Solar Superhighways

Researchers are developing a solar collector to turn roads and parking lots into cheap sources of electricity and hot water. "Asphalt has a lot of advantages as a solar collector," says Rajib Mallick of Worcester Polytechnic Institute. "For one, blacktop stays hot and could continue to generate energy after the sun goes down, unlike traditional solar-electric cells.

Plus there's already gynormous acreage of installed roads and parking lots. They're resurfaced every 10 to 12 years. The solar retrofit could be built into that cycle. No need to transform other landscapes into solar farms. Or maybe not as many.

Furthermore, extracting heat from asphalt would cool the urban heat-island effect, cooling the planet a wee bit. Finally, solar collectors in roads and parking lots would be invisible, unlike those on roofs. Cuz we all know how attractive roads are.

The team's lab tests showed that asphalt's highest absorption temperatures are found a few centimeters below the surface. So that would be the place to install a heat exchanger. When they added highly conductive aggregates, like quartzite, to the asphalt, absorption increased significantly. So too when they coated the asphalt with an anti-reflection paint.

They also tested slabs of asphalt embedded with thermocouples (to measure heat penetration) and copper pipes. Hot water running through those pipes could be used "as is" for heating buildings or in industrial processes. Or it could be passed through a thermoelectric generator to produce electricity.

Pedal to the metal.

Julia Whitty is Mother Jones' environmental correspondent, lecturer, and 2008 winner of the Kiriyama Prize and the John Burroughs Medal Award.