Free Energy for All

Civilization, and life in general, can be thought of as being powered by negative entropy. We need to get low entropy energy from somewhere, extract some useful work from it, and dump the resulting high entropy energy into some cool reservoir. For living systems, this usually amounts to Gibbs Free Energy, but our machines are less picky.

Except for little bits of nuclear energy stored in our rocks by ancient supernovae, and a tiny bit from various gravitational sources (tides, continuing contraction of the Earth) all that energy comes from the Sun. Three and a half billion years or so ago, certain autotrophs learned how capture a photon and hook up its energy to power some chemical reactions to store energy C. We could plausibly call this the most important invention in the history of life. All told, such reactions capture roughly 100 terawatts of solar power.

Heterotrophs, like us, evolved to consume those autotrophs and get our (Gibbs) free energy from them. As Eli has noted, we humans are approximately 100 watt machines, and since the process of autotrophs turning sunlight into us isn't perfectly efficient, it takes quite a bit more than 100 tera watts of sunlight to keep one of us fed - a lot more if most of it is processed through animals before getting to us.

Our remote ancestors collected their 100 watts (plus, since they led active lives) by gathering roots, berries, insects, carrion, and whatever animals they could catch. Our first great inventions, tools, fire, and language, enabled us to become more efficient at collecting food and extracting nutrition from it. Those inventions were enough to turn us from a minor East African plains ape into a species indigenous to much of the world, but population densities remained extremely low by modern standards - fewer people in the whole world than there are now in one fairly big city.

If there were five million people then, each consuming (say) a net of 600 Watts counting, fire, plant and animal food, the total consumption would be just 3 GigaWatts - or about 3 parts in 100,000 of the total.

The invention of horticulture allowed us to concentrate plants that we could eat, and domestication of animals allowed us to consume (indirectly) a wider variety of plants. We multiplied in numbers in return for which we got to work harder and be much less well nourished.

Currently there are seven billion of us, and an average American uses about 11.4 kilo watts of power. If we all lived as large as an average American, that would amount to 80 tera watts - or nearly every bit of energy life captures from the Sun.

That's not possible, of course, so instead we spend the energy the planet stored up over the past billion years or so.