Thursday, April 16, 2009

200 billion slaves

A human needs around 2500 kcal per day (2.9 kWh, most of it, around 80 percent is used just to stay, alive, think, sleep etc, so around 600 Wh are used for work as a power output. But let’s say that a person who is really doing physical work – which this is about anyway – generates some 800 Wh per day. On a yearly basis a person consumes some 1.16 MWh in the form of food.

Let us contrast this against how much other energy we have put to use in this modern world. The Swede use 5.65 toe (toe is ton oil equivalents, i.e. the energy in one metric tonne of oil), the American 7.71, the Britton 3.8 and the Senegalese use 0.20. Let’s look at the Swede: 5.65 toe corresponds to 65.7 MWh which means that we use ”external energy” corresponding to the energy of 57 human beings. But that is brut. If we look at hour conversion rate we said that we use only 20 percent of the food energy for actual work, so then we would use more than 250 peoples’ power. On the other hand, the external energy also has a lot of conversion losses. If we assume them to be 40 percent (this is now a bit of ”back of the envelope calculation) we are down to 100 energy slaves as I would call them. If we look at the global average energy use it is about one third of the Swede’s which means that there are about 200 billion energy slaves working for us all year round. It is not surprising that we can produce a lot more things than our savage ancestors. And it is not surprising that we also can make much greater mess than they could by using those forces in the wrong way!

Another way to look at the same condition, but adding an economic perspective is that one barrel of oil corresponds to 25 000 man-hours of work (around 12 man-years). The cost to actually produce this barrel is some few dollars per barrel. One can see that even with a price of 200 dollars per barrel that is a very cheap price to get 12 man-years of work done. Of course the barrel of oil is not as intelligent as the 12 humans and its use is thus a bit more limited…

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