The heat that pavement gives off is something everyone is familiar with. Researchers at the University of Rhode Island are exploring how this radiant heat energy can be used to melt ice, power streetlights, illuminate signs, heat buildings and generally make our lives better.
“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, URI 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.”
The URI team has pinpointed four potential methods to make use of the heat; and they range from simple to complex. They are currently working on research projects designed to make each of them a reality.
One simple idea involves wrapping photovoltaic cells around the tops of Jersey barriers dividing highways to provide electricity to power streetlights and light up road signs. The cells could also be inserted in the roadway between the Jersey barrier and the adjacent rumble strip.
URI researchers say that the photovoltaic cells project can be developed and implemented soon because the technology to do so is already in existence.
Another functional way to harvest solar energy from hot pavement is to install water filled pipes under the asphalt to allow the sun to heat the water up. This heated water could then be diverted beneath bridges to melt ice that gathers on the surface and reduce the amount of road salt that is used.
The water could also be pumped to nearby buildings to fulfill heating or hot water needs, similar to how geothermal heat pumps work. It could even be transformed into steam to move a turbine in a small, traditional style power plant.
Busy graduate student Andrew Correia has constructed a prototype of a similar system in a URI laboratory to judge how effective the piping system can be. He is using different mixtures of asphalt and piping systems, he wants to show the world that the system can work in a real life setting.
“One property of asphalt is that it retains heat really well,” he said, “so even after the sun goes down the asphalt and the water in the pipes stays warm. My tests showed that during some circumstances, the water even gets hotter than the asphalt.”
A third option makes use of a thermo-electric effect to invoke a small but usable amount of electric power. When two types of semiconductors are joined together to form a circuit linking a hot and a cold spot, a small amount of electricity is generated in the circuit.
URI Chemistry Professor Sze Yang thinks that thermo-electric materials can be installed in roadways at different depths, some in sunny areas, and some in shaded areas. He says that an organic semiconductor could be used and that they would be able to be manufactured on the cheap.
The craziest, most futuristic proposal the URI team has considered is to fully replace current asphalt roadways with ones that are made big, sturdy, electronic blocks that house photovoltaic cells, LED lights and sensors.
Lee says the technology to build a system like this exists, but it is very expensive. It would certainly take some innovation before such a system were to become economically viable.
“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.”
One thing is for sure, it is definitely time for somebody to find a way to make use of all of the “free” energy laying around.