Highway Robbery? Vibrating Freakin’ Roadways to Generate Electricity

August 7th, 2016 by Roy W. Spencer, Ph. D.

Just when I thought it couldn’t get any more stupid…

Solar Freakin’ Roadways was a bad enough idea…now, the California Energy Commission has agreed to fund several projects to investigate the generation of electrical energy from piezo electric cells placed in road surfaces. The idea is that since a piezo device can convert mechanical vibrations into electricity, they can regain some of the energy lost by cars and trucks that are constantly vibrating the roads.

At first it seems like a reasonable idea…until you think about the tiny amount of energy involved compared to the cost of such devices.

While I’ve seen estimates that assume up to 40% of the energy expended by a vehicle is available for recapture, this amount is not available to produce road vibrations. Most of the energy losses are elsewhere — wind resistance, waste heat generation, friction in the driveline — and only 4% goes into the rolling resistance of the tires.

And most of THAT 4% rolling resistance is lost by generation of heat as the tire flexes….I’ll bet less than 1% goes into vibration of the road surface itself, which is what the piezo devices would be capturing a part of.

Then, what portion of that 1% could be harvested? Maybe a tenth of it? So, now we are talking about retrieving about 0.1% of the energy expended by moving cars and trucks. And that’s if the cells have 100% efficiency, which they don’t.

So, no…not “up to” 40% is available to capture by piezoelectric devices. And considering the cost of the piezoelectric cells, this would be a really bad idea…except for whatever company is getting rich off of manufacturing them.

Plus, there is the additional question of whether the devices are passively harvesting some of the road vibrational energy that would occur anyway…or would they be an active additional source of rolling resistance of the tires? If it’s the latter, then it would be ‘highway robbery‘, because it would be reducing the fuel efficiency of cars, and stealing a small portion of that extra energy required to push against the devices to convert it to electricity.

While a pilot project in the Netherlands found that Generating Electricity from Vibrations in Road Surface Works, reading of that article reveals the amount generated isn’t enough to even power a street light.

And this does not even address the practical issues involved in replacing a portion of road surfaces with piezo strips. Will it be like driving over rumble strips (see the photo above)? That won’t be very popular. What will it do to the integrity of the road surface? What if one breaks free and flies through a windshield and kills someone?

Sounds like just another energy boondoggle to me.

99 Responses to “Highway Robbery? Vibrating Freakin’ Roadways to Generate Electricity”

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  1. Michael van der Riet says:

    David Mackay set it out pretty neatly in SEWTHA, Sustainable Energy Without The Hot Air. See page 29 of the book (page 42 of the pdf) and page 256 (page 267 of the pdf). City driving, he wrote, is dominated by kinetic energy and braking. Rolling resistance is linear and independent of speed. It occurred to me that a better place for the piezo effect would be the car’s own shock absorbers. Probably cheaper without the safety concerns noted by Dr. Spencer. https://www.withouthotair.com/download.html

    • yes, I’ve read about recapturing energy through the shock absorbers, which makes somewhat more sense…but I have no idea whether it is cost effective.

      • Lewis says:

        Dr. Spencer and Mr. van Riet,

        Would not the energy available to a set of shock absorbers be a result of the energy produced by the motor? If so, no matter how rough the road, the same reduction in available force would apply as in the piezo scam. Very little of a relatively cheap energy would be converted by an expensive device. Then, you’d have to convert the energy, or transfer it to a device which could use it.

        Another bad idea which, obviously, makes it worthy of taxpayer funding and a free ride at the trough.

        • Yes, the energy was originally generated by burning fuel in the motor. But the resulting kinetic energy (f forward motion, rough road, rolling resistance) can either be dissipated as heat through friction, or some of it can be captured with a device that converts some of it to electricity. That’s what a hybrid car does.

      • D MacKenzie says:

        Alas, if it was cost effective, you can be pretty sure that one of the thousands of automotive engineers in the world over the last more than 100 years would have made use of the idea. They have been an inventive bunch over the years. Some of the first cars were electric, and their conclusion was that internal combustion engines were lighter and less expensive, and they have been right for over a hundred years.

  2. FTOP says:

    No project is too outlandish when funded by OPM (Other People’s Money). This is the insidious underbelly of socialism. Waste and fraud cloaked in a “cause”.

    This is why we need a government small enough to fit in the Constitution.

    • jimc says:

      It’s California.

    • Gordon Robertson says:

      FTOP…”This is the insidious underbelly of socialism”.

      Puleeeze…the only government California has ever seen is right of Attila the Hun. There is no such thing as socialism in the US.

      If there is socialism, it’s corporate socialism but that hardly works in the same way as true socialism which is geared to the working class. Corporate socialism works for the benefit of the corporation at the expense of the workers.

      Many of us have worked for companies that encourage ‘family’. Let’s all be one big family and work as a team. Trouble is, when it comes to wages and working conditions, the godfathers disappear. They don’t want anything to do with family when it comes to paying decent wages.

  3. mpainter says:

    What source of the mechanical stress for the crystals? Is it road vibrations (isometric?) Or vertical compression by weight of the vehicle (through the tires)?

    The latter effect seems more sensible, imo, and might work. In this case, rolling resistance is of no consequence.

    • the weight of the vehicle producing compression and generation of energy only occurs if the tire is moving and thus is a portion of rolling resistance.

      • mpainter says:

        Each tire applies a force equal to its share of the vehicle’s weight. This is not rolling resistance. For example, a 4,000 pound vehicle applies a vertical force of 1.000 pounds through each tire, whether moving or still. Presumably, it is this force that is being harnessed piezoelectrically as the tire passes over the device.

        • to generate energy the force has to be applied over some distance. The act of vertical compression (and decompression) could generate energy, but it only occurs if the tire is rolling against some resistance. So, it is a portion of rolling resistance. Otherwise, you could generate electricity just by having cars sitting still and deforming the road surface…which you can’t.

          • mpainter says:

            The US.army has experimented with piezoelectric cells in the soles of soldiers boots, see Wikipedia. No rolling resistance there, but momentary compression. The weight of the vehicle is the same at rest as while moving. I did not mean to imply that a vehicle at rest generated piezoelectricity.

            My point is simple: the device might be effective if it harnesses the vertical compression exerted by the vehicle. This force is gravitational and has little to do with rolling mechanics except in the momentary effect of compression and release.

            The experiment will give some insight as to the effectiveness of these devices.

          • Lewis says:

            But if you add a device which deflects any amount, rolling resistance to the vehicle will increase, increasing the cost of operation.

          • Not if the resistance is no more than the resistance offered by the portion of road surface the device replaces.

          • Bart says:

            It can’t generate net power that way. Gravity is still a conservative force. It can store energy, but it cannot produce it.

            Think of it this way: At one instant, you roll onto the surface, compressing it and generating power. Now, to do that again, you’ve got to climb back up out of the depression you just created. When you do that, you have to put in at least the amount of mgh (mass X gravity constant X height) energy you just produced.

            The net will be negative because of inevitable losses due to friction from slippage between the tire and the material, flexing of the tire and suspension system, etc…

            Any power you get is ultimately drawn from the car engine, only with substantial losses along the way. There is no free lunch.

    • Gordon Robertson says:

      @mpainter..something from Stanford…


      The problem as I see it, having worked with piezo devices in electronics, is the fragility of the devices and the problem of attaching and maintaining electrical connections to quartz.

      Pads have to be etched onto the quartz to take an electrical connection and the pads are subject to corrosion.

      I think it would be a nightmare trying to synchronize generated currents, summing them and distributing them.

      The idea is more science fiction that reality based.

  4. Ovi says:

    Isn’t the whole idea fundamentally flawed from an energy conservation perspective.

    Since adding the PEC will modify the roadway in such way as to generate energy, we need to ask where does this extra energy come from. I think adding the PEC reduces the Fuel Economy of the vehicle by a very small amount. Maybe a good modeller could try to verify this.

    I think the basic question is whether the hill on the upside of the PEC is slightly bigger that the down hill before the PEC.

    • yes, we need a mechanical engineer to chime in here. Does extraction of energy from the road vibrations exert additional resistance to the rolling tires? If so, then it really is “highway robbery”.

    • mpainter says:

      Does the PEC harness road vibration or compression exerted by the weight of the vehicle. Who knows the answer to this question?

      • This document suggests it’s the vertical movement of the road surface that is used to generate electricity.


        Local deformation vertically leads to traveling waves both vertically and horizontally…but it looks like only the vertical component is utilized.

        • mpainter says:

          Thanks, Dr. Spencer. The source can be understood if one parses it carefully. First of all, it is advocacy. The talk of wasted power, rolling resistance, vibrations, etc. is smoke and fog which they threw in for some reason, perhaps as scientific fluff. It is clear that vertical compression of the piezoelectric cells is the generative force.

          The road has to be asphalt, which provides the needed surface compressibility. The PE cells are set in the asphalt at 5 cm below the surface. This concept is also applicable for _pedestrian_ traffic, according to the article. Has to do with rolling resistance, you see☺

          The article admits to one big problem: roads would have to be relaid.
          Oh, well.

          • Roy Spencer says:

            Another way to phrase my point is this: If there was no vertical deformation of the road, rolling resistance of the tires would be less. Vertical deformation adds to rolling resistance. That’s all I was saying.

      • Per Simmersholm says:

        Audi is on this with suspension generating up to 600W they call it eRot

  5. So you make the roads really bumpy to maximise the generation of energy?

    Sorry; you lose. You put more energy into getting out of the dips via the drivetrain if you convert some of the “rebound” energy from the suspension movement on the way down. TANSTAAFL.

    Places that want to conserve energy with moving traffic do so by making the roads smooth and stiff (rigid) so that they deform very little. Selection of the wear surface is also critical.

    Rolling resistance on e.g an Autobahn built on concrete vs traditional bitumen rolled out onto e.g. crushed rock and soil that is available locally is at least a third lower; even before the poorer road gets rutted and pot-holed.

    For modern cars (not “trucks or SUV’s), most of the fuel consumption when moving on level ground is to overcome rolling resistance. Only at speeds above 80 km/h (50 mph) does aerodynamics become more important.

    “Parasitic losses” dominate fuel consumption in urban traffic situations. Airconditioning, heating, ventilation, lighting, “distrac-tainment”, etc.

    Keeping traffic moving on good, smooth and firm highways is a way that a country can substantially reduce its consumption of transport fuels. Alas, taxes on fuel often send the wrong signal to governments which see the easy revenue from taxes instead of the benefits of higher productivity from people moving themselves and good more quickly and cheaply. (vis Laffer curve)

    • mpainter says:

      The worst aerodynamics is in pickup trucks. These guzzlers get about 18 mpg, highway.

      Concerning aerodynamics, a bicycle can be peddled over 80 mph if following close behind a truck where air resistance is nil.
      Otherwise, top speed is about 40 mph?

      • Gordon Robertson says:

        @mpainter …”…a bicycle can be peddled over 80 mph if following close behind a truck where air resistance is nil”.

        Only a climate alarmist would try that. We skeptics know what happens if the truck suddenly applies the brakes. The slipstream where that drag is effective is right behind the truck.

        • mpainter says:

          This was first demonstrated over 100 years ago by a bicyclist behind a locomotive and tender over a specially laid course of track prepared by a cooperative railroad.

          • mpainter says:

            Which gives me an idea! The motive force of today’s locomotives is electro-mechanical, right?☺

        • dave says:

          “…only a climate alarmist would try that…the truck suddenly applies the brakes.”

          Encourage it.

  6. Marcus Landry says:

    Has no one in this thread ever taken the third year physics course, Thermodynamics? The answer to all of these questions is… A very small amount of energy can be harvested. That harvested energy amount, multiplied by a factor of three or four (it’s not very efficient) comes from extra fuel burned by the vehicle unfortunate enough to bounce over these devices.

    The shock absorber idea is actually a good one if, and only if, a way can be devised to turn most of the energy a regular shock absorber normally converts to heat can be converted to electricity. Don’t hold your breath.

    • Roy Spencer says:

      Ummm…I don’t see anyone defending the scheme here, Marcus. I’m not sure you read my post or discussion. If the piezoelectric cell offers no more resistance than the road surface it replaces, then it wouldn’t cause reduced gas mileage. If it causes more resistance, then it would. In any event, the amount of energy available to be recovered is, as you say, tiny.

      • Gordon Robertson says:

        @Roy…”If the piezoelectric cell offers no more resistance than the road surface it replaces, then it wouldnt cause reduced gas mileage”.

        The piezo device is apparently buried a few centimetres below the surface. The wheels wont be in contact with it. It’s the flexing on the road surface that causes the device to flex, which creates a potential difference.

        The same principle is used on drum pads. The pad surface is a vinyl covered rubber and the piezo device is stuck to the back of the rubber with two way sticky tape. When the pad is struck, the vibration passes through the pad and activates it.

        You can use them in reverse. Applying a varying voltage to them causes them to vibrate, hence a small speaker or buzzer.

        Those piezo devices are a slab of quartz or a ceramic and are non-conductive. They will generate a potential difference but you could not run a current through them. They are also very thin, like a wafer. The device is mounted in a brass holder and a contact is etched onto the quartz/ceramic. Another lead attaches to the brass ring.

        The potential developed between the device and the brass ring is taken off on the two leads.

        On my drum pads, the piezo device will generate a half volt spike with each hit on the drum pad. Obviously the current generated is tiny.

        I agree with you, it’s a dumb idea.

  7. Tom Waeghe says:

    Probably turbines capturing wind from cars and trucks going by might be better but what an eyesore those would be…

  8. Svend Ferdinandsen says:

    It seems that when the energy harvested is free and somehow EV or “green”, there is no limit for the investment.
    Especially if the method is strange.

    • dave says:


      Not even the greatest morons in the world could consider such energy to be ‘free’, could they? Well, Gwyneth Paltrow steam-cleans her vagina ‘to provide an energetic release’ at $50 a pop.

  9. Pop Piasa says:

    Doc, the only thing I can suggest as a more practical application of piezo power would be to incorporate it into the vibration dampers in bridges and other elevated traffic structures. Using places where movement naturally occurs might even get you enough juice to light the (LED) lights on the bridge, but at what cost?

  10. Milton Hathaway says:

    Steel tires rolling on steel roads should reduce rolling resistance dramatically. Seems like an equally plausible approach to me.

    There could be side effects, though. But investigating those possible side effects would create new well-paying jobs, no?

  11. Massimo PORZIO says:

    Five years ago I did a consult for the department of mechanics of the Politecnico di Torino.
    I designed a system for the structural analysis of bridges based on three axis accelerometers radio controlled probes. I remember that I spent a lot of time designing the single probes which were installed directly on the structural points of the bridge and anyone of them were powered by a single Lithium-polimer cell, dimensioned to give the probe a maintenance free life of 7 years.
    After we ended the first in-laboratory tests on their acceleration simulator, the professor informed me that to get the funds for the design they wanted an “alternative energy” source for the probes (in Italy with “alternative energy” they mean solar, wind and all this kind of new energy sources).
    The very same proposed me to substitute the Lithium-polimer battery with a piezoelectric vibration scavenger. It sufficed to me to read its data-sheet to understand that the “energy source” was unreliable, because it was well stated that for getting out 1.5mW from it, it needed a continuous 400Hz oscillation of the scavenger capable of bend it of at least +/-45!!!
    I warmed him that for getting that tiny amount of energy the probes were no longer useful for that bridge because with those rate of vibration the bridge was surely fallen down, but the professor was not convinced of my conclusion and needed to try it on the acceleration simulator.
    The results were 2 scavenger destroyed and no more than 2mW of power generated.
    So, finally the probes have the Lithium-polimer battery for power the electronics and the scavenger is mounted inside just to “sustain” the energy of the battery.
    I’m absolutely sure that (as predicted) those probes will need maintenance in 7 years.

    Crazy world.

    Have a great day.


    • Gordon Robertson says:

      @massimo…”I designed a system for the structural analysis of bridges based on three axis accelerometers…”

      Interesting stuff. What did you use to detect acceleration as opposed to a straight harmonic oscillation?

      The only application I have seen for piezo devices was crude in nature. I described in an earlier post the detection of drum stick strokes on a rubberized pad with a piezo device stuck to the back of the rubber, and the reverse situation where a varying voltage applied to a piezo device caused it to act as a buzzer or crude speaker.

      • Massimo PORZIO says:

        Hi Gordon,
        the system was based on MEMS three-axial accelerometer from Analog Devices. The piezo “scavenger” was just left there for the funding purpose indeed.
        The MEMS accelerometers are electrostatic interdigitate micro-mechanical capacitive bridges driven with a know frequency and the outputs are measured in amplitude and phase to get the acceleration induced shift the bridge.
        In that application I just designed the wireless probes and the data acquisition to get synchronized signals from all the probes.
        The professor said to me that they use those data to perform a lot of DSP to get the structural reliability of the bridge, The data were collected after applying a consistent stimulus to the structure. When we checked it in Aosta they used a sand charged truck, and acquired the data during the truck transit on the bridge.
        AFIK the surely do a FFT for getting the structural resonances, but I don’t really know what other they do on the data for complete their analysis.
        The professor don’t tell me, he argued it was a new way to accomplish that task and it was covered by such kind of patent.

        Have a great day.


        • Gordon Robertson says:

          @Massimo …”The MEMS accelerometers are electrostatic interdigitate micro-mechanical capacitive bridges driven with a know frequency and the outputs are measured in amplitude and phase to get the acceleration induced shift the bridge”.

          That’s a clever way to get the acceleration.

          I have a set of drum pads gathering dust while I figure out a better way to detect pad fluctuations than using piezo pickups. Your mention of such MEMS devices has me thinking.

          In modern MIDI devices, the device does not detect only a hit, or a key press, it detects how hard the pad or key was struck. A piezo device will respond like that on a drum pad giving the amplitude of the output signal proportional to how hard the pad was struck.

          I’d like to find a more elegant solution, perhaps using a MEMS device.

          Capacitance microphones have been in use for some time and I’ve seen inductors with a ferrite plunger used to detect rate of change. Either a capacitance or inductance based device would be preferable to the mechanical idiosyncrasies of piezo devices.

          • Massimo PORZIO says:

            Hi Gordon,

            a MEMS accelerometer could be a good choice for you, keep in mind that as any mechanical device it has some resonances.
            For example the ADXL250 had two peaks at about 12kHz (the package) and at about 22kHz (the inner beam).
            For this reason the accelerometer frequency response is usually limited to 1…2kHz.

            Have a great day.


  12. JustAnOldGuy says:

    Increased activity of the San Andreas fault might also contribute a few volts by flexing the roadways. There must also be a way to capture the energy generated by animal lovers stroking their cats. Just think how much energy could be contributed by volunteers or individuals sentenced to community service engaged in rubbing all the cats being held in no-kill shelters. And then there’s all those children. We need a study to determine how much green energy could be produced by school children scuffing the right type of shoe over the right type of carpeting in schools and daycare centers. Tiny children still moving about on all fours could be equipped with appropriate pads for their toes, knees and palms. Piezo generators installed in under the flooring of basketball courts could also contribute. My god! What a bright future awaits.

  13. Mathius says:

    Wait just a second here….

    California has decided they want to test this on roadways where minor vibrations occur, but don’t even consider the possibility of harnessing seismic waves?!


    The roads may vibrate a little, but the entire state could vibrate a lot! Imagine the potential!

    Step 1: Ignore the cost of these mechanical vibration energy producing devices.

    Step 2: Imaginary profit!

  14. Groty says:

    I have a miracle fuel for you. It is the cheapest liquid a consumer can buy. On a per gallon basis, it is cheaper than: vodka; Pepsi; apple juice; spaghetti sauce; salad dressing; chicken noodle soup; laundry detergent; and maple syrup. This miracle fuel is even cheaper than most brands of bottled water.

    It’s called gasoline.

    Oil companies invest hundreds of billions in capital expenditures to find the crude oil and suck it out of the ground, often miles below the surface of land and ocean. Then it is transported on fleets of ships, trucks or via pipelines to refineries, which also require billions of dollars in investment to turn the crude into gasoline. Then the gas stations where we buy it invest in safety devices so we don’t blow ourselves up or the gas station when we refill our tanks. Yet after going through all the steps required to find it, extract it, ship it, refine it, and put it in gas stations it is cheaper per gallon than Coca-Cola, vinegar, milk, and some brands of bottled water.

    It’s a miracle fuel.

    • mpainter says:

      And it yields that wonderful, life giving compound CO2, the magical bounty provided the earth by a beneficent Creator.

    • Mike Flynn says:


      One might even say concentrated solar power in liquid form!

      Grand stuff. As mpainter points out, it even helps to replenish CO2 levels which were dropping to dangerously low levels a few short years ago.

      Nature seems to have left quite a lot of it lying around for the taking – cleverly secreted so it won’t evaporate or catch fire due to lightning strikes.

      Might as well use it. It’s organic, biodegradable, recyclable and renewable (eventually).


  15. WOW .!. That was interesting and informative reading, (as a physics post-grad and resident of Southern California). Hopefully, this will be put to rest.

    How about a discussion on the propaganda at the Rio Olympics in Brazil in the Opening Ceremony? I’ll send a note to Dr Spencer ([email protected]) suggesting his insights would be greatly appreciated and beneficial. You may have seen the audiovisual going on and on about Global Warming.

  16. Mike Flynn says:

    From the press release –

    “The project partners also concluded that integrating piezo elements in an existing road surface is problematic.”

    I hope they didn’t charge the taxpayers too much for that gem.


  17. ren says:

    I’m sorry, that is not the topic.
    Will be strong convection over the Rocky Mountains.

  18. charles the moderator says:

    I thought the idea of a low powered laptop which harvested piezo-electric power from the keystrokes might be practical, but even that low power an application may be impossible.

    It would need a low power screen, such as an old fashioned LCD, but modern color screens may be able to match the efficiency.

    The roadway thing? Idiotic.

  19. Mickey says:

    Do a Google search for “MotionPower” by the former company New Energy Technologies. It was a device that would be installed in locations where vehicles are slowing down or stopping like speed bumps, pick-up windows, tollbooths, etc. As the vehicle drove over the device, it would compress and it would convert this motion to electricity. It was tested at a Burger King drive-thru and at a convention center in the City of Roanoke. In the City of Roanoke test, 580 vehicles drove over the device during a 6-hour period. This test showed that the device “could produce enough sustainable electricity to power lights for the average American home for an entire day”. Lights on average are about 10-15% of total electricity usage in a home. That’s about $10-$20 a month. The unit is estimated to cost $2k-$3k. So the rate of return is around 16 years. Is it any wonder the product is no longer under development and the company no longer exists?

    • this article addresses the MotionPower device and raises the same issue as I and others have raised: Does such a device actually cause the car to exert more energy in order to completely pass over it? If so, it is probably wasting more energy than it is saving.

      • Mickey says:

        In the case of the MotionPower device, it was to be installed in locations where vehicles were coming to a stop or slowing down. So I would not think that it would cause an exertion of more energy. It’s interesting that the article you site states that “The energy harvested could power an average U.S. home for a day”. That isn’t true. It could only power the LIGHTS in a home for a day. Big difference.

        • just a thought says:

          Maybe if they install them on downgrades, where you are breaking anyway? It could then be break sparing, and still come up with something, probably not much, but at least then it wouldn’t be stealing energy from you. And on steep long downgrades, they could install quite a few without any adverse effects on auto efficiency. That would seem like a best case scenario.

  20. Chuck L says:

    Far be it from me to be cynical but I can’t help but wonder if certain members of a certain political donor class might be on the receiving end of contracts to pursue this “revolutionary” technology

  21. Dan says:

    I have been a program manager for several piezoceramic based vibration energy harvesting devices resulting in several patents but no product.

    These devices were designed to augment or replace batteries for remote sensor applications.

    There are a lot of issues for using piezoceramics for power generation. The foremost is the low coupling coefficient between input strain and available electrical power. When one loads up piezoceramic material the can harvest about 20% of the mechanic work going into the material the rest is stored in stain energy and goes back into the structure when released.

    Most energy harvesting devices get around this by operating at mechanical resonance where stain energy cycles between kinetic and stain energy allowing higher conversion efficiencies. So the device works great at one frequency and doesn’t work at any others. Even at resonance fount to back efficacies are likely around 10%

    There are two energy harvesting products that are successful. Head has tennis racket and down hill skies that harvest vibration energy and send it back to dampen vibration.

    BTW Vibration energy harvesting research is much like climate science, It makes a ton of conference, journal papers and PhD dissertations but very little of value.

  22. Gordon Robertson says:

    Dan…”Most energy harvesting devices get around this by operating at mechanical resonance…”

    Like the knock sensor in a car engine. It senses vibration in the expected frequency range of undesired detonation in a cylinder.

  23. mpainter says:

    The real killer is that the roadway would need to be “relaid”, meaning a fresh layer of asphalt applied, three inches at least. A very big expense.

  24. Curious George says:

    I bet most of that money will go to Elon Musk. The rest to other well-connected philantropes. It is all about money.

    The article is beautifully illustrated by a usual picture of a power plant emitting heavy soot from a cooling tower.

  25. Vincent says:

    I’m sure it’s obvious that this technology will be useful only in a limited number of situations where supply from the grid is not available. The impression I get from the following article is that the use of piezoelectric devices could be less costly than the use of solar panels in those situations where both are options to consider, because of a lack of supply from the grid.

    “According to Innowattech, Piezoelectric Electric Generators are easy and inexpensive to install. Embedded between a road’s layers, they are mounted with electronic cards to store traffic-generated energy.

    The system is usually covered with a layer of asphalt, but concrete or composite concrete and asphalt can also be used. Because systems can be installed when new roads are laid or when regular maintenance work is performed on existing surfaces, installation costs are substantially less than those incurred with either wind or solar systems.

    However, IDTechEx sees better potential in providing local harvesting for road furniture, roadside advertising, railway station and airport signage, and the like. Here the installation cost is much less and the benefits go beyond cost to involve such things as energy independence for safety information etc.

    Many companies are now landing orders for this application of harvesting, some using electrodynamic and some using piezoelectric harvesting.”

    Read more at: http://www.energyharvestingjournal.com/articles/1589/energy-harvesting-roads-in-israel

    Hope I’ve managed to clarify the situation for the benefit of the deniers. (wink)

    • dave says:

      “mounted with electronic cards to store traffic-generated energy…Hope I have managed to clarify the situation…”

      Not really. Where do I buy these marvelous cards?

  26. Gordon Robertson says:

    testing happy faces


  27. David Kelly says:

    The road energy thing is a boondoggle provable with a simple energy diagram. Draw a circle around the system and count the energy crossing the circle. Thermodynamics 101. For the piezo system to generate power the road surface has to move more than it currently does. The vehicle will have to generate more power to overcome the moving road. Poorer MPG on gravel roads for the same reason, more resistance because the rocks are moving. What sort of twisted logic thinks this is good? Same applies pretty much for energy-generator shock absorbers however the heat generated by shock absorbers does suggest something is available if the quantity was not so small.

    Hey, why not simply line highways with piezo microphones and generate power from all the noise? 🙂

    Ever stand next to the road as a vehicle passes at speed? Big wall of air pushes out, then in as the vehicle passes. Wind Turbines! Capture this energy! But once again this will increase the wind load and fuel consumption of passing vehicles.

  28. Dr. Strangelove says:

    “there is the additional question of whether the devices are passively harvesting some of the road vibrational energy that would occur anywayor would they be an active additional source of rolling resistance of the tires?”

    Roy, definitely it will increase rolling resistance. The piezoelectric tiles have to be compressed by 5 mm to generate 7 watts. The uneven road surface will increase fuel consumption of cars. Since they are just using the fuel of cars, just build a diesel power plant. It’s more fuel efficient than cars. But they have to pay for the fuel. And they would rather steal your fuel

  29. Milton Hathaway says:

    If the tires are really compressing the road surface by 5mm, then the vehicle is always litterally going uphill on a level surface, right?

  30. Bart Thompson says:

    To me personally, it looks like someone’s selling snake oil.

    As a tire designer for a major tire manufacturer, one area of specialization for me was tire rolling resistance and FEA modeling. Modeling a concrete or asphalt surface as infinitely rigid is a very good approximation … thus …

    The hinge point in the article / concept is:

    When a vehicle passes over a road, the road deflects vertically. This deflection is released as thermal energy. For a road with embedded piezoelectric generators, part of the energy the vehicle expands on roads deformation is transformed into electric energy (via direct piezoelectric effect) instead of being wasted as thermal
    energy (heat).

    Does the road deflect vertically?

    For a tire inflated to 0.2 MPa (30 psi), the applied stress to the road is … 0.2 MPa. Asphalt modulus of elasticity is 5000 MPa. This gives a strain (stress/modulus) of 0.00004. The asphalt is 200 mm thick, laid on a base of material that can be considered incompressible.

    Total “road deflection” = thickness x strain = 200 mm x 0.00004 = 0.008 mm. For a 1000 kg car, the total energy of deformation is 1000 kg x 0.000008 m = 0.008 N-m.

    1 Watt = 1 Nm/s. Therefore for 1 Watt of energy, we need 125 cars / second. To burn a light bulb, we need 5000 cars/second.

    But since we get 10% efficiency we need 50,000 cars / second to burn a light bulb.

    50,000 cars traveling at 100 kph require 9.4 e8 Watts. We thus recoup 4.3e-6 % energy that the cars require.

    Snake oil.

    • Joe Madrid says:

      The best answer….amazing how many interesting people read Dr. Spencer.

    • Bart says:

      Another Bart here. The problem is, once you’ve deflected that part of the road, you’re in a depression. To deflect that next bit of road, you’re going to have to climb out of the depression. And, that will require at least as much energy as the deflection produced in the first place, significantly more considering losses.

  31. Paul says:

    I am working as an engineer in the automotive industry. Some of the people in the thread already explained that this idea physically is a negative effect game making the car consume more energy and transferring it to the piezo generating device. Taking into account all efficiencies of the involved systems it would end up with a total efficiency rate of way below 20% if not 10%. Modern fossil fuel power plants have by far more than 40%. This means burning coal is about three times as efficient as taking it from the road through a piezo element.

    Additionally, this load is artifially added to the system (car-road) increasing the ‘natural’ losses. This means the car is forced to consume more to let the road device take inefficiently a part of that energy instead of making the whole system more efficient.

    This has to be compared to a system that recovers the lost energy of a car rolling over a bumpy road anyway. This makes sense because the kinetic energy created by the shock absorbtion normally is lost and could be recovered by an electrical shock absorber.

    This is what is currently being developped (e.g. for Audi) through a rotational shock absorber system. This absorber can be adjusted electrically to create completely individual driving setups and can be used as a generator at the same time. Depending on the road quality the recovered electrical output is supposed to be between 3 and 600 Watts.


  32. dave says:

    “…between 3 and 600 Watts.”

    Do you mean between 300 and 600 Watts? 3 Watts is not even a joke.

    600 Watts would be to recover about 1% of the power output of an average car cruising along.

  33. just a thought says:

    “…up to 40% of the energy expended by a vehicle is available for recapture”

    Oh, dear. My solar calculator isn’t charged. Could someone please quickly tell me what 40% of nothing is?

    Seriously, if you could recover “40%” of a car’s total energy, that would mean the driver’s gas bill would go up by >40%. (No free lunch + nature’s energy transfer tax)-i.e., the energy transferred from the car would be energy lost to the car, and the driver would have to make up the difference = literally “highway robbery,” as Dr. Spencer wrote.

    California, making it’s citizens a little more miserable every day.

  34. Paul says:


    yes, I meant 3 Watts. This is the value for a nearly perfect road. 600 Watts is for very bad roads. Your fuel consumption would rise on these bad roads and you would be able to recapture a part of it.

    You are right with your 1% calculation if you take the maximum performance of the system. But the people who promote it postulate that they can save about 5 gramms CO2/mile (about 2% in fuel consmption). It was not mentioned that this saving is at max performance. So I interpreted it as corresponding to their average recuperation rate which is supposed to be 125 Watts.

    I doubt that but this is how it is promoted.

  35. Joe Madrid says:

    I thought of this as a possibility when I was an undergraduate at MIT in 1974–It is the sort of thing that has probably been thought of by a jillion nerds a jillion times… By the number of comments you can tell it is a fun thing to work with and think about… In my original thoughts it was the weight of the car that captured my imagination… Dr. Spencer is just a couple steps ahead of us all…he subsumes the weight when he zeros in on vibrations (a feather wouldn’t produce very potent vibrations).. OK, ideally you want a win win situation–the energy lost by the car is some thing that can’t be avoided… compressing the asphalt is energy that is normally disappated as heat…but! you capture some of that energy thus have electricity and less heat. (I am going to ignore things like the piezo elements introduce a micro “pot hole” that the car must climb out of etc…No none of that the piezo device deforms exactly like the un-piezoed asphalt– other energy produced like noise and micro currents of air as the asphalt deforms are for part 2 of this…

    The economics of this have some potential…if you could operate a light locally with out it being hooked into the grid…all come under sourcing power at a remote location. After looking at all the answers I feel the idea is a sadly a no go…as there are alternative remote sources of energy much easier to harness…and getting a lot of energy requires real distortions to the cars normal safe glide path…


  36. Thanks, all, for insights! We’ll be riding it out in So.Calif.

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  39. I have read about recapturing energy through the shock absorbers, which makes somewhat more sensebut I have no idea whether it is cost effective.

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