How Much Energy Do We Actually Need?

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.

8 comments on “How Much Energy Do We Actually Need?

  1. Once more a nice overview of some interesting numbers. It’s also good to think about the energy we need ourselves to live and move on. The comparison of the different countries is also nice: efficiency is an important aspect; so let’s further work on that and also on the applicability of sustainable and renewable resources.

    • At the end of the day, all biological progresses are energy tranforming processes. Thus without (external) energy supply, there would be no life on Earth. The sun is our driving engine, and up to a certain level we are able to satisfy all our needs by using this vast resource.

      • I agree. So, that makes once more clear that we have to use solar energy more efficiently and effectively. It is daily available, but it has to be applied and harvested in a better way. So, how can we satisfy more of our needs or improve our lives by using the solar energy?

  2. Interesting figures to give good thoughts!

    In tropical countries people in general need less energy (no need for heating, there is no winter time) and also in several tropical areas people are smaller because of climate (not directly a food issue). Besides in tropical areas temperature is in general higher which leads to faster plant growth (plant growth rate is 100% temperature determined, besides that you need light).

    More problematic is that more and more people move towards cities, with their energy efficient transport, heating/cooling etc.

    In classes i always asked people to tell me their annual kWh and fuel use, in most cases they did not know/care. When you want change of behavior you start by getting attention from consumers so they get aware and can calculate themselves that just a few PV panels will not solve their private energy needs…

  3. Grin. The Sun does NOT shine equal hours at every lattitude North (or South) of the Equator. I keep reading attempts to plan Solar Power, that ignore the greater and greater energy storage needs, the closer to the Poles the planned Dwelling _is_. And the other silly idea, that it is always warm, when you are close to the Equator, ignores the cooling work of higher altitudes!
    I think that the reasons for the changes, from charcoal to coal, in England, as the English forests were running out, after 1600, would be very instructive.
    Plus, looking up the usefulness of rock wool insulation, to cut down on the needs for heating energy, would really, really, help. And the complete skipping of the needs for energy for lighting, and for transportation, is annoying!
    One of the workings of the Law of Unexpected Consequences, lies in the sharply reduced range of electric vehicles, in the mild New England Winter. Seems the combination of the reduced-by-cold Battery Output, plus the energy demanded by the vehicle heater, left the Happy Owner fuming at the roadside. And discovering that there was zero availability of a 5 gallons of electricity available….

    • Well, the Solar Energy theory ignores weather problems, such as snowstorms or sandstorms. Even the dirt left on windows, by rainstorms, will decrease the energy input to Solar Panels, as will the pitting of the protective glass cover, by dust blowing, here in south Alberta.
      I also point out the uncomforable long, long Arctic Night, plus the very shor days that we see, just to the south of the Arctic Circle. I am a retired Seismic Surveyor, who grew up in SW Albertta, so I also know about the dirty little secret, of Wind Power, where No Wind, and Too Much Wind, result in Zero Output. Then we have too little wind, with Zero Output, changing into a liddle b it of output, until we see Rated Output. Over a year, there is a Total Output of about 29 to 33 percent of Total Rated Output for the year. This is not very useful for anything that has to have reliable electricity, from the Chicken Farm to the Freezer Bins at the local Supermarket!
      And the Solar Farms, or the WindFarms, are not voluntarily installing MegaWatt-scale Storage Systems, even though a Japanese firm has such systems available, for about $30,000,000 delivered, using about 30 semi-trailer loads from Dock to installation site. Of course, we would need a WindFarm 4 times the current size, to deliver Guranteed Electricity.

  4. Pingback: Extremes to drastically reduce CO2 - US Message Board - Political Discussion Forum

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