ERoEI

Alice and the Red Queen illustrate ERoEI

Many people of faith, including seminarians and ordained clergy, are not trained in science or technology. They are charged with activities such as preaching, managing church finances, caring for the sick and leading spiritual retreats. These activities and responsibilities do not require an understanding of technology, systems engineering or quantification. However, as we enter the Age of Limits it will be necessary for us all to have a basic grasp of technology and its limits. Posts such as Essential Petrochemicals, Of Priests and Thermodynamics and Proper 23: The Enemy is Physics challenge such assumptions.

One technical issue that is fundamental to much of what is written at this site is the concept of Energy Returned on Energy Invested (ERoEI). This topic is discussed  in detail in the chapter entitled ‘Alice and the Red Queen’ in the ebook Age of Limits – 1. A summary is provided here.

The basic idea behind ERoEI is that all systems, including all living creatures and all human beings, need energy in order to live, grow and reproduce. But the act of acquiring energy requires the expenditure of energy. Expressed as a simple equation,

Available (Net) Energy  =  (Gross Energy  –  Energy Expended)

Gross Energy is the total amount of energy that is taken in. Energy Expended is the energy needed to find and consume the Gross Energy. Available or Net Energy is what remains. If Net Energy is positive then the system or organism flourishes. If Net Energy is negative then, once it has used up its own internal reserves, the organism will die.

Imagine a person living a simple hunter-gatherer lifestyle. He or she expends energy throughout the day gathering edible plants and hunting animal prey. That is the Energy Expended term. The person eats the food he or she has gathered, thus providing the Gross Energy. The Net Energy is the difference between these two terms.

A term that is frequently used in this context is Energy Returned on Energy Invested (ERoEI), which can be defined as,

ERoEI  =  Gross Energy / Energy Expended

If a living organism has an ERoEI of unity then it will spend all of its energy finding energy (food) just to keep itself alive. If the value falls below unity then the organism dies. Only if ERoEI is greater than one will the organism have surplus energy for growth and reproduction. Hunter-gatherers typically have an ERoEI of about 1.5. In other words, they spend 2/3 of their energy looking for and consuming new sources of energy (food).

About 10,000 years ago societies in different places started to develop agriculture. Doing so gives that society a much higher ERoEI value, probably in the 6-8 range. The surplus energy provides the foundation for civilized society, a society that can now afford luxuries such as armies, buildings, priests and writing.

Then, about 300 years ago we learned how to exploit the energy in fossil fuels such as coal, oil and natural gas. Doing so dramatically increased society’s ERoEI value. Now humans, through the use of this stored energy, have ERoEI values that can be as high as 100:1. This surplus provides the foundation for everything we take for granted in our modern way of living.

The catch is that we have used up the easy-to-find-and-extract energy sources, the low-hanging fruit. So now we are forced to spend an ever-increasing proportion of our energy simply finding and extracting new sources of energy to replace what we have used. The chart plots Net Energy against ERoEI. It can be seen that, as ERoEI falls from 100 to 20, most of the Gross Energy is available as Net Energy. But, below an ERoEI of about 5:1 Net Energy plummets. We fall off the Energy Cliff.

The ERoEI energy cliff
It is this decline in ERoEI, particularly the fact that we are reaching a point where we will soon be falling off the cliff’s edge, that is the root cause of so many of our difficulties. There are no high-density sources of energy available to use that would allow us to move back along the curve (with the possible exception of nuclear power, but that comes with its own set of problems).

It is difficult to calculate ERoEI values for various reasons. For example, government subsidies will skew any analysis. Nevertheless, we can develop some very rough ERoEI values for various energy sources.

  • Hydro                                       100
  • Oil (conventional onshore)    20
  • Wind                                           18
  • Oil imports                                12
  • Natural gas                                10
  • Solar                                             5
  • Shale oil                                       5
  • Bitumen tar sands                     3
  • Ethanol from corn                    <1 to 5

Regardless of the energy source ERoEI for society overall is declining inexorably and new technologies and sources of energy have lower values than more traditional sources (with some exceptions — the cost of solar panels has come down a lot in recent years, although even in this case there is a large amount of embedded energy in a solar panel, and that energy likely came from oil, gas or coal.)

There are also qualitative issues to consider. For example, low ERoEI projects generally impact the environment much more adversely than those with a higher value. In the “good old days” all you had to do was “stick a straw in the ground” and high quality oil flowed under its own pressure into the production pipeline. No longer — now the development of resources such as the bitumen tar sands has a huge environmental impact. And the Deepwater Horizon/Macondo catastrophe showed just how severe the environmental problems to do with deepwater drilling can be.

Political issues can also be a factor. For example, ethanol produced from corn may have an ERoEI that hovers around one, hence it does not make economic sense to bother with this activity. But the ethanol does provide a local source of fuel thus providing those countries that grow corn and make ethanol with some political independence. And the production process provides jobs for the local population.

Like the Red Queen in Alice in Wonderland, we are running faster and faster to stay in the same place.

Author: Ian Sutton

Ian Sutton is a chemical engineer who has worked in the chemical, refining and offshore oil and gas industries. He is the author of many books, ebooks and videos.

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