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How much of a slave master am I ?
august 2005
website of the author : www.manicore.com - contact the author : jean-marc@manicore.com

For all individuals that work in the energy sector, kWh (or, for those twisted anglo-saxons, BTUs) are as familiar as litres of water to the gardener, or kg of flour to the baker. Actually, when thinking about it, no one knows what a kWh really is, not even me ! One cannot "touch" energy ; it is just some abstract figure on a piece of paper, sometimes the prerequisite to an invoice, and to grasp fully the meaning of these figures, it will always be necessary - one cannot escape one's senses - to associate to a given figure a real action or a real thing that will make it meaningfull to everyone.

It is therefore very difficult, with kWh, tonnes oil equivalent and other gigajoules, to make people understand how much our present energy consumption - that of each one of us, and not only that of the SUV driver or frequent flyer - has become totally "out of normality" compared to what the standard human condition has always been.

In order to facilitate the understanding of this fact, I will do something that morals highly disapprove : bring back slavery. Indeed, men (and women !), like all machines, uses energy, that (s)he will afterwards transform - with a very poor efficiency, as we will see - into mechanical energy, and of course thermal energy. Men also transform the energy they use into information, what cannot be forgotten, but this is another story.

Men, how many kWh ?

Actually, the energy unit that each one of us knows the best is not the kWh, but, most probably... the Calorie. Indeed, almost each one of us knows (and mostly women a couple of months before the summer while reading their favourite magazine !) that a sedentery person consumes about 2000 Calories per day, through eating. These Calories represent nothing else than the extractible energy content of what we eat, and our body will of course make the best use of it, except when some diet seller persuades us of the opposite.

Since we are discussing energy here, it is then possible to convert our 2000 daily Calories in kWh, which is another energy unit, and therefore can be used with any form of energy, and not only electricity. As 1 Calorie (with a capital C) = 1000 calories (with a small c) = 4,18 kilojoules, and as 1 kWh = 3,6 megajoule (if this is too hard just trust me), we can conclude that a man (or woman, sorry again !) remaining still absorbs about 2,3 kWh per day. In other words, the basic metabolism of a (wo)man uses 0,1 kWh per hour : we use the same amount of energy than a light bulb (100 Watts), most of this energy (and even all of it when we are perfectly still) goes back into the environment as heat (so that's all the use of cooking delicate meals : all will end in heat just as in a vulgar light bulb !). This is why rooms heat up they are crowded : with 100 Watts per stockholder, the general assembly of HP becomes hot in the true sense of the word before any other meaning applies to the same adjective !

Let's now come back to our slaves (fictive, of course), to see how many we should each have at our service to get the same level of comfort we have with machines and "modern" energy. Everybody, unfortunately, will not have the luck to have Schwarzenegger or Stallone at his service, with bodies that absorb more than 1 kW when in full effort, and one will probably have to do with "ordinary" slaves, such as me, whose body probably doesn't go over 500 watts of input when I sweat like hell. If a fictive "regular" slave works very hard 10 hours per day, (s)he will have consumed 5 kWh (that is 500 watts x 10 hours) then, and the remaining 14 hours, as (s)he will rest because I am a good master, (s)he will use 100 watts as mentionned above, with a total of 1,4 kWh (that is 100 watts x 14 hours). Daily total : 6,4 kWh.

Pardon me, all feminist movements, but if our slave is a woman, using only 400 watts in full effort, and authorized to work only 8 hours per day (except if equal conditions are a must here also !), the energy consumption for the whole day will be limited to 4,8 kWh, and if we consider labour which is not physically intesive (washing, cooking, or whatever), requiring only 250 watts to be performed, but done 12 hours per day, we will need 4,2 kWh over 24 hours to feed the organism. In first approximation, a body working hard will use about 5 kWh per day.

This is where we start to understand that our species has performed a fantastic "power breakthrough" when domesticating fossil fuels : with 1 euro (which is about 1 dollar, Wall Street specialist will excuse me to concentrate on magnitudes), I can buy 1 litre of petrol (or gas), that contains about 10 kWh of energy, which is about the equivalent of two "slaves" working for a full day. And oil would be expensive ?

But the price of energy will seem even more ridiculous if we take into account the efficiency of the human machine, equally ridiculous. Let's picture a worker that digs a big hole, and shovels earth all day long to do so. If our man (it's seldom a woman, as a matter of fact) throws up one shovel or earth every 5 seconds during 8 hours of work, he will have carried 17 tonnes when the working day ends. If the hole is 1 metre deep, a magnificent formula that all those that did not sleep to much in physics lesson certainly remember (E = mgh) allows to conclude that the mechanical energy used to do so is worth... a little less than 180.000 joules, that is an utmost ridiculous 0,05 kWh ! If our man has absorbed 5 kWh during the day to stand this continuous effort (just try to do it one day and you will understand), we see that the mechanical efficiency of the human machine is something around 1%. Abracadabrantesque !

The efficiency of legs, however, is better than that of arms : if the same worker, weighting 70 kg "all naked", has climbed 2000 metres in the mountain, with 30 kg on his back, he will have produced (70+30)x2000x9,81 = 2 megajoules of mechanical work, that is 0,5 kWh in rough figures. In this case, the efficiency makes an astronomical leap : becoming almost 10%.

In the same time, a classical thermal engine has an efficency around 40%, which means that the mechanical energy produced by the engine represents about 40% of the thermal energy enclosed in the fuel. 1 litre of gasoline, poured into such an engine, will therefore produce 4 kWh of mechanical energy. If my sole purpose of having slaves is for the mechanical work they produce, then we see that with one litre of gasoline, and its 4 kWh of mechanical energy once being processed by an engine, we get the equivalent of 100 (large) pair of arms (at 0,05 kWh each) during 24 hours, or 10 pairs of legs (at 0,5 kWh each) over the same period of time. And oil would be expensive (bis) ?

It is obvious, when seeing this astronomical price difference between human energy and fossil energy that, if the price of energy remains constant, anything a machine can do will eventually be done by a machine if micro-economic logics apply everywhere and before any other consideration. Fortunately it is not always the case, and fortunately also it is not frequent that a worker produces only mechanical energy, without the slightest bit of intelligence (which is worth much more) or ability to manage something not expected (which is considerably more expensive - if possible at all - when done by a machine).

How many slaves in our modern life ?

Now that we know that a working human being uses about 4 to 5 kWh per day, and restitutes 0,05 to 0,5 kWh of mechanical energy over the same period of time, we can convert almost any energy consumption of the present daily life in "slave equivalent", which is like saying that through our energy consumption for this or that we have so many fictive slaves at our service. You don't fear to feel dizzy ? Then here goes...

In 2000, A French - but this is valid, in rough figures, for any European, and for bid bag Americans, Canadians or Australians just multiply by 2 - consumes about 47.000 kWh per year, all usages and energies taken into account.

Primary energy consumption per usage and per French, in kWh, in 1999. The total represents about 47.000 kWh.
For "Industry", only the energy used in processes is accounted for (not heating of premises, which is accounted for in "heating"). "Specific" electricity is that which is not used for thermal applications (it is therefore most of the electricity, which is used for engines, domestic appliances, lifts, light, etc). "Used as a raw material" corresponds to the oil, gas and coal that are used in industrial chemical processes to manufacture plastics, soap, etc.
Source : Observatoire de l'Energie.

We will now "play at being slave master" (as gentlemen, still) by converting all these energy consumptions into "slave equivalents". We will use the following rules :

when energy is used to obtain heat, the equivalence will be one man = 5 kWh per day, or 1825 kWh per year,

when energy is used to obtain a mechanical effect, the equivalence will be one man = 1 kWh per day when the power can be obtained with legs (to take into account the fact that an engine has at best an efficiency of 50%, which is over what it is for a thermal engine, and below what it is for an electric engine), or about 400 kWh per year, and if it is arms that we use, then the equivalence will be one man = 0,1 kWh per day, or 40 kWh per year.

and at last we will suppose that we can apply the simple (simplistic ?) following breakdown between "heat", "legs", and "arms" :

agriculture uses mostly mechanical energy (tractors, conveyors, crushing machines, etc ; fertilizer maanufacturing will go into "industry"), and mostly "arms" (to plough, harvest, cut, spread, etc),

Industry uses half meachnical energy and half thermal, and the closest equivalent for the mechanical energy is "legs" (because most machines could be actionned by people cycling),

heating and energy industries (refineries, power plants) use only heat,

transportation use only mechanical energy, with "legs" equivalent.

Well, the result is that our modern energy consumption is equivalent to giving to each French (or european)... about 100 slaves !

"Slave equivalent" (still fictive !) that correspond to our present energy consumption per usage, with the above described hypotheses. In other words, the mechanical power that tractors and harvesters in agriculture represents the equivalent of 20 slaves per French. This is why it has been possible to multiply the agicultural output by 3 to 4 while, in the same time, the number of workers has been divided by 10 : our "mechanical slaves" have replaced human workers !
With the composite "conversion factor" described above we see that the "slavery" is also particularly important in industry, non thermal use of electricity, and most of all transportation.

As we see on the above graph, it's transportation that uses the largest amount of our modern slavery. Some additional figures will probably help to understand why :

If we replaced a car engine by human slaves cycling, the most modest subcompact car (a Twingo), with 42 kW of engine power (that is about 60 HP), would consume as much as 90 people cycling like hell, and, in terms of mechanical power, given the very poor efficiency of the human machine (10% at best when a thermal engine reaches close to 50%), it's rather 500 people cycling that it represents ! Another parallel might be used : knowing that a HorsePower used for an engine really represents the equivalent of a horse in terms of power, it means that any worker paid at the minimum wage, in France, can buy - then feed - the equivalent of 60 to 80 horses with 6 to 8 months of salary. And oil would be expensive (ter) ?

When flying, any passenger consumes 1 kWh for 2 km on average. A return flight from Paris to Rome, that anyone can afford today, represents 2.240 km, thus 1.100 kWh of energy. A single flight in Europe represents as much energy as 6 pairs of legs over a full year...

Even a small 50 cm3 moped, with its 2 ou 3 kW of engine power, is already the equivalent of 15 to 20 human beings cycling...

In short, today energy is almost free. Who had the possibility, only a century ago, to afford the equivalent of several tens of servants to get fed, washed, transported, diverted, and so on, with the sole product of one's work ? Not many people...

Incidentally, a division by 4 of the fossil energy consumed by each French, which is what it takes to mitigate climate change, still means, with the present technologies, sevel tens of "slave equivalent" by French. It would not exactely be "back to the Stone Age", as some say !

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