Think of the human body as the ultimate distributed energy resource.
Of all the renewable fuels, there is perhaps none more sustainable than your own body.
Today, there are already a few ways the human body can help produce electricity -- from simple exercise to human waste.
None of these outlandish technologies are going to help save the grid anytime soon, but it's fun to imagine a future where your organs can power the supercomputer in your brain.
1. Blood flow
A team of Swiss researchers led by biomedical engineer Alois Pfenniger are showing the world a promising glimpse of the future: microturbines implanted in human arteries.
The microturbines work much like a hydroelectric power plant by using the flow of the bloodstream to generate electricity. Of the three turbines Pfenniger’s team tested, the most productive generate about 800 microwatts of power – far more than needed to run a pacemaker.
"The heart produces around 1 or 1.5 watts of hydraulic power, and we want to take maybe one milliwatt," Pfenniger said. "A pacemaker only needs around 10 microwatts."
Today, the microturbines' use cases are limited to powering blood-pressure sensors, drug-delivery pumps and neurostimilulators – all of which need a power source. In the future, the possibilities are more outlandish.
Humans walk a lot, so why not capture that effort and use it to generate electricity? That’s the initial thought behind Pavegen, a startup that wants its footstep-powered tiles to become the way of the future.
Depending on how hard you step, one footstep on the company’s tiles can produce one to seven watts of power. That’s not enough electricity to power a home, but it is enough electricity to light up a street LED for 30 seconds, according to Pavegen.
For Pavegen, the use of its tiles extends beyond renewable energy, however. The startup’s tiles can provide previously hard-to-capture data about humans’ walking patterns.
“Our aim is to take the same price as normal flooring,” said founder and CEO Laurence Kemball-Cook. “And then it can be in every normal floor in the world.”
At gyms all around the country, there are stationary bicycles, elliptical trainers, and steppers. Now imagine if each one generated electricity.
Some already do. Giving ‘man power’ a whole new meaning, startups including ReRev, Green Revolution and Human Dynamo are making exercise more environmentally-friendly by rigging these machines to produce electricity.
Some, like ReRev, wire up ellipticals with DC generators to a central unit with an inverter, which converts the power produced to AC and sends it back to the building and the grid. Some, like Green Revolution, decided to hook up exercise bikes to batteries. Others, like Human Dynamo, built a custom stationary bike that sports ‘hand cranks’ and pedals that turn a flywheel tied to a generator, which can connect to multiple bikes simultaneously.
But these machines do not yet produce a grid-saving amount of power – the average can produce between 50 and 150 watts in an hour while a top-level cyclist can generate over 400 watts over the same period.
Calculations show these types of machines would produce, given 5 hours of daily use at 100 watts per hour, only 183 kilowatt-hours per year -- or about $18 worth of electricity.
“I hope this technology is in every piece of equipment in 10 or 15 years,” Adam Boesel, owner of the Green Microgym, said. “A few watts here and there from all of us as we sweat may add up to something significant.”
4. Body heat
Researchers at several prominent institutions, including the Georgia Institute of Technology, are developing wearable fabric that can generate electricity.
David Carroll, physics professor at Wake Forest University, is one of those researchers. He’s created Power Felt, a flexible fabric that can both conduct electricity and provide thermal insulation.
Power Felt has a number of use cases, but was intended to capture body heat and reuse it to charge phones.
“From a body that is producing 100 to 120 watts of power, you might be able to get one or two watts of power out of that,” Carroll said. “If you make clothing out of that, that's enough to start running electronics, like cellphones and things of that nature.”
Carroll estimates it would cost $1 to produce enough Power Felt to cover your smartphone.
“While I’ve been talking to you, the back of my phone has gotten hot,” he told Bloomberg. “Our $1 piece of fabric would give you the same amount of boost as a $50 battery would.
5. Urine and feces
We thought about making this number one and two on our list.
Jokes aside, there are a few promising energy uses for human waste. Human feces can be digested at bioreactor to release biogas, according to Chinese researchers who have developed a toilet that helps produce fertilizer and electricity. Caitlyn Butler, a professor of environmental engineering at the University of Massachusetts, has developed a Microbial Fuel Cell Pit Latrine. As opposed to your regular pit latrine, this one takes composted waste and oxidizes it in an anode chamber. Electrons are then released and passed through a load-bearing circuit, which generates electricity.
There’s also a way to use human urine to generate electricity. The recipient of a £500,000 grant from the Bill and Melinda Gates Foundation, a research team led by Dr. Ioannis Ieropoulos, professor at University of the West of England in Bristol, has developed another microbial fuel cell – but this one runs on urine.
“The beauty of this fuel source is that we are not relying on the erratic nature of the wind or the sun,” Ieropoulos said. Urine-fueled electricity "is about as eco as it gets."
"We are very excited by the potential of this work," but more research is needed, he added. “So far the microbial fuel power stack that we have developed generates enough power to enable SMS messaging, web browsing and to make a brief phone call on a phone.”