Sweating for the Grid: Harnessing Human Power

With municipalities and green-minded companies looking to create energy out of everything from sewage to agricultural waste, it’s no wonder that people might start thinking about harnessing the original source of workable energy: humans. While no one is planning on commanding an army of workers to rebuild the great pyramids, some are wondering if it isn’t worth a look, at least at the microeconomics level, at capturing a little of the energy people expend on an average day.


Human power will never run cities: an average, healthy person can produce only about 0.1 horsepower for eight hours, which translates to about enough energy to light a 75-watt light bulb. A top athlete might be able to generate around 0.4 horsepower during the same period. It has been estimated that Lance Armstrong produced about 400 to 500 watts each time he raced up the French Alps. But most of us (all of us, actually) are not Lance Armstrong.

Since humans individually can’t produce very much power, some newer technologies (and their intrepid purchasers) are looking to harness the power of humans in groups. A number of health clubs have already installed exercise equipment that captures the energy of the workout and feeds the power back into the grid. Generally, the technology is best suited for group workouts – think group cycling classes — that will collectively generate more than a tiny trickle of power. Theoretically, a typical group cycling class using 20 exercise bikes can create about three kilowatts of power per session. If the gym operates four classes per day, it can create up to 300 KW each month, which corresponds to the amount of energy needed to light a typical home for about six months.

It’s certainly not going to save the world on a grand scale – but it may help offset the energy use of the gym, and interest in the technology is growing.

“We have seen a significant increase in interest in the past six months, which is a good sign that fitness centers are ready to invest in green technologies,” said Mike Curnyn, who co-founded the Green Revolution, a Connecticut-based company that makes the

Sweating for the Grid: A Group Cycling Class Using Green Revolution Technology

technology to wire exercise bicycles into a central battery that stores workout energy. The company’s technology can be used on existing fitness equipment without significant modification, and it has been tested on most brands of group cycling bikes. But if you’re looking to set up your home exercise equipment to power your house, the technology isn’t really there yet. The cost of connecting a single bike to the grid far exceeds what one person could put back into the grid. The Green Revolution believes that as the cost of grid-connection equipment drops, it will make more economic sense to offer home products to consumers.

The Green Microgym in Portland, Oregon is a 3,000 square-foot gym that first opened in 2008; a second location was opened in November. Owner Adam Boesel positions the gym as the ultimate workout experience for green-minded people: not only do you get a workout, but you help offset the energy use of the gym while you pedal. The gym is outfitted with six exercise bikes and one elliptical trainer that, when in operation, generate electricity that can either charge battery packs or be fed back into the grid. An average workout, according to Boesel, creates about 37.5 watt hours, which is about enough to power a phone for a week. Though the gym claims a 60 percent carbon offset figure, it’s important to note that this number includes not only the “people power,” but judicious selection of energy-saving equipment, conservation efforts by the gym’s management, and eco-conscious choices of building materials and supplies.

“We haven’t created all that much electricity, but because we’re focused on saving energy, we are very energy-efficient compared to other gyms,” Boesel told LiveScience.

Nobody really knows how much power a system like this could generate. Two universities in Texas, the University of North Texas and Texas State University, have invested in energy-generating workout equipment for students. The project has been underway at Texas State, which has 30 bikes, for about 10 months, and it’s still unclear exactly how much power is being fed back into the grid by sweating students. The University, however, views the program as not only a power-saving initiative, but a learning opportunity: the school hopes that using the equipment will induce students to stop and think about their own impact on the environment. The larger program at UNT started more recently and was installed on 36 bikes. Both universities have revealed that their initial costs were about $20,000. With the modest amount of electricity being generated, it may take as many as 15 years to break even, at which time the bikes will probably need to be replaced, erasing any net gain.

Exercise isn’t the only type of human power that’s being fiddled with by science and technology. Some innovators foresee harnessing the energy of your footsteps as you walk. Outfitted with special shoes, people can generate usable energy with the help of stepping or compression generators that use piezoelectric materials – substances that generate an electrical charge when mechanical stress such as bending or twisting is applied — to generate a current from the constant compression and expansion of the walking motion. Theoretically, with special inserts in the soles of one’s shoes, a strolling individual could generate enough electricity to power a phone, an MP3 player or a GPS device.

An even cooler application of piezoelectric materials are devices that can actually convert energy from body movement and the stretching of muscles into electricity via nanoscale components or “nanogenerators.” A scientist from the Georgia Institute of Technology, Zhong Ling Wang, and his graduate student partner Jinhui Song, have invented a protoptype nanogenerator that generates electrical current via the bending and flexing of zinc oxide “nanowires.” When the nanowires are stretched or bent, they emit a piezoelectric discharge that can be collected and stored. According to Wang and Song, because zinc oxide is non-toxic, the wires could theoretically be implanted into the human body to harness muscle energy. “Our bodies are good at converting chemical energy from glucose into the mechanical energy of our muscles,” said Wang said. “These nanogenerators can take that mechanical energy and convert it to electrical energy for powering devices inside the body.” Wang also outlined a less cringe-inducing and invasive application for the technology. “You could envision having these nanogenerators in your shoes to produce electricity as you walk. This could be beneficial for soldiers in the field, who now depend on batteries to power their electrical equipment. As long as the soldiers were moving, they could generate electricity.”

Of course, one commercially available application of human power into energy are flashlights that charge from just a shaking motion: such flashlights have been commercially available for years. The science behind it is very simple: inside the flashlight is a magnet that passes through coils of wire to generate a current, which is stored in the flashlight’s battery for future use. Radios that operate on batteries that can be charged with a hand crank have been around for decades. With a little searching, you can even buy a combination emergency light and radio that operates via hand cranking; some of the devices will also allow you to charge your cell phone. The devices are touted as the ultimate in emergency preparedness for homeowners.

Human power is, of course, only “green” when the power harnessed is energy that would be otherwise wasted. Sure, you could set up a stationary bike in your house and decide to ride it three hours a day for the purpose of generating a small amount of electricity, but if that’s not your normal activity, you’ll probably be using extra energy from elsewhere to create the power: more exercise requires more calories, which means purchasing more food. Bang: there goes any net savings. To be most effective, human power needs to be harnessed from everyday activities such as walking to work, regular exercising, climbing stairs or doing yard work – activities that generate power that would otherwise be wasted.

Many municipalities are thinking of more and better ways to generate electricity out of human activity. A busy railroad station in the Netherlands, after realizing how many people pushed through its revolving doors during the day, installed an electric generator system on the door. The company that produced the technology estimates that a single traveler using the door can generate enough electricity to power a 50-watt light bulb for one second. During the course of a year, the power generated by millions of people using the door could generate about 50 kilowatt-hours. This is, on average, the amount of energy consumed by five households in the U.S. It’s not a lot – no one is going to get rich reselling the power – but it could meet the needs of the station itself, helping the train station reach net-zero in energy consumption.

As technology marches forward and the equipment becomes more efficient (and, more importantly, cheaper), we may all of us find ourselves doing a little power generation as we go about our daily routines. Even if we’re not Lance Armstrong.

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