Sunshine highways

Walk barefoot across an asphalt road on a hot sunny day and you'll soon realise how well the material absorbs heat. Road temperatures in direct sunshine often reach 15°C higher than the ambient air temperature while summer surface temperatures in cities easily top 50°C. One way to harness this solar energy is to install a solar collector typically an array of pipes and thermal stores beneath the road. In the summer, fluid circulates through the pipes to absorb heat from the road surface and is then piped to an insulated tank. Come winter, the warm fluid is pumped back along the pipes to clear ice from the road or even to a connecting building to provide under-floor heating, Simple and effective, a handful of engineers are building on this concept of seasonal heat transfer for new applications.