Infinite Free Energy Reported...But Not Found

The level of misinformation in this article is atrocious - both intentional and unintentional. Let's get started.

Alan Boyle, long-time editor at MSNBC, writes:

Someday, your pulse could provide all the power you'll need for your iPod.

If we base our calculations on the power consumption of an iPod Touch being 180 milliwatts (a number I remember reading somewhere but can't find now), then what Alan and others are clearly missing is that the human heart must output an additional 180 milliwatts worth of generating power - and thats assuming 100% conversion efficiency of the nanogenerator device you've hard-mounted to your arteries. Chances are the capture efficiency would be more like 65%, and then including downstream losses while converting that power into a 3 VDC supply, you end up with about 55% efficiency (which is reasonable to assume). That means your heart needs to pump an additional 330 milliwatts of power in order to power your iPod. Based on the fact that the nanogenerator is working from conversion of mechanical energy, and the general rule for food to mechanical energy conversion is "about 20%", we need to essentially multiply that power output by 5 to get input watts. So now we're at 1.65 Watts, and to run it for 24 hours you need about 40 watt hours - which is somewhere around 35 calories.

Alan then describes the device:

Their latest prototype chips are about a quarter the size of a postage stamp, but when you stack five of the chips on top of each other like a sandwich, you can produce 1 microampere of current at 3 volts.

One microamp at 3 volts is 3 microwatts. So to produce the 1.65 watts above calculated to power your iPod, you'd need 550,000 of the devices. If each one has a footprint of "a quarter the size of a postage stamp" which is about a quarter of an inch. So you'd need a device 954 square feet in size to power your iPod.  The average human skin is 21 square feet. So you'd need to cover your body with 45 solid layers of this stuff to power just your iPod. Hmm...


Alan really loses himself in the electronics here and blows it:

That's enough power [from a single piezo unit] to light up an LED bulb or a liquid crystal display on a calculator or computer.

Three volts certainly is a normal operating voltage for many LCD displays and LED bulbs. But there smallest LED bulb you can buy on digikey still pulls 500 microamps. LCD displays use much, much more than that. Voltage really doesn't matter. I have made this really handy chart to explain what I mean. Call this Waller's Law of Micropower Generation:

I know its hard to read, but click to zoom. The point is that voltage is almost totally irrelevant when designing a scaled micro-power supply because you can always put the nodes in series to increase voltage. What IS important is your per-unit current production, and in this case, 1 microamp is really not usable at all.

Boyle (and apparently Zhong Lin Wang from Georgia Tech) are missing is the age old "Conservation of Matter and Energy" which states that matter and energy cannot be created. Devices that draw power from the human body require the human body produce extra energy to make up the difference. In this case, Wang suggests the pumping power of the heart be used. That's fine, but why are we assuming the heart has extra power? In a refined organism like a human, the heart pumps with exactly the right amount of force to move all the blood that need be moved, and not a single muscle fiber extra fires. Why would the human body produce extra heat (that's where the other 80% of the burned calories goes) if it didn't need to?  So Wang suggests the heart's pumping could provide the input force to a piezoelectric that would power an insulin pump.
Great. Let's put even more load on a diabetic's heart.

Then we get a clear test of XKCD's Law of Research Translation:

Wang estimates that the first nanogenerators will make their appearance on the market in the next three to five years, most likely as power sources for environmental sensors or infrastructure monitoring devices.

Which XKCD translates to "I've solved the interesting research problems. The rest is just business, which is easy, right?"


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