Energy harvesting from the human body

After all, the human body would be the ultimate source of renewable energy - it is an incredibly sophisticated piece of machinery, not to mention extremely energy efficient. Now, you might be wondering if this is some kind of an outlandish fantasy but in recent years, there have been very promising developments in the area of energy harvesting. In a bid to power the hundreds of billions of IoT edge devices that we will have deployed in the near future, scientists are looking at a variety of solutions to produce low amounts of energy without using batteries.

The era of energy harvesting is here.

Batteries just don’t make any practical sense, be it economically or environmentally. But apart from these two concerns, there is also a near-impossible logistical challenge which makes it essentially impossible to consider batteries as a long-term solution to power IoT devices. It is this bottleneck which has catalysed significant innovation and research in the field of energy harvesting technologies. The results have been incredible! We have made rapid advances in this field and as of today, there are a number of self-powered sensors and devices on the market, which employ technologies like RF-energy harvesting, piezoelectric harvesting etc. Essentially, these technologies use ambient energy from the surrounding environment to produce small amounts of electricity.

This area of research has grown so considerably that recently, a team of scientists were able to generate electricity from thin air! 

For as long as energy harvesting has been around, there has been widespread interest within the scientific community about the possibility of harnessing electricity right from the human body. Now, this might understandably sound a bit far-fetched, but today, it's no longer the stuff of mere speculation. Throughout this decade, scientific interest in this area has been growing steadily. A number of research teams have come up with their own technologies to harvest energy from the human body. 

Why harvest energy from humans?

You might well be wondering, “it’s cool and all but why do we need to harvest energy from humans?”.

The answer largely lies in the realm of implantables and wearables. In one of our earlier posts, we’d explored the many reasons why a booming internet of things needs energy harvesting to power its rapidly growing number of edge devices. One of the key reasons we’d highlighted was the fact that edge devices are likely to be placed in extremely remote locations, which would make maintenance and replacement of batteries pretty much unfeasible, if not impossible. 

This is especially true when it comes to implants. After all, what could be a more remote location for an edge device than the inner recesses of the human body? Reliable human-powered energy harvesting technologies are poised to go a long way in powering the bio-hacking revolution that is fast gaining traction.

As such, we are in the midst of a wearables boom. Health and fitness trackers are no longer a niche category for tech-geeks. Wearable health technology is assuming greater levels of significance and is likely to form an integral part of any connected healthcare system. 

So, this brings us back to harvesting energy from the human body. There are basically, two ways this can be done - passively or actively. Passive power refers to drawing energy in an unobtrusive manner from the user’s regular activity; think of a piezoelectric pavement as an example of this. Passive energy harvesting technology could also use blood flow or body heat. The basic idea is that the user isn’t required to do any “extra” work. Conversely, active power refers to technologies where the user is required to take specific action in order to power the device. A mechanically-powered flashlight is a simple example of this.

“The heart produces around 1 or 1.5 watts of hydraulic power, and we want to take maybe one milliwatt, while a pacemaker only needs around 10 microwatts.” 

- Prof.Alois Pfenniger, University of Bern

Real-world examples of human body energy harvesting

There have been some truly path-breaking research conducted in this area. In the last few years, a number of viable human body energy harvesting technologies have emerged. Some of these may not yet be viable outside a laboratory setting, but nevertheless contribute to the momentum of innovation in this area.

We may not quite be able to solve the problem of powering our homes and factories with solutions like these, but they are definitely very promising when it comes to powering IoT devices, which typically don’t require a lot of power. 

In the sections below, we take a look at some of the most promising technologies based on drawing electricity from the human body. 

1. Bloodstream

Most of us are familiar with how a turbine works - think of dams and hydroelectric power. Much in the same way, microturbines implanted in human arteries are being used to generate electricity.

A team of Swiss scientists from the University of Bern came up with this ludicrous sounding idea all the way back in 2011. Led by biomedical engineer Prof.Alois Pfenniger, the team successfully designed and tested “vascular turbines” that are tiny enough to fit inside a human artery!

"The heart produces around 1 or 1.5 watts of hydraulic power, and we want to take maybe one milliwatt; a pacemaker only needs around 10 microwatts." explains Pfenniger. 

If successfully brought to market, this type of technology could make a dramatic impact on pacemakers, blood-pressure sensors and other such implantable devices which are already in wide use. These devices either use a battery or a power cable in order to function. Eliminating the need for external power supply could be revolutionary - it would allow doctors to be able to implant them with minimal fuss and risk of side effects for the patient. 

This technology, although incredibly promising, met with an early roadblock. Although it was demonstrated to be able to produce about 800 microwatts under supervision, there was widespread concern among experts about the turbulence that it caused. When subjected to turbulence, blood tends to coagulate or clot. Pfenniger and his team acknowledge that this might be a tricky challenge to overcome and have been working on design tweaks.

A team from China has gone further. In a paper published recently, the team from Fudan University in Shanghai, China revealed that they have developed a fiber that is less than a millimeter thick, which produces electricity when immersed in a saline solution (read:blood).

2. Body Heat

There has been a lot of buzz around smart clothing recently. Just a few years ago, this was seen as a gimmicky category that clothing giants could exploit for a PR opportunity or two. Smart features on clothes were viewed as a “cheap thrill” of sorts, with no real utility. 

But as of today, there has been a steady spate of innovative fabric technologies that are aimed at converting body heat into tiny amounts of usable electricity. Researchers from many of the world’s premier institutions have been working on creating thermoelectric fabrics that could generate power from body heat. 

A notable example is Power Felt, a flexible fabric that can, interestingly, conduct electricity while providing thermal insulation. 

Power Felt is the brainchild of David Carroll, a professor of physics at Wake Forest University. Originally, he intended Power Felt to charge phones using body heat. 

From a body that is producing 100 to 120 watts of power, you might be able to get one or two watts of power,” Carroll said. “If you make clothing out of that, that's enough to start running electronics, like cellphones and things of that nature.”

One of the key selling points of Carroll’s technology is that it is extremely affordable. It is estimated that a dollar’s worth of Power Felt could be enough to cover your smartphone. 

3. Exercise

Sci-fi buffs have seen this one coming for ages. You might have daydreamed about this while driving past a gym’s front and seeing people riding stationary bikes and ellipticals. After all, it’s not a giant leap to consider generating electricity from exercise equipment. 

A number of startups including ReRev and Green Revolution have been working on developing exercise machines that make your workout go that little distance in making the environment greener. 

There are a number of methods that have been adopted to this end. ReRev, for instance, connects DC generators to elliptical trainers, which then send the current back to the building (after having passed through an inverter). 

Green Revolution, on the other hand, have hooked stationary bicycles up to batteries, which get “charged up” during a workout. 

While these technologies are definitely novel and fun, they are far from being utilitarian. The amount of power generated by these technologies, in their present iterations, is fairly trivial. 

Say you rode one of these bikes for 5 hours every day, you would still produce only $18 worth of electricity at the end of a whole year! 

4. Footsteps

This one’s probably the most popular of the lot. Chances are, you have encountered or at least, heard of, piezoelectric energy harvesting. 

Say for instance, let’s take a pavement that is loaded with piezoelectric tiles. Each footstep is estimated to generate somewhere around 7 watts of power. Now, this may not sound like a lot, but in a busy place with a lot of footfalls, this sort of setup could easily power the streetlights in a neighbourhood. 

Piezoelectric energy harvesting is a very promising trend within sustainable energy. 

5. Human waste

There is a significant amount of scientific research happening in this area. All the way back in 2012, a Chinese-produced toilet that converted human waste into electricity and fertiliser attracted tons of attention.

On the other side of the world, The Bill and Melinda Gates Foundation invested a whopping $500,000 in a microbial fuel cell that runs on urine! The project, which was spearheaded by Dr.Ioannis Ieuropoulos and his team from England, 

The major advantage of human waste is that, unlike solar or wind, it is perennial and reliable. 

"The beauty of this fuel source is that we are not relying on the erratic nature of the wind or the sun." quips Dr.Ieuroloulos. “This is as eco as it gets”.