Energy Return on Energy Invested (EROEI)

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Judhajit Chakraborty, Assoc. AIA, LEED® AP, WSP Built Ecology

In February 2016 I attended the Net Positives Conference organized by the International Living Futures Initiative (Living Building Challenge) in San Diego, CA and I was very impressed with the quality of both the presenters and the presentations. Unlike the Greenbuild it was more of a closed group conference with about 350 attendees, digging deep into the water and energy problems of the world and providing far-fetched but definitely achievable solutions.

In this article I would like to mention one presentation that I really liked. On a conceptual level it talked about a term which is not generally used while talking about energy efficiency in the built environment. This is Energy Return on Energy Invested (EROEI) and this term has been in use in the world of Energy Economics and Carbon Economics for a long time now. But now as high performance design is looking more towards embodied energy (total energy from source – production + transportation), having a basic understanding of EROEI is important.

So, what actually is this Energy Return on Energy Invested (EROEI)? Mathematically it is a simple ratio: ratio of the amount of usable energy acquired from a particular resource to the energy expended to acquire that energy.green1

The higher the EROEI, the more “profitable” the energy resource (from an energy standpoint). If the EROEI drops below 1, it means that it takes more energy to produce the usable energy than is contained in the finished product. In other words, EROEI is a measure of the amount of energy society gets, as a ratio of the amount of energy we put in to get that energy. Net energy available is thus the amount of energy left for a modern society to function (Food production + support and education of people + healthcare for people + arts, entertainment, sports and other amenities) after spending the initial energy to get that energy. The more it costs to extract the energy, the less net energy is left for use. This leads to the energy cliff exponential graph to the left.

green2The dark gray area is the net energy available for a society to run smoothly and the light gray area is the energy used to procure that energy. According to this graph, a minimum EROEI of 14 is required for a smooth functioning of society. The graph also shows EROEI’s of major fuel sources. The conventional fossil fuels have the highest EROEI’s and that is why they are continuing to sustain our society. Even a reduction of 50 to 25 EROEI (which means gradual depletion of natural resources and hence more energy required to extract) have an inconsequential effect on the percent energy out. However that percentage changes sharply when unsustainable means of fuel is being brought into practice (corn ethanol, shale oil, bitumens etc). This also means that going forward, as our natural resources gets depleted, we as a society need to make smarter choices and invest in the right form of energy. Alternative clean fuel sources such as PV, nuclear and wind play a huge part in this. They have low EROEI’s but they don’t consume natural resources. However, currently these fuel sources are nowhere close to replacing the conventional fossil fuels. It can make good economic sense for an individual — or a society — to invest in a renewable energy producing system as long as the system can be maintained and operated for a long time.

As we debate our future energy choices and policies, energy return on investment should be an important part of such discussion. This gives us a “reality check” as we figure out where to put our energy investments.

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