Solar Power Takes a Road Trip

A research team at Worcester Polytechnic Institute (WPI) is studying ways to use the heat-soaking property of parking lots and other paved surfaces for an alternative energy source. The researchers are developing a solar collector that could turn roads and parking lots into ubiquitous and inexpensive sources of electricity and hot water.

Rajib Mallick, associate professor of civil and environmental engineering at WPI, is directing the research project. The study looks at how well asphalt can collect solar energy and the best way to construct roads and parking lots to maximize their heat-absorbing qualities.

“Asphalt has a lot of advantages as a solar collector,” Mallick said. “For one, blacktop stays hot and could continue to generate energy after the sun goes down, unlike traditional solar-electric cells. In addition, there already is a massive acreage of installed roads and parking lots that could be retrofitted for energy generation, so there is no need to find additional land for solar farms. Roads and lots are typically resurfaced every 10 to 12 years, and the retrofit could be built into that cycle. Extracting heat from asphalt could cool it, reducing the urban ‘heat island’ effect. Finally, unlike rooftop solar arrays, which some find unattractive, the solar collectors in roads and parking lots would be invisible.”

Mallick and his research team studied the energy-generating potential of asphalt using computer models and by conducting small- and large-scale tests. The tests were conducted on slabs of asphalt in which thermocouples were imbedded to measure heat penetration and copper pipes to gauge how well that heat could be transferred to flowing water. Hot water flowing from an asphalt energy system could be used for heating buildings or could be passed through a thermoelectric generator to produce electricity.

In the lab, small slabs were exposed to halogen lamps, which simulated sunlight. Larger slabs were set up outdoors and exposed to more realistic environmental conditions, including direct sunlight and wind. The tests showed that asphalt absorbs a considerable amount of heat and that the highest temperatures are found a few centimeters below the surface. This is where a heat exchanger would be located to extract the maximum amount of energy. Experimenting with various asphalt compositions, the researchers found that the addition of highly conductive aggregates, such as quartzite, can significantly increase heat absorption, as can the application of a paint that reduces reflection.

“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,” Mallick said.

Earlier this year, ELECTRICAL CONTRACTOR reported on a Dutch company that was outfitting a village in Holland with a similar system that stored the heat gathered by pavement for use in the winter to heat roads, preventing ice buildup. The company found there was so much stored heat, that it was able to pipe the leftovers to an aquifer that would then heat homes in the winter. Read that story here.

The potential for using pavement as a source of energy is certainly there, and the success of this study could change the solar power world. Depending on this project’s development, electrical contractors could find themselves working in an area of construction they never thought possible.

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