Imagine yourself walking down the sidewalk on your way to work or school or the grocery store. You’re taking your usual route, but today you notice this is no ordinary sidewalk. Instead of the usual concrete slabs bordering busy 2-lane streets designed for efficient traffic movement, you are surrounded by greenery. Instead of car traffic buzzing by, you hear birds chirping and cheerful bicyclists zooming past in their own lane. The pavement, made out of recycled car tires, has a nice bounce to it. Not so much that you can’t keep your balance, like on a trampoline, but just enough to avoid the stress of impact you get on hard surfaces such as concrete. When you look down you notice an illuminated circle in the center of this rubber slab. This glow lets you know that the step you just took has generated electricity.
You’re walking on technology from Pavegen Systems, which converts the kinetic energy from your footsteps into electricity stored in a lithium battery below. Each footstep slightly compresses the pavement a measly 5 millimeters, which seems to create a miniscule amount of energy, but absorb the energy from the up to 50 thousand footsteps a busy street receives daily and you’ve got yourself about 2 watts of electricity every hour. And that’s just one slab of this stuff! If an average sidewalk stretching corner to corner consists of 500 paving slabs, that’s a whole kilowatt of electricity produced per hour. Since only 5% of the generated energy supplies the informative glow, the rest can be utilized for other electric demands, such as streetlamps, traffic signals, or public transit stops. Whatever doesn’t get used can be stored in the battery for up to 3 days, and with efficient lighting, excess production is quite possible. An LED street light, for example, has only a 60-watt power consumption rate while an LED lighted MUNI stop would require just under 75 watts per hour. Imagine walking those three or four blocks to the bus stop knowing that by doing so, you supplied the energy source powering the monitor to tell you the next Inbound 38 will be arriving in just three minutes. Walking doesn’t have to be a chore, something for people who can’t afford any better means of transportation. It can even be more than an effort to conserve energy. Walking can create electricity!
Now imagine the possibilities beyond just sidewalks. Think of yourself stepping out of a train onto the station’s platform. Surrounded by people, you move with the crowd all heading in the same direction to eventually exit onto the street. But first you must all pass single-file through an electronic ticket gate that confirms you have paid the proper amount for your trip. What if your footsteps and those of everyone around you could help power that ticket gate? Next, picture yourself in a dance club, music blaring, lights flashing, and people dancing all around you. In fact, the floor is a sea of moving limbs. What if the energy from all those dance steps was utilized to help power the stereo and lights? Now visualize yourself walking down the hallway to your first class. Schools experience phenomenal amounts of foot traffic with students, teachers, and administrators making their way to classrooms and offices throughout the day. According to the Environmental Protection Agency (EPA), nearly 84 million Americans attend colleges, universities, primary and secondary schools on a daily basis. Imagine if all of the energy from those myriad footsteps were harnessed for electricity. It might not supply the schools’ entire energy demands, but it would certainly relieve some of the pressure on other sources. Peak hours of need would inherently correspond to peak hours of production so that the hours when we need electricity the most to light hallways, power ticket gates, and play music, the highest number of people are there generating electricity.
Kinetic energy can be harnessed in more ways than just walking, though. Picture yourself in a spin class at the gym. There are close to a dozen other people around you furiously peddling on their stationary bikes while catchy pop tunes blare from mounted speakers. Only ten percent of your expended energy powers the machine while the rest dissipates as waste heat, some of which could be converted into electricity. Exercising at a moderate pace the average person can only produce about 50 to 100 watts per hour, enough to power a small stereo or an incandescent light bulb. But with dozens of us at one time, the contribution becomes significant, especially when using energy efficient appliances. Gyms like this are few but already popping up in Hong Kong, Portland, and even Texas. Imagine waking up at sunrise to get to the gym just as it is opening. At first the lights are very dim, you hear no music playing and see the television sets are still off. You think to yourself, well, if I want to hear some music or watch the morning news, I better start moving. What a great motivator! And even better than that, you are burning calories while simultaneously preventing fossil fuel emissions. Not only are you keeping yourself fit and healthy, you are keeping the planet fit and healthy too.
Human-powered electricity provides an important resource that, in conjunction with other more substantial forms of alternative energy, such as wind and solar, could prove very useful in a post-carbon environment. Yet even with all the human-powered energy in the world, I can’t stress enough that improved efficiency is still the most important strategy as it gets to the source of the problem: demand. David Fridley of the Post Carbon Institute points out that while alternative energy sources will have to form the backbone of our energy system, we can’t use it the way we use fossil fuels. Continuous, uninterrupted supply will shift to intermittency. Demand, forced to comply with whatever limited supply is available, will require a dramatic reduction. Does that mean we are wasting our time in exploring every possibility in alternative energy technology? No. But it does mean that replacing fossil fuels with alternatives alone won’t quite cut it. All of the examples I have given function most effectively when coupled with energy efficient use. Pavegen sidewalks and electricity-generating gym equipment can only produce as much energy as we provide. But if we use that energy efficiently, it can certainly go a long way.
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