Joules and calories

01.07.2012 21:20

I recently finished reading The windup girl, a science fiction novel by Paolo Bacigalupi. The story is set in a future where the world has all but ran out of fossil fuels and where the mechanical energy is provided mostly by either physical workers or draft animals. This makes the economy revolve around calories and joules, used to measure chemical energy bound in food versus work done by muscles and springs. It's all mixed up with copious amounts of biotechnology that tries to make the conversion from the former to latter as efficient as possible. This backstory itself makes the book fascinating to read and makes you think about the energy footprint of modern living.

I've browsed back in my records and compiled the sum of all my consumption of general-purpose energy sources I bought in the last year:

  • 5.9 MWh, heat
  • 3.3 MWh, fuel
  • 2.4 MWh, electricity

Obviously, this includes only energy sources I bought directly to use as I please and doesn't include the energy needed to manufacture any products I consumed or the use of public transportation where I didn't directly buy the fuel. So at best this is at the very low end of the energy footprint estimate.

The numbers above add up to 11.6 MWh per year or an average of 31.8 kWh per day or 1.3 kW of continuous power. To put this into perspective with some back-of-the-envelope calculations:

  • Two draft horses would need to be working around the clock to cover this consumption.
  • If perfect conversion from food energy to work would be possible, this would require 6.7 kg of carbohydrates per day.
  • Or, it would require around 100 m2 of photovoltaic cells (a technology curiously absent in the novel).
  • Or, 70 s of exclusive use of our national nuclear power plant's output per year.

Energy consumption is often considered one of the indicators of progress and I don't subscribe to any movements that we should return to pre-industrial age energy footprints. I am all for using resources responsibly and as efficiently as possible though. And such little calculations do show a bit what kind of power is available from your wall socket compared to what was available merely a century or two ago.

Posted by Tomaž | Categories: Life


Did you heard of '2000 W society' ( A few years back, a Swiss professor François E. Cellier had a presentation at the faculty (FE), where he mentioned this term. It was quite a thing to think about..

Posted by Matevz

Thanks for the link Matevž. I haven't heard of it before. That Wikipedia page also has a nice breakdown of average energy consumption for Swiss citizens.

Posted by Tomaž

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