San Francisco held a Pedestrian Day on 27 May 1937 to open the newly completed Golden Gate Bridge to the public. Nowadays, around 10,000 people, mainly tourists, cross the 2,7 km bridge for the spectacular views of the city, the bay and Alcatraz.
It’s estimated that the vibrations generated by bridge crossers, who take an average of 3,600 steps to reach the other side, could generate around 170 million joules per day. That would be enough power to charge 5,000 smartphones or to keep a desktop PC running for three weeks.
Energy harvesting pavements have already been installed in some heavy pedestrian traffic locations such as train stations, office buildings or sports installations for powering energy-efficient lights or other systems. It works by embedding piezoelectric crystals beneath the surface.
Piezoelectricity is the electric charge produced by the crystals when a mechanical stress is applied. As pedestrians walk, or cars drive, they exert a force that causes these crystals to deform and generate electrical energy, which can then be used to power street lights, or stored in batteries for later use.
Standards for piezoelectric technology are developed by IEC TC 49, which addresses piezoelectric, dielectric and electrostatic devices. The IEC 62830 series, prepared by IEC TC 47, includes methods for evaluating the performance of vibration-based piezoelectric energy harvesting devices.
However, challenges remain. Factors that increase piezoelectric road efficiency are inversely related to the durability of a road. Roads with sizeable traffic flows from heavy-duty vehicles travelling at high speeds will generate a greater energy output compared to roads with little traffic, light-weight cars and slow speeds.
It has also not yet been confirmed whether the costs associated with installing and maintaining roads embedded with piezoelectric technology are offset by the electricity generated, given its relatively low energy conversion efficiency. Other energy harvesting solutions, such as PV modules alongside roads, may be cheaper to install and generate higher volumes of electricity.
Energy harvesting solutions making use of roads are still in their early stages. Because much of the current research and development has been undertaken by private companies, there is limited public availability of data. Costs remain high given the lack of mass production.
Some of these solutions may yet gain traction. Additional technologies such as sensors and microprocessors could be incorporated that monitor infrastructure and vehicular traffic conditions in real-time. Such solutions will rely upon Standards developed by the ISO/IEC Joint Technical Committee, JTC 1/SC 25 for microprocessor systems and IEC TC 47 for sensors. It is not yet clear which technologies, if any, will be implemented. But the enthusiasm remains in the pursuit of renewable energies.