|Fig. 1: Pavegen tiles convert footsteps into usable electricity.|
With each passing year, the problem of the world's increasing energy needs, but decreasing energy supply becomes a greater worry for society. But this conundrum has also become a great inspiration for innovators like Laurence Kemball-Cook, CEO and founder of the London-based start- up, Pavegen. Over the last five years, Pavegen has iterated on a modular floor tile that converts the kinetic energy from a person's footstep into storable electricity.  So is Pavegen on the right track? Is human generated electricity a viable solution to the energy crisis?
The structure of a Pavegen tile allows it to compress an indiscernible 5 mm per footstep and produce up to 8 Watts of energy. 5% of this power goes toward powering the device itself and the other 95% is stored in a battery for external use. To put that in perspective, Kemball-Cook claims that one footstep is capable of powering an LED-streetlamp for 30 seconds. Although that may not seem like much, Pavegen technology is meant to be placed in high traffic areas such as train stations and malls. A recent Pavegen setup at a large outdoor festival attracted 250,000 steps and the power generated was used to charge 10,000 mobile phones. 
Since these energy converting tiles are under heavy footfall, they are made to be rather durable. They are rated to last about 5 years, as well as withstand harsh outdoor conditions including rain and snow. The company hopes to increase the tile lifespan to 20 years. Pavegen also hopes maintain a small carbon footprint by manufacturing tiles with 80% recycled materials. 
The exact technology for energy conversion is not public knowledge, but is speculated to utilize piezoelectric sensors. Kemball-Cook also claims that Pavegen is 200 times more efficient at producing power than any competitor product. 
Granted this all sounds amazing, but Pavegen's real issue right now is price. T. K. Grose, writer for The National Geographic, pens "High costs are a hurdle, however. Like a lot of green technologies, early iterations of Pavegen tiles weren't cheap. Kemball-Cook said the price of the tiles has dropped 70 percent in the past year, but he was not willing to publicly divulge the current price because it's changing so rapidly." Although the company refuses to comment on the current price, they hope to see the price drop to under $100 per tile in the next two years. [1,2]
Pavegen seems to make a lot of inspiring and inspired statements about their product. For example, Kemble-Cook has said "The average person takes 150 million steps in their lifetime, just imagine the potential."  But beyond these grand statements, I think that something may be overlooked, mainly the principle of the conservation of energy. The energy output of humans is limited by their energy input and the amount of energy it takes simply to remain alive.
The average male eats 2620 calories per day or 11 MJ and his bodily processes require about 7.53 MJ to function, [3,4] Therefore he has a daily excess of 3.47 MJ. This is just under 1 kWh. And note that this is a generous estimation of daily excess energy, since not everyone is as large as a fully grown man. Based on some of Pavegen's previous case studies, 1 kWh is approximately 8,800 steps.  Knowing that a common fitness goal is 10,000 steps a day, if an average sized man wanted to produce 1 kWh of energy he would need to expend nearly his entire day's worth of time and energy to reach that goal. A thought experiment by Stanford student Seth Winger produced similarly disheartening results when he calculated that a popular nightclub of 1400 guests that uses an energy harvesting dance floor would only produce about 4 × 107 joules in a night.  That number translates to only 11.1 kWh.
Now looking at the bigger picture, if we took the 3.5 MJ of daily excess from a single man and multiply by the world population of roughly 10 billion, we have 3.5 × 1016 joules. Then multiply that by the 365 days in a year for a total of 1.3 × 1019 joules per year. Unfortunately our grand total, which is an overestimation, is an order of magnitude less than the world energy budget of 5.5 × 1020 joules. 
And so essentially, these numbers from the previous two paragraphs make it clear that not only is Pavegen's product rather inefficient at converting human produced kinetic energy into usable electricity, but if we were to total all of the energy humans are capable of producing, it is still much less than the amount of energy the world uses.
So now here we stand, with an incredibly innovative and hopeful technology that has an unfortunately high cost and comparatively low energy output. However, personally, I am optimistic. I am of the mindset that any little bit helps and using footsteps to charge cellphones at a concert or light Christmas lights in a mall means saving that little bit of non-renewable energy for future use. I also want to give Pavegen a round of applause for pushing the boundaries and for helping the world to be more receptive to other technologies like Bionic Power, a knee brace that harvests energy while walking.  And I also have faith that Pavegen will continue to improve on its technology and lower costs.
However, I do think Pavegen has been doing something very well. They have been engaging people of all ages to be involved in the solution to the energy crisis. Their technology effectively raises awareness in two ways. The first is by providing immediate feedback of numbers and LEDs lighting up and phones charging, empowering people to produce green energy. Secondly, they show the world, through the perspective of footsteps, the large amount of energy we use and bring us face to face with the conclusion that we are using energy un-sustainably. Pavegen encourages society to be a part of the solution, one step at a time.
© Alyssa Fujimoto. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 T. K. Grose, "Tiles May Help Shrink Carbon Footprint by Harnessing Pedestrian Power," National Geographic, 18 May 12.
 G. Webster, "Green Sidewalk Makes Electricity - One Footstep at a Time," CNN, 13 Oct 11.
 A. B. Hatow and J. Heslin, The Calorie Counter, 4th ed. (Simon and Schuster, 2007).
 W. K. Purves et al., Life: The Science of Biology, 7th ed. (W. H. Freeman, 2004), p. 962.
 S. Winger, "Piezoelectricity From Dancing," Physics 240, Stanford Universitity, 24 Oct 10.
 "BP Statistical Review of World Energy," British Petroleum, June 2014.
 D. Khadilkar, "Energy-Harvesting Street Tiles Generate Power from Pavement Pounder," Scientific American, 20 Apr 13.