Harvesting the Power of Footsteps

Generating power through the piezoelectric effect may help soldiers with a portable energy source. Courtesy of HDIAC

Generating power through the piezoelectric effect may help soldiers with a portable energy source. Courtesy of HDIAC

By: HDIAC Staff

While developments in collecting power from rain, waves and sunlight seem to be standard sources for power generation, the goal of less reliance on fossil fuels causes researchers to look for energy generation methods in some unexpected places. One of the newest trends in renewable and sustainable energy harnesses the power of kinetic energy produced by people as they go about everyday tasks. This energy harvesting concept works off of the piezoelectric effect; creating energy by converting mechanical stress into electric energy. As this technology evolves, piezoelectric materials continue to become more efficient and highly portable, opening themselves up for use in multifaceted applications.

The piezoelectric effect was discovered in 1880 by brothers Jacques and Pierre Curie when they noticed an electric charge could be created by placing crystals under pressure. Piezoelectric materials generate electricity when subjected to tension or compression in opposite polarity as well as in proportion to the force applied. The vibration caused by shoes striking a piezoelectric pad under a floor tile creates a voltage that can be converted into electrical energy, which can be used in place of the electrical grid. Vibration energy produces greater electrical energy density than other energies, making it highly efficient for piezoelectric energy harvesting.

The most common form of piezoelectric energy collection is found in floor tiles used in areas that see high commuter traffic. Japan installed piezoelectric flooring tiles at their busiest train stations in front of ticket turnstiles, while both London and Rotterdam designed dance clubs that used the tiles to bolster their light and electricity needs. This sustainable dance floor technology brought about a push in sustainable business practices. At full capacity one of the piezoelectric dance floor models can mitigate more than 30 percent of the dance club’s total energy usage.

These tiles may not replace the power grid, but lessen the amount of power drawn from it. The floor tiles need a large number of steps to become practical, and for this reason are best suited for areas with a reliable, high frequency of foot traffic. Each step, depending on weight and the type of movement, only produces between two and 20 joules. This power can be used for lighting, charging small devices such as cell phones and other low energy consuming uses. This power would otherwise be drawn from traditional power stations, many of which produce electricity by running on fossil fuels and contribute to pollution and global warming.

The overreaching strategy is not to replace all energy needs with piezoelectric energy, but to couple it with other sustainable technologies to increase overall effectiveness. This energy generating technology was combined with other eco-friendly practices in Rotterdam’s Club WATT, which also incorporated rain-water flush toilet systems, LED lighting and a zero-waste bar that serves organic drinks in recycled plastic cups. This concept of sourcing minute amounts of energy from one or more surrounding sources and then accumulating and storing them for later use is known as energy scavenging.

Researchers miniaturized this technology and tested it for use in footwear. This becomes a feasible alternative power source for soldiers in the field, far from other electrical sources. Portable devices, such as computers and wearable devices needed in remote station posts, could potentially be powered by sustainable piezoelectric devices powered by the steps of the combat soldier. These devices would otherwise require batteries, which present health and environmental risks as well as limited energy storage capacity and, unlike the piezoelectric devices, contain toxic chemicals.

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