I have an idea for generating electricity using the national highway system. Yes, that’s what I said. No, I’m not insane. I’m not a scientist either but it seems logical to me. Now I need intelligent dopers to tell me what about it is idiotic and won’t work. The idea is simple:
Take a busy section of interstate. Put some sort of spring-type mechanism or pressure plate under the road. The kinetic energy generated by the difference in weight between car-on-road and road-without-car is converted to electricity.
Would this work? I’m guessing it wouldn’t or someone would already be doing it… but if it wouldn’t, why?
it could work but it would take a massive maintance crew to maintain such a network. A better solution is a home co-generation plant. Most homes burn fuel (oil or gas) - how about instead of just burning it for heat have it power a generator and use the waste heat to heat your home.
What do you mean “sure it would work”? If you mean getting any energy for free sure it would not work! First the generating equipment would be complex and expensive and high maintenance. But where is the energy coming from? The motors in the cars! You think it is a good idea to burn more gasoline to generate more power so you can recover a miniscule part of that at a huge cost?
You could make a power generation system like this, but I’m not sure how much energy you could get out of it. It wouldn’t matter, anyway, since whatever energy you got out of it would just come from the gas the cars are burning: A car sitting on a slightly depressed segment of road driving onto the next, non-depressed section would need to burn more gas than a car driving on a level, firm road. Either you piss off a bunch of drivers for basically stealing energy from them, or you reimburse them somehow for the extra gas they have to buy, and you might as well just buy the gas directly and burn it in a conventional generator.
I never said anyone was getting energy for free. I said “sure it would work” because it is perfectly possible to get energy from the motion of cars. Like I said originally, it would be very inefficient, and probably useless. But it [i[would* work.
Well, of course, my idea was that if the cars are going to be driving on the road, spending that energy anyway it might be a good idea to recapture some of it.
I suppose putting windmills on the road to capture the breeze from passing cars or solar panels along the stretches of highway which point at car headlights at night wouldn’t work too well either.
Efficiency aside (and it’s ridiculously inefficient), I’m not sure the postulated mechanism would work. On a busy road, you’d have an almost continous stream of cars so your springs or whatever would never really have a chance to spring back. (Or even worse, it would be like driving down a very washboarded road – bumpy as hell.)
I’m not sure if it’s the relevant equation, but work = F*D. So any large amount energy would have to be extracted from a fairly significant depression of the road bed. This is pretty much what road engineers spend a lot of time making sure doesn’t happen.
Basically the idea you’re groping for here is the same as tidal energy generation and no one’s managed to make that practical yet, despite the much larger mass of displaced ocean water and significantly easier logistics.
How do power plants generate electricity? They pass a magnet past a wire or two a few jillion times a second, no? Or maybe that pass wires through magnets. I don’t know, but those are the basics, I think.
Asking from the perspective of would this work, I wonder if a chunk of the car’s frame could be magnetized and driven over a series of wires embedded in the road. The force pulling the car down wouldn’t be that great, would it? And even if it was more than marginal, wouldn’t it add to a car’s traction, allowing for different tire designs to overcome the extra burden?
I can’t imagine it would be practical, but would it be feasible?
I was thinking of more like a sensor that when compressed would produce a voltage not so much springs as in the OP - the compressability would not be much more then asphalt
The problem is that the reaction force felt by the car wouldn’t be downwards, it would be backwards. Every time the car drove over a road-imbedded coil array it would experience drag. To overcome that the car’s engine would have to work harded, burning a bit more fuel in the process.
It could be built, but the net effect would be to generate a little bit of surplus electricity at the cost of lowering the fuel efficiency of every car on the road. You’d be better off just building a big oil-fueled power plant and burning the fuel there instead - it would be chaper and more efficient. The same goes for the pressure plate system in the OP. There’s no free lunch - the energy has to come from somewhere.
No, the Rance scheme is a tidal power plant, not a wave power plant.
Wave power is still under development and is approaching commercialisation.
The idea expressed in the OP has been suggested in all seriousness by an engineering lecturer at the Dundalk Institute of Technology. It is perfectly feasible, and would involve taking a little energy from motorists as they drive over “speed bumps”.
It’s probably feasible, but why make drivers pay for other people’s electricity? If you were going to do that, it’d be cheaper and more efficient to just add another tax on gasoline.
>> The idea expressed in the OP has been suggested in all seriousness by an engineering lecturer at the Dundalk Institute of Technology
I have seen it proposed by some guy on TV once and in a newspaper another time and both times it was treated seriously which is a sad reflection on the reporters who did the interview. They were treating the idea like they had just discovered a huge untapped source of free energy when any physics teacher could and would have set them straight.
I have also read similar reports about motors which would work with water (fuel cells) and other such things. The latest was a report on TV saying that “In China they have passed a law so that defendants would be considered guilty until they proved their innocence… in civil trials” Of course, the reporter ignores that in a civil trial two parties are settling a dispute and there is no such thing as guilt or innocence. She had mixed up things so badly that the blurb was meaningless… but I am sure that day many people’s opinions about China were worsened.
A car spends energy doing two things: Getting up to speed, and overcoming friction (mostly air resistance). About all you can practically do about the energy lost to air resistance is to reduce it, by making cars more aerodynamic. This is done to some degree, but appearance of a car is also a major factor to most consumers, which limits how much car engineers can change the shape.
On the other hand, there is the energy you need to spend to get up to speed. In most cars, when you hit the brakes, this energy is just lost. This is one of the virtues of hybrid or electric cars: They use something called regenerative braking, where most of the kinetic energy the car looses during braking is re-converted to electrical energy and stored in the battery. One might conceivably also put coils in the road at intersections to slow down conventional cars and feed the energy into the grid, but this would probably present more problems than it’d be worth.
It might work if you put it on a downhill road. The cars will use the brakes to slow down anyway, so that’s wasted energy that might be recovered. Same with a freeway off ramp.
Still, I don’t think it will be very practical for the reasons already given.
In order to “feed energy into the grid” the source has to be of precisely the correct frequency. And the power company is finicky about frequency. You can tell this by the accuracy with which your electric clock keeps time.
None of the schemes mentioned so far would generate 60-hz alternating current with any degree of precision.
The connection to the grid also has to be done when the source and and the grid are in phase. This is has to be done with precision, otherwise there would be a large transient current which shouldn’t bother the grid any but could easily damage your low power source.
It’s would probably be wise to move on to some other idea, this is a loser.
this has been discussed many times on the SDMB - clocks keep time on the vibration of a quarts crystal - older clocks will run in peridiodic movment of a pendulem or spring-mass system.
