Tapping the hot asphalt jungle for energy

Pavement, it turns out, is a pretty good place to look for free energy.

A handful of Massachusetts researchers on Monday published a paper detailing a technique for using water-carrying pipes to convert the built-up heat in asphalt roads into usable energy.

Researchers measure ways to transfer heat from a source, such as this lamp shining over asphalt, to water.

(Credit: Worcester Polytechnic Institute)

Released at the International Symposium on Asphalt Pavements and Environment in Zurich, Switzerland, the paper argues that asphalt roads have a number of advantages over solar-electric panels as a source of distributed energy.

"The significance of this concept lies in the fact that the massive installed base of parking lots and roadways creates a low-cost solar collector an order of magnitude more productive than traditional solar cells. The significantly high surface area can offset the expected lower efficiency (compared to traditional solar cells) by several orders of magnitude, and hence result in significantly lower cost per unit of power produced," according to the paper.

Blacktops can continue to generate energy after the sun goes down, and upgrades with heat exchangers could be fit into road constructions, which are done every 10 to 12 years, Rajib Mallick, associate professor of civil and environmental engineering at Worcester Polytechnic Institute, said in a statement.

Also, wicking heat away from roads could reduce the "heat island" effect in densely populated areas where temperatures rise when buildings and pavement release heat accumulated during the day.

The researchers used computer modeling and small-scale prototypes to test alternatives to pipes for transferring asphalt heat to water.

It found that the depth of the heat exchanger was critical and that a material with higher heat conductivity, such as quartzite, can be added to asphalt to improve heat transfer.

The hot water from the roads could be used in neighboring buildings, something that has already been done in the Netherlands. A more sophisticated approach would be to convert the heat into electricity using thermoelectric modules.

"Our preliminary results provide a promising proof of concept for what could be a very important future source of renewable, pollution-free energy for our nation. And it has been there all along, right under our feet," Mallick said.

[headinclouds]

what about the vibration from constant traffic is this useable energy

[Harlan879]

In theory, but it's a bad idea. Capturing the vibration from traffic would, from a car's point of view, make the road surface less rigid. To capture the energy, you have to let the road flex as cars drive over it, then capture the energy of the motion. In addition to possibly reducing handling, it would reduce gas mileage of the vehicles that drive on it. (Think about the extra effort it takes to walk on sand.) So no net gain in energy.

[bigmc6000]

That's freakin' genius! Now that's the kind of stuff we need!

[No Man]

I love the theory, but I'm doubtful about its application. Asphalt roads are already high maintenance without filling them with pipes. Road repair costs would increase by several orders of magnitude if every road crew had to include plumbers and plumbing materials for every job, not to mention the extra hours of labor spent waiting for the piping to be repaired before the surface could finally be patched. For any area prone to potholes, or any road allowed to have heavy trucking, this would be a totally unfeasible plan, and that probably eliminates 90% of U.S. roads. My guess is that it would end up cheaper to cover the adjacent buildings with solar panels.

[billmosby]

You're right, No Man.

One other thing might deserve consideration, and that is that the heat collected by the paving material is already in use to some extent where I live- to help de-ice the road in winter. After a snowfall it looks to me like both previously stored heat plus heat from the sun that does penetrate the snowfall hastens the snow melt process. They do use salt around here, but I have lived in places where it was not used and the melting still proceeded almost as fast on a sunny day. Carry all that heat away and we might just have ice roads in places like this. Salt doesn't work below a certain temperature- I think it takes both salt and sun, or just sun, to get the job done.

Instead of covering the adjacent buildings with solar panels, though, how about using this asphalt system. Not too pretty, and awfully heavy, but perhaps cost-effective? Or would that be going a bit too far!

[mbk_2k3]

I agree with No Man that implementation would be difficult, but I doubt it'd cost more than covering a building with solar panels.

I do think that he's right on several issues. What about insulation? How do people prevent these pipes from freezing over?

[shoffmueller]

the problem with this concept is the group who is responsible for the paving maintenance. For parking lots, its the mall. For streets, it's the city. They would have no incentive to incorporating heating/energy into their building/maintenance costs.

[kieranmullen]

Should we not build things to last out of concrete instead of oil laden Asphalt?

KieranMullen
http://360oregon.com

[billmosby]

Concrete doesn't seem to last as long in freeze-thaw conditions as asphalt does, at least where I have lived. Plus, asphalt seems to be easily recyclable- in the last several years, asphalt repaving jobs on highways around here seem to have partly included use of asphalt removed and ground up using pavement mills and put right back down mixed in with some fresh asphalt.

Making the portland cement component of concrete takes a large amount of energy, so I have read.

[squished]

Surfaces of mall parking lots rarely get repaved and I'm sure many mall owners would be interested in saving loads on their electric bills by implementing such a system (assuming cost effectiveness and capability of thermoelectric modules).

To those concerned about freezing in the winter, perhaps this tech could double as a de-icer by heating the water with supplemental power source thereby eliminating much of the costly plowing, sand/salt, and accidents that occur with snowfall and ice. Roads might last longer too without the freeze/thaw cycle.

Regular road maintenance is an interesting hurdle and I'd be curious to know how deep these pipes get buried. If deep enough, most repaving maintenance probably wouldn't interfere. Overall, this seems like one of those inventions where you think why haven't we thought of or done this before?

[billmosby]

I'd think the pipes would have to be closer to the surface rather than deeper, because the deeper you go the closer to the constant-temperature part of the soil you get.

As to putting energy into the system to de-ice it in the winter, roads already do that by themselves to a great extent, at least in the daytime. To make an active system out of it would be fine (in fact, it is done now by rich people in cold climates for their driveways etc), but it seems to me you would just be coming out somewhat even as far as energy production was concerned, if not actually losing it depending on the climate involved.

[gilmichlin]

In which year do you predict will be the first asphalt road that produced renewable energy?
http://digg.com/environment/Using_pipes_to_convert_heat_in_asphalt_roads_into_energy

[AVE_fan]

While the idea of recovering heat from urban areas is sound, this method would be way too expensive.

A much cheaper method for recovering excess urban heat has already been invented. It's called the Atmospheric Vortex Engine (ref: http://vortexengine.ca)

When combined with the Convective Available Potential Energy (aka CAPE) also contained in the atmosphere, especially during the summer, hundreds of MW of energy can be recovered using conventional turbo-generators (windmills) which make electricity by recovering the energy contained in the flowing air. This "spent" air is then "exhausted" to the upper troposphere within a vortex created by the device by installing thousands of internal airfoil "deflectors" (or by other means).

The device is similar in concept to the Enviromission project, except much cheaper. For an animation, check out the technology tab at their website. The AVE, however, needs no tall tower nor does it need a large "skirt" covered with transparent plastic. It also will not require solar ponds that collect heat during the day and give it up during the evening.

In a city, the buildings and asphalt surfaces collect heat during the day and give it up to the in-rushing air during the evening as the AVE operates 24/7. For a lesson on how solar energy is stored in CAPE, visit http://tornadochaser.net (CAPE_class)

There is evidence that "natural" tornadoes intensify over urban areas containing excess heat. The one which hit downtown Atlanta about 6-9 months ago intensified unexpectedly to an F-2 at the last moment.

[knyghts01]

AVE fan Great idea, but completely irrelevant.

As far as maintenance, the pipes below the surface would be something cheep, like PVC plastic or something. there would be no maintenance. theses things would be completely locked in, like radiant floor heating systems. asphalt lifespan is around 10-15 years, so any system installed would be there for the long haul, and the decreased temperature differential would likely increase the roadways' lifespan!

The only feasible way to do this would be to install it in surfaces being repaired anyway. you see roads getting replaced all the time why not install the energy generating feature then?