Since before the days of Tesla, we have dreamed of a “free” source of energy – something that would allow us to tap into power that already permeated the very space we occupied. Aside from a few conspiracy theorists, Tesla’s magnetic generator has not gained much traction as a sustainable energy source. We are, however, gradually tapping into seemingly “wasted” energy that is created by the simple collective movement of people.
Piezoelectric properties have long been known in many materials – natural mineral crystals, wood, silk, even cartilage. With a name referring to electricity resulting from pressure, piezoelectrics generate a voltage and corresponding electric field when compressed. This process also functions inversely, in that applying an external electrical field will cause a piezoelectric material to undergo a proportional compression.
Piezoelectric pads at Tokyo Station’s north exit.
The use of artificial piezoelectrics to harness energy has seen mixed but gradual success, given the proper circumstances. At smaller scales, there has been implementation in dance floors and a more utilitarian application at Tokyo Station. Both have shown less than practical results – the dance floor intended more as a novelty and showcase of the material, and the Tokyo Station project yielding the following:
“Production of electricity reached a maximum of 10,000 watt-seconds per day (equivalent to the electricity needed to light a 100W light bulb for 100 seconds). From the 3rd week of the experimental period (a total of 800,000 people passing), production of electricity decreased due to a degradation in durability.”
At a large scale, piezoelectrics show substantially more promise. Israel has seen two major installations, one highway and the other railway. A pilot study along coastal Route 4, capitalizing on the compression provided by heavy vehicles (as compared to people), yielded enough power to conclude that, “expanding the project to a length of one kilometer along a single lane would produce 200 KWh, while a four-lane highway could produce about a MWh – sufficient electricity to provide for the average consumption in 2,500 households.”
The range of piezoelectric pads manufactured by Innowattech, the supplier for Israel’s projects.
As a result of this study, Israel Railways has seen their own installation of piezoelectric pads, similar in size and configuration to traditional railway pads. The hope is that power for railroad infrastructure would be supplied, with the remaining power spilling into the grid.
Piezoelectrics, while moving into the realm of practicality, still remain an expensive and highly experimental endeavor into power generation. As the products themselves become more efficient, durable, and afffordable, their benefits will become clear. For now, we can only speculate on the ways they will assuredly transform our transportation infrastructure in the future.
Material Strategies 