In the not-too-distant future, asphalt roadways may supply solar energy to power streetlights, melt ice on roads, heat buildings, and more, according to researchers.

If there's one thing we have in abundance, it's pavement. Miles of asphalt and other road materials cover large amounts of the surface of our cities, and need to be regularly repaired and replaced. One research team at the University of Rhode Island is exploring ways to use those roadways to meet some of our power needs, by harvesting solar energy from them.

"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." - K. Wayne Lee, URI professor of civil and environmental engineering

Four different approaches have been identified by the research team, ranging from the simple, such as using flexible PV cells on highway barriers to power streetlights and provide power for road signs, to the complex, such as replacing roadways with large blocks containing PV cells, LED lighting, and sensors.

The simple approach could begin to be implemented today, as flexible solar cell technology already exists, and one of the team's pilot programs will focus on studying the feasibility of doing so.

The most complex concept, building roads out of durable electronic blocks which can generate electricity, light the roadway, and provide feedback via embedded sensors, is technically possible right now, but due to the extremely high costs involved, isn't as feasible. Lee suggested that corporate parking lots may become the early adopters of this technology, as it may become years before they become practical for general roadway use.

Falling in the middle are two non-PV methods of harvesting solar energy: using water in pipes beneath the asphalt to collect heat, and using thermo-electric materials embedded in the roads to generate electricity.

The first, using pipes filled with water beneath the roads, would take advantage of one of the most obvious abilities of asphalt, retaining heat, as well as taking advantage of the great thermal storage properties of water.

"One property of asphalt is that it retains heat really well, 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." - Andrew Correia, Grad student and team member

Research is underway to evaluate different pipe systems and asphalt mixes to increase the effectiveness of each and to demonstrate the practicality of the technology in the real world.

The other non-PV approach to harvesting solar energy from roads is embedding thermo-electric materials in roadways at different depths or different solar exposures and using a circuit of them to link cold and hot spots and generate a usable amount of electricity.

"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. With enough additional research, I think it can be implemented in the field." - Sze Yang, URI Chemistry Professor

The team is pursuing research projects for each of these solar energy harvesting approaches, exploring ways to make them both feasible, and a reality.

[top image: Jesse Kruger at Flickr]