Thursday, March 17, 2011

250 billion energy slaves

Swedish peasant (yours truly some thirty years ago) weeding his veggies with primitive tool

One can contrast the energy content in humans with the external energy sources we have conquered, to give us an idea how important the development of external energy sources are. Let us do a back-of-the-envelope-calculation[1]. A human needs around 2,500 calories per day (2,9kWh[2]). We use around 80 percent of that just to stay awake, think, eat, sleep, breath etc. So a bit less than 600 Wh is perhaps for work. Hard working people could perhaps develop 800 Wh, but they will also eat more. On a yearly basis the average person consume around a million calories, which correspond to 1.16 MWh. The average American uses 7.71 tons of oil equivalents (toes)[3] of energy (the average Brit 3.8, the Swede 5.65 and the Senegalese 0.25), which corresponds to 90 MWh, i.e. the energy in the annual food consumption for 77 persons, or if we calculate with the twenty percent that we actually use for work it would correspond to roughly 380 persons. On the other hand there are also energy losses for the conversion of external energy to useful work. If we assume that it is forty percent we land at 150 persons.

So depending on how we count, each American has somewhere between 75 and 400 “energy slaves” working for him or her, and the richer ones have thousands. The global average energy use is of course lower, and represents figures between 18 and 90, which translated to the total population would mean somewhere between 120 and 600 billion energy slaves. In that perspective it is certainly no surprise that we have taken over this place! Another way of looking at it, and also to put in an economic perspective, is that a barrel of oil represents the energy of 25,000 hours of human toil, i.e. 14 persons working a year with normal Western labour standards. The cost for pumping the oil is not more than a few dollars per barrel, but even with an oil price of many hundred dollars per barrel, it is very cheap even compared to human slave labour. The beauty of the oil slaves is that we don’t have to feed them at all. The slaves of the past, even under huge oppression and extortion took most of the feed for themselves, just to survive. With this perspective, our current wealth is easily understood and de-mystified. Even hundreds of years ago, the person that had hundreds of others working solely for him, could lead a comfortable life, long before industrial society and capitalism.

[1] Making energy calculations is tedious if for no other reason that so many different units are used and sometimes in-energy and out-energy in process are confused or it is not clear what is referred to. So there are may possible errors in the calculation presented here, and the main reason to present the calculation instead of just giving the figure is to be transparent, and perhaps that a brain better than mine can present more solid figures in the future.

[2] 1kWh = 3.18 MJ = 860 kcal.

[3] a toe is a common unit for energy and express the amount of energy released when a ton of oil is burnt. 1 toe = 42 GJ = 11 MWh = 10 Gcal.

(I have posted something similar one and a half year ago, but these figures are updated)

Other major postings about energy:

Our energy debt

Humans and energy, the long view


  1. Gunnar - Thanks for your comments on the Rob Hopkins' analysis. I posted a couple of lengthy posts on my Local Harvest blog, which I will link to instead of use up your webspace.
    I suggest you consider my 125 kilocalories per hour. In your terms of watt hours that would be 145.3 watts in an hour or 1162 in an eight-hour day. I can do that all day long without breathing hard and I am 61. In short, I see your figure of 600 as being about half what it should be. All the best.

  2. Apart from Walter's blog above there is now a lot of input on the Transition blog. Read them all at:

    Essentially I don't think it matter so much if we have 150 billion of 500 billion energy slaves at our service. My point is that we have to realise how much "extra" energy we get through oil. And that it is quite easy to understand the fundamental impact of this. Walter has made a number of points showing that the human is as efficient or more than the engines. I don't doubt that at all. But even if we are double as efficient, if a farmer using only his body has to compete with another farmer using the equivalent of fifty farmers of energy, for peanut costs, it is not difficult to understand who will win in global competition...