Can solar energy contribute to road safety?
by W van Zanten, CADDET Dutch National Team

Common road surface problems, such as track formation in summer and icy conditions in winter, could be things of the past if road surfaces could successfully be used as solar collectors.  A Dutch experiment is putting this idea to the test.

The principle

In summer, asphalt road surfaces absorb heat from the sun - so much so that the surface can become damaged.  If this heat could be safely channelled away from the surface, using a heat transfer medium such as water pumped through a pipework system under the road surface, it could be stored in underground aquifers (deep wells) and recovered in winter.  Hot water stored in this way could be pumped back under the road in winter to prevent icy conditions. The potential benefits of this concept are better road safety in winter and reduced road maintenance, leading to fewer traffic jams.  If the technique successfully prevents heat damage to the road surface, a less expensive asphalt mixture may be able to be used in road construction.  There is also an environmental benefit, as the road would not have to be sprayed with salt to prevent freezing.

Alternatively, using heat pump technology, the heat from road surfaces could be used for low-temperature heating of nearby buildings.  The Amsterdam ring road, for instance, could collect 10 times more energy than is needed to heat all the homes in the city.

The concept is not new.  In Switzerland, the surface of a bridge is used to collect heat in summer, which is stored in rock and used again in winter to prevent freezing (see issue 1/95 of this Newsletter).  Other road heating projects have included waste heat from a Swedish power station being used to clear snow from 250,000 m2 of streets and pavements, and geothermal heat used to melt snow on roads in Japan (see CADDET Renewable Energy Technical Brochure No 76).

Now, the concept is also being put to the test on a stretch of road in the Netherlands.

Project Background

A motorway bridge over the Haringvliet tributary in the province of South Holland recently needed to be renewed.  An asphalt-concrete mixture is the preferred surface of the Dutch Department of Public Works, as it requires little maintenance. This mixture cannot normally be used on structures such as bridges because heat absorbed by the asphalt can lead to material fatigue in the bridge's support structure.  So, a decision was taken to test the 'solar collector' idea on this bridge.

The heat collection system under construction

 

The project

For the experiment, an under-floor heating specialist installed a mains system under 30 m of road surface. The system is similar to under-floor heating in a house or football stadium - the only difference in this case is that the pipes were embedded in reinforced concrete to protect them from the hot asphalt when the road was constructed.  Water is pumped from the Haringvliet tributary through this mains system where it collects heat absorbed by the road surface.  Because this experiment focused on the properties of the road surface, no heat storage aquifer was drilled.  Instead, the amount of heat collected is measured and the warmed water is simply discharged back into the tributary.

Results

The preliminary results of the project show that useful amounts of heat can be generated in asphalt-concrete road surfaces in warm weather. Tests on the Haringvliet bridge will continue until the end of 1999, but already the initiators of the experiment are excited by the potential for this technology.

For more information contact the CADDET Dutch National Team in Sittard.

The CADDET Renewable Energy Newsletter is a quarterly magazine published by the CADDET Centre for Renewable Energy at ETSU, UK.

The articles published in the Newsletter reflect the opinions of the authors. They do not necessarily reflect the official view of CADDET.

Enquiries concerning the Newsletter should be addressed to Pauline Toole, Editor, CADDET Centre for Renewable Energy, ETSU, Harwell, Oxfordshire OX11 0RA, United Kingdom. Tel: +44 1235 432968, Fax: +44 1235 433595.