California’s Piezoelectric Energy Harvesting Aims to Turn Traffic into Green Energy

June 19, 2017 by Robin Mitchell

California wants to turn one of its weaknesses—its traffic—into an energy-harvesting strength.

Is high-volume traffic a good source for energy harvesting? The California Energy Commission intends to find out. Here's how piezoelectric devices could turn nightmare traffic into the dream of renewable energy.

Energy harvesting methods have been growing in popularity lately, especially with regards to renewable sources of energy. Renewable sources are not just limited to solar; there are others such as wind, geothermal, and tidal. The only problem with all these forms of energy is that they are either location-dependent or weather-dependent and are not always available.

But what about human activity as a source of energy? Could energy be harvested from our day to day activities to help power our modern society?

There's a particular form of human activity that California has in spades: traffic. California has decided to run an experiment to see if energy can be harvested from vehicle vibrations on the road.

The Piezoelectric Idea

California has funded an experiment whereby roads which experience heavy traffic will be fitted with piezoelectric transducers to convert the vibration generated by vehicles (both stationary and in motion), into electricity. This electricity can then be fed into the grid to provide power for everything including buildings, homes, and street lights.

Piezoelectric energy harvesting is not “new” technology. It's actually been around for some time. In fact, energy harvesting from foot traffic has not only been proven but is in use in some places. For example, several train stations in Tokyo use piezoelectric energy to generate the power needed to run the ticket machines and electronic displays. Another example is a Dutch nightclub which uses piezoelectric tiles on the floor to power lights.


Tokyo uses piezoelectric tiles in some of its stations to power billboards. Image courtesy of the Japan Railways Group


However, will such a system work in traffic conditions and will enough electricity be generated to compensate for the cost?​

Cost For Piezoelectric Devices and Energy Output

Piezoelectric devices are more commonly used for generating sounds and measuring vibrations as opposed to generating electricity for energy consumption. This makes finding energy data for piezoelectric energy harvesting rather difficult. Luckily, there is a transducer for sale that is specifically designed for generating electricity in energy harvesters. Here are some of the specs given:
  • Open circuit voltage at rated deflection = 20.9V
  • Closed circuit current at rated deflection = 57 microamps
  • Power output at rated deflection = 7.1mW
  • Operating temperature = -20°C to 90°C
  • Dimension = 70mm x 31.8mm (height 1.5mm)
  • 1 piece = $301  :  100 pieces = $132
Given this data, we can roughly project that the amount of energy generated by piezo devices (50Hz vibration) is 3.189 W / square meter.
The cost for a single transducer (if purchased in bulk) would be $132 per device which gives a total cost of $60,000 per square meter (450 devices in a square meter). While this may seem like an unusually hefty sum of money, this is for a square meter of material that can stretch a long way if made narrow. In the case of California, the idea is to create a 60 meter stretch of road and use 2 cm wide piezoelectric generators in stacks. However, this suggests that the piezo devices used in the project will be of a more common type found in everyday electronics as opposed to devices specifically designed for energy harvesting (such as the one produced by Piezo Systems Inc).
Ler's look at an example where the pavement that is to be fitted with energy harvesters will be a complete strip of piezo material. Taking a pavement width of 1.5 meters, the total area of such a strip would be 90 meters square which results in a piezo cost of $5,400,000 and a total energy generation (assuming that all paving is occupied by people jumping at 50Hz) of 287.01W. It's more likely, however, that piezo devices would be scattered so, if we change the example to require a 10% coverage of piezo devices, the cost would be $540,000 with an overall energy output of 28.7W. 
Considering that a single 1KW solar panel can cost as little as $1000, the price for harvesting electricity from walking seems extreme.
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A Place for Cars?

There are issues beyond the costs of such a system; there is the practical side to consider, too.

Piezo generators work well in night clubs and train stations because people are generally unlikely to destroy their pathways. Since piezo devices rely on deflection to generate electricity, the footpath needs to allow for movement and vibration to maximize efficiently of the energy harvesting devices. This is not a problem for pedestrian areas as people are not very destructive, but roads that handle vehicle traffic are a different matter.


Piezo discs: Great for buzzing, not so much for cars. Image courtesy of Adam Wysocki [CC-BY-SA-3.0]


Roads must be built to resist damage from tires and debris if they are to be safe and reliable. As a result, roads have a tendency to not move around and deform under impact (instead they break into pieces). This makes placing transducers under roads problematic on two fronts. Either the road is built to allow vibrational energy to reach the transducers which potentially makes the road weaker or the transducers do not reach anywhere near their potential making them a costly investment.

Also, the world is shifting from internal combustion engines to electric batteries. Combustion engines tend to vibrate a lot, even when stationary. This is what the Californian system would rely on during heavy traffic. However, electric cars do not vibrate nearly as much when stationary, thus rendering the energy harvesters less effective.

This raises the question of whether this piezo road idea will age well as more and more consumers turn to electric cars. As a matter of fact, California has arguably been the global leader in the electric vehicle movement, giving China a run for its money in electric car sales. This isn't to say that electric vehicles would render traffic energy harvesting moot, but it's a factor that should be considered when investing millions of state dollars into infrastructure. 


Cars are incredibly destructive to modern roads. Image courtesy of the United States Department of Transportation


Perhaps the researchers working on this proposal will use a new type of device that can generate more electricity or maybe the stacks will be much larger. It's difficult to project how effective this system will be without knowing more details. It's difficult to imagine, however, how such a system could be successful enough to warrant expanding.

  • AEKron June 19, 2017

    I thought solar feakin’ roadways were bad enough, but piezo freakin’ roadways? why not stack the two together, and get double government grants?

    Like. Reply
  • I do not Consent June 22, 2017

    Be aware though, that these piezo devices are also used as microphones.

    Imagine the possibilities of microphones everywhere, matched with voice recognition systems…

    Arrays of microphones, which can determine where a person is, where they are, and how fast they are going - imagine the applications…

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  • O
    ozjon69 June 22, 2017

    Well, it doesn’t read like a practical concept - certainly not with Piezo generators at the prices suggested.
    However, MUCH cheaper piezo generators can be made with pieces of solid-dielectric coaxial cable, made so that the dielectric has high residual stress.
    Maybe, that could improve the economics enough to make the concept viable?
    This is proven technology (at low power levels)  - stressed cable has been used for many years on intruder detecting security fences.

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    pmd34 June 23, 2017

    So energy from nowhere huh?! Oh but wait, the deflection causes added road resistance, so the car fuel consumption has to go up to compensate. Still im sure they will get lots of research funding from the usual committees! Maybe you could make them out of graphine! Thats a sure fire application winner!

    Like. Reply
    • viki2000 June 23, 2017
      I find this idea not very smart and without a real future. The piezo ceramic membranes or buzzers used to produce a sound when a voltage is applied, the known application, suffers of low lifetime due to one reason: vibration. Most of the time the contact between membrane and the wire is cracked, the wire are broken right in that point. We speak here about thousands of hour’s lifetime under continuous vibration. Here is the opposite effect, with vibration due to mechanical tension in the membrane to get the voltage, but the connection is the same, the continuous vibration will reduce the lifetime of the transducer. It is not going to work for long time under continuous vibrations.
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  • T
    theace June 23, 2017

    This idea is so stupid that it cannot be described as it should using words (and yes, it’s on the same level as solar freakin’ roadways), but I’ll just make two remarks:
    1) you want your roads to be as stable and as long lasting as possible. Promoting something as vibration is extraordinary counter productive. You don’t want your roads to vibrate at all. Because vibration goes to potholes and in order to fix them you’ll spend more money than what you get on the energy you produce.
    2) where would that energy come from? you guessed it: from the cars. So, you’ll get the energy from burning fuel to the car to the road to the power grid. How stupid is that? So my car has to bounce up and down to give energy to the road. So I have to spend money on fuel to power the road with losses instead of producing more energy from the same fuel in a power plant.
    Yes, yes, the vibration could be collected from static cars (engine vibration), but wouldn’t be efficient to put this vibration generators on the cars themselves and power the battery instead of using fuel to spin the alternator?
    An the discussion can continue, but is pointless (see solar roadways).
    Now I’m asking the reporters on this site to stop posting this kind of bullshit on an otherwise interesting site. Just because it contains electronics, doesn’t mean it actually has a place here. You can do all sort of things with electronics, but this doesn’t mean that they belong here.

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      pmd34 June 23, 2017
      I wouldn't be too hard on the site, its important to know what people are up to, but more a brief "look at the crazy idea" angle, or debunking it would be better!
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  • P
    pmd34 June 23, 2017

    How do they get 7.1mW from Open circuit voltage 20.9V & Closed circuit current 57 microamps? Surely that’s an absolute maximum 1.1mW?!

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  • M
    MVPTrophies June 23, 2017

    I’m just glad I’m not the only one that thinks this is a dumb idea and waste of tax dollars… unless they have some crazy cheap new tech that also increases the Current generated, it’s not worth it. California needs to get its head out the smoke from the gravity bong. Some highschool math in a feasibility study would save them a lot of trouble for nothing.

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  • A
    amatbrewer June 23, 2017

    “$540,000 with an overall energy output of 28.7W” We could probably get more electricity out of simply burning the cash…

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  • F
    Frangi78 June 23, 2017

    This is absurd ! In order to get some energy transferred from a car to the road underground, the surface must be slightly flexible, thus increasing the drag against the wheels then fuel consumption ! Why not burn that extra fuel in a power station, with a much better efficiency than the piezo transducers. But the device may be considered for pedestrian actuation, adding some extra workout to their walk.

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  • B
    BarryR June 23, 2017

    There is no such thing as free energy. Someone is going to have to pay for it and you can be assured that it won’t be the government.

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  • J
    jjustin June 23, 2017

    You don’t identify the names and backgrounds of the people involved with this fiasco. I sense that they are of the same ilk as the charlatans that created Solyndra and bilked the taxpayers of over a half billion dollars.

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  • M
    mgksmoke June 23, 2017

    Uhm… really expensive delicate energy harvesting devices with no practical means to distribute insignificant power that get wiped out with the 1st pot hole and “create” energy from nowhere ...  This makes solar freak’n roadways look good. OK not good, but this is a new high in low. Lets steal some tax dollars, because, you never know…Oh wait there is that whole pesky physics thing.

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  • D
    Doktor Jones June 23, 2017

    While I’m still not sure this technology is viable, I think a lot of the naysayers here are grossly oversimplifying the physics.

    1. Many people here seem to think of asphalt as this rigid, immobile substrate; it’s not. Have you ever stood on the side of the road as a large truck goes by? Feel that vibration? Yup, asphalt isn’t immobile. Transducers beneath the asphalt would still pick up plenty of vibration.

    2. Some people are wondering where the energy is coming from or where it is going, positing that fuel consumption will go up because of “added road resistance” or the like. Guess what, cars vibrate already, and that vibration is already going into the asphalt. The only difference is, we’d be recapturing it instead of letting it dissipate into the asphalt (causing potholes!) and the ground (causing sinkholes!). Now I’m not suggesting that piezoelectric roads will magically be the end of potholes and sinkholes… heck, it probably won’t even significantly reduce them… but we’re simply taking energy that’s already there and redirecting it toward a constructive (if costly) use.

    3. Many people are concerned about the longevity of the transducers. While your usual cheapo transducers probably wouldn’t hold up to the stresses of a road very long, if the transducers were modified slightly to have a solid dielectric and either reinforcement or suspension around the electrical connections, I’m sure the lifespan could be significantly increased with a relatively minor increase in cost.

    4. Someone brought up the idea of the transducers being used as giant microphone arrays to identify and locate people. I don’t think this is likely, as most substrates durable enough to be driven over constantly by multi-ton trucks isn’t going to very easily transmit even the lowest frequencies of the human voice (the fundamental frequency of an adult male’s speech bottoms out around 80Hz).

    Finally, the author shoots down their own math, consistently running calculations based on the cost of the special energy harvesting transducers, continuing with these numbers even after extrapolating from other data that cheaper, more common transducers will be used… sounds like a bad case of confirmation bias to me.

    I’m not saying that piezoelectric roadways are technologically feasible in the long run (assembly, installation, durability) or cost effective… but people need to consider all the factors before immediately dismissing new technologies. Besides, I doubt California will just rip up all their roads willy-nilly and install piezoelectric roadways statewide. More likely, they will pick a couple of spots to do test runs (probably with different hardware and layouts), figure out how much electricity it generates, and do a cost analysis with *actual data* instead of wild speculation.

    Like. Reply
    • uwezi June 24, 2017
      ...of course you give some valid counter-arguments here, but the author of the original article even jumped over one aspect: energy/power density! If you are tapping into a very dilute source of power you also have to count in all the cabling and installation costs. The numbers for the 3W per square meter are quite sound - even on a cloudy day you will get about 15W electricity out of 1 square meter of solar cells assuming a modest 15% efficiency...
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  • R
    rep828 June 23, 2017

    Wow. This is the worst idea ever, in terms of green energy. Summary: Energy must come from somewhere, so the energy you harvest (however it’s harvested… piezoelectrics sounds like a terrible source, but whatever) comes from making it harder for the vehicles to move along the roadway, meaning they will burn more fossil fuels to generate whatever energy is produced. The better approach would be to just burn that extra fossil fuel directly and use a proven and relatively highly efficient power generation system, vs a really bad method like is being proposed in this article.

    Or was this just click-bait and I fell for it?

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  • A
    adx June 24, 2017

    Unfortunately it couldn’t be used for electric cars, because some smart alec would cotton on to the idea of running the cars off the power generated, and this would spiral out of control, leading to cars uncontrollably going faster and faster, ending in one single state-wide crash of epic proportions, leaving nothing to puncture the silence but the gentle tinkle of electrons rolling away from the scene (because they’re perfectly spherical, and blue). Maybe the odd creak from the enormous tangled pile of mangled Teslas. Autonomous control is no solution, because it hasn’t been invented yet.

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  • A
    alphaOmega June 29, 2017

    wow, nuts!
    How about this… instead of messing with something that is highly inefficient, take power from cars directly. The reverse of a plug-in hybrid, when you get home, Plug the car into an inverter that takes power from the car battery until the voltage drops by say 1volt, depending upon season/local temperature. 263M cars in the USA, 36M (registered for use) in the UK. (say 5Ah at 11.5V = about 207 000 joules. with a 0.5% usage would give about 37 billion joules per day in the UK, or about 430kw! 250+ Homes powered
    Convert parking meters to ‘dis’Charge units, and so pay for parking by fuelling the grid with excess current. A few sockets and diodes connected to a local inverter, cheap(er) & efficient.

    Like. Reply
  • A
    alphaOmega June 29, 2017

    wow, nuts!
    How about this… instead of messing with something that is highly inefficient, take power from cars directly. The reverse of a plug-in hybrid, when you get home, Plug the car into an inverter that takes power from the car battery until the voltage drops by say 1volt, depending upon season/local temperature. 263M cars in the USA, 36M (registered for use) in the UK. (say 5Ah at 11.5V = about 207 000 joules. with a 0.5% usage would give about 37 billion joules per day in the UK, or about 430kw! 250+ Homes powered
    Convert parking meters to ‘dis’Charge units, and so pay for parking by fuelling the grid with excess current. A few sockets and diodes connected to a local inverter, cheap(er) & efficient.

    Like. Reply