Energy Return on Energy Invested (ERoEI)

One of the other areas that will be driving change in our world is the reduction in the availability of resources. We live on a finite planet and it is reasonable to expect the availability of these resources to become tougher and tougher to discover and extract. One of our society’s most important resources are the ones used to produce energy. We can use Energy Return on Energy Invested to understand how the availability is changing as we move into the future.

Energy Return on Energy Invested (ERoEI) is a metric to help understand how much of an energy benefit comes from a particular source. In short, this tells you for every X amount of energy extracted or harvested you get Y amount of energy when it is burned or utilized. An ERoEI that is equal to or less than 1 is an energy sink, meaning you get less energy than you put into a process. An ERoEI greater than 1 provides a surplus to the energy added into a process. While no one really agrees on what factors to measure when calculating this metric it is important to understand the general concept behind the idea. As ERoEI gets closer to 1 it becomes harder for our modern society to function in the status quo.  

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The developed world’s current standard of living is the result of energy such as oil and other fossil fuels that had a high ERoEI through the 20th Century. The amazing advances in our world were influenced by the discovery and refining of oil. According to a peered review article by Guilford, Hall, Conor, and Cleveland (http://www.mdpi.com/2071-1050/3/10/1866/htm) that investigated the long-term ERoEI of oil, when oil was first discovered and processed in the early 1900s it had an ERoEI of 1200! This helped drive advancement in machinery and progress. Today even with the most advanced extraction and surveying methods the ERoEI for oil has decreased to just 5!

ERoEI solar oil over timeOil is the dominant source of energy for the world and has had an ever decreasing ERoEI over time, but it is important to follow other sources of energy to understand the big picture. Another form of energy that is getting more and more attention is solar. Solar energy’s ERoEI has been increasing since the 1970s. Up from below 1 in the 1960s and 1970s to somewhere between 2 and 4 today. Note this is a rough range for typical parts of the world. In the most ideal solar conditions, the ERoEI for solar energy can be north of 10!

Hall, Balogh and Murphy (http://www.mdpi.com/1996-1073/2/1/25/htm) suggest that an ERoEI of 5:1 is required to maintain the current civilization. Oil as our primary source of energy is reaching the point where we will start seeing impacts on our way of life as it is expected that oil will continue to see a decreasing ERoEI. It will be interesting to see how the ERoEI of other sources of energy, such a solar and wind, evolve to take on a more dominant role in the energy system and if the speed of innovation can boost the average ERoEI of these sources higher than 5. Regardless, a world with systems that use solar and wind will more than likely function differently compared to today’s oil-driven systems.

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