How every step you take could reduce Earth's carbon footprint

In the United States alone, people collectively take more than 900 billion steps every single day. Expand that number on a worldwide scale, and it's almost unfathomable. Eyeing those strides is a company reimagining humankind's impressive walking record as a treasure trove of cheap, sustainable energy.

It all started when Laurence Kemball-Cook, CEO of clean-energy company Pavegen, began regularly sauntering through London's Victoria Train Station as a design and technology student. Watching travelers headed to their destinations underneath the arched glass ceiling, he witnessed hundreds of thousands of footfalls on the ivory floor. 

As with those commuters, when we walk around, our steps' kinetic energy pushes us forward. But after the job is done, that energy doesn't just disappear. Energy can't be destroyed, only transferred. You can think of it sort of like a trail of power left behind as you walk forward. 

"All of this unharnessed energy wasn't being put to use," said Ciara Chantrey, a member of Pavegen's marketing team. 

An idea was born: Sidewalks that collect the secondhand energy of footsteps and store it in a usable format. Simple strolls could power things like street lamps or LED screens.

"An obscene number of prototypes were developed," Chantrey said. More than 700 blueprints were drafted before Kemball-Cook perfected his invention. "He ended up installing it outside a building in London. Then that's when people started using it, and it worked."

Pavegen is one of a slew of companies looking for ways to advance sustainable energy, work that's happening against the backdrop of the climate crisis. The state of the climate is in the spotlight right now as world leaders gather in Glasgow, Scotland, for the COP26 summit, which has been called the "world's best last chance" to get the crisis under control.

CNET Science is highlighting futuristic strategies intended to aid countries in cutting back on carbon emissions. Next-gen tech alone may not solve our climate problems, but green innovation could be invaluable to the 2015 Paris Agreement goal of limiting global warming to well below 2 degrees Celsius by the end of the century. 

With energy-generating sidewalks, we may be able to vote with our feet.

Steps that don't leave carbon footprints

Pavegen's sidewalks are made of tilelike, triangular platforms, with each corner containing a generator called a flywheel. When someone steps on a tile, the wheels are activated to spin extremely fast, Chantrey explained, generating power that's sent to and stored in a battery. 

As people walk on the sidewalk, each of their steps produces between 2 and 5 joules of energy. In isolation, that isn't a lot. A standard lightbulb calls for about 60 joules per second -- so these smart sidewalks don't have the capacity to power entire cities. 

However, the team says its form of clean energy can have a pretty big impact on a smaller, more accessible scale. These sidewalks could provide energy to office spaces, shopping malls, neighborhoods with street lamps, sports games or music festivals.

Think about it. One music festival goer walks about 15 miles, which translates to about 30,000 steps. In 2019, over 107,000 people attended New York City's Electric Zoo musical event. Combined, that's over 3.2 billion steps taken in just one weekend. Events like these often require a huge amount of energy to maintain onstage lights, audio equipment, food stalls and LED screens. 

With little to no effort from festival goers, who'd be walking around anyway, a smart sidewalk could make a dent in a festival's energy usage. 

Pavegen's invention, Chantrey says, could also potentially help to power developing countries or areas that are off the grid. That's because of the device's battery, which stores every bit of the step-based energy. It wouldn't need costly, complex power lines to work -- it's a closed system.

"Our sectors at the moment are kind of smart cities," Chantrey said, particularly "cities in the development period, who are looking to become greener and more sustainable."

She says the team has already installed a permanent running track in Hong Kong and is working on a project in the Philippines, too. In the meantime, as it works to lower the sidewalks' costs and strategize how to have a wider reach in application, Pavegen has been using the platform as an educational tool for sustainability awareness.

For example, in proximity to COP26, the team collaborated with Ikea.

"At the store in Glasgow," Chantrey said, "there's a paved array with a big 100% sign that lights up when you step on the array. ... That's basically them announcing stores worldwide will be ... 100% powered by renewable energy by 2030."

Power-walking 

So far, Pavegen has installed both temporary and permanent energy-producing sidewalks in countries around the world. For instance, there's one at a railway station in the United Kingdom that powers USB charging benches nearby. The company has also laid its tiles all along a football pitch in Nigeria -- foot power lights up the stadium.

So what's stopping us from retiling the planet? 

Right now, Pavegen's main limitation is the sidewalks' high price for a relatively small amount of energy. But on the bright side, Pavegen isn't the only group tackling the concept of harnessing footstep energy. A team from India is working on a gadget that appears similar to Pavegen's tile-based design but may offer a much higher power output. 

Unfortunately cost will still likely be a roadblock, just in a different way. Any tile mechanism, in fact, will likely have a couple of inherent hurdles to leap over.

"A key question is the cost in terms of watt per square meter or watt per dollar," said Fred Jiang, an associate professor at Columbia University's School of Engineering and Applied Science. "One would have to also include the cost of construction, for example, tearing up the existing pavement and disruption to the road."

He also notes another possible challenge. "The pavements will have to use some mechanism to bounce back, most likely springs, and springs can fatigue over time, especially under heavy load and frequent depressions." 

And in the coming years, we may be seeing other engineers finding a way around such worries. One European group has been working on wooden floors laced with a material that could generate electricity in a different way from Pavegen. Depending on the price of their invention, perhaps these high-tech patterns could enter the smart home market.

Overall, however, Jiang emphasizes that such efforts to improve sustainability like Pavegen's tiles should be encouraged despite a difficult pathway to fruition.