Understanding Energy Part 1: You Are as Powerful as a Lightbulb

Posted July 31st, 2012 at 1:17 pm.

Thomas Great Hall Chandelier

The chandeliers in the great hall now use energy saving LED bulbs, but all the bulbs together still pull more energy than a human can produce.

By: Lee McClenon

Understanding Energy

We all know that light bulbs usually are labeled between 40 and 100 watts, but can you conceptualize what that actually means? When you turn off that light, how much energy are you saving? What could be done with that amount of energy? In order to start making a dent in reducing our energy use, we have to understand the magnitude of the energy that we currently use- and it is huge. I will be writing a series of blog posts aiming to explain the magnitude of energy that we use, what we do with it, where it comes from, and what our options for the future are.

First, a Quick Physics Review

Starting at the bottom, a newton is a unit of force and is equal to about a quarter pound. So, a hamburger sitting on a countertop exerts about a newton of force downward and the counter exerts a newton back to keep it in place.

Energy, or the ability to do work, is force times distance. A joule, a unit of energy, is one newton over one meter. Lifting the hamburger one meter off the counter uses about one joule of energy.

A watt is a measure or power, or work over time. If a force says how strong you are and energy is how much work you do, power says how fast you can do that work. So, moving the hamburger 1 meter in 1 second takes about 1 watt of power. If you move it slower, in 4 seconds, you are less powerful, at only .25 watts.

If you’re still a bit confused, this video may help.

Human Power

Humans do not generate much power. Think about a person who consumes 2000 calories in a day. Every calorie from food (kCal) is equal to 4200 joules of energy. Used over the course of a day (86,400 seconds), this person uses an average of 97.2 joules a second, meaning they have an average power of 97.2 watts. Certainly a person could juggle quite a few hamburgers, but in the end humans only average the power of a bright lightbulb.

Of course, that is an average usage. A person can be more powerful than that, but not by a whole lot. The world record holder furthest biked in one hour, Ondrej Sonsenka, generated an average of 430 watts during his ride of about 30 miles. This elite athlete might be able to power your living room for a movie night (100 w for 32” LCD TV, 50 w for DVD player, 50w for the cable box and a couple light bulbs), but couldn’t create the power needed for the microwave popcorn to go with it (modern microwaves average 1000 w while in use).

Though there are clever technological advancements to hook gym equipment up to ipod chargers, we simply cannot revert to using only human power, or even animal power, to create the energy used in our society. Lets consider cars. There are about 746 watts in one unit of horsepower. The power of an average 110 horsepower car is equal to 82,000 watts. It would take 190 Sosenka-caliber-athletes to power that one car. If all 6.5 billion people on the planet pedaled that hard at the same time, we could power more than 34 million cars. It sounds like a lot, but there are an estimated 250 million passenger cars in the United States alone. It also does not include delivery trucks, or airplanes, or trains. We can no longer go the places we go, at the speeds we do it, under our own power. Not even close.

Fossil Fuels vs Human Power

The power we use as a nation has far exceeded the ability to power ourselves, as other organisms do. We are the only creatures that do not simply absorb our energy (from the sun, or by eating), but we extract it, manipulate it, store it externally, use it consciously and for specific purposes. We are able to use and transport all the energy that we do because it is incredibly cheap to do so.

New technology has created the ability to turn gym equipment into generators for small appliances, like iPod chargers. While it is convenient and worth it to plug into your energy if you are working out anyway, it’s doubtful that we could pay people to power our homes. Currently citizens of philadelphia pay about 16 cents for a kWh of energy (1000 watts of power for an hour). If we hooked up Ondrej Sonsenka to a perfectly efficient generator and he pedaled at a power of 430 watts, it would take 2.33 hours to create 1 kWh of energy. Because federal minimum wage is currently $7.25 cents, one kWh of athlete-power would cost, at minimum, $16.89. That is 100 times more expensive than electricity from the power plant in Philadelphia.

For a second comparison, the cost of a gallon of gas is getting pretty steep- maybe $3.75 a gallon. This one gallon releases 36.6 kWh of energy when burned. To generate the same power using an olympic athlete would take almost 85 hours of hard work. This would cost you $616.25. Gas is dirt cheap, comparatively.

Why we Use Fossil Fuels

Human power is the truest “renewable” energy resource. There is no extra input, no construction, no maintenance, no dangerous waste products and no extra CO2. Yet to hire someone to jog laps to power your appliances would be absurd. Because of our intelligence, a person’s time is much more valuable than the physical labor that we can do. From the moment a horse was first hooked to a plow, humans have exported our energy needs. Since then, the industrial revolution allowed us to harness the true efficiency of our being by not having to do physical work, unless the job requires human intelligence or dexterity. The rise of fossil fuels has allowed human thought, creativity and interaction to be valued far more than labor, even more than ever before. This is the power of our fuels and why we use them.  Energy has allowed our society to flourish, but unfortunately the negative environmental and social impacts are becoming more and more apparent.

Next time you flick a light switch, consider this. What is the value of that energy to you? What does it mean for your life? What could you live without if it became too costly?


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