative braking and maybe some sort of energy harvesting shock absorbers on vehicles.

The piezoelectric effect has already been used to generate power from pedestrian traffic, most notably in Tokyo railway station, it’s not a question of if it could work but whether is economically feasible.

And whether it’s actually capturing waste energy or just increasing rolling resistance and stealing energy from the vehicles.

Pedestrian traffic may actually be a good idea, depending on the economics.

The point is that cars moving on a road already deform the road surface by a small amount, specifically in the form of vibration that the piezoelectric crystals use to generate electricity.

Luckily, some folks who are considerably better at physics than you have done the calculations. The numbers they’ve come up with appear to be on the order of 80 kwh per kilometer of road.

Undeniably, there are a number of economic issues involved in this form of power generation that would have to be studied carefully, and it may prove not to be cost-effective in general in the long run.

But that’s not what this thread is about. This thread is about you complaining that piezoelectric energy harvesting from road traffic would be somehow “stealing energy from cars and trucks”. From your apparent wish to change the subject to maintenance costs, I assume you’ve now realized that you didn’t know what you were talking about.

:dubious: So you’re suggesting that energy obtained from braking or from shock absorption occurring within the vehicle’s own systems, as opposed to being transferred from the vehicle to the road, should or could be harvested for storage or use outside the vehicle?

How are you proposing that would work, exactly? And ISTM that such a scheme actually would count as “stealing” energy that could otherwise be devoted to saving fuel for the vehicle itself (as it is in, e.g., regenerative braking, which captures energy from the car’s own brake system to help charge the car’s own battery). Surely you wouldn’t be on board with that?

We have some control over that deformation. Rigid roads cost more. I haven’t seen a cost benefit analysis on increasing road rigidity vs adding piezos.

That said, using these where people already need to slow down may still make sense even if they don’t make sense elsewhere. On-vehicle regenerative braking has its limits.

No, that number was come up with by someone who’s terrible at physics. 80 kwh is an amount of energy, which is utterly meaningless in this context. What’s that energy per? Per vehicle, per hour, per year?

And yes, current road materials already deform some. But with this system, you’d have deformation in the asphalt and deformation in the piezoelectric material. And even if it were a matter of deformation in the piezoelectric material instead of in the asphalt, you’d be better off with a material that just didn’t deform as much in the first place. Concrete has almost no deformation, and the only reason it’s not already used everywhere is that it’s more expensive. Do you really think that these electric roads would be cheaper than concrete?

To be useful (in terms of not making motor vehicles even less efficient), the piezo-enhanced road would need to provide less net rolling resistance to the vehicles than asphalt or concrete, but have enough compressibility to be able to develop a voltage. To be useful economically, the power extracted would have to be worth more than the cost of installing the system. Color me skeptical.

Per hour, AFAICT, but you’d have to ask the author of the linked IEEE Spectrum article that I quoted.

Well, as it says right there in the abovementioned linked article:

? You sound as though you’re assuming that the goal of this technology is to reduce road deformation by cars, but actually it’s to harvest energy from road deformation by cars, via piezoelectric cells.

? Again, you sound as though you’re assuming that the goal of this technology is just to make roads deform less, so we might as well just use concrete instead of piezoelectric harvesters. Which misses the point that the goal of the technology is actually to generate electricity.

And that means that its cost-effectiveness would depend on whether enough energy would be generated from piezoelectric sensors underneath road surface to offset the costs of installing the sensors in the first place. As I already noted, the answer to that isn’t clear, but it has nothing to do with the OP’s silly claim that the technology would be “stealing energy” from vehicle traffic.

This is California. They are already discussing “taxing” people based on how many miles they drive annually. Now they can have a special tax for people who did not drive enough and contribute their fair share to the energy pool.

If they were smart, they’d work on a way to turn dog turds into gold.

*I never had a chance to shine
Never a happy song to sing
But suddenly half the world is mine
What an amazing thing
'Cause I’ve got a golden dog nugget…

Special thanks to Grandpa Joe and Charlie and Mr. Wonka.

Well, as noted in my above quote from the previously linked article, that is indeed the claim that is being made for this technology.

Which, of course, is a separate issue from what the OP started off ranting about.

Fucking useless journalists. The actual “grant funding opportunity” as they call it is here: Solicitations

I like how the word “renewable” gets thrown a lot. Never mind that this power is being generated from, at best, grid-mix (i.e. not renewable) EVs*, and at worst, class-8 diesel trucks.
ETA: * Ok maybe a few off-grid folks with solar panels. All five of them.

No, he doesn’t. You sound as though you’re assuming the goal of this technology is to generate electricity.

Why yes, I am. What part of

—which is a direct quote from the OP’s own linked article—do you feel is incompatible with that assumption?

Note that the grant funding opportunity you linked to includes other energy generation and conservation technologies besides this specific proposal for piezoelectric cells in road surfaces, several of which involve what we commonly think of as “renewable” energy.

Note also that technically, the proposed piezoelectric harvesters would generate electricity from the mechanical energy of the vehicle deforming the road surface, which is a renewable form of energy. Anything heavy moving along the road would be a mechanical energy source, no matter what type of fuel happened to be powering its engine.

Likewise, biomethane is conventionally considered a renewable energy source, despite the use of fossil fuels to get the methane-producing materials to the energy harvesting site (e.g., carting manure to processors, dumping trash in landfills).

The journalist also seems to think that the goal of this technology is to generate electricity.

While it is true that marginal renewable generation can be completely negated or even leave you worse off due to factors like transportation/processing or the need for inefficient peekers, that does not appear to be an issue here. Electrical power generated from the combustion of biogas is renewable energy because biogas is a renewable energy source that in turn is also generated from renewable energy sources. PE from roads is not, for the most part, generated from a renewable resource. Nor is TE or ORC added to an ICE vehicle’s exhaust system (or to a road, if someone were into that) for waste heat recovery. Generating PE power from a road requires a road that parasitizes energy from vehicles. While converting that energy to something useful is better than allowing it to dissipate as heat, it is also possible to instead reduce this parasitization. But that of course reduces the strain available for the PE generation.

Probably not coincidentally, whoever wrote the grant funding opportunity description you linked to in your own previous post also seems to think that the goal of this technology is to generate electricity. From the info session presentation file in your link:

Emphasis added.

Yes. “Parasitization” seems like an odd term to use in this context, since a “parasite” is generally defined as an organism that derives nutrients at the expense of its host, rather than simply scavenging the discarded waste products of its host. In this case, the piezoelectric cells are more analogous to scavengers than parasites, since they’re harvesting mechanical energy which would otherwise, as you note, simply be dissipated rather than used to propel the vehicle.

Y’all are missing an obvious point: There are roads where increased rolling resistance is desirable, and will not lead to increased fuel usage: downhill roads, freeway exit lanes & off-ramps, approaches to stop signs & toll booths, before sharp curves, etc. Basically, any place where most cars would be using their brakes.