The Power in Every Step: How Sidewalks Can Generate Electricity

Imagine walking in New York City—your steps powering the phone you have in your hand or the street light blinking across the crosswalk. While this may seem far-fetched, sidewalks in various cities across the globe have been designed to produce energy from people’s steps, providing another sustainable and renewable energy source. As of now, these sidewalks only generate enough energy to power small electronic devices such as phones, Bluetooth devices, or traffic lights, but further development is underway on technology that could power homes and cars.

These sidewalks were invented by a company called Pavegen and use kinetic pavement technology to convert the mechanical energy from footsteps into electrical energy. Beneath the pavement’s surface, there is an ecosystem of sensors and generators that capture pressure and movement from walking. As we walk, our footsteps cause small deflections in the sidewalk tiles that activate the piezoelectric mechanisms that produce electricity. Electromagnetic induction by copper coils and magnets allows for each step to produce two to four joules—an average of five watts of energy. This induction works when the force of a footstep is applied and a magnet is compressed. The magnet is close to copper wire, so the magnetic field around the copper wire changes, thus producing a voltage and electrical current.

These sidewalks are made of composite materials that contain piezoelectric fibers, which are able to generate an electric charge in response to applied mechanical stress or, conversely, to change shape under the influence of an electric field. Piezoelectric fibers are made from various materials ranging from inorganic ceramic to organic polymers. Some of these materials include quartz and lead zirconate titanate—structures whose crystal lattices (molecule structure) don’t have a center of symmetry. This means the positive and negative charge centers don’t perfectly overlap. When pressure is applied, the dipoles—separation of positive and negative electrical charge—are distorted, leading to an unbalanced charge distribution. The difference in charges creates a voltage—electrical charge—across the material. To harvest this electricity, metal electrodes are placed on both sides of the material. These electrodes are connected to a circuit so that electrons can flow in a continuous electrical current. The electricity generated can then be stored or used to directly power devices.

Japanese scientist Kohei Hayamizu wanted to test the efficiency of such piezoelectric tiles in 2008 and installed a one square meter of the tiles at the Shibuya Crossing in Tokyo, Japan, where over 900,000 people cross everyday. Over the 20 day period, the tiles produced enough electricity to power 1,422 televisions for one hour—over 60,000 watts of energy. This experiment was done to show that while one step doesn’t produce much electricity, global implementation of piezoelectric technology could allow for large quantities of electricity to be produced in a sustainable way.

Many researchers also want to implement piezoelectric technology into flooring systems, especially in buildings and dance floors, so maximum energy can be harnessed. Piezoelectric floors also allow scientists to harness energy that would’ve otherwise been “wasted,” increasing the efficiency of urban infrastructure. Furthermore, piezoelectricity is an independent source of energy from standard power lines, so even if power outages occur, energy recycled from piezoelectric floors and sidewalks could still keep essential services running.

While piezoelectric technology seems the most promising method to generate energy from sidewalks, there are other possible methods currently being researched. For example, thermoelectric generators are able to produce electricity by harnessing the temperature difference between a pavement’s surface and its underlying layers. This model was tested in an asphalt pavement system and subjected to full-spectrum lights—lights that encompass a wide variety of wavelengths. Researchers concluded that about 62,000 microwatts of electricity—about enough to power a small LED light bulb—per square meter could be generated.

Since this technology is very new, it is unfortunately very expensive to implement and is only feasible for a few streets in big cities. In addition, these piezoelectric technologies will wear down over time and need to be replaced, adding extra costs. Ongoing research is focused on making the technology more cost-effective and durable. So, the next time you’re on a walk with your friends around the city, take a moment to think about how your steps could power your phone or potentially (and hopefully one day) your entire city.