This posting is rather philosophical than technical. Whenever we talk about energy, we tend to think in terms of oil, gas, nuclear, electricity, and the like. But throughout the longest part of its history mankind has been living without any of these “modern” energy types. And yet, throughout its entire history humanity has been dependent on energy, even without knowing it to the degree we are aware of it.
Why is that so? Every living being needs energy, just to stay alive. From a very basic point of view, what you essentially need to keep yourself alive is food, the nutritional value of which is measured in kcal which, in turn, is a measure for energy. So we have to supply our body with energy if we want to stay on this planet.
The basic energy need of a human being is about 2000 kcal per day. This is an average value which may vary according to age, sex, physical activity etc. Our basic value is meant to be valid for no or little physical activity. Thus, for people who are physically active it may be significantly higher (30 – 50 % or more). Since in the energy business it is rather uncommon to use kcal as a unit we may remark here that the above-mentioned 2000 kcal are equivalent to 2.33 kWh. From this we may calculate that the annual energy needs of a human being are about 1 MWh, taking into account a slight level of physical activity.
However, even for a society where technology has not yet developed to the level we are used to, the energy requirement per capita may well exceed 1 MWh per year. For the sake of simplicity let us consider a human being living in the Middle Ages. This means that the technological standard of that society is still much lower than nowadays, whereas at the same time its living standard is much more sophisticated than the one of, say, a society of Stone Age people.
In the Middle Ages, the vast majority of people were living an agricultural life. Thus, their energy needs reflected their living conditions. The technology of that time made extensive use of animals which was essential in order to produce a sufficient amount of food. Needless to say that the animals themselves had to be fed, too, and were thus energy consumers. The most important labour animals in such a society are horses and cows (oxen). Since they are, in general, bigger and doing much more labour than the humans, they also require more energy. Let us assume that, on average, we have one cow or horse per human being. A horse requires about 12000 kcal (14 kWh) per day, and the same is true for a cow (ox). This corresponds to about six times the energy requirements of a human. A largely inactive horse will need some 5 MWh per year. In case the animal is used for labour purposes this value will increase dramatically.
In our simple model, the minimum energy needs of a human being (plus his/her labour animal) may be estimated to about 6 MWh per year. In practice, this value might be considerably higher (30 % or more). Life was not easy then and certainly more physically demanding than in our times.
What we have considered so far was a very basic life mostly devoted to producing food and satisfying the elementary needs only. In some parts of the world, however, an additional factor comes into play: heating. Especially during the winter and the colder seasons, people need to keep a certain temperature for survival. In order to get an idea how much energy we need for heating purposes we may take the corresponding value from Switzerland which is about 6.5 MWh per person and year. This is a modern value. Linking it to a society several centuries back we have to take into consideration that on the one hand people living centuries ago might have been happy at a lower average temperature than today. On the other hand, however, we may also consider that then heating was not as efficient as it is in our times. Thus, taking the present day values may be a justified approach as the correcting factors go into opposite directions and may cancel each other.
Putting everything together leaves us with an energy need of about 13 MWh per person and year in an environment with present day climatic conditions in central Europe. One should not forget that all those basic energy needs (with the notable exception of heating) may be coverd by solar energy. In our model society it´s the sun which makes the crops grow which, in turn, serve as essential food for both humans and animals.
It goes without saying that the average energy requirements per person will increase with technological progress. Not only do we produce a number of goods nowadays which simply were not existing in the distant past, but we also enjoy a higher level of mobility. Thus both the production of goods other than the ones needed for satisfying elementary surviving conditions and mobility lead to additional energy requirements.
The above considerations are far from being simply of an academic nature. We may compare our estimates with present day statistical data. Let us look at some countries with different economic development. Taking the UN figures for energy per capita from 2008 reveals the following (GDI = gross domestic income per person):
Zambia 6.9 MWh (GDI: 950 USD)
Zimbabwe 8.9 MWh (360 USD)
Paraguay 8.1 MWh (2110 USD)
Mongolia 13.7 MWh (1670 USD)
Romania 21.3 MWh (8280 USD)
Uzbekistan 21.5 MWh (910 USD)
UK 39.5 MWh (46040 USD)
US 87.3 MWh (47930 USD)
There is a clear correlation between the level of industrialization and energy consumption. In addition, there is a climatic factor which must not be neglected. As we climb up the economic ladder we require more and more extra energy.
However, by using energy in a smart and efficient way we may limit the extra requirements. The average energy consumption per capita in the UK corresponds roughly to the EU value (40.8 MWh). Whereas the GDI of a US citizen is only slightly higher than the one of a UK citizen, his/her energy consumption exceeds the one of a person living in UK more than twofold. Thus, energy efficiency in the US is only half as good as it is in the UK.
Where are the limits? On the one hand we have to live with the fact that getting wealthier comes at a price in terms of energy consumption, on the other hand we want to squeeze as much wealth as we can from every MWh. As I have discussed in some of my previous posts (here, here and here) there is a clear tendency to become more energy efficient. Extrapolating those tendencies may give us a clue where we are heading to.