The skate-shoe charger and the trouble with walking power

What it was

The concept is credited to Soledad Martin, an industrial designer from Argentina, and was published in July 2010. It is a small pod that sits on top of a sneaker, held by a strap. A nanogenerator inside was meant to turn the movement of the foot into electricity and store it in a battery. When your phone ran low, you would take off the lid and plug in a USB cable.

The idea came from watching skaters, and the published photos show the device being strapped over the laces of a skate shoe. The straps closed with snap buttons and came in several colors. The Italian magazine Focus added that they could also go around the ankle. None of the reports gave a power figure, a battery size or a maker. We could not find the designer’s own page for the project.

Charging a phone by walking is easy to draw and has proved hard to deliver.

Where the idea went

The nanogenerator was real science but not a product. Zhong Lin Wang’s group at Georgia Tech published piezoelectric nanogenerators made from zinc oxide nanowires in 2006 and first demonstrated a second type, the triboelectric nanogenerator, in 2012. We could not find a nanogenerator phone charger on sale.

The companies that tried to sell walking power used small conventional generators. SolePower, founded in Pittsburgh by Hahna Alexander and Matthew Stanton, raised $60,000 on Kickstarter in summer 2013 for an insole that spins a tiny electromagnetic generator with each heel strike and feeds an external battery. By 2017 the company was building its charger into the heel of work boots, where it powers sensors and lights for industrial crews.

Ampy, from Chicago, made a wearable battery that uses magnets moving inside inductors. Its Kickstarter had passed $245,000 when TechCrunch covered it in October 2014. The maker said an hour of exercise would give an hour of normal smartphone use. Under The Gadgeteer’s write-up in 2016, a reader pointed to backers who said it did not work as advertised.

What it means now

The 2010 concept was not alone. A year earlier another Argentine designer, credited as Lola Mensa, had shown a kinetic charger that slides into the tongue of a running shoe. The appeal is easy to see. You move anyway, so why not keep the energy.

The catch has been quantity. Ampy’s own figure was up to three hours of smartphone battery life for 10,000 steps, and SolePower ended up powering sensors, not phones. What works today is less elegant. You carry a small battery that was filled at the wall, and for emergencies you keep something with a crank.