Turning Pavement Into Energy

Heat from the pavement makes summer in the city a hot time. So one group of scientists asked why they couldn't make use of all that energy.

Heat from pavement is one reason city temperatures are often warmer than nearby suburban or rural areas. With this in mind, researchers at the University of Rhode Island hope to turn this heat into solar energy that can power streetlights, illuminate signs, heat buildings and melt ice.

"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. If we can harvest that heat, we can use it for our daily use, save on fossil fuels, and reduce global warming," said K. Wayne Lee, professor of civil and environmental engineering at URI and the leader of the joint project.

The researchers have looked at both simple and complex approaches to harvesting the pavement heat into energy. One idea involved wrapping flexible photo-voltaic cells around the top of Jersey barriers dividing highways to provide electricity to power streetlights and illuminate road signs.

"This is a project that could be implemented today because the technology already exists. 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," said Lee.

The team also has looked at embedding water filled pipes beneath the asphalt and then allowing sun to warm the water. The heated water could then be piped beneath bridge decks to melt accumulated ice on the surface. This in turn would reduce the need for road salt.

The heated water could also be used in nearby buildings to satisfy hot water needs or turned into steam to turn a turbine into a small power plant. A prototype of such a system was built by URI graduate student Andrew Correia. "My tests showed that during some circumstances, the water even gets hotter than the asphalt," Correia said.

Asphalt has a lot of advantages as a solar collector. When the sun goes down it stays hot for significantly longer than traditional solar collectors and could continue to generate power. Roads and other asphalt covered surfaces already account for a huge amount of real estate in the U.S. and, ironically, in most of the energy guzzling nations around the world. These could be converted to produce energy, reducing the land required for solar power generation. Additionally, extracting heat from asphalt will cool it, and may reduce the "heat island" effect noticed in many cities. And unlike rooftop solar panels, solar collectors in roads would be hidden.

The URI researchers also explored using thermo-electric materials in the roadway at different depths. These materials would be placed in both hot and cold locations to generate a current.

The team also looked at replacing asphalt roadways with roads made of large, durable electronic blocks that contain photo-voltaic cells, LED lights and sensors. However, Lee said this would take time and money, but is doable today. He said a group in Idaho made a driveway out of these materials for $100,000.

"This kind of advanced technology will take time to be accepted by the transportation industries. But we've been using asphalt for our highways for more than 100 years, and pretty soon it will be time for a change," Lee said.

Source:
International Business Times, "Turning Pavement Into Energy", accessed November 11, 2010