A multi-disciplinary team of students and faculty from the Worcester Polytechnic Institute in Massachusetts has designed an underground, invisible and simple way to collect solar energy.
Capture the heat of blacktop.
By running an array of insulated copper tubes about an inch below pavement, the team gathered solar energy cheaply and efficiently with asphalt, said Rajib Mallick, team leader and associate professor at WPI.
“You can use the heat for energy,” said Mallick. “You can use it for whatever you want.”
Solar energy bathes asphalt: think of a highway shimmering. The team's system pumps water through imbedded tubes, absorbing the sun's heat and delivering it to the power grid. An average parking lot of 200 sq ft could produce 800kWh per day with the system, Mallick said, and cost $5 a sq ft to install.When repairs are made to roads, parking lots, or sidewalks, the copper tubing array could be installed and solar energy would be continuously harnessed underground and out of sight, according to WPI.
“Unlike conventional solar cells,” Mallick said, “you don’t need any new real estate or space.”
WPI was approached two years ago by Michael Hulen of Novotech Inc., with the idea for subterranean solar collection.
"If you're a city of local government looking at sustainability issues, this would be a good fit," Hulen said, whose started Roadway Power System to commercialize asphalt energy.
Mallick and others studied the concept, and decided it was solid enough to spend two years running computer models and building test plots of copper and blacktop.
The team improved the design by increasing the absorption rates of the materials. By adding quartzite aggregate to the asphalt, more solar energy was absorbed. Acrylic paint on the copper conducted more heat directly to the water. Burying the tubing an inch below the surface put it in the hottest part of the asphalt, insulated from wind.Bao-Liang Chen developed his PhD thesis around the work and presented their findings to the International Society for Asphalt Pavements in Zurich, Switzerland on August 18, 2008.
"This concept is quite a new development in the entire asphalt industry," Chen said. Asphalt energy sparked an ISAP environmental committee, Chen said, right on time for the 2010 ISAP conference in Nagoya, Japan. In Zurich, Chen met other researchers pushing the boundaries of blacktop: Chinese using graphite in the aggregate mix and Japanese studying relfective coating to curb the urban heat island effect.
Comparatively, cities are hot. Roads and large concerete buildings absorb enough solar heat to raise urban temperatures by an average of 2 degrees. The effect is dirty and deadly: the heat island effect can increase peak energy deman, air conditioning costs, air pollution levels, and heat-related health dangers, according to the Environmental Protection Agency.
By collecting the heat behind this urban problem, asphalt energy drains the urban heat island effect, Mallick said.
The next step for asphalt energy is in the lab and out in the field. The system will be tested in an undesignated parking lot - ground under less stress compared to roads. WPI's team will study thermal conduction in their materials, surface painting for the asphalt to maximize solar absorption, serpentine pipe layout, and gaseous liquid alternatives to water in the system.
"How much heat can you soak up and how can you transfer it?" Mallick said. "How effectively can you transfer that heat into something else, like electricity?"
The team will also test plastic and polymer alternatives to copper for the tubing, Mallick said. Copper's price has risen with global demand for the ubiquitous metal, instigating a series of scrap thefts across the US.
Availability of asphalt energy hinges, Mallick said, on finding at least $500,000 in funding for the next series of tests. After they've optimized the system through research, they will commercialize the technology.
"We are actually doing these studies and conducting this research," Mallick said, "and probably very soon we will be ready."
Photos courtesty Rajib Mallick
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