# Would power generating roads be possible?

**URL:** <https://boards.straightdope.com/t/would-power-generating-roads-be-possible/706165>\
**Category:** Factual Questions\
**Created:** [December 2, 2014, 9:47pm UTC](https://boards.straightdope.com/t/would-power-generating-roads-be-possible/706165 "2014-12-02T21:47:44Z")\
**Posts on this page:** 20\
**Page:** 1

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**Author:** ![boffking](https://avatars.discourse-cdn.com/v4/letter/b/858c86/32.png) [@boffking](https://boards.straightdope.com/u/boffking)\
**Post date:** [December 2, 2014, 9:47pm UTC](https://boards.straightdope.com/t/would-power-generating-roads-be-possible/706165/1 "2014-12-02T21:47:44Z")

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I have heard of systems being installed in train stations that produce electricity from all of the people walking on the floors. Would it be possible to have roads that do the same thing when cars drive over them?

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**Author:** ![YamatoTwinkie](https://avatars.discourse-cdn.com/v4/letter/y/cc9497/32.png) [@YamatoTwinkie](https://boards.straightdope.com/u/YamatoTwinkie)\
**Post date:** [December 2, 2014, 9:59pm UTC](https://boards.straightdope.com/t/would-power-generating-roads-be-possible/706165/2 "2014-12-02T21:59:02Z")

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Sure, its possible, but that energy doesn’t come for free. The car would need to burn an extra amount of gas to maintain its current speed, after being restricted by whatever mechanism you’re proposing to harvest kinetic energy from the moving car. Once you factor in electricity generation efficiencies, the net result is that you’re just wasting energy.

If power generation is the goal, its far better to just skip the middle man and burn the gas directly in a generator.

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**Author:** ![MichaelEmouse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/michaelemouse/32/101_2.png) [@MichaelEmouse](https://boards.straightdope.com/u/MichaelEmouse)\
**Post date:** [December 2, 2014, 9:59pm UTC](https://boards.straightdope.com/t/would-power-generating-roads-be-possible/706165/3 "2014-12-02T21:59:13Z")

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Possible, yes. Economic, no.

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**Author:** ![lazybratsche](https://avatars.discourse-cdn.com/v4/letter/l/ba8739/32.png) [@lazybratsche](https://boards.straightdope.com/u/lazybratsche)\
**Post date:** [December 2, 2014, 9:59pm UTC](https://boards.straightdope.com/t/would-power-generating-roads-be-possible/706165/4 "2014-12-02T21:59:30Z")

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In theory, sure. But it’s not free. You’ll only capture a fraction of the energy created by each small, inefficient car engine. Car engines are only ~20-30% efficient anyways, and there will be additional losses in whatever mechanical gubbins you use to generate electricity.

It’s way more practical to just build a power plant which is 50-60% efficient.

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**Author:** ![ExTank](https://avatars.discourse-cdn.com/v4/letter/e/35a633/32.png) [@ExTank](https://boards.straightdope.com/u/ExTank)\
**Post date:** [December 2, 2014, 10:02pm UTC](https://boards.straightdope.com/t/would-power-generating-roads-be-possible/706165/5 "2014-12-02T22:02:11Z")

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[Any objections to Solar Roadways?](https://www.youtube.com/watch?v=Ep4L18zOEYI)

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**Author:** ![MichaelEmouse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/michaelemouse/32/101_2.png) [@MichaelEmouse](https://boards.straightdope.com/u/MichaelEmouse)\
**Post date:** [December 2, 2014, 10:17pm UTC](https://boards.straightdope.com/t/would-power-generating-roads-be-possible/706165/6 "2014-12-02T22:17:53Z")

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> [@ExTank](#):
>
> [Any objections to Solar Roadways?](https://www.youtube.com/watch?v=Ep4L18zOEYI)

They’re a great example of the fact that delusions and scams can be difficult to tell apart in business ventures.

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**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\
**Post date:** [December 2, 2014, 11:20pm UTC](https://boards.straightdope.com/t/would-power-generating-roads-be-possible/706165/7 "2014-12-02T23:20:28Z")

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> [@ExTank](#):
>
> [Any objections to Solar Roadways?](https://www.youtube.com/watch?v=Ep4L18zOEYI)

Yes, lots.

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**Author:** ![Habeed](https://avatars.discourse-cdn.com/v4/letter/h/a587f6/32.png) [@Habeed](https://boards.straightdope.com/u/Habeed)\
**Post date:** [December 2, 2014, 11:21pm UTC](https://boards.straightdope.com/t/would-power-generating-roads-be-possible/706165/8 "2014-12-02T23:21:41Z")

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> [@ExTank](#):
>
> [Any objections to Solar Roadways?](https://www.youtube.com/watch?v=Ep4L18zOEYI)

Specifically, the issue is that it costs a certain amount of raw materials and labor, M, to make a section of good roadway.

It costs a certain amount of materials and labor, S, to make a good solar panel.

It costs a huge amount of materials and labor, X, to make a section of solar roadway, and

X \>\>\>\> S + M. That is, a piece of solar roadway of a given size costs a lot more money than a piece of roadway and a piece of solar panel that each do the same jobs.

Another way to look at it : a jet fighter dump truck isn’t impossible. You could make an absurdly huge vehicle that had the cargo capacity of a dump truck and yet was big enough to compensate for the dead weight of the dump truck load and still be a usable jet fighter(see the space shuttle for an example). But the cost of doing that is far, far more than just making 2 separate vehicles.

The only way a solar roadway ever made sense is if land were incredibly expensive, such that the equation looks like :

X + land\_cost \<= S + M + 2\* land\_cost

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**Author:** ![drachillix](https://avatars.discourse-cdn.com/v4/letter/d/48db29/32.png) [@drachillix](https://boards.straightdope.com/u/drachillix)\
**Post date:** [December 3, 2014, 12:16am UTC](https://boards.straightdope.com/t/would-power-generating-roads-be-possible/706165/9 "2014-12-03T00:16:12Z")

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I had heard it opined that something like pole barns over freeways would be more cost effective than solar embedded roadways. Bonus, shaded roads.

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**Author:** ![jtur88](https://avatars.discourse-cdn.com/v4/letter/j/e9c0ed/32.png) [@jtur88](https://boards.straightdope.com/u/jtur88)\
**Post date:** [December 3, 2014, 12:25am UTC](https://boards.straightdope.com/t/would-power-generating-roads-be-possible/706165/10 "2014-12-03T00:25:13Z")

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Not to mention the fact that every car would need two completely separate power plants – one to run on the road-sourced energy, and one to operate on roads that are not power-producing.

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**Author:** ![USCDiver](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/uscdiver/32/354_2.png) [@USCDiver](https://boards.straightdope.com/u/USCDiver)\
**Post date:** [December 3, 2014, 12:33am UTC](https://boards.straightdope.com/t/would-power-generating-roads-be-possible/706165/11 "2014-12-03T00:33:18Z")

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> [@jtur88](#):
>
> Not to mention the fact that every car would need two completely separate power plants – one to run on the road-sourced energy, and one to operate on roads that are not power-producing.

What? The Solar Roadway doesn’t directly power the vehicles.

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**Author:** ![Tim\_T-Bonham.net](https://avatars.discourse-cdn.com/v4/letter/t/46a35a/32.png) [@Tim\_T-Bonham.net](https://boards.straightdope.com/u/Tim_T-Bonham.net)\
**Post date:** [December 3, 2014, 12:35am UTC](https://boards.straightdope.com/t/would-power-generating-roads-be-possible/706165/12 "2014-12-03T00:35:21Z")

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> [@YamatoTwinkie](#):
>
> Sure, its possible, but that energy doesn’t come for free.

> [@lazybratsche](#):
>
> In theory, sure. But it’s not free.

Well, it could be free, to the owner of the road, since it’s the car drivers who are paying.

Say, for example, that the owner of a parking ramp put a weight-activated generator at the entrance & exit of the ramp, that would generate electricity when cars drove over it. Then the car driver would pay a bit more in reduced mileage when driving over this, and the ramp owner would get electricity that is free to him.

(In real-world economics, it seems like it would be real tough to generate enough electricity to pay back the costs of installing this system in a reasonable number of years, though.)

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**Author:** ![Tastes\_of\_Chocolate](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tastes_of_chocolate/32/3232_2.png) [@Tastes\_of\_Chocolate](https://boards.straightdope.com/u/Tastes_of_Chocolate)\
**Post date:** [December 3, 2014, 5:38am UTC](https://boards.straightdope.com/t/would-power-generating-roads-be-possible/706165/13 "2014-12-03T05:38:24Z")

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A more reasonable idea would be small wind generators (think pinwheels) lining the sides of the road, and harvesting small amounts of wind energy. Cars wouldn’t become less efficient by using it, but the amounts would be small and stretched along hundreds of miles of road.

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**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\
**Post date:** [December 3, 2014, 6:06am UTC](https://boards.straightdope.com/t/would-power-generating-roads-be-possible/706165/14 "2014-12-03T06:06:18Z")

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> [@Tastes\_of\_Chocolate](#):
>
> A more reasonable idea would be small wind generators (think pinwheels) lining the sides of the road, and harvesting small amounts of wind energy. Cars wouldn’t become less efficient by using it, but the amounts would be small and stretched along hundreds of miles of road.

Are you suggesting harvesting the wake energy from cars as they pass by? Because that would, in fact, make cars less efficient.

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**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\
**Post date:** [December 3, 2014, 8:10am UTC](https://boards.straightdope.com/t/would-power-generating-roads-be-possible/706165/15 "2014-12-03T08:10:12Z")

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> [@Tastes\_of\_Chocolate](#):
>
> A more reasonable idea would be small wind generators (think pinwheels) lining the sides of the road, and harvesting small amounts of wind energy. Cars wouldn’t become less efficient by using it, but the amounts would be small and stretched along hundreds of miles of road.

You’re overestimating the available energy in wake energy by a factor of lots.

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**Author:** ![Der\_Trihs](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/der_trihs/32/233_2.png) [@Der\_Trihs](https://boards.straightdope.com/u/Der_Trihs)\
**Post date:** [December 3, 2014, 11:49am UTC](https://boards.straightdope.com/t/would-power-generating-roads-be-possible/706165/16 "2014-12-03T11:49:15Z")

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> [@YamatoTwinkie](#):
>
> Sure, its possible, but that energy doesn’t come for free. The car would need to burn an extra amount of gas to maintain its current speed, after being restricted by whatever mechanism you’re proposing to harvest kinetic energy from the moving car. Once you factor in electricity generation efficiencies, the net result is that you’re just wasting energy.

Not necessarily; cars themselves for example can scavenge useful energy that would be otherwise wasted by using [regenerative braking](http://en.wikipedia.org/wiki/Regenerative_brake). That however demonstrates the actual problem with the idea; while you could build some kind of system into the road to do that, it’s just much simpler to build it into the car.

> [@ExTank](#):
>
> [Any objections to Solar Roadways?](https://www.youtube.com/watch?v=Ep4L18zOEYI)

> [@Habeed](#):
>
> Specifically, the issue is that it costs a certain amount of raw materials and labor, M, to make a section of good roadway.
> 
> _\<snip\>_
> 
> X \>\>\>\> S + M. That is, a piece of solar roadway of a given size costs a lot more money than a piece of roadway and a piece of solar panel that each do the same jobs.
> 
> _\<snip\>_
> 
> The only way a solar roadway ever made sense is if land were incredibly expensive, such that the equation looks like :
> 
> X + land\_cost \<= S + M + 2\* land\_cost

Or, technology is developed that greatly reduces the price of materials and labor for making a solar road - which we can’t do _yet,_ but likely isn’t _impossible._

For example, one idea I’ve heard of for making solar roads, solar paint and the like is to mix in microscopic solar-gathering devices in the base material which link themselves together during or after the material sets. Spray-on solar panels, basically. Then you just attach a cable to the edge to draw off the gathered energy. Something like that if we could make it could make solar roads sensible, since the difference in labor would be negligible, and the difference in material costs might be not that bad depending on what the microscopic widgets are made out of.

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**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\
**Post date:** [December 3, 2014, 1:19pm UTC](https://boards.straightdope.com/t/would-power-generating-roads-be-possible/706165/17 "2014-12-03T13:19:46Z")

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> [@Habeed](#):
>
> a jet fighter dump truck isn’t impossible.

That’s great news. How do I get on the waiting list?

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**Author:** ![Dag\_Otto](https://avatars.discourse-cdn.com/v4/letter/d/439d5e/32.png) [@Dag\_Otto](https://boards.straightdope.com/u/Dag_Otto)\
**Post date:** [December 3, 2014, 1:38pm UTC](https://boards.straightdope.com/t/would-power-generating-roads-be-possible/706165/18 "2014-12-03T13:38:56Z")

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> [@Machine\_Elf](#):
>
> That’s great news. How do I get on the waiting list?

Read the next sentence of **Habeed’s** post. It’s a DIY project.

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**Author:** ![enipla](https://avatars.discourse-cdn.com/v4/letter/e/54ee81/32.png) [@enipla](https://boards.straightdope.com/u/enipla)\
**Post date:** [December 3, 2014, 1:59pm UTC](https://boards.straightdope.com/t/would-power-generating-roads-be-possible/706165/19 "2014-12-03T13:59:48Z")

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I like the comparison of ‘Solar Roadways’ to fighter jet dump trucks. Could we do it? Sure. Does it make a lick of sense? Not at all. Anyone with a bit of common sense, and 10 minutes of time to think about it would come to the same conclusion.

Another example I like is ‘Could we make a car with square wheels’? Yep, we could.

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**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\
**Post date:** [December 3, 2014, 2:25pm UTC](https://boards.straightdope.com/t/would-power-generating-roads-be-possible/706165/20 "2014-12-03T14:25:20Z")

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> [@Der\_Trihs](#):
>
> Spray-on solar panels, basically.

Used on a roadway, you’d have the problem that the vehicles are constantly wearing away your valuable solar panel. Repairing by re-spraying looks difficult - very tricky to re-establish electrical connections.

Sounds like a promising technology for the year 2200.

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