Pavement Can Be Source of Energy

Wednesday, November 10, 2010 @ 04:11 PM gHale

Heat radiating off roadways may someday become the energy source to melt ice, power streetlights, illuminate signs, heat buildings and other purposes.
“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 K. Wayne Lee, University of Rhode Island professor of civil and environmental engineering and the leader of the joint project. “If we can harvest that heat, we can use it for our daily use, save on fossil fuels, and reduce global warming.”
There are four potential approaches, from simple to complex, and URI teams will pursue research projects to make each of them a reality.
One of the simplest ideas is to wrap flexible photovoltaic cells around the top of Jersey barriers dividing highways to provide electricity to power streetlights and illuminate road signs. They could also embed the photovoltaic cells in the roadway between the Jersey barrier and the adjacent rumble strip.
“This is a project that could be implemented today because the technology already exists,” Lee said. “Since the new generation of solar cells are so flexible, they can be installed so that regardless of the angle of the sun, it will be shining on the cells and generating electricity. A pilot program is progressing for the lamps outside Bliss Hall on campus.”
Another practical approach to harvesting solar energy from pavement is to embed water filled pipes beneath the asphalt and allow the sun to warm the water. The heated water could then go beneath bridge decks to melt accumulated ice on the surface and reduce the need for road salt, an environmental plus. The water could also pipe to nearby buildings to satisfy heating or hot water needs, similar to geothermal heat pumps. It could even convert to steam to turn a turbine in a small, traditional power plant.
Graduate student Andrew Correia built a prototype of such a system in a URI laboratory to evaluate its effectiveness. By testing different asphalt mixes and various pipe systems, he will demonstrate the technology can work in a real world setting.
“One property of asphalt is it retains heat really well,” Correia said, “so even after the sun goes down the asphalt and the water in the pipes stay warm. My tests showed that during some circumstances, the water even gets hotter than the asphalt.”
A third alternative uses a thermo-electric effect to generate a small but usable amount of electricity. When two types of semiconductors connect to form a circuit linking a hot and a cold spot, there is a small amount of electricity generated in the circuit.
URI Chemistry Professor Sze Yang believes you can embed thermo-electric materials in the roadway at different depths – or some could be in sunny areas and others in shade – and the difference in temperature between the materials would generate an electric current. With these systems installed in parallel, you could generate enough electricity to defrost roadways among other uses. Instead of the traditional semiconductors, Yang proposes to use a family of organic polymeric semiconductors developed at his laboratory in the form of plastic sheets or painted on a flexible plastic sheet.
“This is a somewhat futuristic idea, since there isn’t any practical device on the market for doing this, but it has been demonstrated to work in a laboratory,” Yang said. “With enough additional research, I think it can be implemented in the field.”
Perhaps the most futuristic idea the URI team considered is to completely replace asphalt roadways with roadways made of large, durable electronic blocks that contain photovoltaic cells, LED lights and sensors. The blocks can generate electricity, illuminate the roadway lanes in interchangeable configurations, and provide early warning of the need for maintenance.
The technology for this concept exists, Lee said, but it is very expensive. He said one group in Idaho made a driveway from prototypes of these blocks, and it cost about $100,000. Lee envisions corporate parking lots may become the first users of this technology before they become practical and economical for roadway use.
“This kind of advanced technology will take time to be accepted by the transportation industries,” Lee said. “But we’ve been using asphalt for our highways for more than 100 years, and pretty soon it will be time for a change.”

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