Can human activity count as clean energy?

By Dominic Pietro

Is it possible for the power generated by humans to be count as renewable energy certificates or carbon offsets? As the threat of climate change becomes increasingly severe, more and more novel solutions are being sought out to combat the problem. Bio-based carbon mitigation is an important and growing sector of carbon reduction strategies. So far though, the strategies focus on plant-based carbon sequestration and biofuels. The potential for plant-based carbon mitigation is high, but if we, as a country, or a world, want to seriously tackle global warming as much as possible, perhaps using human-based energy is a feasible option.

Bio-based carbon mitigation is the removal and storage of carbon (mostly in the form of carbon dioxide, CO2) from the atmosphere using plants natural ability to take in CO2 as part of the photosynthesis process. It also includes the prevention of net CO2 emissions by using plant-based biofuels rather than fossil fuels.

Everyday human motion results in a great deal of “lost” energy; i.e., a lot of the energy we use to move ends up being transferred into the surrounding environment and dissipates as low-level, unusable heat. Researchers and inventors have, especially in recent years, been figuring out ways to capture that lost energy and make it useful. A good website for reading about such advancements is Inhabitat, located at Examples of wasted energy that could be captured include opening and closing doors, pushing revolving doors, the energy transferred into the ground from footsteps, the energy generated at the knee when the leg swings back down during a step, and so on. When capturing this energy, it is important to capture energy that is normally wasted, and not to design an energy capture device that required the person to expend extra energy, or at the least, to require only a small amount of additional energy to be expended, especially if these devices become used in great numbers.

One place in particular where there is a lot of human-generated energy is wasted is a gym or health club. Several such gyms already exist throughout the world (Levesque, n.d.). More go into business as time goes on. Any piece of gym equipment that moves in order to operate could theoretically capture energy. Stationary bicycles are an obvious choice, but others can be used, such as treadmills, weight machines, steps (for step aerobics), and the list goes on.

According to the President of California Fitness, a person using an electricity generating bicycle at a moderate rate for one hour a day, each day, they can generate 18.25 kWh of electricity per year. This is essentially clean energy. In order to really figure out the environmental impact of this energy, once must use a life cycle approach in calculating emissions.

The average calorie consumed by an American has 1.59 grams of CO2 equivalent greenhouse gases associated with it (Eshel & Martin, 2006), due to the growing, processing and transporting of the foodstuffs and associated materials. There are also greenhouse gases associated with the production of the exercise equipment and transportation of members to the gym. If only food CO2 is accounted for, based on approximately 600 calories burned per hour on a stationary bicycle (“Cycling – Calories Burned Bike Riding,” 2005) then 0.95 kg of CO2 per year would be produced from bicycle-generated electricity.

Using data from SimaPro, life cycle assessment software, 1 kWh of electricity in the U.S. generates about 0.67 kg of CO2 equivalent greenhouse gases. That means that 18.25 kWh of electricity used in a year, the same amount that could be generated by one person on a bike, would emit 12.3 kg of CO2 equivalent. Minus the 0.95 kg CO2 from the food eaten, there is still a large net benefit. A careful life cycle assessment would need to be performed to find out the CO2 emissions associated with each kWh of electricity generated from the bikes (from manufacture), and for personal transportation to and from the gym, but bicycle-energy is likely still has a net benefit over coal-produced energy.

Renewable Energy Credits, or RECs, are a tradable commodity indicating that 1 megawatt-hour (MWh) of renewable electricity has been produced (“Renewable Energy Certificates – Wikipedia, the free encyclopedia,” 2009). While there is some scrutiny and controversy over RECs, there are nevertheless a popular means of offsetting carbon dioxide emissions.
Could RECs be applied toward gyms where electricity is generated by human-power? For starters, it would be to be verified that human-generated electricity at gyms is really a clean or renewable source of energy, though it looks promising, and the owners of green gyms claim so (of course). Second, enough electricity would need to be generated for it to be worthwhile. A single person won’t likely generated more than 18.25 kWh per year. But let’s look at nationwide gym membership. In 2007, there were 41.5 million gym members in the U.S (Kufahl, 2008). Granted, many gym members only use the gym once or a few days a week, some use it a few times a month, others use it only occasionally, and then there are the members who go once and never return. But let’s assume only 10% of members use the gym every day, or conversely, that the average member uses the gym 10% of the days each year. This works out to be a CO2 savings over standard grid electricity of 47,103 metric tons (referred to as tons from here on out) per year.

This also works out to be over 75,700 MWh per year. Currently, the price per ton of carbon dioxide on the Chicago Climate Exchange is around $1.50 (“Chicago Climate Exchange,” 2009). This would work out to be only a little of $70,500 per year of carbon offset for the 4.15 million gym members. RECs are worth a bit more however, ranging from around $5 to $90 per MWh (“Renewable Energy Certificates – Wikipedia, the free encyclopedia,” 2009), which works out to between $380,000 and $6.8 million per year. Still not a tremendous amount of money, but this is fairly conservative estimates. And even if the money for clean energy doesn’t work out to be very much, the value of the electricity saved from the grid would be over $8.3 million dollars, using the December ’08 average U.S. price per KWh (“Electric Power Monthly – Average Retail Price of Electricity to Ultimate Customers by End-Use Sector, by State,” 2009).

When the savings and the REC money are added it, it is still not enough to really “rake in the dough.” But it may be enough of an incentive for more gyms to go “green” and capture as much of that wasted energy as possible.
And from a non-monetary standpoint, the savings can still be an important part of fighting global warming. Saving 47,103 tons of CO2 per year is approximately equivalent to removing 8,500 cars from the road per year (“Emission Facts: Greenhouse Gas Emissions from a Typical Passenger Vehicle | US EPA,” 2005). This is not insignificant, especially as part of an overall, nation- or worldwide carbon reduction strategy.

Again, this is only looking at the potential from gyms. As devices to capture wasted energy become cheaper and more widely available, the implementation of such products could vast. Humans would themselves become small power plants, perhaps producing enough energy to satisfy a significant portion of our daily energy needs. Counting this energy as renewable, and thereby opening it up to some of the financial benefits of renewable energy, may not incentivize individuals, but it could be just enough to encourage organizations and corporations to adopt such technologies.


Chicago Climate Exchange. (2009). . Retrieved April 21, 2009, from
Cycling – Calories Burned Bike Riding. (2005). . Retrieved April 21, 2009, from
Electric Power Monthly – Average Retail Price of Electricity to Ultimate Customers by End-Use Sector, by State. (2009). . Retrieved April 21, 2009, from
Emission Facts: Greenhouse Gas Emissions from a Typical Passenger Vehicle | US EPA. (2005). . Retrieved April 21, 2009, from
Eshel, G., & Martin, P. (2006). Diet, Energy, and Global Warming. Retrieved April 21, 2009, from
Kufahl, P. (2008). U.S. Health Club Memberships Decrease in 2007. Retrieved April 21, 2009, from
Levesque, T. (n.d.). Inhabitat » HUMAN-POWERED GYMS in Hong Kong. Retrieved April 21, 2009, from
Renewable Energy Certificates – Wikipedia, the free encyclopedia. (2009). . Retrieved April 22, 2009, from


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