Can asphalt roads and parking lots be used as a ubiquitous and inexpensive means for collecting and utilizing solar energy? Researchers at Massachusetts’ Worcester Polytechnic Institute say: Yes. Led by Rajib Mallick, associate professor of civil and environmental engineering, a WPI research team says it has found a way to use asphalt’s heat-absorbing properties as an alternative energy source. Initiated at the request of Novotech Inc., a Mass.-based manufacturing firm that holds a patent on the concept of using heat absorbed by pavement, the WPI project examines - not only asphalt’s ability to collect solar energy - but also the most effective and cost-efficient means of transforming miles of blacktop into a generator of electricity and hot water.

“Asphalt has a lot of advantages as a solar collector.For one, blacktop stays hot and could continue to generate energy after the sun goes down, unlike traditional solar-electric cells.

He also points out:

• Since installed roads and parking lots already exist, the need to find additional land for solar farms is eliminated.
• Because “roads and lots” are typically resurfaced every 10 to 12 years, they could easily and cost-effectively be retrofitted for “energy generation.”
• Extracting heat from asphalt would cool pavement and reduce the urban ‘heat island’ effect.
• Unlike roof-top solar arrays, which some people find unattractive, solar collectors in roads and parking lots would be invisible.

Mallick’s research team, which includes Sankha Bhowmick of the University of Massachusetts in Dartmouth, has shown that hot water flowing from an asphalt energy system could not only be used “as is” for heating buildings or in industrial processing but also could be passed through a thermoelectric generator to produce electricity. The team’s findings, he says, have been derived from the use of computer models and by conducting small- and large-scale tests. These tests entailed embedding thermocouples into asphalt slabs and copper pipes and, then, measuring penetration and transfer of heat into flowing water. In the lab, the team exposed small slabs of asphalt to halogen lamps, which simulated sunlight. They tested larger asphalt slabs outdoors, where it was exposed to direct sunlight and wind. Mallick says such testing has shown that heat’s highest temperatures are concentrated a few centimeters below the asphalt’s surface, where a heat exchanger could be placed to extract the maximum amount of energy. The team also found that heat absorption could be significantly boosted by adding highly conductive aggregates, such as quartzite, to the composition of the asphalt. Mallick concludes:

“Our preliminary results provide a promising proof of concept for what could be a very important future source of renewable, pollution-free energy for our nation. And it has been there all along, right under our feet.”

Full details of the team’s results have recently been presented to the International Society for Asphalt Pavements in Zurich, Switzerland.