Heat from city streets often makes urban areas warmer than rural ones, and U.S. researchers say that heat can be harvested to create energy.

Engineering researchers at the University of Rhode Island are examining methods of harvesting solar energy absorbed by street surfaces to melt ice, power streetlights, illuminate signs and heat buildings, an RUI release said Tuesday.

"We have mile after mile of asphalt pavement around the country, and in the summer it absorbs a great deal of heat, warming the roads up to 140 degrees or more," said K. Wayne Lee, URI professor of civil and environmental engineering and the leader of the joint project. "If we can harvest that heat, we can use it for our daily use, save on fossil fuels, and reduce global warming."

Researchers say they are looking at a number of approaches to utilize this "wasted" solar energy.

One of the simplest ideas is to wrap flexible photovoltaic cells around the top of highway dividers to provide electricity to power streetlights and illuminate road signs.

Another practical approach to harvesting solar energy from pavement, they say, is to embed water-filled pipes beneath the asphalt and allow the sun to warm the water.

The heated water could be piped to nearby buildings to satisfy heating or hot water needs, similar to geothermal heat pumps.

Graduate student Andrew Correia has built a prototype of such a system in a URI laboratory to evaluate its effectiveness.

"One property of asphalt is that it retains heat really well," he said, "so even after the sun goes down the asphalt and the water in the pipes stays warm.

"My tests showed that during some circumstances, the water even gets hotter than the asphalt," he said.