World’s first solar road opens in France

Usefulness aside, the main problem with constructing solar roads is their crippling cost. One of the main selling points of Wattway, according to Colas, is that each panel is just a few millimetres thick, and can thus be installed on top of an existing road, which in turn massively reduces construction costs. Having said that, the 1km road in Normandy cost €5 million (£4.3m) to build. And that's for a single lane of a two-lane highway!