Anyone who’s taken a barefooted tryst across a paved parking lot knows that blacktop can reach sweltering temperatures when exposed to the summer sun. Now researchers at the Worcester Polytechnic Institute have found a way to use to employ the heat-soaking properties of asphalt as an energy source by inserting heat exchangers a few centimeters below its surface. The development may pave the way for an inexpensive source for electricity and hot water that re-imagines our existing auto infrastructure as a massive conduit for solar-thermal energy.

The United States’ highway network consists of a tremendous expanse of roads and streets stretching 4 million miles. All day long these transit routes soak up the sun’s rays, storing an immense amount of energy that is left to dissipate by nightfall. The concept of asphalt-absorbed solar energy is enticing because it offers an inexpensive way to collect solar energy by utilizing an extensive infrastructure that already exists.

Rajib Mallick has taken the helm of a group of researchers at Worcester Polytechnic and touts the many benefits of using roadways as solar collectors:

“For one, blacktop stays hot and could continue to generate energy after the sun goes down, unlike traditional solar-electric cells. In addition, there is already 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 roof-top solar arrays, which some find unattractive, the solar collectors in roads and parking lots would be invisible.”

Mallick’s team envisions a network of highly conductive water pipes that would run beneath our roadways, taking advantage of their untapped solar potential. Once heated, this water can be used as-is to heat buildings or can be passed through a thermoelectric generator to produce electricity.

The key to making this technology efficient will be to find the optimum materials for heat conductivity; to do this the team has been experimenting with various compositions of asphalt as well as specially designed heat exchangers that will soak up the maximum amount of thermal energy. Mallick states that “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.”

+ Worcester Polytechnic Institute


Photo Credit: dusted