Recently when athletes took part at the 37th Paris Marathon, they were doing more than running. They were generating electricity thanks to some innovation from a London based company. As the athletes thumped their feet on 176 special tiles laid on a 25-meter stretch, they generated 4.7 kilowatt-hours of energy, enough to power a five-watt LED bulb for 940 hours, or 40 days electricity!
These special “energy harvesting tiles” work on a hybrid black box technology to convert the energy of a footstep into electricity, which is either stored in a battery or fed directly to devices. A typical tile is made of recycled polymer, with the top surface made from recycled truck tires. A foot stomp that depresses a single tile by five millimeters produces between one and seven watts. These tiles generate electricity with a hybrid solution of mechanisms that include the piezoelectric effect (an electric charge produced when pressure is exerted on crystals such as quartz) and induction, which uses copper coils and magnets.
Using piezolelectrics to generate power has been in since some time, at various places. These come with some challenges. Installing the tiles in the ground is one of the hardest things to do as they have to be very durable, weather resistant and should have high fatigue resistance as well. Also, these tiles could get vandalized. While the technology application need be lauded, we need to ask some critical questions too. Beyond demonstrating the technology, can such innovations help improve the overall energy situation? What is the EROI? Can we compare the cost of materials that go into the making of these tiles to the amount of energy generated? Should we be focussing on such ideas or go for more scalable ones?