How to Use Asphalt Pavements As a Solar Collector

Asphalt

• When the internal combustion engine took over from horse power as the primary mode of transportation in the early 20th century, asphalt began covering roadways and parking areas. If you've ever walked barefoot on asphalt on a hot summer day, you know its capacity as a heat conductor. In the continuing search for renewable energy resources and less dependence on fossil fuels, scientists are devising ways to harness this energy and use it on a massive scale.

How It Works

• Researchers at the Worcester Polytechnic Institute in Massachusetts are testing asphalt's capacity to generate energy. The asphalt slabs in these tests contain copper piping and thermocouples for gauging heat transference to water flowing through the pipes. Results show that the asphalt absorbs a great deal of heat, with the highest temperatures found slightly below the surface. That is the area in which manufacturers would place a heat exchanger for maximum energy extraction. Researchers also found that adding conductive material to the asphalt, such as quartzite, increases the heat-absorption capability. The surface may be coated with reflection-reducing paint to also increase absorption. As of the time of publication, additional tests must be conducted before this use is commercially applicable.

Other Applications

• In cold weather, municipalities all over the country must deal with roadway safety when water on pavement turns to ice, making driving dangerous. In addition to energy generation, roadways constructed with solar collectors may enable the temperature to remain above freezing, preventing ice formation. This application would not only benefit motorists, but could eliminate the need for the environmentally questionable use of salt on the roads. Local governments and their taxpayers could also save money on road maintenance with stable asphalt temperatures, reducing cracks and potholes.

Energy Production

• According to the Idaho-based company Solar Roadways, 440 solar panels are needed for each one-lane mile of roadway, with each panel designed to produce 7600-watt hours of electricity each day. This amount requires a minimum of four hours of sunlight daily. The company cites a study by the Energy Information Administration, stating that the average U.S. home uses 936 watt hours each month, or 31.2 watt hours daily. The company estimates that the energy collected from a four-lane solar roadway experiencing at least four hours of sunlight each day allows approximately 428 homes to receive power off the grid.