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Four ways to harvest solar heat from roads

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November 10, 2010

University of Rhode Island graduate student Andrew Correia (left) and Prof. K. Wayne Lee, ...

University of Rhode Island graduate student Andrew Correia (left) and Prof. K. Wayne Lee, measuring the solar energy generated by a patch of asphalt

Walk barefoot on an asphalt road and you'll soon realize how good the substance is at storing solar heat – the heat-storing qualities of roadways has even been put forward as an explanation as to why cities tend to be warmer than surrounding rural areas. Not content to see all that heat going to waste, researchers from the University of Rhode Island (URI) want to put it to use in a system that harvests solar heat from the road to melt ice, heat buildings, or to create electricity.

“We have mile after mile of asphalt pavement around the country, and in the summer it absorbs a great deal of heat, warming the roads up to 140 degrees or more,” said Prof. K. Wayne Lee, leader of the URI project. “If we can harvest that heat, we can use it for our daily use, save on fossil fuels, and reduce global warming.”

The research team has four main ideas for how that harvesting could be performed.

Cells on barriers

A relatively simple method of harnessing the sunlight shining on the road, if not the heat stored in it, is to wrap flexible photovoltaic cells around the top of the Jersey barriers on divided highways (Jersey barriers are those long rectangular concrete slabs). These cells could also be embedded in the asphalt between the barriers and the adjacent rumble strips. The electricity generated by the cells could be used to power streetlights and illuminate road signs.

Water pipes in the road

Another approach would be to install water-containing pipes within the asphalt. As the road heated up, so would the water, which could then be piped underneath a bridge deck to reduce icing, used to heat or provide hot water for nearby buildings, or even turned to steam at a power plant. URI grad student Andrew Correia has created a prototype for such a system, which he hopes will demonstrate how it could actually work in the real world.

Thermo-electricity

A small amount of electricity can be created by connecting two semiconductors to form a circuit linking a hot and a cold area. If those semiconductors were embedded in the road at different depths, or in sunny and shady areas, then the difference in temperature between them could conceivably be used to generate electricity. If enough of them were used together, their electrical output could be used for purposes such as defrosting roadways. URI’s Prof. Sze Yang proposes that instead of traditional semiconductors, inexpensive plastic sheet organic polymeric semiconductors could be used.

Electronic block roadways

In what the researchers admit would be the most costly option, asphalt roads could be replaced with roads made from clear-yet-durable electronic blocks. These would contain photovoltaic cells, LED lights and sensors, and could generate electricity, display changeable lane markings, and display illuminated warning messages. Idaho’s Solar Roadways has been working on just such a system, although according to Lee, a driveway made with the blocks cost US$100,000 to create. He believes that such technology may first show up in corporate parking lots, before decreased costs allow it to be used for public roads.

About the Author
Ben Coxworth An experienced freelance writer, videographer and television producer, Ben's interest in all forms of innovation is particularly fanatical when it comes to human-powered transportation, film-making gear, environmentally-friendly technologies and anything that's designed to go underwater. He lives in Edmonton, Alberta, where he spends a lot of time going over the handlebars of his mountain bike, hanging out in off-leash parks, and wishing the Pacific Ocean wasn't so far away.   All articles by Ben Coxworth
7 Comments

I am intrigued by the idea of using heat generated by the sun to melt ice on the road. It is not something that happens naturally? Presumably the road gets hot mostly in the summer months, and in the winter doesn't get very hot at all. If the road is frozen, is not hot!

This idea of using heat from Tarmac, probably applies to a large number of flat roofs in cities. Why can't this heat be used as part of an air conditioning system?

windykites1
11th November, 2010 @ 06:03 am PST

Where I live in Canada,the winter is bitterly cold,-35 quite often.I can't see this being any use in winter,but in our short summers,the roads often get blisteringly hot. Maybe we should go back to what was done 100 years ago: saw and store blocks of ice for use in the summer.Summer heat could be stored as hot water in modern,super-insulated containers for winter heating needs.

michael_dowling
11th November, 2010 @ 07:41 am PST

These are interesting ideas. Has anyone thought of using piezoelectric sheets under the asphalt to generate electricity. The weight of the vehicles passing would deform the crystals, generating electricity.

Dr. Douglas L. Weed

Douglas L. Weed
11th November, 2010 @ 08:27 am PST

One of the reasons why the roads don't heat up as much in the winter: salt. The white salt (and salt residue) coats the road surfaces reflecting the energy back. We definitely need a light colored asphalt for summer use.

Vadim
11th November, 2010 @ 10:36 am PST

I always questioned if it was possible to use the heat of the surface of a body of water and whether one could actually capture the heat from the surface of road or even the desert surface.

I think it's not a question of possible but how soon we can put the technology to work.

The cost of asphalt mentioned above for comparison lets say of concrete or asphalt is about the same if we look at the cost overall cost repairs roads every 7 years vs electronic road 21 year is about even. Not only does it look like a worthwhile and economic investment headache free for 21 years but we are moving towards cars that run on electricity. And it makes good sense to use the road as a electricity generator in a sense for internet and heating building if the turning of the tires of a car running over the road creating some heat could also do something that would just be bonus plus.Anyhow this is very interesting article and glad someone could work out the details of how to go about this with many possibilities. Save the wood from cutting trees to replace the outdated poles its real environmental friendly I like it.

naeemhstar
11th November, 2010 @ 01:50 pm PST

Just one thing about solar roads and block electronic roads

Whats not mentioned is that there is a return of the investment from the energy that will be derived from these electronic roads sources as expensive as the input but there is no output for a asphalt or concrete its just wasted money with constant repair which does not pay back while this does. We will never see a dime returned from the asphalt or concrete that is currently used for roads

naeemhstar
11th November, 2010 @ 05:30 pm PST

Now if only they would embed inductive strips down the centers of a lane or three of highway and let us use them to charge our cars and (maybe) even engage an autopilot based on it....would make cars with a 100 mile range suddenly practical. Even if I had to pay extra to use the lane, it would be worth it.

Bryan Paschke
14th June, 2011 @ 10:06 pm PDT
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