Asphalt may not be thought of as the most obvious material to be an important source of solar power, but anyone who has touched the surface of a road with their bare feet during summer knows only too well that it has superb heat retention. Researchers in both the UK and US have been looking into the potential - with promising results.
The idea of asphalt for solar power isn’t particularly new - the theory was first conceived a decade ago, although its only been fully realized in the last couple of years. In 2007, a Dutch engineering company began siphoning the heat from asphalt to heat several homes and offices, as well as an aircraft hanger. The system used a network of plastic pipes through which the asphalt heated the cold water and fed it into underground storage containers where it was kept hot until needed.
More recently, researchers at Worcester Polytechnic Institute (WPI) have conducted tests using actual pieces of asphalt as well as computer models. The scientists found that hot water created by an asphalt energy system could be used to produce electricity by being passed through a thermoelectric generator. Heated asphalt can also heat buildings by the method of passing the water through pipes under the asphalt - just as the Dutch team had discovered.
The team also found that the maximum temperatures were found just a few inches below the road surface. Ideally, a heat exchanger would be located there so that the maximum amount of energy could be produced. And other measures such as applying a reflection reducing paint to the asphalt; or adding aggregates known for their conductive properties would also increase efficiency.
Asphalt has several advantages as a source of solar power. It’s a huge infrastructure that is already in place - in the United States for example, there are an estimated four million miles of asphalt road surface. In general, asphalt is removed and the roads are resurfaced every decade or so; this would provide the opportunity to put in the necessary equipment with minimal expense.
Asphalt also retains its heat after the sun has gone down - giving it an advantage over solar panels. Removing the heat from asphalt can actually reduce the temperature of the road surface too - making towns and cities cooler during hot weather. And unlike solar panels, which are all too visible, practically all the asphalt collection equipment would be hidden under the groundunderground.
Fascinating though these results are, don’t expect to see the widespread use of asphalt solar power any time soon. It may be a long time before a system of pipes under the roads is able to provide energy - but at least it’s a step in the right direction.