Everyone knows that tarmac and asphalt are various shades of dark grey rather than green but tarmac has the potential to be truly green if we use it wisely. Green in the sense of environmentally sound, that is.
Both tarmac and asphalt have the capacity to absorb the heat of the Sun very well. Engineers are in the process of learning how to use this to generate large amounts of electricity through harnessing the solar energy that can be held by tarmac. Why go to the trouble of building solar panels when we already have ready-made solar energy collectors in the form of roads, runways and car parks?
Companies in The Netherlands and the USA have designed systems that can collect the solar energy that falls on car parks and roads to power nearby buildings or to even add to the national grid to contribute a renewable source of energy.
Proof of Concept
Since 2005, several projects demonstrating that the technology involved can work have been built. The heating system in an apartment block in Avenhorn in The Netherlands is already powered from solar energy that is collected from the car park and a 180-metre piece of road nearby. An industrial park in Hoorn also gets some of its heating from the pavements that run through between the buildings. Most impressively, the hangers of an airforce base are heated from the solar energy that falls on the runway – this is also used to heat the runway so that freezing in winter is never a problem.
This proves that such a system will work, even in a northern European country that does not have intense sunlight all year round.
Reducing the Expense
The drawback of the current technology that has been used in these projects is that it is very expensive and needs to be fitted into the tarmac or asphalt as it is being laid down. It cannot be fitted retrospectively to a road or runway that has already been built. During the construction process, flexible pipes made of plastic are laid down in a lattice pattern, held in place by a rigid plastic grid. The pipes are filled with cold water that is then heated up as sunlight falls on the road or car park. Then, either the water is used directly in heating systems, or pumps send the warm water underground to be stored in natural aquifers. As the temperature underground tends to be fairly constant at 8 degrees Celsius, the water does not lose its energy. The heat energy can then be retrieved months later.
The water is not really warm enough to actually make a radiator in an office or home very warm, so it does need to be heated further. The energy required, however, is much less than if the water was cold to start with, which is why the heating method is more environmentally friendly. It saves about half the cost of gas or electricity bills, it reduces carbon emissions – but it does cost more than standard heating systems to install. Reducing this installation cost will be a key factor in determining whether the system can be used on a wider scale.
The idea of using roadways as sources of solar energy is now beginning to take off in the USA, where more pilot programs are planned. The advantage in a region of the world that has a great deal of intense sunshine is that the energy collection capacity would be much greater. But heating water for heating buildings isn’t such a great need if the weather is warm anyway, so US projects will concentrate on converting the heat energy collected into electrical energy and feeding it into the national grid. Sunlight will then produce electricity that can power lighting and even air conditioning systems to cool everyone down. Some experts think that the use of the heat normally captured by the tarmac would reduce city temperatures by a degree or two if the system were used in a great enough area.