Monday, September 17, 2007

Human energy harvesting--a reply

Human energy harvesting--a very silly idea | Tech news blog - CNET News.com

The above link is a response to an MIT report that endorses generating power from the everyday movement of people. The initial report suggests using dynamos in the flooring of a subway station to generate electricity from the stompings of you and I. Here is the Cnet reply:

But if there's enough motion to provide harvestable energy, there's enough motion for the humans to notice. Ever walked along a pedestrian suspension bridge that bounced under your feet? It takes more energy to walk on such a surface than it does on a rigid surface.

Where does that energy come from? From you, of course. It's like carrying a parasite that takes a little bit of your energy. In fact, this approach is also called parasitic power generation. By keeping the parasite fed, you get a little more tired and you eat a little more food. In effect, you become a highly inefficient motor that runs on food.

Food calories are inefficient to produce. A wheat field is a giant biochemical solar panel that turns a small part of the sun's energy into chemical compounds that you can eat.

And then those compounds have to be kept cool and transported large distances, then cooked and eaten. By comparison, traditional electric power generation is hugely more efficient.

So when you see celebrity Ed Begley Jr. using a stationary bicycle to turn a generator to power his toaster, remember that this is a crime against the environment--not environmentalism.


Ok, I'm with you for the most part. It's a horrible fallacy to think we can result in a net gain by using humans as generators because ultimately, we are awfully inefficient. It's like saying that an electric car is better for the environment than a gasoline powered car... well perhaps, but you have to consider where that electricity comes from. If you're on a nuclear plant's grid then great. If the electricity is made by burning coal then you aren't much better off than with gasoline. I'm actually surprised the MIT report made this error.

I have to comment on that last sentence though. Stationary bicycles and the like are the one exception to the rule. It is inefficient to use normal day to day activities to produce electricity, because we generally want our day to day activities to be as efficient as possible. If only there were some activity we engage in that is deliberately inefficient. The gym! Why do people ride stationary bikes in the first place? To burn as many calories as they can! They're putting their inefficient body to the red line on purpose, and that energy is just being wasted in the artificial resistance of the machine. Why not use a dynamo to produce the resistance rather than weights, springs, or friction straps? If the person is going to be expending that extra energy anyways, there is no harm in harnessing it.

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