Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Highway Generator?

  1. Jun 26, 2008 #1
    A friend of mine posed the idea of having magnets on the bottom of cars drive over a large cage of conductor material buried under the pavement on the highway, as a way to generate electricity. Does this pose any practical application? Any immediate problems/concerns come to mind? I haven't had much time to give it thought, so I figured I'd ask around.
  2. jcsd
  3. Jun 26, 2008 #2


    User Avatar

    Staff: Mentor

    The drivers would be pretty pissed at the lower gas mileage they would be getting. The energy produced by the generator apparatus has to come from somewhere, and that somewhere is the extra load (extra "rolling resistance") on the cars, with increased gas consumption to offset the higher load. It would be more efficient to use that amount of gas in simple gasoline-fired generators.
  4. Jun 26, 2008 #3
    Eddy currents generated in the metal chassis of the car as it crosses the magnetic field lines would exert a force thus slowing the car down. To overcome that, the car would to use burn more gas.

    Magnetic braking like this is utilized in roller coasters.
  5. Jun 27, 2008 #4
    Oh man, this is one of the stranger ones I have heard. One could absolutely generate electricity in this manner, but the practicality depends heavily on the motivation. If you are trying to generate power for the community, many problems arise. This system is reliant on petrochemicals, and as pointed out by Berkeman, would likely be incredibly inefficient. The only way to make this happen would be through some really bizarre political corruption scenario. However, if this were done covertly for an individual, it might work. I guess that if an array of coils were placed under a busy highway, one could generate quite a bit of electricity. Though, start up costs would be high and it would be difficult to this subtly. Yet, in the end, inefficiencies don't matter much if the outcome is cheap- having been stolen. This idea could only be useful as a some pyramid scheme or something you'd read about in your email's spam folder between messages about foreign bank accounts and anotomorphic pills. Interesting idea though. It is good to be brainstorming solutions to the world's greatest dilemma ever. Keep it coming!
  6. Jun 30, 2008 #5
    What if the car was not made of metal? Get the car companies in bed with the electric companies to create an entire system...at least theoretically, if a magnetic core was strapped to the bottom of a strong non-metallic chassis, would there still be a problem with eddy currents? Or what about using a different fuel rather than gasoline...like I said, theoretically, in some i-robot society could this work? Rather than flaws, are there any improvements that could make this a viable form of energy production?
  7. Jul 1, 2008 #6


    User Avatar
    Science Advisor
    Gold Member

    No, there is no way to generate energy this way simply because energy has to come from somewhere (remember that you can neither create nor destroy energy, just "convert it" between different forms), in this case whatever is used as a fuel in the car.
    Fuel is just a form of "chemical energy" and a car works by converting that energy to kinetic energy (+compensate for losses due to friction etc), the only thing that would happen if you put magnets (or whatever) in the road is that some of that fuel would be converted to "electrical energy" instead.
    I.e. since the total energy would be the same the cars would either slow down or consume more fuel, the details of how you do it does not matter.
  8. Jul 1, 2008 #7
    I understand all of that. I think the point is being lost...no matter what, there will be inefficiencies for the driver, whether it simply be needing more gasoline to push the extra weight of the magnet, or the eddy currents (which, if the car was not made of metal, could this be avoided?). But the point is that it is a system that not only gets a person from point A to point B, but also generates (through conversion) electricity. More fuel will always be needed, but is there a practical way to incorporate two systems into one (transportation and power production)?

    Also, even though more fuel will be required, there will be an extra source of electricity being produced, which will bring down energy costs. So economically the costs of fuel would rise but the cost of electricity SHOULD, in a perfect classical economy, fall. *Perpetual motion device alarm: what if the cars RAN on electricity! haha

    Rather than post the proposed answer, how about more simply, the question:

    "Is there any energy being "wasted" by moving cars that can be harnessed (converted) into electrical energy in a practical way?"
  9. Jul 1, 2008 #8
    Removing the power production from the cars entirely, and instead powering them from the grid, would be a much better idea than trying to use gas cars to generate electricity. It would take less infrastructure, and be more efficient, than sucking energy back out of gas cars.

    Yes, but it wouldn't fall by nearly as much as fuel costs would increase, because the system would be drastically less efficient than regular power generation. Nor would it fall by as much as if you simply burned the extra fuel in a gas-fired generator.

    That is the only possible way that such a system could be worthwhile. You could imagine building such a system into intersections, and providing extra stopping force to vehicles approaching the red light, and generating electricity in the process. However, I'd think that just using regenerative braking in the cars themselves would be both more efficient and cheaper.
  10. Jul 1, 2008 #9
    quadraphonics, thank you for the insight. I think you've satisfied all my questions regarding this idea.
  11. Jul 1, 2008 #10


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    You are running the system backwards, rather then using the cars to drive a power grid, we could use the power grid, supplied by a clean efficient source, to drive the cars. This would eliminate the need for batteries or fuel in the individual car. Of course either of these plans require a huge investment in the infrastructure required to make it work. How many miles of copper wire do you suppose it would take?

    I have been dreaming of this system for years, however the expense of materials and installation would be HUGE. Beyond that the sacrifice of individual freedoms, because the whole system would be controlled by a master computer, would be incompatible with the American way of life.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook